Pulsed Nd:YAG Lasers Instruction Manual GCR-L4 GCR-18

—© Quanta-Ray

Pulsed Nd:YAG Lasers

Instruction Manual

, . .

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GCR-12GCR-L4

GCR-18

Spectra-PhysicsSpectraPhysics Lasers

4.’—

—© Quanta-Ray

Pulsed Nd:YAG Lasers

Instruction Manual

GCR-12GCR-14GCR-16GCR-18

Spectra-PhysicsSpectra-Physics Lasers

1330 Terra Bella AvenuePost Office Box 7013

Mountain View, CA 94039-7013

International HeadquartersSiemensstrasse 20D-61 00 Darmstadt

Germany

Part Number 0000-225A, Rev. AApril 1992

Preface

This manual contains information you will need for day-to-dayoperation and maintenance of your QuantaRay® OCR SeriesNd:YAG Laser System. You will find instructions for installation,operation, preventive maintenance, a brief description of its circuitiy,and a troubleshooting and repair guide. The system comprises threeelements—the laser head power supply, and remote control. In addition to instructions for these components, the manual describes theinstallation and operation of the HG-2 harmonic generator.

While this manual contains a brief installation procedure, it is notintended as a guide to the initial installation and set-up of your laser.Please wait for the Spectra-Physics service engineer who has beenassigned this task as part of your purchase agreement. Allow onlythose qualified and authorized by Spectra-Physics to install and setup your laser system.

The Service and Repair section is intended both as an aid to helpyou guide your field service engineer to the source of problems, andas a guide to repairs you may choose to do yourself. Do not attemptto repair the unit while it is under warranty; instead, report all systemfailures to Spectra-Physics customer service for warranty repair.

The OCR Series lasers emit laser radiation that can permanentlydamage eyes and skin, ignite fires, and vaporize substances. Moreover, focused back reflections of even a small percentage of its output energy can destroy expensive internal optical components. TheLaser Safety section contains information and guidance about thesehazards. To minimize the risk of injury, death, or expensive repairs,carefully follow these instructions.

If you encounter any difficulty with the content or style of this manual,please let us know. The last page is a form to aid in bringing suchproblems to our attention. Thank you for your purchase of SpectraPhysics instruments.

III

Table of Contents

1—11—11-31-41-61-71-81-101—111-121-14

2-12-12-32-3

2-4

3—13-13-13-13-23-33-53-53-53-63-63-63-73-7

Chapter 1 Introduction

Emission and Absorption of LightPopulation InversionNd:YAG as an Excitation MediumQ-switchingResonant Optical CavityLongitudinal Modes and LinewidthProducing Other WavelengthsResonator Structural ConsiderationsPulse Triggering Sequence and TimingSpecifications

Chapter 2 Laser SafetyPrecautions for the Safe Operation of Class IV-High Power LasersFocused Back Reflection SafetyMaintenance Required to keep this Laser Product...in Compliance with Center for Devices andRadiological Health (CDRH) Regulations

Sources of Laser Safety Standards

Chapter 3 Installation and OperationUnpacking your LaserInstalling the Laser

Connecting the Electrical ServiceFilling the Cooling System

Controls and Connections—Remote Control ModuleControls and Connections—Power Supply

OUTPUT ConnectorslNPUTConnectorsREMOTE ConnectorCOMPUTER ConnectorPOWER ControlsPURGE ControlsPower Supply Rear Panel

V

Table of Contents (cont.)

Chapter 33-83-83-83-83-9

Installation and Operation (cont..) 3-1

Controls and Connections—Laser HeadQ-switch Driver (Marx Bank) BoxEmission IndicatorConvenience Receptacle

Starting the Laser

Chapter 4 Computer Interface Module 4-1

Functional Overview 4-1

Computer Control and Diagnostic Functions 4-3

Power-On Default State and System Initialization 4-3

Computer Safety (Watchdog) Interlock 4-4

IEEE 488 Interface 4-4

Operation 4-4

Remote Reset 4-4

Serial Poll Status Byte 4-5

SW2 DIP Switch Setting 4-6

RS-232-C Serial Interface 4-6

Operation 4-6

Data Transfer and Handshaking 4-7



Message Formats 4-8

Command Format 4-8

Response Format 4-9

CIM-1 Commands 4-10

CONFIGURE p, OUTPUT, NONCLOCKED 4-10

4-11

SELECTc 4-11

WRITEp,n 4-11

SELECT 1, WRITE 4, n 4-13

SELECT 1, WRITE 5, n 4-13

SELECT 1, WRITE 6, n 4-13SELECT 1, WRITE 7, n 4-13SETd,n 4-15

Examples 4-15

External lamp fire 4-15

Variable rep rate 4-15

Q-switch Advance Sync 4-16

Sample Analog-to-Digital Conversion 4-17

SAMPLE a

Example Commands Using GW BASIC on a Personal Computer 4-18

VI


Chapter 5 Installing and Operating the 5-1HG-2 Harmonic Generator

HG-2 Controls 5-3Installing the HG-2 5-3Operation 5-4Type I and II Crystals 5-5

HG-2 Temperature Controller 5-6Controls 5-6Operating Voltage 5-6Second Harmonic (Types I and II) 5-7Third and Fourth Harmonic Generation

Chapter6 Maintenance 6—1Maintaining the Cooling System 6-1Maintaining the Air Purge System 6-iMaintaining the HG-2 6-iReplacing the Deionizing Water Filter 6-2

Procedure 6-2Replacing the Air Filters 6-3

Procedure 6-3Replacing the Flash Lamps 6-4

Procedure 6-4

Chapter7ServiceandRepair 7-1System Description 7-i

Computer/Internal Switch 7-1Enabling Signals 7-iAnalog Signals 7-1Q-switch Delay 7-2Q-switch Advanced Sync Generator 7-2Mode Switch (Ui 1) 7-2Q-switch Drivers 7-3Single-Shot Operation 7-3Inhibit Switch 7-3OFF [STOP]/ON [ENABLE] buttons 7-3Interlock Logic 7-4Pulse Forming Network 7-4Flash Lamp Simmer Supply 7-5

System Start-up Tests 7-5

VII


ChapterlOCustomerService 8-1

Warranty 8-1

Return of the Instrument for Repair 8-2

Service Centers 8-2

List of Figures

Figure 1-1: Electrons occupy distinct orbitats defined by the 1-2

probability of finding an electron at a given position,the shape of the orbital being determined by theradial and angular dependence of the probability.

Figure 1-2: A Typical Four-level Transition Scheme (a) 1-4

Compared to that of Nd:YAG (b)

Figure 1-3: Energy Level Scheme for the Nd:YAG Laser Source 1-5

Figure 1-4: The Q-switch comprises a polarizer, a quarter-wave 1-6

polarization rotator, and a Pockets cell.

Figure 1-5: Stable and Unstable Resonator Configurations 1-7

Figure 1-6: Frequency Distribution of Longitudinal Modes for a Single Line 1-9

Figure 1-7: Etaton Loss Minimum Tuned to Laser Gain Maximum 1-9

Figure 1-8: Simplified Block Diagram of GCR Series Electronics 1-12

Figure 2-1: Radiation Control Drawing 2-5

Figure 2-2: Warning Labels 2-6

Figure 3-1: Main autotransformer is tapped for several operating voltages 3-2

Figure 3-2: Cooling System Component Identification 3-3

Figure 3-3: Remote Control Panel 3-4

Figure 3-4: Power Supply Control Panel 3-6

Figure 3-5: Q-switch Driver (Marx Bank) Box 3-8

Figure 3-6: Head Emission Indicator 3-9

Figure 4-1: Location of CIM-1 PC Boards 4-2

Figure 4-2: Diagram of the serial poll status byte 4-5

Figure 4-3: Standard RS-232-C Interconnections 4-7

Figure 4-4: Command Word Abbreviations 4-10

Figure 4-5: CIM-1 Proprietary PC Board 4-14

Figure 5-1: HG-2 Component Identification 5-1

Figure 5-2: Temperature Control Panel 5-6

Figure 6-1: Short together posts A and B to prevent shock 6-5when servicing the flash lamps.

VIII


List of TablesTable 4—1: SW2 DIP Switch Settings for Selecting Device Address 4-6Table 4-2: SW1 Baud Rate Settings 4-8Table 4—3: SW1 Mode Select Settings 4-8Table 4—4: Sample a Command Functions 4-11Table 4—5: SELECT 1, WRITE Command Functions 4-12Table 4-6: SELECT 2, WRITE Command Functions 4-13Table 5—1: Summary of Translation Arm Positions 5-2Table 5—2: Summary of HG-2 Positions 5-2Table 7—1: System Start-up Tests 7-7Table 7—2: Replacement Parts 7-13

SI Units

The following System International (SI) units, abbreviations, andprefixes are used in Spectra-Physics Lasers manuals:

Quantity Unit Abbreviationmass gram glength meter mtime second sfrequency hertz Hzforce newton Nenergy joule Jpower watt Welectric current ampere Aelectric charge coulomb Celectric potential volt Vresistance ohm Winductance henry Hmagnetic flux weber Wbmagnetic flux density tesla Tluminous intensity candela cdtemperature kelvin Kpressure pascal Pacapacitance farad Fangle radian rad

Prefixes

tera (1012) T deci (10-1) d nano (10) ngiga (1O) G centi (102) c pico (1012) pmega (106) M milli (10) m femto (10-15) fkilo (10) k micro (10-6) atto (10-18) a

xi

Warning Conventions

NOTEStatement to cover exceptional circumstances orreference.

CAUTION Statement to warn against or to prevent poorperfomance or error.

WARNING Statement to warn of possible damage toequipment.

DANGERStatement to cover situation involving personalsafety or injury.

XII

Chapter 1 Introduction

Emission and Absorption of Light*

Laser is an acronym derived from “Light Amplification by Stimulated Emission of Radiation.” Thermal radiators, such as the sun,emit light in all directions, the individual photons having no definiterelationship with one another. But because the laser is an oscillatingamplifier of light, and because its output comprises photons that areidentical in phase, direction, and amplitude, it is unique among lightsources. Its output beam is singularly directional, intense, monochromatic, and coherent.

Radiant emission and absorption take place within the atomic ormolecular structure of materials. The contemporary model of atomicstructure describes an electrically neutral system composed of anucleus with one or more electrons bound to it. Each electron occupiesa distinct orbital that represents the probability of finding the electronat a given position relative to the nucleus. Each orbital has a characteristic shape that is defined by the radial and angular dependence ofthat probability, e.g., all “s” orbitals are spherically symmetrical, andall “p” orbitals surround the x, y, and z axes of the nucleus in a double-lobed configuration (Figure 1—1). The energy of an electron is determined by the orbital that it occupies, and the over-all energy of anatom—its energy level—depends on the distribution of its electronsthroughout the available orbitals. Each atom has an array of energylevels: the level with the lowest possible energy is called the groundstate, and higher energy levels are called excited states. If an atom isin its ground state, it will stay there until it is excited by externalforces.

* “Light” will be used to describe the portion of the electromagnetic spectrum from farinfrared to ultraviolet.

1—1

Quanta-Ray GCR Series

Figure 1—1: Electrons occupy distinct orbitals that are defined by

the probability of finding an electron at a given position, the shape

of the orbital being determined by the radial and angular depen

dence of the probabiit

Movement from one energy level to another—a transition—happens

when the atom either absorbs or emits energy. Upward transitions can

be caused by collision with a free electron or an excited atom, and

transitions in both directions occur as a result of interaction with a

photon of light. Consider a transition from a lower level whose energy

content is E1 to a higher one with energy E2. It will only occur if the

energy of the incident photon matches the energy difference between

levels, i.e.,

hv=E2—E1 [1]

where h is Planck’s constant, and v is the frequency of the photon.

Likewise, when an atom excited to E2 decays to E1, it loses energy

equal to E2—E1.Because its tendency is toward the lower energy

state, the atom may decay spontaneously, emitting a photon with

energy hv and frequency

[2]

Spontaneous decay can also occur without emission of a photon, the

lost energy taking another form, e.g., transfer of kinetic energy by

collision with another atom. An atom excited to E2 can also be stim

ulated to decay to E1 by interacting with a photon of frequency v,

shedding energy in the form of a pair of photons that are identical to

the incident one in phase, frequency, and direction. By contrast,

spontaneous emission produces photons that have no directional or

phase relationship with one another.

x.

x

1-2

Introduction

A laser is designed to take advantage of absorption, and both spontaneous and stimulated emission phenomena, using them to createconditions favorable to light amplification. The following paragraphsdescribe these conditions.

Population InversionThe absorption coefficient at a given frequency is the difference between the rates of emission and absorption at that frequency. It canbe shown that the rate of excitation from E1 to E2 is proportional toboth the number of atoms in the lower level (N1) and the transitionprobability. Similarly, the rate of stimulated emission is proportionalto the population of the upper level (N2) and the transition probability.Moreover, the transition probability depends on the flux of the incident wave and a characteristic of the transition called its “cross section.” It can also be shown that the transition cross section is thesame regardless of direction. Therefore, the absorption coefficientdepends only on the difference between the populations involved, N1and N2, and the flux of the incident wave.

When a material is at thermal equilibrium, a Boltzmann distributionof its atoms over the array of available energy levels exists with nearlyall atoms in the ground state. Since the rate of absorption of allfrequencies exceeds that of emission, the absorption coefficient atany frequency is positive.

If enough light of frequency v is supplied, the populations can beshifted until N2= N1. Under these conditions the rates of absorptionand stimulated emission are equal, and the absorption coefficient atfrequency v is zero. If the transition scheme is limited to two energylevels, it is impossible to drive the populations involved beyondequality; that is, N2 can never exceed N1 because every upward transition is matched by one in the opposite direction.

However, if three or more energy levels are employed, and if theirrelationship satisfies certain requirements described below, additionalexcitation can create a population inversion, in which N2>N1.

A model four-level laser transition scheme is depicted in Figure 1—2(a). A photon of frequency v1 excites—or “pumps”—an atom from E1to E4. If the E4 to E3 transition probability is greater than that of E4 toE1, and if E4 is unstable, the atom will decay almost immediately toE3. If E3 is metastable, i.e., atoms that occupy it have a relatively longlifetime, the population will grow rapidly as excited atoms cascadefrom above. The E3 atom will eventually decay to E2, emitting a photon of frequency. Finally, if E2 is unstable, its atoms will rapidly returnto the ground state, E1, keeping the population of E2 small and reducing the rate of absorption of v2. In this way the population of E3 iskept large and that of E2 remains low, thus establishing a populationinversion between E3 and E2. Under these conditions, the absorptioncoefficient at v2 becomes negative. Light is amplified as it passesthrough the material, which is now called an “active medium.” Thegreater the population inversion, the greater the gain.

1-3


Figure 1—2: A Typical Four-level Transition Scheme (a) Compared to

that of Nd:YAG (b).

A four-level scheme has a distinct advantage over three-level systems,

where E1 is both the origin of the pumping transition and the terminus

of the lasing transition. In the four-level arrangement, the first atom

that is pumped contributes to the population inversion, while over

half of the atoms must be pumped from E1 before an inversion is

established in the three-level system.

In commercial laser designs the source of excitation energy is usually

optical or electrical: arc lamps are often employed to pump solid-

state lasers; the output of one laser can be used to pump another,

e.g., a liquid dye laser can be pumped by a pulsed Nd:YAG laser;

and an electric discharge is generally used to excite gaseous media

like argon or krypton.

Nd:YAG as an Excitation Medium

The properties of neodymium-doped yttrium aluminum garnet(Nd:YAG) are the most widely studied and best understood of allsolid-state laser media. Its transition scheme is compared to the model

in Figure 1—2(b) and its energy IeveJ diagram is depicted in Figure1-3. The active medium is triply ionized neodymium, which is opticallypumped by a flash lamp whose output matches principle absorption

bands in the red and near infrared. Excited electrons quickly drop tothe F372 level, the upper level of the lasing transition, where theyremain for a relatively long time—about 230 lisec.

E3

E2

11502 cm1

2111 ctrf1

(a)

I9/2 Nd + 3

(b)

1-4

Introduction

Figure 1—3: Energy Level Scheme for the Nd:YAG Laser Source

The most probable lasing transition is to the ‘1i12 state, emitting a photon at 1064 nm. Because electrons in that state quickly relax to theground state, its population remains low. Hence, it is easy to build apopulation inversion. At room temperature the emission cross sectionof this transition is high, so its lasing threshold is low. While there arecompeting transitions from the same upper state—most notably at1319, 1338, and 946 nm—all have lower gain and a higher thresholdthan the 1064 nm transition. In normal operation, these factors andwavelength-selective optics limit oscillation to 1064 nm.

A laser made up of just the active medium and resonator will emit apulse of laser light each time the flash lamp fires. However, the pulseduration will be long, about the same as the flash lamp, and its peakpower will be low. A Q-switch is used to shorten the pulse and raiseits peak power.

20—

PumpFZ Bands

18

16 -

14 -

12-

- - -_____

EC.)

10 -

_— 11502 cm R2—------. 11414 R1Laser Transition

8-

Laser I15/2,

Transition

______

6- 115/2

- - - -- 113/2,:

_______

4.

6000 cm1

“4000 cm

2-

0-

___

-- __4

___

—252613/2 - -

-. 111/2 ,:-—---—-- 2473

______

-. -‘:_______

______

- - - - - - -

________________

%/2

_________

.-.-.-.-

Ground Level 311

\ 1340

1—5


0-switchingBecause the upper level of the transition has a long lifetime, a largepopulation of excited neodymium ions can build up in the YAG rod,much as a capacitor stores electrical energy. If oscillation be preventedwhile the population inversion builds, and if the stored energy can bequickly released, the laser will emit a short pulse of high intensity light.

An electro-optic 0-switch introduces high cavity loss to prevent Oscillation. As shown in Figure 1—4 the Q-switch comprises a polarizer,a quarter-wave plate, and a Pockels cell. Applying high voltage tothe Pockels cell crystal changes its polarization retardation characteristics, which determine whether the 0-switch is open (low loss) orclosed (high loss).

5 sec—i’ —

ctor

Quarter-Wave Pockels Cell PolarizerPlate

Figure 1—4: The Q-switch comprises a polarizer, a quarter-wavepolarization rotator, and a Pockels cell.

With no voltage applied, the Pockels cell does not affect the polarization of light passing through it, and the Q-switch functions as follows.The polarizer vertically polarizes light entering the Q-switch, and thequarter-wave plate converts it to circular polarization. As the circularlypolarized light returns from the high reflector, the quarter-wave plateconverts it to horizontal polarization. Because the polarizer only transmits vertically polarized light, it reflects the light out of the resonator,so the cavity loss is high. With voltage applied, the Pockels cell cancelsthe polarization retardation of the quarter-wave plate, so the light remains vertically polarized and suffers minimal loss.

During 0-switched operation the flash lamp excites the Nd ions forapproximately 200 jisec to build up a large population inversion. Atthe point of maximum population inversion, a fast high-voltage pulseapplied to the Pockels cell changes the 0-switch from high to lowloss. The resultant pulse width is <10 nsec, and the peak opticalpower is tens of megawatts.

1—6

Introduction

This short pulse of high peak power is the key to the usefulness ofthe pulsed Nd:YAG laser. Its high peak power permits wavelengthconversion through several nonlinear processes, e.g., frequencydoubling, frequency mixing, dye laser pumping, or Raman frequencyconversion. A short pulse provides excellent temporal resolution offast phenomena like rapid chemical reactions or high-speed motion.

An alternative “long pulse” mode of operation is built in to theGCR. Voltage is applied to the Pockels cell as soon as the flash lampfires, and the Q-switch is held open for the entire lamp firing. Theresult is a train of pulses about 200 i.zsec long, with a separationbetween individual pulses of 2 to 4 isec. The total energy of thepulse train is similar to that of a single Q-switched pulse. This longpulse mode allows safer alignment and set-up, and is useful in experiments where total pulse energy, not its distribution in time, is thecritical factor.

Resonant Optical CavityA resonant cavity, which is defined by two mirrors, provides feedbackto the active medium. Photons emitted parallel to the optical axis ofthe cavity are reflected, returning to interact with other excited ions.Stimulated emission produces two photons of equal energy, phase anddirection from each interaction. The two become four, four becomeeight, and the numbers continue to increase geometrically until anequilibrium between excitation and emission is reached.

Both mirrors are coated to reflect the wavelength, or wavelengths, ofinterest while transmitting all others. One of the mirrors—the outputcoupler—transmits a fraction of the energy stored in the cavity, andthe escaping radiation becomes the output beam of the laser.

There are two major types of optical resonators: stable and unstable(Figure 1—5). The difference between them lies in what happens to aray of light traveling close to, and parallel with the optical axis. Inthe stable resonator the ray is reflected toward the optical axis by itscavity mirrors, so it is always contained along the primary axis of thelaser. By contrast, a ray travelling in an unstable resonator can bereflected away from the axis by one of the cavity mirrors.

Stabl

Unstable

Figure 1—5: Stable and Unstable Resonator Configurations

1—7

Quanta—Ray GCR Series

Stable resonators can only extract energy from a small volume nearthe optical axis of the resonator, which limits the energy of the output. Conversely, unstable resonators can have large beam diameters.Thus, they can efficiently extract energy from active media whosecross-sectional area is large, like that of typical Nd:YAG laser rods.

The output coupler in an unstable resonator can take one of threeforms. In the first case, a small high reflector is mounted on a clearsubstrate and placed on the optical axis of the resonator. Energyescapes the resonator by diffracting around this dot, which gives the“diffraction coupled resonator” (DCR) its name. A second formemploys a partially reflective coating that uniformly covers the wholesubstrate. The third is a variation on the first, where the small highreflector is replaced by a partial reflector with radially variable reflectivity (an RVR optic). This reflector is capable of producing gaussian ornear-gaussian spatial profile at the laser output, and gives the “gaussian coupled resonator” (OCR) its name.

If the energy of the output beam is to be uniformly distributed, theNd:YAG rod must be uniformly illuminated. Placing the flash lampat one focus of an elliptical chamber causes all the light it producesto be reflected through the rod, which is placed at the other focus.

Uniform cooling is also essential to optimal performance of pulsedNd:YAG lasers. When heated, the Nd:YAG rod becomes a lens whosefocal length depends on the average power absorbed. For optimal performance, the high reflector must be matched to the focal length of therod, which must remain stable during operation. The thermal gradientof the rod also causes a radially variable polarization rotation that mustbe carefully controlled for the best beam quality.

Longitudinal Modes and Linewidth

The laser oscillates within a narrow range of frequencies around thetransition frequency. The width of the frequency distribution—theIinewidth—and its amplitude depend on the active medium, its temperature, and the magnitude of the population inversion. Linewidthis determined by plotting the net gain of each frequency and measuringthe width of the curve where the gain has fallen to one-half maximum(full width at half maximum, Figure 1—6).

The output of the laser is discontinuous within the homogeneouslybroadened line. A standing wave propagates within the optical cavity, and any frequency that satisfies the resonance condition

Vm = mc/2L [4]

will oscillate. Vm is the frequency, c is the speed of light, L is the optical cavity length, and m is an integer. Thus, the output of a given lineis a set of discrete frequencies—called “longitudinal modes”—spacedsuch that

zv=c/2L. [51

1—8

Introduction

I

Longitudinal /Modes / 220 MHz

-/ Spacing

I

/

__________

30GHzLinewidth

Figure 1—6: Frequency Distribution of Longitudinal Modes for aSingle Line

An etalon, which is a frequency-selecting element, must be insertedin the cavity in order to reduce the linewidth. Spectra-Physics utilizesan optional Fabry-Perot interferometer that acts as a bandpass filter,introducing enough loss in other modes to prevent them from reaching the lasing threshold (Figure 1—7). The coherence length—thedistance over which the output beam maintains a fixed phase relationship—is inversely proportional to the linewidth:

1= c/v. [4]

Reducing the linewidth increases the coherence length. If the line-width is reduced from 30 0Hz to about 6 0Hz, the coherence lengthincreases from 10 mm to 50 mm.

Longitudinal z Etalon LossModes\ Curve

Figure 1—7: Etalon Loss Minimum Tuned to Laser Gain Maximum

1—9


Producing Other Wavelengths

The high peak power of the Q-switched pulses permit frequency con

version in nonlinear crystals like potassium dideuterium phosphate(KD*p). In the simplest case the 1064 nm Nd:YAG fundamental

interacts with the crystal to produce a secondary wave with half the

fundamental wavelength.

For maximum efficiency the waves must maintain the same speed

and phase relationship throughout the crystal. The index of refrac

tion of most materials depends on the wavelength, decreasing as the

wavelength gets longer. However, some materials are birefringent:

their index of refraction depends on the polarization of the propa

gating waves. In these materials, if the ordinary index of one wave

length matches the extraordinary index of the other, the waves

propagate in phase and at the same speed. Frequency conversion is

most efficient under these “phase matching” conditions.

Phase matching is critically dependent on the temperature of the

crystal and the angle between the direction of polarization and the

axes of the crystal.

With KD*P two phase matching alternatives exist. In Type I phase

matching, the input is along the ordinary axis, and the output is polarized along the extraordinary axis. This leaves the residual inputwavelength linearly polarized. In Type LI the input polarization is atan angle between the extraordinary and ordinary axes, while the output remains polarized along the extraordinary axis. The residual inputwavelength is elliptically polarized. Although either type of phasematching can be used to generate the second harmonic of Nd:YAGin K1)*P Type II is more widely used because of its higher conversionefficiency. However, some experiments require linear polarization ofthe residual 1064 nm light for highest efficiency, and Type I doublingmay yield better overall system performance.

The resultant 532 nm wave can be doubled again by passing itthrough a second crystal, which yields a 266 nm wave. It can also bemixed in KD*P with the residual 1064 nm fundamental to produce a355 nm wave. These four wavelengths— 1064, 532, 355, and 266 nm—cover the electromagnetic spectrum from the near infrared tothe ultraviolet, which enhances the usefulness of the Nd:YAG laser.532 and 355 nm will pump dye lasers with high conversion efficiency.355 and 266 nm are useful for dissociation and photodestructivestudies of many molecules. 1064 nm and 266 nm are widely used foroptical modification of materials and probing of semiconductors.

These fixed frequencies can be extended further through Ramanshifting or by using them to pump a dye laser. The result of the latteris continuously tunable output over a wide range of wavelengths.

1—10

Introduction

Resonator Structural Considerations

The stability of the oscillating frequency depends on the design ofthe resonator structure. Small changes in cavity length, which haveseveral sources including temperature changes and mechanical shifts,cause corresponding changes in the resonant frequency. Cavitylength changes due to temperature can be expressed as

L= oLT [5]

where L is the cavity length, c is the thermal expansion coefficient ofthe resonator structure and T is temperature change. In order toeliminate frequency drift, either c or T must be zero.

The choice of materials affects the length stability of the structure.The ideal material has both a low thermal expansion coefficient anda high ability to distribute heat evenly, causing a constant zT alongthe length of the structure.

Graphite composite, such as that used in the OCR series resonators,have the lowest thermal expansion coefficient of any currently usedstructural material. Since its coefficient is also negative, the thermalcompensation system of the resonator structure can be kept simple.The negative expansion of the graphite rods offsets the positiveexpansion of the metal parts, so the net change remains near zeroover a wide range of temperatures.

Frequency stability also depends on the mechanical rigidity of theresonator structure. Modulation due to “jitter,” the microphonicmovement of cavity mirrors, can be caused by external shock to theresonator structure or acoustic noise. Isolation of the resonator fromthe case that surrounds the laser helps reduce jitter.

1—11


Pulse Triggering Sequence and Timing

Figure 1—8 is a block diagram of the GCR electrical system. It alsodepicts the order and timing of control signals within the system.This simplified diagram provides a means for understanding the operation of the laser and the nomenclature of its input and output signals.A more detailed block diagram, a schematic diagram, and a briefcircuit description are provided in Chapter 9, “Service and Repair.”

.4

A0-switch

Mode

To

A. Trigger .fl_________

B. SCR Gate CurrentC. Lamp CurrentD. 0-switch DelayE. Advanced Sync DelayF Advanced SyncG. Fixed DelayH. 0-switch SyncI. 0-switch Voltage

The source switch selects one of three possible lamp triggering sources:an internal 10 Hz oscillator (10 pps setting), an internal voltage-controlled oscillator (variable setting), or an external signal at thelamp trigger input (external setting).

AdvancedSync

Pulse

0-switch

To

SimmerCurrent

0-switchSync

Ji11

JL

__rn__

Optical Output

Figure 1—8: Simplified Block Diagram of GCR Series Electronics

Long PulseMode

1—12

Introduction

This signal (A) is the trigger source for all subsequent functions. Itfires the SCR gate current generator for the pulse forming networkand the 0-switch delay. The SCR gate current (B) fires the pulseforming network, whose discharge produces a critically damped current pulse (C) through the lamp. The Q-switch delay prevents opening of the Q-switch until the population inversion has built up in theNd:YAG rod. After approximately 225 jisec, its output (D) increasesthe 0 of the cavity to maximum by applying high voltage (I) to thePockels cell.

The mode switch selects the configuration of the 0-switch. ThePockels cell can be fired internally (normal mode), externally by atriggering pulse at the 0-switch trigger input (external mode), or in along pulse mode that provides a pulse of low peak power useful forsystem alignment.

In the normal mode, the 0-switch delay (D) fires a fixed delay (0).Subsequently, the pulse generator is fired (H), providing a sync signal and triggering the electro-optic driver (Marx bank). The highvoltage output of the Marx bank (I) changes the polarization retardation characteristic of the Pockels cell, opening the 0-switch after atotal delay of D +0.

The Q-switch advanced sync signal is also derived from the 0-switchdelay (D). Signal D triggers both the fixed delay (G) described aboveand a variable delay (E), setting up a race between these two pulses.The variable delay pulse is adjustable, so it can end either before orafter the end of the fixed delay pulse. The variable delay pulse triggersthe advanced sync pulse generator (F), whose output either precedesor follows the opening of the 0-switch (I). This creates a pre- orpost-trigger pulse with a range of ±500 nsec.

In the long pulse mode the Pockels cell is triggered at the moment oflamp firing. It is internally charged to provide a long, high voltagepulse that yields a long optical pulse. The 0-switch sync output isinhibited in this mode.

4

1-13


Specifications1’2

GCR-12 GCR-14 GCR-16 GCR-18Model1

s{N S N S(N SjN

Spatial Profile2

Near Field (1 m) 70% 90% 70% 9O% 70% 90% 70% 90%Far Field (cc) 95% 95% 95% 95% 95% 95% 95% 95%Maximum Deviation3 40% 15% 40% 15% 40% 15% 40% 15%

Output Energy (mJ)41064nm 350 275 425 300 675 500 850 600532nm 155 115 180 125 330 215 425 260355nm 70 40 85 45 170 100 185 120266nm 40 30 50 35 80 55 90 65

Repetition Frequency (Hz)Optimum 10 10 10 10 10 10 10 10Range 2—14 2—14 2—14 2—14 2—14 2—14 2—14 2—14

Rod Diameter (mm)’ 8.5 8.5 8.5 8.5 8.5 8.5 8.5 8.5

1. All specflcations subject to change without notice. Unless otherwise specified, specifications are givenfor Q-switchedoperation as 1(364 nm with a standard (nominal 8 ns) pulse width.

2. Nearfield spatial profiles measured 1 mfrom laser using a commercially available beam diagnostic system. 70% and90% refer to the correlation between the actual beam profile and the best least-squaresfit Gaussian profile. Farfieldprofiles are measured at thefocal plane ofa 1 mfocal length lens.

3. Refers to the maximwn deviationfrom the best-fit Gaussian profile measured in the nearfield (1 m) between the FWHMpoints.

4. Harmonic energies are spec(fIed after separation using dichroic mirrorpairs. 532 nm energies are specified using TypeII second hannonic generation (SHG). 355 nm energies are specjfied using Type II SHG. A 10% increase in 355 nmenergies can be specfled when Type I SHG is used.

5. Actual beam diameter will varyfrom rod diameter depending on laser configuration.

Note: These specifications are given in goodfaith and are set at levels that ensure manufacturability and allow reliable longterm operation. Due to the complexity involved in measuring many of the individual specflcations, we cannot demonstrateall performance parameters at the customer site. We will ensure that all energy specifications are met by maldng theappropriate energy measurements and that copies ofourfinal test beam profiles and burn patterns are included with theinstallation ofeach laser. Pulse width and single mode operation can also be demonstrated. All other specflcations can bedemonstrated either at the customer site or at the Quanta-Ray manufacturingfacility. A varying range ofadditional chargesdepending on the complexity of the measurement will be added to the sales price. Please contact your local Spectra-PhysicsLosers representativeforfunher details.

1-14

Introduction

X Pulse Width1 Energy Stability2 { Power Drift3

1064nm 8-9 2% <3%

532nm 6—7 3% <5%

355nm 5—6 4% <6%

266nm 4-5 8% <10%

Beam Divergence4 <0.5 mrad

Pointing Stability3 <250 I.Lrad

Timing Jitter5 <0.5 ns

Linewidth6Standard <1.Ocnr’w/ICE <0.2 cm-1w/Model 6300 Injection Seeder (SLM) <0.003 cm’

1. Nominalfull width halfmaximum (FWHM) pulse width. The shortpulse mode, standard on all GCR lasers, reduces the1064 urn pulse width to approximately 2S us and reduces the pulse energy by approximately 10%. (Short pulse modeavailable on seeded versions on special request only).

2. Pulse to pulse stabilizyfor >99% ofpulses, measured over a 1 hourperiod.3. Over an eight (8) hour period at 1064 nrn, with temperature variations of less than ±3°C.4. Full angle measured at FWHM points.5. nnsfltterfrom Q-,switch rync pulse. Jitter is 1 ns rms when using the Model 6300 injection seeder.6. Insertion lossesfor systems using either an ICE-i intracavity etalon or the Model 6300 injection seeder are less than

10% at1064 nm.

1-15


GCR-12,_-14, -16, and -18

Flash Lamp Life 30 million pulses

Water Service no external service necessary

Electrical Service 10 A

Voltage (nominal)2 190—250 V, single phase

Umbilical Length 305 cm (10 ft)

Size3Laser Head 1022.0 x 343.0 x 230.0 mm (40.25 x 13.48 x 9.06 in.)Power Supply 590.0 x 495.0 x 548.0mm (23.25 x 19.50 x 21.56 in.)

WeightLaser Head 26 kg (57 ib)

Power Supply 70 kg (154 ib)

1. All specflcations subject to change without notice.2. Input transformer has taps at 180,200,220,240, and 260 V. Once a tap is chosen, actual input voltage differing by

more than 65% from nominal voltage may t’4ject operation of the laser.3. Dimensions are listed in order, as: length x width x height.

1-16

Chapter 2 Laser Safety

DAJ’JGER. INVISIBLE LASER RADIATION

The Spectra-Physics Quanta-Ray GCR series are Class IV-High Power Lasers whose beam are, by definition, safety andfire hazards. Take precautions to prevent accidental exposureto both direct and reflected beams. Diffuse as well as specularbeam reflections can cause severe eye or skin damage.

Because the 1064 nm output of an Nd:YAG laser is invisible, it isespecially dangerous. Infrared radiation passes easily throughthe cornea, which focuses it on the retina, where it can causeinstantaneous permanent damage.

Precautions for the Safe Operationof Class IV-High Power Lasers

• Keep the protective cover on the laser head at all times.• Avoid looking at the output beam; even diffuse reflections are

hazardous.• Avoid wearing reflective jewelry while using the laser.• Use protective eyewear at all times. Selection depends on the

wavelength and intensity of the radiation, the conditions of use,and the visual function required. Worldwide vendors are listed inboth the Laser Focus World and Lasers and Optronics buyers’guides. Consult the ANSI, ACGIII, or OSHA standards listed atthe end of this section for guidance.

• Operate the laser at the lowest beam intensity possible, giventhe requirements of the application.

• Operate in the “long pulse” mode whenever possible, especiallyduring alignment of the experiment.

• Expand the beam wherever possible to reduce beam intensity.• Avoid blocking the output beam or its reflection with any part of

the body.• Use an IR detector or energy detector to verify that the laser

beam is off before working in front of the laser.• Establish a controlled access area for laser operation. Limit access

to those trained in the principles of laser safety.

2—1


• Maintain a high ambient light level in the laser operation areaso the eye’s pupil remains constricted, reducing the possibility ofdamage.

• Post prominent warning signs near the laser operation area.

• Set up experiments so the laser beam is either above or beloweye level.

• Provide enclosures for beam paths whenever possible.

• Set up shields to prevent unnecessary specular reflections.

• Set up an energy absorbing target to capture the laser beam,preventing unnecessary reflections or scattering.

CAUTION

Use of controls or adjustments, or performance of proceduresother than those specified herein may result in hazardous radiation exposure.

Follow the instructions contained in this manual for safe operationof your laser. At all times during operation, maintenance, or serviceof your laser, avoid unnecessary exposure to laser or collateral radiation* that exceeds the accessible emission limits listed in “Performance Standards for Laser Products,” United States Code of FederalRegulations, 21CFRI.040 10(d).

* Any electronic product radiation, except laser radiation, emitted by a loser productas a result of or necessary for, the operation of a laser incorporated into that product.

Focused Back Reflection Safety p

Focused back reflections of even a small percentage of the outputenergy of any OCR series laser can destroy its optical components.To illustrate, consider an uncoated convex lens, which reflects about4% of the energy incident on each of its surfaces. While the reflection off the first surface diverges harmlessly, the reflection off thesecond focuses, and the power density at the point of focus is highenough to destroy the Q-switch, Nd:YAG rod, and output coupler ofthe laser. Even antireflection coated optics can reflect enough energyto damage optical components of the laser.

To avoid damage to your laser, minimize back reflections of its out-put beam, and where they are unavoidable, direct them away fromthe optical axis.

WARNING

The OCR warranty does not cover damage caused by focusedback reflections.

p2-2

p

Laser Safety

Maintenance Required to keep this Laser Productin Compliance with Center for Devices and Radiological Health (CDRH) Regulations

This laser product complies with Title 21 of the United States Code ofFederal Regulations, Chapter 1, Subchapter J, Parts 1040.10 and1040.11, as applicable. To maintain compliance, verify the operationof all features listed below, either annually or whenever the producthas been subjected to adverse environmental conditions (e.g., fire,flood, mechanical shock, spilled solvents). The features are identifiedon the radiation control drawing (Figure 2—1).

1. Verify that removing the remote interlock plug prevents laseroperation.

2. Verify that the laser will only operate with the key switch in theON position, and that the key can only be removed when theswitch is in the OFF position.

3. Verify that the emission indicator works properly; that is, it emitsa visible signal whenever the laser is on.

4. Verify the time delay between turn-on of the emission indicatorand starting of the laser; it must give enough warning to allowaction to avoid exposure to laser radiation.

5. Verify that removing the cover shuts off the laser.

6. Verify that, when the cover interlock is defeated, the defeatmechanism is clearly visible and prevents installation of the coveruntil disengaged.

DANGER: HIGH VOLTAGE

Both the laser head and power supply contain electrical circuitsoperating at lethal voltage and current levels. Whenever possible,turn off the laser and disconnect the power line before removingprotective covers. After waiting at least 1 mm for bleed downafter power is off, short high voltage components to groundbefore touching them.

If you must have the covers off while operating the laser, be extremely careful to avoid contact with high voltage terminals andcomponents.

Allow only those trained in high voltage, high current electronics, and who understand the circuitry of the OCR, to service andrepair the laser.

Disconnect the power line and short high voltage electrical components to ground where appropriate, before working on thepower supply.

2-3


Sources of Laser Safety Standards

“Safe Use of Lasers” (Z136.1)American National Standards Institute (ANSI)11th West 42nd StreetNew York, NY 10036Tel: (212) 642—4900

“A Guide for Control of Laser Hazards”American Conference of Governmental andIndustrial Hygienists (ACGIH)6500 Glenway Avenue, Bldg. D-7Cincinnati, OH 45211Tel: (513) 661—7881

Occupational Safety and Health Administration (OSHA)

U.S. Department of Labor200 Constitution Avenue N.W.Washington, DC 20210Tel: (202) 523—8148

2-4

Laser Safety

Figure 2—1: Radiation Control Drawing

0

,,— Protective Housing Aperture

/ Interlock (Far Side) Label

iZ7 HInterlock Certification and ‘Naming EmissionLabel Identification Label Logotype Indicator

Protective Housing Interlock(Far Side/Back)

Key Activated

E Master Control

I r Emission Indicator“ON” Lamp

Remote Interlock—j-”-Connector(Far Side/Back)

11111 IIIININIIIIIIIIIIINIIIIIIIIIIIIIIIIIIIII [

Th

0

r

0 0

lull ulIIlllIullIllIllIllllll 11111

2—5


SPECTRA-PHYSICS INC.1330 TERRA DELLA AVE.MTN. VIEW, CA 94043

MANUFACTURED:

MONTH YR

_______

MODEL SIN_______ThIS LASER PRODUCT COMPUESWITh 21 CFR 1 D40 AS APPUCABLE

MADE IN U.S.A.

Certification andIdentification Label

AIBtSAND INVISIBLE .ER RADIATION

EMITTED FROM ThIS APERTURE

[AVOID EXPOSURE]

Aperture Label

DANGER

k

VISIBLE AND INVISIBLEI LASER RADIATiON WHEN OPENI AND INTERLOCK DEFEATEDI AVOID EYE OR SKIN EXPOSUREI TO DIRECT OR SCATTERED

LON

Interlock Label

VISIBLE & INVISIBLELASER RADIATION

• AVOID EYE a SKIN EXPOSURE TODIRECT OR SCATTERED RADIATION

Nd/1.5J/10CLASS IV LASER PRODUCT

SEE UANLIA.

Warning Logotype

Figure 2—2: Warning Labels

2—6

Chapter 3 Installation and Operation

Unpacking your Laser

Your OCR series laser was carefully packed for shipment; if its cratesarrive damaged, have the shipper’s agent present when you unpack.Inspect each unit as you unpack it: look for dents, scratches, or otherdamage. If you discover any damage, immediately file a claim againstthe carrier and notify your Spectra-Physics representative. Spectra-Physics will correct the problem without waiting for settlement ofyour claim.

Keep the shipping crates. If you file a claim, you will need themto show that shipping caused the damage. If you must return the unitfor service, these special crates provide maximum protection.

Installing the Laser

The following installation procedure is provided for reference only; itis not intended as a guide to the initial installation and set-up of yourlaser. Please call your service representative to arrange an installation appointment, which is part of your purchase agreement. Allowonly those qualified and authorized by Spectra-Physics to install andset up your laser system.

CAUTION

Use of controls or adjustments or performance of procedures other than those specified herein may result in hazardousradiation exposure.

Connecting the Electrical Service

1. The main autotransformer (Figure 3—1) has several taps, eachmarked with a different operating voltage. The range of the auto-transformer is 171 to 252 V. Connect the black wire to the tapthat most closely matches available line voltage. The operatingrange of the OCR is ±5% of this voltage.

2. Connect the power cord to the power line circuit breaker; besure the green wire is connected to earth ground, not neutral.

3-1


Figure 3—1: Main autotransformer isvoltages.

To prevent damage due to freezing, the cooling system of the OCRwas drained before shipment. The following instructions are providedin the event the power supply is moved and the cooling system drained.

1. Pull the return line from the middle of the coolant reservoircover. Insert a long neck funnel in the opening. Fill the reservoir with distilled water.

WARNING

Avoid spilling water on the control board, which contains highvoltage circuitry.

2. Set the laser controls as follows:

Control Setting

Circuit Breaker Closed

Key Switch ON

LAMP Toggle Switch OFF

3—2

Refer to Controls and Connections below for control descriptions.

Filling the Cooling System

tapped for several operating

WARNING

The system must be filled with water before you can operatethe laser. Your Spectra-Physics service representative shouldperform this task during initial installation. Provide 201(5 gal)of distilled water for filling and flushing the system.

p

p

Installation and Operation

Figure 3—2: Cooling System Component Identification

3. Hold the coolant return line over a drain or bucket, then pressthe ON button to start the cooling system pump. Md water to thereservoir, keeping it full, until water flows from the return line.

4. Shut off the laser, then fill the reservoir to capacity. Shove thereturn line back into the hole of the reservoir cover.

Controls and Connections—Remote Control Module

SIMMER indicator—glows when the flash lamp simmer current is on.

LAMP ENERGY control—sets the energy of the flash lamp; its scaleis calibrated in lamp joules (U).

Q-SWitch DELAY control—adjusts the timing of Q-switch firing. Therange is 150—550 psec; the surrounding scale is relative.

VARIABLE control—sets the variable lamp firing rate; the range isapproximately 1—15 pps.

3-3


Figure 3—3: Remote Control Panel

REP RATE selector—selects the source of the lamp firing pulse: 10 Hzoscillator (power line synchronous), VARIABLE oscillator, or anEXTernal source. External control requires a firing pulse at theLAMP TRIG input. Please refer to “Controls and Connections—Power Supply: INPUT Connections—LAMP TRiGger Input” for signalrequirements.

ERROR indicator—located above the SOURCE controls; blinks ifthe computer has selected more than one source of lamp firingpulses at the moment of firing.

ADVanced SYNC control—adjusts the timing of a signal used to synchronize auxiliary equipment with the opening of the Q-switch. Thesignal is available at the 0-SW ADV SYNC output of the power supply:its range of adjustment is ±500 nsec. Refer to “Controls and Connections—Power Supply: OUTPUT Connectors—Q-SWitch ADVanceSYNC Output” for signal specifications.

0-SWitch MODE selector—determines source and timing of controlsignals for the Pockels cell. In the Q-SWitch mode, firing of thePockels cell follows firing of the flash lamp (see Q-SW DELAYcontrol above). In the LONG PULSE mode, Pockels cell and flashlamp firing are synchronous (see REP RATE selector above). In theEXTernal mode, a signal at the 0-SW TRIG input fires the Pockelscell. Refer to “Controls and Connections—Power Supply: INPUTConnectors—Q-SWitch TRIGger Input” for a description of signalrequirements.

ERROR indicator—located above the ADV SYNC ADJ and Q-SWMODE controls; blinks if the computer has selected more then oneQ-switch trigger mode at the moment of firing.

3-4

installation and Operation

SINGLE SHOT switch—determines whether the laser will fire repetilively or in single pulses on command. When in the REPetitive position (down), the REP RATE selector controls the firing rate. When inthe SINGLE SHOT position (up), pressing the FII.E button triggers asingle pulse that is synchronous with the next available flash lampfiring signal, regardless of its source.

COMPUTER/INTernal toggle switch—selects either the remote control module or a computer as controller. This switch remains activewhen the laser is under computer control, so manual control can berestored by switching it to INTERNAL.

LAMP switch—turns on the switching power supply, allowing the flashlamp to fire. If the switch is OFF, the lamp is off, and the INHIBITindicator will glow.OFF button—turns off the laser. The button serves as a power indicator, glowing whenever the power supply is on but the laser is off.

ON button—starts the laser; only operates after the power supplycircuit breaker is closed and the key switch is turned on. The buttonserves as an emission indicator, glowing whenever the laser is on.

Controls and Connections—Power Supply

OUTPUT Connectors

LAMP SYNC (BNC) —provides a pulse synchronous with lamp firing.Pulse width is approximately 2.5 msec having an amplitude of 2 V(p-p) when loaded with 50 . Rise time is approximately 20 nsec.

0-SWitch SYNC (BNC) —provides a pulse synchronous withQ-switching of the laser. Pulse width is approximately 5 msec with anamplitude of 2 V (p-p) when loaded with 50 2; rise time is approximately 20 nsec.

0-Switch ADVance SYNC (BNC)—provides a pulse that appearseither in advance or slightly after firing of the Q-switch. The range isapproximately ±500 nsec. Pulse width is approximately 5 msec with anamplitude of 2 V (p-p) when loaded with 50 . Rise time is approximately 20 nsec.

INPUT Connectors

0-SWitch TRiGger (BNC)—accepts a 5 V signal to fire the Q-switch(Zm = 16 k). The circuit is overload protected. An external timedelay is required.

LAMP TRiGger (BNC)—accepts a 5 V signal to externally fire theflash lamp (Z = 16 k2). The circuit is overload protected.

3—5


Figure 3—4: Power Supply Control Panel

ANALOG STROBE (BNC)—a 5 V signal enables transmission of analoginformation from the remote control module (Z = 16 kfl). Thecircuit is overload protected. The port is wired high which allowsdata transfer. Shorting the BNC connector to ground stops datatransfer. This allows analog programming to be done before the laserfires. This function may be operated in a level or edge triggeredmode. Please refer to Chapter 4, ‘Analog/TrL Computer Interface,”for details.

REMOTE Connector

Accepts a 37-pin “D” connector from the remote control cable.

COMPUTER Connector

Access to the basic computer port; 50-pin “D” connector.

POWER Controls

Circuit Breaker—applies power to power supply circuitry, the keyswitch, and all 110 V convenience receptacles.

Key Switch—applies power to the control electronics. Both the circuit breaker and key switch must be turned on before the remotecontrol module will operate. The OFF lamp on the remote controlpanel glows when power is applied but the laser is off.

IuhIIIIIIIIIIIlIIIIIIlI :... •

IIIlIIIIIIIIIIlIIIIIIIh: .

.

pIaI,iiat.i..*at.liii; IhnhI1IlIlllhlllll 11111

3-6


INTERLOCK FAULT lamp—indicates the status of the interlock loop,which comprises the switching supply air flow sensor, water flow sensor, auxiliary interlock, laser head water temperature sensor, powersupply cover interlock switch, and two laser head cover interlockswitches. When the circuit breaker and key switches are on but thelaser is off, the INTERLOCK FAULT lamp will glow because thecooling water flow is shut off. Pressing the ON button starts the coolant pump, clearing this interlock fault. An interlock fault shuts offthe laser. To restart, clear the fault, then turn the LAMP ENERGY tozero (0 LI) and wait for the time delay to actuate, about 10 sec.

PURGE Controls

PUMP ON—starts the air purge system.

Flow meter—monitors purge gas flow. It should be set at 0.25 scf/hfor normal operation. Allow about 10 mm between turning on thepurge system and starting the laser.

NITROGEN IN—fitting for an external nitrogen supply. Turn off thepurge pump when using external gas. A pressure control valve capable of regulating under 1 psi should be used on the nitrogen source.

Desiccant condition monitor—the desiccant cartridge, which ismounted behind the control panel, can be seen through the horizontal row of ventilating holes above the flow meter. As the desiccant isconsumed, its color changes from blue to pink. Since the gas flow isfrom left to right, the boundary between the colors will progress tothe right as the cartridge ages. Change the desiccant cartridge, theoil filter, and the particle filter when all of the desiccant has changedcolor, i.e., when the pink portion reaches the white molecular sievesection. At a flow rate of 0.25 scf/h, the cartridge should last morethan 1000 hrs under conditions of moderate humidity.

Power Supply Rear Panel

Convenience receptacle—provides 110 V for relay control of accessories, e.g., a dye pump. Maximum power available is 10 W. Closingthe power supply circuit breaker energizes the receptacle.

Remote interlock plug—allows use of other safety interlock devices,e.g., a switch mounted on the door of the laser operation area thatshuts off the laser if the door opens while the laser is on. Wire remoteinterlocks using a shielded pair of twisted wires that are isolatedfrom ground.

WARNING

Accidental grounding through the remote interlock will damage the laser circuitry.

If no remote interlock is used, install a jumper to close the circuit.

3-7


Controls and Connections—Laser Head

0-switch Driver (Marx Bank) Box

INPUT connector (BNC)—accepts the Q-switch control signal.

OUTPUT connector (BNC)—transmits the Q-switch control signal.FAST produces a 2.5 nsec optical pulse from the cavity; SLOW produces an 8 nsec (nominal) optical pulse.

DANGE& HIGH VOLTAGE

5 kV is present at these connectors. Shut off the laser (press theOFF button) before changing outputs.

Figure 3—5: Q-switch Driver (Marx Bank) Box

Emission Indicator

The indicator glows whenever the laser is capable of emitting laserradiation.

Convenience Receptacle

110 V is available for low-power (approximately 10 W) auxiliaryequipment, e.g., the harmonic generator temperature stabilizer.Closing the power supply circuit breaker energizes the receptacle.

3-8


Starting the Laser

Figure 3—6: Head Emission Indicator (Convenience Receptacle is onopposite side.)

1. Set controls as follows:

Control Setting

LAMP ENERGY START

Q-SW DELAY 25

REPRATE lOpps

Q-SW MODE LONG PULSE

COMPUTER toggle switch INTERNAL

SINGLE SHOT toggle switch SINGLE SHOT

LAMP toggle switch ON

2. Make sure the power supply circuit breaker is open (off), thenclose the power line circuit breaker.

3. Close the power supply circuit breaker.

3—9


4. Press the ON button.

5. Switch on the air pump and set the flow rate to 0.25 scf/h; allowabout 10 mm. operation to purge the cavity before proceeding.

6. Raise the LAMP ENERGY to position 7 on the dial.

7. Obtain a burn pattern. Place a piece of unexposed but developedPolaroid film in the beam path about 1 m from the output couplerand press the SINGLE SHOT FIRE button once.

DANGER

Avoid looking at the film when taking a burn pattern.

p

8. If the burn pattern is asymmetrical or has flared edges, check thecavity alignment. If the burn pattern is symmetrical, switch theQ-SW MODE to Q-SW. Obtain another burn pattern by pressingthe SINGLE SHOT FIRE button once. If the burn pattern remainssymmetrical, you can safely raise the LAMP ENERGY to maximum and increase the repetition rate, i.e., switch the REP RATEto 10 pps or switch it to VARIABLE and increase the rate to thelevel desired.

NOTE

Low line voltage or a momentary line dropout will trigger protective circuitry in the laser. If this happens, an LED on theswitching power supply will glow. To restore operation, openthe power supply circuit breaker, then close it again.

WARNING

Only allow those trained and authorized by Spectra-Physics toadjust the alignment of your GCR series laser. Misalignmentcan permanently damage cavity optics, and such damage is notcovered by warranty.

3-10

Chapter 4 Computer Interface Module (CIM-1)

Functional Overview

The OCR laser system comes standard with both a REMOTE controller and COMPUTER interface, the latter being a proprietary analog/TTL interface. The optional Computer Interface Module(CIM-1) offers two standard interfaces to connect the laser to a localor remote computer or terminal source. The remote controller, ifconnected, is active no matter if the computer interface is used. Forthe system to operate with the CIM-1, both the OCR circuit breakerswitch and key switch must be on.

With the CIM4 the GCR can be operated from either a serialRS-232-C or parallel IEEE 488 interface (the latter also known as theGeneral Purpose Interface Bus or OPIB). Setup and programmingfor each is described in detail in this chapter. Connectors for bothports are located on the control panel of the power supply, to theright of the REMOTE connector.

The OCR can be controlled by computer with or without the remotecontroller attached. Using the system with the remote controllerattached requires someone to manually enable the system. The INT/COMPUTER switch must be set to COMPUTER and theON/ENABLE pushbutton pressed in order to transfer control to thecomputer. Because someone is required to manually start the system,this mode provides an extra measure of safety when the computer islocated in a remote area.

Disconnecting the remote controller transfers control entirely to thecomputer, including automatic turn on, without intervention by alocal operator. This mode of operation requires a jumper plug to beconnected in place of the remote controller.

4-1

I

The CIM- 1 computer interface module contains separate inputs forthe IEEE 488 parallel and RS-232-C serial interfaces. There are noswitches or jumpers used to select one or the other. However, onlyone interface can be used at a time; each controls OCR hardwarecommon to both. Simply connect the computer to the interface ofchoice, set the parameters for that interface, and use it.

The CIM-1 module comprises three components: power supply, standard interface pc board (the bottom pc board, Figure 4-1), and theproprietary interface pc board (the top pc board). The CIM-1 moduleis located behind the front panel, to the right of the COMPUTER andREMOTE interface connectors. This chapter describes how to program and use the CIM-1.

Figure 4—1: Location of CIM-1 PC Boards


CIM-1 Low VoltagePower Supply

CIM-1 StandardInterface Board

I

I

I

RS-232-CInterface

CIM-1 ProprietaryInterface Board

IEEE 488Interface

4-2

Computer Interface Module

Computer Control and Diagnostic Functions

The following control and diagnostic functions are available under

computer control:

Control Functions

• Laser on/off

• External lamp fire enable

• Variable rep rate enable

• 10 pps enable

• Q-switch fire enable

• Long pulse enable

• External Q-switch fire enable

• Single shot/rep rate select

• Single shot fire

• Analog strobe

• Lamp blank

• Lamp fire

• Computer interlock clock

• Computer interlock enable

• Q-switch delay

• Pulse forming network (PFN) voltage set

• Rep rate set

• Q-switch advance sync

Diagnostic Functions

• PFN voltage monitor

• Simmer voltage monitor

• System interlock monitor

• Computer interlock monitor

Power-On Default State and System Initialization

When the system is first turned on, the C1M-1 interface is disabled toprevent the occurrence of random events before the controlling software can configure and control the system. Two initializing commands must be used before the system will operate. The firstinitializes the CIM-1 module itself. “CIM-1 Commands: CONFIGURE” provides information about this routine.

Secondly, the command SET 2,0 must be used to set the lamp energy(PFN voltage) to zero, a pre-requisite for operating the GCR. (Thisis the same as setting the remote control’s Lamp Energy control toSTART.)

4-3


Computer Safety (Watchdog) Interlock

The CIM-1 can detect a communication failure between itself and theGCR. If a failure occurs, the CIM-1 opens the interlock circuit andshuts down the laser. This feature can be disabled. Refer to “C]M-1Commands: WRiTE 7, n” for information on initializing this function.

IEEE 488 Interface

Operation

The IEEE 488 interface conforms to the ANSI/IEEE standard488-1978 and comprises a user-supplied bus controller and from 1 to32 I/O devices that are defined and addressed by the controller astalkers, listeners, or talker-listeners.

Talkers are input devices that can only monitor events and send datato the controller, e.g., digital voltmeters. They “talk” to the controller.Conversely, listeners are output devices that “listen” to the controllerand send signals from it to the real world, e.g., digital to analog converters (DACs). Talker-listeners operate in both directions. TheCIM-1 is just such a device. When the C1M-1 is properly programmed,the controller will execute data transfers to and from it via theIEEE 488 bus.

Command strings sent from the controller to the CIM-1 need to beterminated by a comma (,) or line feed (<LF>). Unlike some IEEE488 interfaces, the CIM-1 does not require the END command toterminate messages to it (refer to “Message Formats” below).

Nevertheless, to conform with controllers programmed to recognize theEND command, the CIM-1 sends it to terminate all data transfers.

Remote Reset

The CIM-1 can be reset to the power-on default state any time bysending it either a Device CLear (DCL) or Select Device Clear(SDC) bus message, or Inter Face Clear (IFC) bus reset. Refer to“Power-On Default State” above and to your controller’s user manualfor details.

NOTE

After receiving a DCL or SDC command, or TFC signal, theCIM-1 takes about 0.5 sec to reinitialize. Therefore, the controllermust not send messages to the CIM- 1 during this time. Programswill require a delay routine immediately following any resetcommand.

4-4


Serial Poll Status Byte

The CIM-1 responds to the IEEE 488 Serial Poll Enable (SPE) message by returning a status byte indicating (a) the execution status ofthe last command received, and (b) the version number of the CIM-1firmware (used for factory diagnostic purposes). Figure 4-2 shows thecomposition of the status byte. This status byte is provided primarilyto facilitate error masking and recovery. This feature is standard onall IEEE 488 controllers.

Most LeastSignificant SignificantBit Bit

7 6 5 4 3 2 1 0

I I0 0 Firmware Version Command Data Operation

Error Ready Complete

Figure 4—2: Diagram of the serial poll status byte.

Bit 0 is set (1) when the CIM-1 finishes executing a command. It isreset (0) during the execution of a command.

Bit 1 is set when the CIM-1 has finished executing the SAMPLEcommand, and response data is ready for output to the controller. Itis reset when the CIM-1 has finished sending the response to thecontroller.

Bit 2 is set when an error is detected in the command line, and theCIM-1 has aborted the command.

Bits 3, 4, and 5 indicate the firmware version as a three-bit binarynumber. Bit 5 is the most significant bit.

Bits 6 and 7 are always zero.

The IEEE 488 controller performs a serial poll of the CIM-1 by executing an SPE command. The CIM-1 will automatically respond bysending back the status byte.

NOTE

Each IEEE 488 controller manufacturer has its own way ofquerying the input device for the serial status byte. Refer to yourIEEE 488 controller hardware manual for samples of BASICstatements to be used.

4-5


The following is a BASIC statement used by the JO-Tech Personal 488GPIB Controller Card:

?rnt #1, “SPOLE’Input #2, A$

Print is a BASIC output statement. The controller attached to theCIM-1 has been designated device #1 for output. “SPOLE’ is theSPE command that causes its controller to request a status byte. Refer to your IEEE 488 controller manual for specific I/O device setupinformation and command language.

Input is a BASIC input statement. The controller attached to theCIM-1 has been designated device #2 for input, even though onlyone controller card is likely to be used for both input and output.The requested status byte is read into the IEEE 488 controller as BASIC variable ‘A$.”

SW2 DIP Switch Setting

The CIM-1 IEEE 488 hardware interface is easy to configure. Simplyselect a device address that is different from that of all other devicesattached to the same bus. Dll switch SW2 on the standard interfaceboard sets the address from 0 to 31. The factory setting is 25.

Table 4—1: SW2 DIP Switch Settings for SelectingDevice Address

Switch Number 1 2 3 4 5

Bit Weight 16 8 4 2 1

Factory Setting (25) On (16) On (8) Off Off On (1)

RS-232-C Serial Interface

Operation

The RS-232-C interface standard classifies serial I/O devices as eitherData Terminal Equipment (DTE) or Data Communications Equipment (DCE). The standard further identifies a serial connector as a25 pin, D-sub type, and defines its 25 pins as various data and control lines. However, the standard does not narrowly define each ofthese signals and, unfortunately, manufacturers of serial I/O deviceshave provided incompatible definitions. As a result there is no guaranty that any two devices will communicate with each other until allhardware and data format settings have been configured to matchthe requirements of the mating device.

4-6


The serial interface of the CIM-1 is an RS-232-C compatible interfaceconfigured to emulate DCE equipment. Signal inputs and outputs ofthe serial interface will be compatible with most computers and terminals configured as DTh equipment. If the CIM-1 is connected toanother DCE device, an interface cable adapter that switches thedata signal lines, pin 2 with pin 3, and control signal lines, pin 4 withpin 5, is usually all that is required to make the devices compatible.

The following diagram shows the interface signals and interconnections used by the CIM-1. The data link signals are named relativeto the DTE.

Terminal (DTE) RS-232-C Link CIM-1 (DCE)

TXD (2) . - - - - Transmitted Data a (2) RXD

RXD (3) . --. Received Data (3) TXD

RTS (4) - - - - Request To Send . (4) CTS

CTS (5) * - - - - Clear To Send . (5) RTS

DSR (6) .., - -- Data Set Ready a (6) DTR

DCD (8) .. - - -- Data Carrier Detect - - a (8) DCD

DTR (20) - - - - Data Terminal Ready - , (20) DSR

(7) . - - - - Signal Ground (7)

(1) - - -. Protective GrouncL ,.. (1)

Figure 4—3: Standard RS-232-C Interconnections

Data Transfer and Handshaking

The RS-232-C serial interface operates in the full duplex mode: datamay be sent and received simultaneously. To synchronize data transmissions with the RS-232-C controller, the CIM-1 implements a simple hardware handshaking protocol to monitor and control theinterface signals. The following interface signals are named relativeto the data terminal device.

Data Terminal Ready and Request To Send

The CIM-1 checks both lines when it has response data to send. Itsends data only when both signals are high (1).

Data Set Ready, Clear To Send, and Data Carrier Detect

The CIM-l. keeps these lines high at all times; thus, it is always readyto receive commands from the RS-232-C controller.

4-7


SW1 DIP Switch Setting

Both the CIM4 and the RS-232-C controllers must be configured tosend and receive data at the same rate. Positions five through eighton DIP switch SW1 on the standard interface board set the bit transmission (baud) rate for the C]M-1. Match the controller baud rate tothe chosen (DIM-i rate. The factory setting for the CIM-i is 4800 baud.

Table 4—2: SW1 Baud Rate Settings

Switch Number Switch Position

5 Off Off Off Off Off Off Off Off On

6 Off Off Off Off On On On On Off

7 Off Off On On Off Off On On Off

8 Off On Off On Off On Off On Off

Baud Rate 75 110 150 300 600 1200 2400 4800 9600

There are also three data format settings on the two communicationsdevices that must match: character length, parity, and stop bit(s). SW1also sets these parameters. The factory setting is eight-bit characterlength, parity disabled (odd/even is ignored), and two stop bits.

Table 4—3: SW1_Mode_Select_Settings

Switch Number Switch Position Condition Switch Position Condition

1 Off Parity Disabled On Parity Enabled

2 Off Odd Parity On Even Parity

3 Off One Stop Bit On Two Stop Bits

4 Off Seven Bits per On Eight Bits perCharacter Character

5W3 DIP Switch Setting

DIP switch SW3 on the standard interface board can be used toforce the Data Terminal Ready (DTR) and Request To Send (RTS)signals high (1). This may be necessary because some computers andterminals ignore one or both signals. If so, the appropriate signal(s)must be set high to enable communications between the two devices.To force the DTR or RTS line high, set the DTR or RTS switchesON. The two switches are clearly marked on the standard interfaceboard next to SW3.

Message Formats

Command Format

Information in this section applies for both the IEEE 488 andRS-232-C interfaces.

4-8


A command is a string of ASCII characters that the computer sendsto the CIM-1. A command consists of a single command word andup to three additional data or keyword elements using one of the following forms:

<command word> <LF><commandword> <data> <LF><command word> <data>, <data> <LF><commandword> <data>, <keyword>, <keyword> <LF>

For each command word, the CIM-1 expects to find appropriate dataor keyword elements following it. Data is always in integer form.

Command words and keywords are reserved words that have uniquemeaning to the CIM-1 and can only be used for narrowly definedpurposes.A command includes delimiter characters that separate commandelements and terminate each command. The comma (,) and line feed(<LF>) characters are used interchangeably for this purpose. Typically the comma is used between elements of a command with<LF> used to terminate the command. The delimiter between thecommand word and the element(s) following may be omitted.

Command words and keywords may contain either upper or lowercase alpha characters. Spaces and all nonprintable characters, except<LF>, are ignored by the CIM- 1. Consecutive delimiters are interpreted as a single delimiter, and all but the first is ignored.

Examples

SET 1, 127 <LF>WRITE 4, 1001B, WRITES, O11OB <LF>Sample 3 <IF>

Command words and keywords may be abbreviated (Figure 4—4), butthey must include at least the first three characters. Whether spelledout or abbreviated, commands must be spelled correctly or they willbe aborted.

An input error occurs if any part of a command is invalid, e.g., a misspelled command word or keyword, a data value out of range, or anincorrect number of elements in the command. When an input erroris detected, the CIM-1 aborts command processing and waits for thenext command. Bit 2 of the IEEE 488 interface status byte register isset (1) (refer to “IEEE 488 Interface: Serial Poll Status Byte”).

Response Format

After executing a SAMPLE command, the CIM-1 sends the requesteddata to the computer followed by a carriage return and line feed:

<response> <CR> <LF>

The CIM-1 also sends the END message to terminate transmission ifthe IEEE 488 interface is used.

4-9


CIM-1 Commands

The following five commands allow you to control and monitorselected digital and analog I/O lines of the CIM-1:

Command Word Shortest Abbreviated Form Acceptable

CONFIGURE CON

SAMPLE SAM

SELECT SEL

UTE WRI

SET SET

Keywords used with CONFIGURE Command

NONCLOCKED NON

OUTPUT OUT

Figure 4—4: Command Word Abbreviations

CONFIGURE p, OUTPUT, NONCLOCKED

where p = 4, 5, 6, or 7

For the CIM-1 to work properly, every program must begin by initializing four internal CIM-1 ports using the CONFIGURE commandonce for each port.

Example

These four BASIC statements must be written to the CIM-1 beforeany other commands:

Print #1, “Configure 4, Output, Nonclocked”Print #1, “Configure 5, Output, Nonclocked”Print #1, “Configure 6, Output, Nonclocked”Print #1, “Configure 7, Output, Nonclocked”

Refer to your IEEE 488 controller manual for specific hardware setup information and to your BASIC manual for information on BASICcommand statements.

4-10


SAMPLE awhere a = 1 to 4

This command directs the CIM-1 to sample the following:

Table 4-4: SAMPLE a Command Functions

a Monitor Function Interpretation

Value from 0 to 254

1 PFN Voltage Data = 1 10 V PFN Voltage

Data = 200 1800 V PFN Voltage

• Data > 200 Simmer is ON2 Simmer

Data < 200 Simmer is OFF

Data > 200 Interlock fault3 Interlock

Data < 200 All interlocks closed

Data > 200 Computer interlock

4 Computer faultInterlock Data < 200 Computer interlock

closed

SELECT c

where c = 1 or 2The CIM-1 multiplexes two major groups of I/O ports on the proprietaiy interface board. The SELECT command singles out one of twomajor groups to be addressed by the WRiTE command. (Refer toTables 4—5 and 4—6 for a functional listing of the two groups.)

WRITE p, nwhere p = 4, 5, 6, or 7, and

n = a four-bit binary number (0000b to hub) or a decimalequivalent from 0 to 15

The WRiTE command sets and resets four control lines at a time (n)that belong to one of four sub-groups (p) that make up one of twomajor groups selected using the SELECT command. Refer to Tables4—5 and 4—6. The four-bit number used with the WRITE commandis represented as either a binary or decimal number. Binary numbersrequire four digits followed by the suffix b; decimal numbers requireno suffix.

Examples

WRITE 4, ilOOb orWRITE 4, 12

Some functions require other functions to be preset, while others aremutually exclusive. Often two or three WRITE commands will berequired to perform a single operation because of the interaction ofcontrol functions. Refer to Chapter 1, “Introduction: Pulse TriggeringSequence and Timing,” and Chapter 3, “Installation and Operation,”for details on operation and control.

4-11


4-12

Table 4-5: SELECT 1, WRITE Command Functions

Command Function

WRITE 4, xxxlb Turn system onmOb Turn system offxxlxb External lamp fire enabledxxOxb External lamp fire disabledxlxxb Variable rep rate enabledx0xxb Variable rep rate disabledlxxxb lOpps rep rate enabled0mb lOpps rep rate disabled

WRiTE 5, xxxlb Internal Q-switch trigger enabledxxx0b Internal Q-switch trigger disabledxxlxb Long pulse enabledxx0xb Long pulse disabledxlxxb External Q-switch fire enabledx0xxb External Q-switch fire disabledlxxxb System set for repetitive firingOxxxb System set for single shot

WRITE 6, xxxlb Single shot trigger pulsedxxx0b Single shot trigger reset (must be reset

after each shot)xxlxb Analog strobe readxx0xb Analog strobe latch (last value latched)xlxxb Lamp blank enabled (lamp cannot fire)x0xxb Lamp blank disabled1mb Lamp trigger pulsedOxxxb Lamp and Q-switch trigger reset

WRITE 7, xxxlb Computer interlock clock reset (low tohigh transition)

xxx0b Reset pulse (high to low transition)from WRITE 7, xxxlb

xxlxb Computer watchdog interlock enabledxxOxb Computer watchdog interlock disabled


Table 4-6: SELECT 2, WRITE Command Functions

Command Function

WRITE 4, n Sets the lower four bits for Q-switch advance sync(—700 to + 400 nsec)

WRITE 5, n Sets the upper four bits for Q-switch advance syncWRITE 6, n Sets the lower four bits for lamp repetition rate

(0.1 to 15.0 pps)WRITE 7, n Sets the upper four bits for lamp repetition rate

SELECT 1, WRITE 4, n

Turns system power on or off and selects one of three modes of lampoperation: external lamp fire, variable rep rate, and 10 pps fixed. Ifmore than one lamp trigger source is selected, the SOURCE ERRORlamp lights on the remote control box, and the OCR is disabled untilthe error is cleared by writing a correct command sequence.


Selects the configuration of the Q-switch: internal or external trigger, orlong pulse , and also determines whether the OCR will fire repetitivelyor in single shots. If more than one Q-switch mode is selected, theQ-SW MODE ERROR lamp on the remote control box will light, andthe OCR is disabled until the error is cleared by writing a correctcommand sequence.


Controls lamp trigger, lamp blank, analog strobe, and single-shot trigger.Lamp trigger and Q-switch trigger both require a programmed positive-going pulse; therefore, the corresponding bit must be toggled high totrigger, then reset to get ready for the next pulse. Lamp blank is aninhibit function. Analog strobe is a sample-and-hold function where ahigh logic level causes the set point to follow the analog input and alow logic level latches the last analog reading. It is used to set analogset points for controlling Q-switch advance sync, Q-switch delay, variablerep rate, and PFN voltage monitor.


Controls the computer interlock system. Three conditions are requiredto enable the computer watchdog interlock:

1. The watchdog interlock interval timer must be preset to a valuebetween 1 and 255 sec via the watchdog timer DIP switch SW1on the proprietary interface board (Figure 4—5). The bit weightsfor each of the switches are marked on the pc board.

2. The computer interlock enable line must be high.

4— 13


3. Software must toggle the computer interlock clock line with thefollowing commands:

WRITE 7, 3WRITE 7,2

Your program must constantly issue this pair of commands tocontinuously toggle the computer interlock clock, and the timebetween toggles must be shorter than the time-out period set bythe watchdog timer switch SW1. In essence, your program mustkeep reseting the interlock watchdog to prevent it from timingout and causing an interlock fault. Thus, if your program crashesand fails to reset the watchdog, an interlock fault results and thesystem shuts down.

The computer interlock function can be defeated by setting the computer interlock enable line low.

Two diagnostic LEDs indicate the status of the computer interlock(Figure 4-5). The computer interlock clock LED blinks once for eachprogrammed toggle. Then, when and if there is a fault condition, thelaser will shut down and the computer interlock monitor LED turns on.

fr

r1 ua

LJLj I

N. P;Zc23

RIG

H9

XR11 Un EXPAISIOGI Pta

?.SSY D44UtUO V

air _.a0

pta

C

•

a,02

sauna

SW 1

- IO1R)

CaP OFF- ONI()‘OFF Ic[OFF I•-JOFF_I

°QEEJ

/Computer InterlockClock LED, DS 1

Computer InterlockMonitor LED, DS 2

Figure 4—5: CIM-1 Proprietary PC Board (Top Board)

4-14


SETd,nwhere d = 1 and n = 0 to 250 (to set the Q-switch delay)

or d = 2 and n 0 to 200 (to set the PFN voltage)*

The SET command is used to set analog values that govern the0-switch delay time and the PFN voltage.

To set the 0-switch delay in the range 60 to 278 p.sec:

n = INT (—-- (delaY)+318)

To set the PFN voltage in the range 0 to 1800 V:

= desired voltage10

* The maximum PFN voltage ilamp energy is hardware limited by theelectronics on the CIM-1. Each laser system is individually adjusted atthe factoiy. This feature prevents the software program from creatingdangerous energy levels in the laser cavity, thereby avoiding potentialdamage to various optical components. The value of the limit is providedon the test report accompaning the laser for the software programmer

NOTE

If precision is required for setting the PFN voltage, it is necessary to correct for an inherent offset in the electronics. Measurethe real sense voltage at TP24 on the control pe board or bysampling PFN voltage monitor, and compare this value to theprogrammed value of PFN voltage set. The difference is the inherent offset of the system. Either add this offset to (if the PFNvoltage is less than the measured voltage) or subtract it from (ifthe PFN voltage is greater than the measured voltage) the programmed value used to set the PFN voltage.

ExamplesExternal lamp fire

If external lamp fire is selected:

SELECT 1, WRITE 4, xxlxb

the command

SELECT 1, WRITE 6, lOxxb

must follow it to disable lamp blank and to enable lamp trigger, thusallowing external triggering.

Variable rep rateIf variable rep rate is selected, an 8-bit value equal to the rep rate(0.1 to 15 pps) must be written using two, four-bit binary or decimalnumbers. To determine that number, first find the value for countwhere rep rate is 0.1 to 15 pps:

4-15

IQuanta-Ray GCR Series

rep ratecount = 255

15

Next, find m, the integer value of count divided by 16:

m = INT count16

Next, find n, the integer remainder from the above division:

n = INT(count—(l6xm)) orn = TNT (count MOD 16) [BASIC statement]

Finally, insert the values for n and m in the appropriate WRITEstatements:

SELECT 1WRITE 4, xlxxb [selects variable rep rate]

SELECT 2WRITE 6, n [sets lower 4 bits]WRITE 7, m [sets upper 4 bits]

Example

To set a rep rate of 12 pps:

count = 255 ---- = 20415

m=TNT =1216

n = count (16 x m) = 12

Plug in the values for m and n:

SELECT 2WRITE 6,12WRITE 7, 12

Q-switch Advance Sync

Selecting Q-switch advance sync also requires an 8-bit number representing the value chosen to be written in two, 4-bit binary or decimalnumbers. To determine that number, first find the value for count,where adv sync is a value from —700 to + 400.

count = —47+ 66656adv sync + 945

Next, find the integer m:

=count

16

p

4-16


and n, the integer remainder from above:

n = INT (count) 16— m)) orn = INT (count MOD 16) [BASIC statement]

Finally, insert the values for n andm in the appropriate WRITEstatements:

SELECT 2 (selects Q-switch advance sync)WRITE 4, n (sets lower 4 bits)WRITE 5, m (sets upper 4 bits)

Example

To set Q-switch advance sync for —500 nsec:

count = —47+ 66656= 103

—500 + 945

Next, find the values for m and n:

m=INT- =616

n = count — (16 x m) or

n=103—(16x6) =7

Plug in the values for m and n:

SELECT 2WRITE 4, 7WRITE 5, 6

Sample Analog-to-Digital Conversion

Actual PFN voltage is four times the sampled voltage. To find theactual PFN voltage (0 to 1800 V), query PFN voltage monitor usingthe SAMPLE 1 command, then multiply by 10:

PFN voltage = SAMPLE 1 x 10

Example

If SAMPLE 1 returns a count of 100,then PFN voltage = 100 x 10 V orPFN voltage = 1000 V

Lamp energy can now be determined from PFN voltage using thefollowing equation:

Lamp energy = 0.000025 x (PFN voltage)2L J

Example

If PFN voltage = 1000 VThen lamp energy = 0.000025 x 10002

Lamp energy = 25.0

4—i 7


Example Commands Using GW Basicon a Personal ComputerExample 1: RS—232 set—up, laser turn on and off

OPEN “COMi: 4800,N,8,2,” FOR RANDOM AS 1pB.II’T’#1,PRINT#1, “CONFIGURE 4, OUTPU] NONCLOCKED”PRINT#1, “CON 5, OUT, NON,”PRINT#1, “CON 6, OU’l NON, CON 7, OU’I NON,”PRINT#1, “SELECT 1,”PRINT#1, “WRI 4, 0, WRI 5, 0,”PRINT#1, “WRI 6, 0, WRI 7, 0,”PRINT#1, “SELECT 2,”PRINT#1, “WRI 4, 0, WRI 5, 0,”PRINT#1, “WRI 6, 0, WRI 7, 0,”PRINT#1, “SEL 1, WRI 4, 0001B,”PRINT#1, “WRI 4, 0000B,”

‘Initialize COM1 as input/output‘Clear CIM-1 RS-232‘Initialize CIM-1

‘Open CIM-1 digital ports‘Initialize CIM—1 digital ports

‘Open expansion digital ports‘Initialize expansion digital ports

‘Turn on power‘Thrn off power

Example 2: Start simmer (assumes power is on—see Example 1)

PRINT#1, “SEL 1,”PRINT#1, “WRI 6, OO1OB,”PRINT#1, “SET 2, 0,”

‘Analog read‘Set PFN to 0 V

Example 3: Q-switch off, lamps at 10 Hz/60 U (assumes simmer is on)

PRINT#1, “WRI 5, 000DB,”PRINT#1, “WRI 4, 1001B,”PRINT#1, “WRI 6, OO1OB,”PRINT#1, “SET 2, 155,”

‘Q-switch disabled‘Enable 10 Hz lamp operation‘Analog read‘Set PFN volts: J = 0.000025 — V2

For6OU,PFNV = 1549See “SET d, n” for algorithm

Example 4: Q—switch on with 100 jisec delay. Lamps at 1 Hz/60 J (assumes simmer is on)

PRINT#1, “WRI 6, OO1OB,”PRINT#1, “SET 2, 155,”PRINT#1, “SET 1, 204,”PRINT#1, “SELECT 2,”PRINT#1, “WRI 6, 1,”PRINT#1, “WRI 7, 1,”PRINT#1, “SELECT 1,”PRJNT#1, “WRI 5, 1001B,”PRINT#1, “WRI 4, O1O1B,”

‘Analog read‘Set lamp to 60 U‘Set Q—switch delay to 100 isec

‘Set rep rate to 1 pps (lower 4 bits)‘Set rep rate to 1 pps (upper 4 bits)

‘Enable Q—switch and repetitive firing

4-18


Example 5: Q—switch single shot lamps at some fixed rep rate and PFN voltage(Assumes some preprogrammed rep rate and PFN voltage setting,as well as a preprogrammed Q—switch delay setting—see example 4)

PRINT#1, “WRI 5, 0001B,”PRINT#1, “WRI 6, 0001B,”PRINT#1, “WRI 6, 000DB,”

‘Enable Q-switch and single shot mode‘Send a single shot trigger pulse‘Reset single shot trigger‘Result: 0-switch will fire on Q-switch delay

from next lamp trigger pulse. Note: Thissingle shot mode of operation producespredictable output mode characteristics.

Example 6: Q—switch single shot lamps simmering(Assumes some PFN voltage and Q—switch delay is set—see example 4)

PRINT#1, “WRI 6, 001DB,”PRINT#1, “WRI 4, OO11B,”PRINT#1, “WRI 5, 0001B,”PRINT#1, “WRI 6, 00018,”PRINT#1, “WRI 6, 1000B,”PRINT#1, “WRI 6, 0000B,”

‘Lamp trigger and single shot off‘Enable external lamp fire‘Enable single shot and Q-switch fire‘Thgger Q—switch Single shot‘Send a lamp trigger‘Thin off single shot and lamp trigger‘Result: 0—switch will fire on Q—switch delay

from lamp trigger pulse. Note: outputmode characteristics are not guaranteed.Example 5 mode of single shot operationis preferred.

Example 7: External Q-switch fire(Assumes lamps at 10 Hz/60 3—see example 2) Setup: a delaying pulse generator is required to inject a 0 to 5 V signal into the “Ext Q—Sw Trig” BNC on the rearpanel. The pulse generator is triggered from the “Lamp Sync” BNC on the rearpanel and adjusted for a pulse width of 1 msec and appropriate 0—switch delay.

PRINT#1, “SEL 1,”PRINT#1, “WRI 5, 110DB,”

PRINT#l, “WRI 5, 000DB,”

‘Enable external Q-switch fireResult: Q—switch will fire at 10 Hz

‘Disable external Q-switch fireResult: 0—switch will stop firing. Note:this method is useful when more precision is required than the 8-bit DAC accuracy of the CIM-1.

4-19


Example 8: Simmer monitor (on/off simmer status)

CALL DELAY (1 SEC)IF LOC (1) <> 0 THEN DUMMY$ = INPUT$ (LOC(1), #1)

PRINT#1, “SAM 2,”CALL DELAY (1 SEC)WHILE EOF (1)WENDSMMER$ = INPUT$ (LOC(1), #1)iF VAL (SIMMER$) < 100 THEN

SIMMER$ = “OFF”ELSE

SIMMER$ = “ON”END IF

Example 9: Computer Interlock (assumes laser is on and expansion PCB DIP switch is set to 8 sec)

i’I

I

PRINT#1, “SEL 1,”PRINT#1, “WRI 7, 0000B,”PRINT#1, “WRI 7, OO1OB,”ON TIMER (5) GOSUB CLOCKPULSETIMER ONWHILE 1WENDEND

CLOCKPULSE:PRINT#1, “WRI 7, OO11B,”PRINT#1, “WRI 7, OO1OB,”

‘Open UIB digital ports‘Disable computer interlock, clock off‘Enable computer interlock, clock off‘Send clock pulse eveiy 5 sec‘Enable event trap 5 sec timer‘Endless loop

‘Create computer clock pulse‘Clock on‘Clock off‘Result: computer interlock clock LED

will blink evexy 5 sec. Computerinterlock monitor LED is always off. Laser will not shut off.

‘Clear input buffer‘Read IJIB ADC, input A-1N2

‘Wait for EOF

‘Let SIMMER$ = data string

‘Simmer off = 0

‘Simmer on = 255

4-20

Chapter 5Installing and Operating the

HG—2 Harmonic Generator

WARNING

KD*P crystals are sensitive to thermal shock, so change temperatures slowly. They are also water soluble, so avoid gettingthem wet and maintain a low relative humidity in their environment. Check the desiccant weekly and have it changed by afactory-trained service engineer when it turns from blue topink.

Figure 5—1: HG-2 Component Identification

5—1


Find the combination of wavelength, polarization, and SHG crystal for the output of interest

on the left-hand side of the table. Set the HG-2 as described on the right-hand side. All output wavelengths are collinear; they can be separated by dichroic beam splitters, dispersive

prisms, or equivalent optics.

Table 5—1: Summary of Translation Arm Positions

Stage Arm Position Crystal Position’

1st 0 1st stage crystals out of beam path

I Type I SHG2crystal in beam path

II Type IT SHG2crystal in beam path

2nd 0 2nd stage crystals out of beam path

T THG3crystal in beam path

F FHG4crystal in beam path

Table 5—2: Summary of EEG-2 Settings

Output of Interest HG-2 Settings1

X nm) Polarization SHG Crystal Main Housing 1st Stage 2nd StagePosition Position Position

1064 Vertical — — 0 0

532 Vertical I Horizontal I 0

Horizontal I Vertical I 0

Vertical II Horizontal II 0

Horizontal II Vertical II 0

355 Vertical I Vertical I T

Horizontal I Horizontal I T

Vertical II Vertical II T

Horizontal II Horizontal II T

266 Vertical I Vertical I F

Horizontal I Horizontal I F

Vertical II Vertical II F

Horizontal U Horizontal II F

1. Table describes an HG-2 with a full complement ofhannonic generation crystals.

2. Second Harmonic Generation (532 nm)3. Third Hannonic Generation (355 nm)—occurs by summing the fundamental (1064 nm) and its second harmonic.

Type I second harmonic produces optimal third harmonic performance.

4. Fourth Harmonic Generation (266 nm) —occurs by generating the second harmonic of the second harmonic of thefundamental. Type II second harmonic produces optimal fourth harmonic performance.

5. Refers to the orientation of the axis of rotation of the first stage crystals. Both the first stage translation ann and thepolarization of the hannonic output are perpendicular to this axis of rotation.

I

5-2

Harmonic Generator

HG-2 Controls

Input Polarization Rotator—rotates the polarization of the inputbeam to align it with the first stage crystal.

Crystal Translation Arm (one for each stage) —slides the crystals inand out of the beam path and serves as a lever for angle tuning thecrystals. The first stage crystal translation arm serves as an indicatorof the polarization of the output beam (see note five following Table5—2). Notches in the arms lock the crystals in position.

WARNING

Never move the crystal into or out of the beam while the laser isrunning.

Angle Tuning Knob (one for each tuning arm) —adjusts the angleof the crystal for the most efficient harmonic generation, opticallyaligning it with the input beam.

Main Housing—rotates about the optical axis to change the polarization of the output. Clamping screws lock the polarization in thedesired orientation.

Installing the HG-2

The HG-2 was optically aligned at the factory, so the result of thefollowing procedure should be optimal harmonic generation from allcrystals in the unit.

1. Remove wrapping, tie-downs, and restrainers from the HG-2.

2. Install the L-frame extension on the OCR; two cap screws hold itin place.

3. Install the HG-2 baseplate on the L-frame extension; threespring-loaded screws hold it down. Three setscrews, each locatednext to a hold-down screw, work against the springs to adjust theHG-2 vertically.

4. Place the HG-2 so the four elongated holes on its yoke line upwith corresponding threaded holes in the baseplate. Start all fourmounting screws, but leave them loose to allow horizontal movement of the HG-2.

5. Slide both crystal translation arms to the “0” position, whichmoves the crystals Out of the beam path.

5—3

IQuanta—Ray GCR Series

________________________________________________

6. Start the laser, then set its controls as follows:

Control Setting

LAMP ENERGY near threshold

Q-SW DELAY 25

REP RATE 10 pps

Q-SW MODE LONG PULSE

COMPUTER toggle switch ]NERNAL

SINGLE SHOT toggle switch REPetitive

LAMP toggle switch OFF

7. Adjust the HG-2 horizontally and vertically to center its windowson both the input and output beams. Use an JR card as a detectorfor the input beam, and reduce the ambient light for easier observation. If you must move the HG-2 vertically more than its spring-loaded screws allow, “walk” the vertical adjustment. Simultaneouslyloosen one spring-loaded screw and tighten the vertical adjustmentscrew next to it. Repeat with the other vertical adjustments.

8. Connect the purge system to the harmonic generator and purgefor 15 mm. before proceeding.

9. Turn on the laser and check for clipping of the output beam: usean IR card. Adjust the baseplate of the HG-2 if the crystal clipsthe beam. Turn the HG-2 to the other polarization orientationand check again for clipping.

Operation

1. Verify the flow through the purge system: purge for 15 mm.before proceeding.

2. Set the crystal translation arms for the wavelength of interest.

WARNING INever move the crystal into or out of the beam while the laser isrunning.

Example—to obtain the second harmonic from a Type I SHGcrystal:

a. Slide the first stage crystal translation arm to “I,” whichplaces the Type I crystal in the beam path.

b. Slide the second stage crystal translation arm to “0,” whichmoves the second stage crystals out of the beam path.

5-4

Harmonic Generator

3. Turn the main housing on its yoke to orient the polarizationangle of the output.

Example—to obtain horizontally polarized second harmonic(from above):

a. Turn the main housing on its yoke until the first stage translation arm is horizontal, which vertically orients the axis of rotation for tuning the crystal.

NOTE

As a rule, the polarization of the harmonic is perpendicular tothe tuning axis of the crystal.

DANGER: LASER RADIATION

Use protective eyewear throughout the rest of this procedure.Make all adjustments with the laser near the lasing thresholdand in the LONG PULSE (Q-switch off) mode.

4. Switch to the 0-SWitch mode, slightly above threshold (LAMPENERGY around position on the control), then angle tune thecrystal for maximum output at the wavelength of interest.

5. Mjust the polarization rotator for maximum output.

NOTE

The rate of rotation of the beam polarization is twice that ofthe polarization rotator.

Type I and II Crystals

The type I crystal creates a 1064 nm residual fundamental that is linearly polarized and is useful when mixing frequencies. It produces upto 10% more 3rd harmonic power than a type II, but has a lowerconversion efficiency overall.

The type II crystal creates a 1064 nm residual fundamental that iselliptically polarized, and has a slightly higher conversion efficiencythan a type I. It is typically used for dye laser applications.

5—5


The temperature controller stabilizes the temperature of the crystals,maintaining stable output despite changes in ambient temperature.

PoWeR Switch—turns on the temperature controller.

CHANNEL 1 HEATER indicator—glows as the controller heats the frsecond harmonic crystals. The lamp will turn on and off periodicallyas the controller maintains the temperature.

CHANNEL 1 INCrease TEMPerature control—sets the temperatureof the second harmonic crystals. Its range is approximately 30—50°Cover 20 turns.

CHANNEL 2 HEATER indicator—glows as the controller heats thethird and fourth harmonic crystals. The lamp will turn on and offperiodically as the controller maintains the temperature.

CHANNEL 2 INCrease TEMPerature control—sets the temperatureof the third and fourth harmonic crystals. Its range is approximately30—50°C over 20 turns.

CHANNEL 2 ON/OFF switch—turns on the heater for the third andfourth harmonic crystals.

HG-2 Temperature Controller

Controls

Operating Voltage

U —

TEMPERATURE CONTROLIJ

I

ON CHANNEL 1 CHANNEL 2

PWR INC HEATER HEATER INCTEMP TEMP

wFigure 5—2: Temperature Control Panel

5-6

Harmonic Generator

The temperature controller is factory-set for either 115 or 230 V acoperation. To change the operating voltage:

1. Remove the cover of the temperature controller.

2. Find the voltage selector, which is located between the fuse andthe transformer. Slide the switch so the voltage displayed matchesthe power line voltage.

3. The fuse must also match the input voltage:

• 115 V— 1/8 A slow-blow;

• 230 V—1/16 A slow-blow;

4. Replace the cover.

Second Harmonic (Types I and II),Third and Fourth Harmonic Generation

1. Turn on the controller and the channel two heater.

2. Select crystals and output polarization as described in Tables 5—1and 5—2.

3. Turn on the laser and adjust the HG-2 for maximum output atthe wavelength of interest.

4. Watch the HEATER indicators. They should remain on for severalminutes while the crystals warm up. Both lamps will blink periodically when the temperature is stable. Try to operate as closeto room temperature as possible, but monitor the indicators tomake sure the crystal temperature remains stable.

If either lamp shuts off and stays that way, turn the INC TEMPcontrol clockwise. The lamp should turn on, glow continuouslyfor a short time, and blink after that.

If either lamp continues to glow after 10 mm of operation, turnits INC TEMP pot counterclockwise until the lamp shuts off. Itshould stay off for a short time and blink after that.

5. The fourth hannonic ciystal is temperature dependant. In additionto generating UV, it also absorbs it. When too warm it approachesits critical phase-matching angle and output power will diminish.At this point, either reduce the input power or turn off the Channel 2 heater, and let the crystal cool off.

5—7

Chapter 6 Maintenance

Maintaining the Cooling System

1. Circulate water through the system for 30 mm every week whenthe laser is not in use.

2. Inspect the water level in the reservoir through the slot in thepower supply cover. Keep the reservoir at least half full. Replacewith distilled water every three months.

3. Replace the deionizing filter when all the yellow resin in thedeionizing filter has changed color to light brown. Refer to“Replacing the Deionizing Water Filter” below.

Maintaining the Air Purge System

1. The air filter assembly, which is mounted behind the power supplycontrol panel, can be seen through the horizontal row of ventilating slots above the purge controls. As its desiccant is consumed,the color changes from blue to pink. Change the air filter assembly, oil ifiter, and particle ifiter when the desiccant is exhausted.Refer to “Replacing the Air Filter Assembly” below.

Maintaining the HG-2

WARNING

Do not attempt to remove, replace, or add crystals. Allow onlyfactory-trained service engineers to open your HG-2.

1. Keep the crystals sealed and heated at all times.

2. Check the condition of the desiccant daily; have it replaced whenit changes from blue to pink.

3. Use only spectroscopic grade methanol and photographic lenstissue to clean window surfaces.

6—1

bQuanta—Ray GCR Series

RepIacng the Delonizing Water Filter

To prevent air from getting into the water pump and causing thepump to lose prime, the deionizing filter cartridge must be replacedwhile water is stifi in the system. Doing so means there is the possibility

of water spillage. The following procedure will allow you to replace thefilter cartridge with minimum chance of spillage. Table 7—2 lists the

part number for the cartridge.

Tools needed:

• Medium flat blade screwdriver

• 3/32 in. Allen wrench


• Small cork for plugging end of cartridge

• Small bucket

• An absorbent towel

Procedure

1. Remove the power supply cover by removing the three buttonhead screws in each handle well, the two screws at the base ofeach side, and the four screws on the perimeter of the controlpanel. Lift the cover off.

2. Loosen the hose clamp at the top of the filter cartridge and,leaving the clamp on the hose, remove the hose from the top ofthe filter cartridge. Keep the hose vertical, and hang it over theedge of the plastic shroud to prevent water from leaking from it.Tape it in place to insure it stays there. Plug the cartridge opening with the cork.

3. Support the filter assembly with one hand, and remove the twoAllen head screws holding the filter bracket to the power supplyframe. Lower the filter assembly below the top frame plate, andpull the cartridge out between the vertical frame member andthe water reservoir. Lay it down horizontally.

4. Place a towel under the filter’s bottom hose clamp to catch anywater that may leak from the hose or cartridge when the cartridge is removed. Have a small bucket close by to put the usedfilter in (it will be full of water). Loosen the hose clamp butleave it on the hose. Hold onto the hose (to provide strain relieffor the pump), and twist and pull the cartridge free of the hose.Quickly place your finger over the end of the hose to preventwater from leaking out and, at almost the same time, place thecartridge upside-down in the bucket.

6—2

Maintenance

5. Attach the bottom hose to the carbon granule end of a new filtercartridge. Water will begin to flow into the filter. Stand the filterupright and tighten the hose clamp.

6. Loosen the large steel clamp holding the filter bracket to the oldcartridge. Remove the bracket, and install it on the new cartridge.Do not tighten the steel clamp yet.

7. Place the new cartridge into the frame, and orient it so the bracketfits properly next to the vertical frame member. To prevent twisting the bottom hose, hold the filter while rotating the bracketaround it. Replace the Allen screws that hold the bracket inplace and tighten the steel clamp. Insure the assembly is secure.

8. Attach the upper hose to the filter assembly.

9. Pull the return hose out of the water reservoir cap, and use along neck funnel to fill the reservoir with distilled water. Re-insertthe hose.

10. Turn the pump on and let it run for 10 mm. If the reservoir levelever drops below half, turn off the pump and add more water.

11. Replace the power supply cover.

Replacing the Air Filters

The three air filters: input oil filter, output particle filter, and desiccant filter assembly, should be replaced at one time and not individually. Table 7—2 lists the part numbers for these components.

Tools needed:

• Medium flat blade screwdriver

• 9164 in. Allen wrench


Procedure

1. Remove the power supply cover by removing the three buttonhead screws in each handle well, the two screws at the base ofeach side, and the four screws on the perimeter of the controlpanel. Lift the cover off.

2. Remove the retaining pin that holds the inlet air hose to the topof the flow gauge (left side of power supply), and separate thehose from the flow gauge. In like manner, separate the large outletair hose from the small air hose (right side of power supply).

3. Support the filter assembly with one hand, and remove the fourAllen head screws holding the desiccant filter brackets to thebottom of the top tray. Lower the filter assembly, and remove itfrom the supply.

6—3


4. Lay the new filter components out in a manner similar to the oldcomponents (note the directions of the arrows on the small filters).The small filter marked “Grade BK” goes on the input end (theend with the longest hose), and is connect to the carbon granuleend of the desiccant filter. Remove the hoses and fittings from theold components and attach them in like manner to the new ones.

5. Loosen the large band clamps and remove the two mountingbrackets from the old desiccant cartridge. Attach them to thenew one, noting proper orientation. Do not tighten the bandclamps.

6. Follow step 3 above in reverse order to place the new assemblyinto the power supply and secure it. The brackets may have toslide a bit on the desiccant cartridge to allow the mounting holesto match those in the tray. Once secured, tighten the bandclamps.

7. Follow steps 1 and 2 in reverse order to reconnect the air hosesand replace the power supply cover.

Replacing the Flash Lamps

For optimal performance, the lamps should be replaced after 550 hrsof operation. Table 7—2 provides part numbers for ordering lampsdirectly from Spectra-Physics.

Procedure

1. Turn off the laser and open the power supply circuit breakers.Allow 5—10 mm. for all capacitors to discharge.

DANGER. HIGH VOLTAGE

As an extra precaution, open the circuit breaker and disconnect the power cord.

2. Remove the cover from the laser head, then remove the plastichigh voltage shield that covers the lamp housings. Short togetherterminal posts A and B (Figure 6—1) on each pump chamber.

3. Disconnect lamp leads from the terminal posts.

4. Disconnect the water hose located at the top of the lamp houseassembly. This will allow the water in the head to drain backinto the power supply.

WARNING

Prevent water from flowing down onto the dust tube, whichcould contaminate the face of the Nd:YAG rod.

6—4

Maintenance

Figure 6—1: Short together posts A and B to prevent shock whenservicing the flash lamps.

5. Loosen and remove the thumb screws and block from both endsof the lamps.

6. Remove the lamps by pulling it out anode end (red lead) first.

7. Handle the new flash lamps using white nylon gloves; avoidtouching it with your fingers. Clean the new lamps with methanol.

8. Reverse steps one through six to install a new lamps.

Insert the lamp cathode end (black lead) first. The anode end isidentified by a red mark on its electrode and an “A’ on the redanode lead. The anode electrode is solid, while the cathode electrode is segmented and cone-shaped.

Make sure all 0-rings are seated snugly in the groove of thelamp housing.

Tighten all thumb screws evenly and snugly. Do not overtighten.

9. Connect the water hose to the top of the rod assemblies.

6—5


10. After installation, test for water leaks as follows: defeat the coverinterlock, then press the ON button long enough to move cooling water into the lamp housing. If no leaks occur, turn on thewater pump and inspect again at full pressure. If there are noleaks after 5 sec., the seals are tight. Turn off the laser, activatethe cover interlock, and install the laser head cover.

If a leak occurs, turn off the laser, observing the danger warningin step one. Remove the thumb screws and blocks, then centerthe lamp in its housing. Check the seating of the 0-rings.

I

I

6—6

Chapter 7 Service and Repair

System Description

Figures 7—1, 7—2, and 7—3 —the system block diagram, schematic,and control board assembly—illustrate the following discussion. Allare located at the end of this section.

COMPUTER/INTernal Switch

Selects either the optional CIM-1 interface or the remote controlmodule as the control unit.

NOTE

If the CIM-1 option is included as part of the system, theRS-232-C and IEEE 488 interfaces are selected (althoughonly one may be used at a time).

Enabling Signals

Enabling signals control laser start-up, analog strobe triggering, flashlamp firing, choice of lamp trigger oscillator, Q-switch triggeringmode, choice of single-shot or repetitive operation, and single-shotoperation. The remote control module supplies enabling signalsdirectly. When the CIM4 option is used, commands may be sent viathe RS-232-C or IEEE 488 interface. Refer to Chapter 4, “ComputerInterface Module (CIM-1),” for instructions.

Analog Signals

Analog voltages control the flash lamp energy, the variable oscillator, the Q-switch triggering delay, and the timing of the Q-switchadvanced sync signal. The remote control module supplies analogvoltages directly. The CIM-1 interface module supplies these analogsignals directly as commanded by the attached computer or terminal.

The analog strobe function can be either edge-triggered or level controlled, depending on placement of jumper #1 on the control board.The laser was shipped from the factory in a level controlled configuration. High current provides continuous analog data transfer. Changingjumper #1 to its alternative configuration allows edge triggering of a5 msec gate aperture. This mode will accept triggered analog datatransfer from the computer bus with a time restricted window.

7—1


Under internal control, the analog strobe is wired “on.” It can beturned off by shorting the ANALOG STROBE IIPTJT connector toground. Under computer control, analog strobe is off until its optoisolator is turned on, then data will flow until it is turned off, which storesthe analog data. Held data will typically drift about 10% in 8 mm.

Q-switch Delay

After the firing signal emerges from the computer test delay, itpasses through a pulse regeneration one-shot that shapes the waveform to meet the drive requirements of the voltage-programmableQ-switch delay. This 150—500 lisec delay allows the population inversion to develop before Q-switch triggering, so the Q-switch opens atthe peak of stored energy.

0-switch Advanced Sync Generator

The signal splits, passing through a pair of delays, one fIxed (800 nsec)and one voltage programmable (300—1300 psec). The variable delaycontrols the timing of the “pretrigger” signal at the Q-SWitchADVance SYNC connector on the power supply panel. The fixeddelay provides the timing reference against which the variable delayis compared. The advance sync pulse generator shapes the waveform to meet output signal requirements: pulse width = 5 msec,rise time = 20 nsec, 5 V.

Mode Switch (Ull)

This function enables one of three sources of Q-switch trigger signals.In the 0-SWitch mode, a signal from the voltage-programmabledelay opens the Q-switch momentarily at the point of maximum inversion. The LONG PULSE mode triggers the flash lamp and Pockelscell simultaneously, holding the Q-switch open throughout the lamppulse. In the EXTERNAL mode, a signal at the Q-SWitch TRIGgerINPUT on the power supply panel fires the Pockels cell.

The source of the enabling signal depends on the position of theCOMPUTER/INTernal switch, or is from the computer if the optionalCIM-1 is installed and the remote control jumper plug is used. Theremote control module supplies the signal under INTernal control;the computer is the source under COMPUTER control. All externalQ-switch triggering signals enter through the 0-SW TRIG INPUTconnector, regardless of the position of the COMPUTER/INTernalswitch.

*

I

7—2

Service and Repair

Q-switch Drivers

The output the fixed delay passes through the mode switch (Q-switchmode enabled) and fires the Marx bank pulse generator. The resultis a pulse a few psec long that is amplified by the Marx bank buffer,which produces the signal that drives the Marx bank. The Q-switchpulse generator stretches the output of the Marx bank pulse generator to produce a signal that appears at the 0-SW SYNC OUTPUTconnector on the power supply and at the computer connector (pin 46):5 V (5 msec and 200 psec rise time).

Single-Shot Operation

Firing a single shot requires two signals: one to enable the single-shot flip-flop and one to fire it. The origin of the enabling signal iseither the computer (pins 27 and 17) or the REPetitive/SINGLESHOT switch on the remote control panel. The firing signal cancome from either the computer (pins 6 and 5) or the FIRE button onthe remote control panel. Once armed, the single-shot circuit willallow the next available pulse to fire the Marx bank. Until it isarmed again, the flip-flop prevents the passage of subsequent pulses.

The single-shot function operates with all trigger sources, and whenunder computer control, can be used to vary the pulse repetition ratewithout adversely affecting focusing of the Nd:YAG rod. To do so,select the 10 Hz oscillator at the lamp source, then fire single shotsat a programmed rate.

Inhibit Switch

Applies voltage to the reset line of the lamp sync pulse generator toprevent lamp firing. The inhibit and source fault signals pass throughan OR gate that allows either of them to inhibit firing. The switchremains active under computer control, so the laser can always beshut off at the remote control panel.

OFF [STOP]/ON [ENABLE] buttons

Function depends on the position of the COMPUTER/INTernalswitch, or is hard wired “on” if the CIM-1 option is installed and theremote control jumper plug is used. Under internal control, pressingthe ON button closes the main relay, activating all power supply circuits and, after a 10 sec delay, starting the laser. Under computercontrol, both an enabling signal, derived by pressing the ENABLE(ON) button (or using the remote control jumper plug with the CIM-1option) and an “on” signal from the computer are required to turn onthe laser. The lighted buttons identify the operating status of the laser,regardless of the position of the COMPUTER/INTernal switch.

The line dropout detector will shut off the laser if it senses a loss ofline voltage. The initializing circuits prevent transfer of laser controluntil all power supplies have energized, preventing mishaps due toerrors in logic start-up.

7—3


Interlock Logic

The interlock logic examines several sensors to ensure safe, trouble-free operation: external interlock, laser head and power supply coverswitches, cooling water temperature and flow, and switching supply airflow. The external interlock connector is included for simple installation of environmental safety devices such as a door switch. If an interlock fault is discovered, the logic trips the main contactor, shuttingoff power to the switching supply and simmer transformer, leavinglogic power on.

The logic also receives input from the lamp voltage level sensor; itwill prevent starting the laser until the lamp energy is reduced tonearly zero upon start-up. This prevents accidental high power output upon start-up.

If no interlock faults are detected, the logic enables the turn-ondelay, and after 10 sec, the laser will start.

If one or more faults are detected, the laser will not start, and an“interlock fault” signal will appear at the computer bus (pin 48) andthe remote control panel.

The external interlock connector operates from the 15 V power supply,and it must be wired using a twisted wire pair. Do not ground theinterlock: grounding will blow a fuse in the 15 V supply, which opensthe interlock loop and prevents starting the laser. The external interlock is a possible source of noise, and the twisted wire pair should beshielded in hostile environments. This shield should be grounded tothe laser case near the external interlock connector.

Pulse Forming Network

The pulse forming network produces a critically damped pulse whenthe silicon-controlled rectifier (SCR) is fired. This pulse drives theflash lamps that pumps the Nd:YAG rods.

The switching power supply transforms line voltage (208 V, nominal)into dc voltage for the pulse forming network (PFN). The PFN voltage (V) is programmable: Vf = 225 • V, where V = 0 to 8 V.It can be set either with the remote control module or via eitherthe RS-232-C or IEEE 488 interface if your system includes the optional CIM-1 computer interface module. A PFN voltage monitor isprovided at pin 20 of the computer interface, 0 to 8 V, and also via theCIM-1 interface (refer to Chapter 4 for details).

Safety circuits associated with the pulse forming network will dischargethe energy storage capacitor. This will occur when the laser isswitched off.

I

7—4

Service and Repair

DANGER. HIGH VOLTAGE

The capacitor discharges slowly, requiring at least 1 mm forcomplete discharge, and no voltage monitor is available.Avoid contact with lamp or capacitor terminals for at least thatlong after turning off the power. As an additional precaution,the capacitor may then be shorted to remove any remainingcharge. Please note that charged, large electrolytic capacitorscan explode when discharged in this manner, so take appropriatemeasures.

Circuitry within the switching supply monitors line voltage. If thevoltage drops, which can cause SCR failure, the supply will shut off.An indicator located next to the switching supply control input connector glows to indicate a low line condition; reset the main circuitbreaker to override.

The lamp sync pulse generator provides a 5 msec signal to the SCRpulse generator, the LAMP SYNC OUTPUT on the power supply panel, and the “lamp triggered” monitor on the computer (pin 47).

The SCR pulse generator conditions the output of the lamp syncpulse generator for the SCR driver. This sends a 1 A pulse throughthe pulse transformer to fire the SCR.

Flash Lamp Simmer Supply

This supply provides voltage to the flash lamp start circuit (200 V),the Marx bank (500 V), and the flash lamp simmer current. The simmer current sensor activates the start circuit, which capacitivelycouples a high voltage pulse through the lamp housing, breakingdown the lamp. After the lamp starts, simmer current flows, shuttingoff the start circuit. Refer to Chapter 4 for information on monitoring the simmer supply via the optional CIM-1 module.

System Start-up Tests

The following table describes events that occur during a normalstart-up of the GCR. They are intended as a guide for identifying thesource of system failure. Use the results of this test to help yourSpectra-Physics field service engineer quickly isolate and repair yoursystem.

7—5


* Refer to Normal Operating Mode Settings next page.

Table 7—1: System Start-up Tests

Action Result

Close the power line Turns on power to the control PC board; lights the OFF lamp onbreaker and turn on the remote control module and both the POWER and INTER-the key switch. LOCK FAULT lamps on the power supply. Energizes all conve

nience outlets at 110 V ac.

Press the ON button Turns on the ON lamp on the remote control; closes K3, accomon the remote control panied by a small noise; starts the water pump, heat exchangermodule fan, power supply fan, laser head fan; enables the air pump; turns

on the EMISSION ENABLE lamp on the laser head.

Turns off INTERLOCK FAULT lamp when water flow is established (about 2 sec).

Turn LAMP ENERGY Initiates a 10 sec safety delay, provided no interlock fault exists.control fully counter- After 10 sec K2 closes, pulling in the main contactor (K1); listenclockwise for a loud click. All timing logic becomes operational; ac power

is applied to the simmer transformer and the switching powersupply; the start circuit, the Marx bank, and its trigger becomeoperational. LEDs one (Q-SW ADV SYNC), two (Q-SW SYNC),and three (P.S. INHIBIT) flash when the laser is in the normaloperating mode*; the LEDs are located on the power supplycontrol PC board.

After a half-second delay the start circuit ignites the flash lamp,establishing the simmer current; the start circuit stops pulsing. Asa result, the SIMMER indicator on the remote control turns on,and the dump relay (K502), located between the auxiliary interlock plug and the large grey capacitor (C504), pulls in with anoticeable click. LED four (P.S. ON/OFF), also on the powersupply control PC board, glows continuously.The laser is fully operational at this point; increase the lampenergy.

Interlock failure K2 opens, de-energizing Ki with a loud click; the INTERLOCKFAIL indicator turns on; the dump relay drops out to dischargeC504; all logic shuts off; LED four turns off; the Marx bank powerturns off; the start circuit power turns off; all pumps and fansremain on.

To restore operation, clear the interlock fault and turn the LAMPENERGY control to zero (fully counterclockwise).

Inhibiting the flash Inhibits the driver to the pulse forming network SCR; the INhIBITlamp by turning on lamp turns on, and the flash lamp shuts off. LEDs three and fourthe LAMP switch turn off. Logic command shuts off power from the switching power

supply. LEDs one and two continue to flash when the laser is inthe normal operating mode.*

7—6

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Table 7—2: Replacement PartsDescription Part Number

Maintenance

Flash lamps 0004-0725

Deionizing cartridge, cooling system 0437-8440S

Filter kit. Includes: desiccant filter assembly, (air purge system),particle (micron) filter, air purge system (output), grade AQ, oil 9800-0040filter, and air purge system (input), grade BK.

Electrical

Control PC board assembly (tested) 0446-3880S

Start circuit assembly 0004-2086S

Marx bank assembly 0004-2087S

Lamp kit. Includes: incandescent lamp, power ON indicator.— 9800-0070power supply and incandescent lamp, remote ON/OFE

Relay, K501, power to switching, simmer supplies 4500-1012

Thyristor, dual, SCR 4803-0540

Diode module 4802-2478

Switch, circuit breaker 5 100-1002

Fuse kit. Includes: 0.25 A FB, 0.5 A FB, 0.5 A SB, 1.5 A SB,4 A SB, switching regulator, 1 A SB, 1 A FB, 1/8 A SB, 1/16 A 9800-0060FB, and 3A SB.

Optical

Thin film polarizer 0005-0020

Output mirror contact factoiy

Q-switch 0100-4460

Gold pump cavity contact factoiy

High reflector contact factoiy

Nd:YAG rods contact factoiy8

7 I

7—8

C)

(

Chapter 8 Customer Service

At Spectra-Physics, we are proud of the durability of our products.Our manufacturing and quality control processes emphasize consistency, ruggedness, and high performance; nevertheless, even thefinest instruments break down occasionally. We believe that the reliability of our instruments is second to none, and we hope to demonstrate that we provide superior service—by providing dependableinstruments and, if the need arises, service facilities that can restoreyour instrument to peak performance without delay.

Spectra-Physics maintains service centers in the United States,Europe, and Japan. Additionally, there are field service offices inmajor United States cities. Call the nearest service center or fieldservice office for assistance.

Replacement parts should be ordered directly from Spectra-Physics.For ordering or shipping instructions, or for assistance of any kind,contact your nearest sales office or service center, providing the instrument model and serial numbers. Service data or shipping instructions will be promptly supplied.

Warranty

Unless otherwise specified, all Quanta-Ray mechanical and electronicassemblies are warranted to be free of defects in workmanship andmaterials for one year from the date of shipment. The warranty onnonlinear crystals, flash lamps, turning prisms, and optics is limitedto 90 days. Spectra-Physics will repair or replace instruments thatprove to be defective during the warranty period without charge. Theobligation of Spectra-Physics is limited to such repair, and does notextend to consequential damages.

Simple misalignment and unclean optics are the most probable causesof low power or instrument failure, and are excluded from warrantyprotection. A service charge will be assessed if an instrument that,when shipped to Spectra-Physics for warranty repair, can be returnedto operating condition by routine cleaning or adjustment.

8-1

IQuanta-Ray GCR Series

Return of the Instrument for Repair

Contact your nearest Spectra-Physics field sales office, service center,or distributor for shipping instructions, and forward the instrument prepaid to the destination indicated. Special Spectra-Physics packing boxesdesigned to securely hold instruments during shipment should be used.If shipping boxes have been lost or destroyed, we recommend that youobtain a new one, for a nominal charge, from Spectra-Physics. Spectra-Physics will only return instruments in Spectra-Physics’ containers.

Service Centers

Australia

Spectra-Physics Pty. Ltd.2-4 Jesmond RoadPost Office Box 141Croydon, Victoria 3136Telephone: (03) 723-6600Fax: (03) 725-4822

Belgium cSpectra-Physics B.V.B.A.North Trade BuildingNoorderlaan 1332030 AntwerpTelephone: (03) 541-7515Fax: (03) 541-8202

Latin America and Pacific Region

Spectra-Physics Lasers1330 Terra Bella AvenuePost Office Box 7013Mountain View, CA 94039-70 13Telephone: (800) 456-2552Telephone: (415) 961-2550Telex: 348-488Fax: (415) 969-4084

France

Spectra-Physics S.A.R.LAvenue de ScandinavieZ.A. de CourtaboeufBP 28-91941 LES UUS CedexTelephone: 1.6907 99 56Telex 601 183Fax: 1.6907 60 93

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Customer Service

Service Centers (cont..)

Germany and Export Countries*

Spectra-Physics GmbHSiemensstrasse 20D-6100 DarmstadtGermanyTelephone: (06151) 708-0Telex: 419471Fax: (06151) 75000Fax: (06151) 710795

JapanSpectra-Physics K.K.15-8 Nanpeidai-choShibuya-ku, Tokyo 150Telephone: (03) 3462-4531Telex: 2466976Fax: (03) 3462-4530

The NetherlandsSpectra-Physics B.V.Prof. Dr. Dorgelolaan 20Post Office Box 22645600 CG EindhovenTelephone: (040) 45 18 55Fax: (040) 466097

Switzerland

Spectra-Physics AGHegenheimermattweg 65CH-4123 Allschwil/BaselTelephone: (061) 481 84 00Fax: (061) 481 37 44

United Kingdom

Spectra-Physics Ltd.Boundaiy WayHemel .HempsteadHerts, HP2 7SHTelephone: (0442) 232322Fax: (0442) 68538

* CSSR, Denmark, Egypt, Finland, Greece, Ireland, Israel, Kuwait,Norway, Pakistan, Portugal, Saudi Arabia, South Africa, Spain,Sweden, Turkey, USSR, and Yugoslavia.

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Service Centers (cont..)

Eastern United States

Spectra-Physics Lasers255 Old New Brunswick Road, Suite N40Piscataway, NJ 08854-4175Telephone: (800) 456-2552Telephone: 921396Fax: (908) 981-0029

Western United States

Spectra-Physics Lasers1330 Terra Bella AvenuePost Office Box 7013Mountain View, CA 94039-7013Telephone: (800) 456-2552Telex: 348-488Fax: (415) 964-3584

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Spectra-Physics Lasers Instruction Manual—Problems and Solutions

We have provided this form to encourage you to tell us about any difficulties you have experienced in usingyour Spectra-Physics Lasers instruments or its instruction manual—problems that did not require a formal call or letter to our service department, but that you feel should be remedied. We are always interested in improving our products and manuals, and we appreciate all suggestions.

Thank you.

From:

Name

Company or Institution

Department

Address

Instrument Model Number Serial Number

Problem:

Suggested Solution(s):

Mail To:Spectra-Physics Lasers, Inc.Quanta-Ray Quality Manager1330 Terra Bella AvenuePost Office Box 7013Mountain View, CA 94039-70 13U.S.A.

Documents

Pulsed Nd:YAG Lasers Instruction Manual GCR-L4 GCR-18