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Laser PCB Milling Machine. Group 18 Nathan Bodnar David Dowdle Ryan Maticka. Project Overview. The system will be capable of laser etching copper coated printed circuit boards (PCBs) for the purpose of rapidly prototyping senior design projects The system will consist of: - PowerPoint PPT Presentation
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Laser PCB Milling Machine
Group 18
Nathan BodnarDavid DowdleRyan Maticka
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• The system will be capable of laser etching copper coated printed circuit boards (PCBs) for the purpose of rapidly prototyping senior design projects
• The system will consist of:– High powered
green laser– Custom software– XY plotting table– Safety mechanisms
Project Overview
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Project Motivation• Current milling machine
used by senior design students has had numerous breakdowns
• We replaced the current milling machine with a more reliable system that is capable of running without continuous user input
• Design and build our own high powered green laser
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Project Goals and Objectives• Capable of producing a quality result in less time
than is required to ship out a PCB to a professional manufacturer
• Capable of vaporizing copper in just a few pulses of a laser
• Capable of burning through the fiberglass substrate with the laser alone
• Capable of handling FR4 copper clad PCBs• Capable of milling warped boards
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Project Goals and Objectives• Safe, most specifically in the area of eye and lung
safety• Capable of accepting a Gerber file from a
mainstream PCB layout software program• Capable of accepting boards to be milled in
PNG format• Capable of interfacing with a computer through
two USB ports
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Project Specifications & Requirements
• Capable of milling a 12 in x 12 in board• Resolution of 1 mil
– 1 mil = 1/1000 in
• Beam waste of 1 mil or lower• Software is protected through the storage of
hashed user passwords (SHA-512)
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Project Specifications & Requirements
• Require 512 MB of main memory (computer) to run after everything else for the maximum supported file size (12,000 x 12,000 pixels)
• Implement a call and answer protocol for the interface between the computer and the microcontroller through the use of 64 Byte data packets
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• User safety– Laser being ran as a class one– Enclosed laser subsystem
• Equipment safety– Housing to protect equipment from the vaporized
copper by product of the mill procedure
Safety
HIGH VOLTAGE
DANGERHIGH
VOLTAGE
DANGER
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Laser Safety
• Desirable to run the system as a class one laser• Laser safety glasses (Five OD as per ANSI Z136.1
standard) still required when testing and calibrating the laser
• Needed to classify the laser as a class one:– Protective housing– Interlocks on the housing– Service access panel– Equipment labels
CAUTIONLASER RADIATION
DO NOT STARE INTO BEAM
CLASS 1 LASER
Enclosed Nd:YAG, 532nm, 10mJ, 40ns
! CAUTIONLASER RADIATION
DO NOT STARE INTO BEAM
CLASS 1 LASER
Enclosed Nd:YAG, 532nm, 10mJ, 40ns
!!
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Burn Testing
Minimum amount of Energy needed: 0.7mJ for 20ns @ 532nm
Ene
rgy
(mJ)
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Laser
• Previous Design– Second harmonic Nd:YAG Q switched laser– Generating second harmonic inside laser cavity is
more efficient than outside cavity– Output:
• Energy: 9 mJ• Pulse: < 40 ns
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Laser Cavity
•Folded cavity Design
•Q switched
•808 nm Diode Pumped
•Output: 532 nm
•Nd:YAG (end pumped) 12
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Laser Cavity Simulations
• With 80 W input = 30 W @ 1064 nm
• ~12 W @ 532 nm CW
• Pulsed: 4 mJ @ 13 ns
• ~307 MW duty 0.0013%13
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Laser Block DiagramMain
Computer
Laser Power Supply
USBUSB
AC Power
Cooling Lines
Thermal Electric Cooler
Laser Diode #1
Wire
Cooling Flow
Thermistor
Cooling Lines
Wire
USB USB
Laser Power Supply
AC Power
Cooling Lines
Thermal Electric Cooler
Laser Diode #1
Wire
Cooling Flow
Thermistor
Cooling Lines
Wire
Main Computer
Laser Power Supply
USBUSB
AC Power
Cooling Lines
Thermal Electric Cooler
Laser Diode #1
Wire
Cooling Flow
Thermistor
Cooling Lines
Wire
USB USB
Laser Power Supply
AC Power
Cooling Lines
Thermal Electric Cooler
Laser Diode #2
Wire
Cooling Flow
Thermistor
Cooling Lines
Wire
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Current Laser System• Laser diode problem
– 808 nm diode ran at 800 nm, and Nd:YAG has acceptance region of 0.6 nm
– To work, the diode must be heated to unsafe operating temperatures• Flash tube based system
– Advantages • Higher output power from oscillator
– Fewer shots to burn through– Disadvantages
• 2% efficient at best• Low duty cycle
– Maximum: 100 pulses per second– Realistic: 1 pulse per second
• Shorter mean time to failure compared to diode system
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Flash Tube System• 15 J electrical input power generates 100 mJ of 1064
nm light• Flash tube based amplifier
– Single pass amplification • Focusing lens creates focal point• Focused light passes through KTP crystal twice via
highly reflective mirror to produce 532 nm • light hits mirror that reflects 532 nm and transmits
1064 nm • 532 nm transmitted to XY table via mirrors and 1064
nm stays in laser section
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Previous Q Switch
Pockel Cell
• Fast Switching Characteristics < 1ns
• Voltage Rating: 3-5 kV
• High Laser Power Operation
• Crystal: KD*P
• Polarization Dependent
Alternative Q Switches
•AOM modulator
•Mechanical
•Saturable Absorber
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Q Switch PSU Block Diagram
Voltage Regulator
DarlingtonTransistor
Microcontroller
+12V
40kHzOscillator
VoltageDivider
FilterCaps
VoltageMultiplier
1:98Transformer
FastFETs
Voltage Regulator
DarlingtonTransistor
Microcontroller
+12V
40kHzOscillator
VoltageDivider
FilterCaps
VoltageMultiplier
1:98Transformer
FastFETs
•Generates 0 - 5 kV output
•Generates pulses with minimal delay
•Emergency Shutoff capabilities18
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Q Switch
• Current Design– Saturable absorber
• Laser cavity < 10 cm long, so no pockel cell• Saturable absorber is 3 mm long
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Stepper Motor Controller
Stepper Controller
•Full bridge MOSFET driver
•120 micro-steps per full step gives 0.0075° per step
Stepper Motor• 0.9° rotation per step• Holding Torque: 30 oz-in• Unipolar
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XY table
• Threaded Rod Design
• Requires material to move
• Requires double the area to travel
Previous Design Current Design
• Belt Driven with linear bearings
• Moves the mirrors and not the material
• Requires only 6” extra for head travel
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Laser Power Supply
• Previous Design– Specifications
• Input: 120 V AC, 60 Hz• Output: 0 - 5 V DC, 60 A• Output voltage ripple < 1 mV• Current controlled• Current monitoring• Temperature monitoring
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DC to DC Converter
• Choices: – Linear regulator
• Low efficiency• Large size• Thermal problems
– Switched-mode DC to DC Converter• Buck converter for voltage gain < 1• Adjusting PWM will control voltage and current output
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Switching• Choices:
– Bipolar Junction Transistor (BJT)• Pros: High current carrying capability• Cons: High driving power, Low frequency
– Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)
• Pros: High frequency, low driving power, low losses• Cons: Low current carrying capability, lowered efficiency at high
voltage– Insulated Gate Bipolar Transistor (IGBT)
• Pros: High current carrying capability, High reverse voltage blocking
• Cons: Lower frequency and higher switching losses than MOSFET
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Switching
• Problem: – MOSFETs carry low
current
• Solution:– Use MOSFETs in parallel
• High current• High switching speed• Low driving power
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Synchronous Switching• Low Power
– Blocking diode can handle low power
• High Power– Risk of diode breakdown from high stress – Power losses on diode is large compared to using a MOSFET
• Replace diode with MOSFET controlled by secondary PWM
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Converter Control
• Pulse width modulation (PWM) changes duty cycle of MOSFETs– Choices:
• Microcontroller detects output and controls PWM to main MOSFET
• LT1339 buck/boost converter controller instead of microcontroller
– More features for better control– Added circuit uses potentiometer to control current output
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Thermoelectric Cooling
• Peltiers cool the laser diodes to desired temperature• ATX PSU: 12V DC• PWM controls MOSFET to control the power to each peltier• Temperature monitored via thermistor on peltier• TEC not used in current design
MOSFET
PeltierLaser Diode MicrocontrollerThermistor
+12VPWM
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Current Laser Power Supply
• Specifications– Input: 120 V AC, 60 Hz– Output: 730 V DC– Flash tube system not susceptible output voltage
and current ripple– PWM controller
• Switching: 17 kHz
– No thermoelectric cooling required for laser
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Boost Converter
• IGBT chosen over MOSFET because:– Better than MOSFET when voltage is over a few hundred
volts
• Discontinuous conduction mode (DCM)– Generates larger peak current compared to continuous
conduction mode (CCM)
• Double converters for faster current response• Regulating Pulse Width Modulator (UC3526)
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Boost Converter
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Snubber
• Active snubber for increased efficiency– LC circuit stores power that would be turn-off losses on
main IGBT– Secondary IGBT delivers to the energy output
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Microcontroller• A different microcontroller will be used to control each part of the project• Needed to be able to do:
– Pulse Width Modulation (PWM) for micro-stepping– Low cost– Easy to implement– Large repository of example code– Easy to reprogram (USB)
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Microcontroller Decision ChartMCU PIC18F2550 MC9S08JS8CWJ C8051F342-GQ ATMEGA162-16PU
Data Bus Width: 8 bit 8 bit 8 bit 8 bit
Family: PIC18 JS 8051 AVR
Program Memory Type: Flash Flash Flash Flash
Program Memory Size: 32 KB 16 KB 64 KB 16 KB
Data RAM Size: 2 KB 256 B 5.25 KB 1 KB
Interface Type: SPI or I2C or EAUSART SPI, SCI I2C / SPI / UART / USB SPI or USART
Maximum Clock Frequency: 48 MHz 48 MHz 48 MHz 16 MHz
Number of Programmable I/Os: 24 N/A 25 35
Number of Timers: 4 1 4 4
Operating Supply Voltage: 2 V to 5.5 V 2.7 V to 5.5 V 2.7 V to 5.25 V 2.7 V to 5.5 V
Maximum Operating Temperature: + 85 C + 85 C + 85 C + 85 C
Package / Case: SOIC-28 Wide SOIC-20 Wide LQFP-32 PDIP-40
Packaging: Tube Tube Tray N/A
Minimum Operating Temperature: - 40 C - 40 C - 40 C - 40 C
On-Chip ADC: 10-chx10-bit N/A 17-ch x 10-bit N/A
Price (for 1): $4.95 $2.00 $10.25 $6.77
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Microcontroller
• Which programming language for the microcontroller?– Choices:
• C• Assembly
– We chose C, as we are the most familiar with it, and there is a large body of software already written for the PIC18F2550. Furthermore, Microchip offers the ability to blend C and Assembly in our source files, so we can get the advantages of both languages
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Software Design Decisions
• Which programming language to use?• Vector or raster mill?• Directly support Gerber files?• Directly support TIFF images?• How should we communicate with the
microcontroller?• How should we control security?
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Software Design Decisions
• Which programming language for the computer program?– Choices:
• C, Java, C#– We chose Java as we are the most familiar with it
other than C, and it is much easier to create GUI’s in Java. C# would have interfaced with our microcontroller easier, but we were not as familiar with it as Java, and we wanted to cut down on development time so that we could have more time to debug and test
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Environment• Window Builder Pro to produce the GUI• Eclipse to integrate everything together• To account for the 12,000x12,000 pixel size
that could result from the convert operation, 512MB of memory was allocated to the JVM– This could be optimized if we were to use the JAI
to tile the TIFF images, and read each tile separately.
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Software Design Decisions
• Vector or raster mill procedure?– Vector: follow the outlines of each object until
you come back to the beginning of the object• Pros: Shorter mill time, less movement of XY head• Cons: more complicated algorithm
– Raster: scan left and right across the area to be plotted
• Pro: simple algorithm• Cons: longer mill time, more movement of XY head
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Software Design Decisions• Directly support Gerber files?
– Would allow for easier implementation of Vector milling– Specification is too complicated for the scope of this
project• Use gerb2tiff (external program) to convert the input Gerber file
to a TIFF• Use the output as a raster mill input
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Gerber File Example%FSLAX43Y43*%%MOMM*%G71*G01*G75*G04 Layer_Physical_Order=1*G04 Layer_Color=255*%ADD10C,0.250*%%ADD11R,3.000X1.800*%%ADD12R,4.700X3.810*%%ADD13R,0.720X1.800*%%ADD14R,4.060X3.810*%%ADD15R,3.810X6.350*%%ADD16C,1.000*%%ADD17C,2.000*%%ADD18C,2.200*%%ADD19C,0.600*%%ADD20C,0.254*%%ADD21R,8.400X1.800*%
%ADD22R,7.000X2.000*%%ADD23R,24.000X17.000*%%ADD24C,1.800*%%ADD25R,1.800X1.800*%%ADD26C,2.000*%
%ADD27C,2.200*%%ADD28C,1.600*%%ADD29C,1.200*%D10*X18192Y29200D02*G03*X17896Y29381I-942J-1200D01*G01*X16805Y30473D02*G03*X16073Y31205I-1305J-573D01*G01*X8012Y50000D02*G03*X8012Y50000I-2013J0D01*
G01*X6890Y40388D02*G03*X6500Y40550I-390J-388D01*G01*X6889Y40389D02*G03*X6500Y40550I-389J-389D01*G01*X81876Y18000D02*G03*X83624Y18000I874J1250D01*G01*X78376D02*G03*X80124Y18000I874J1250D01*G01*X82012Y10000D02*G03*X82012Y10000I-2013J0D01*G01*X76013Y552D02*G03*X76050Y750I-513J198D01*
……continues
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TIFF and Machine Code Result•The Gerber file from the pervious page creates this TIFF file through the use of the gerb2tiff program•This TIFF file is then used to create the PNG file that Java will use
1 364 0 99 1 132 0 98 1 463 0 211 1 1203 0 38 1 35 0 76 1 98 0 31 1 2462 0 39 1 35 0 38 1 24 0 28 1 639 0 28 1 1908 0 21 365 0 99 1 130 0 99 1 463 0 211 1 1202 0 38 1 35 0 78 1 96 0 32 1 2461 0 39 1 35 0 38 1 26 0 27 1 639 0 28 1 1908 0 21 365 0 100 1 128 0 99 1 464 0 211 1 1201 0 38 1 35 0 80 1 94 0 32 1 2461 0 39 1 35 0 38 1 27 0 27 1 112 0 415 1 112 0 28 1 1908 0 21 366 0 100 1 126 0 100 1 464 0 211 1 1200 0 38 1 35 0 81 1 94 0 32 1 2460 0 39 1 35 0 38 1 28 0 27 1 112 0 415 1 112 0 28 1 1908 0 21 366 0 101 1 124 0 101 1 464 0 211 1 1199 0 38 1 35 0 83 1 92 0 32 1 2460 0 39 1 35 0 38 1 29 0 28 1 110 0 417 1 110 0 29 1 1908 0 2
Representation of the Gerber file that will be used to control the milling machineFormat: <laser on/off> <distance to move>
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Software Design Decisions• How should we communicate with the
PIC18F2550?– Initially: Send large amounts of data to PIC, with
no response– Final choice: Send individual commands, wait for
acknowledged response before sending another• Slower method, but we are using a very small amount
of our available bandwidth at any one time, and the latency is low enough to be negligible compared to the rate of dots/s where 1dot = 1/1000in
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Software Design Decisions
• How should we control security?– Option1: None
• Check the user’s input password against a plain text file• Not really an option, we need user access level control
– Option2: Encryption• Encrypt the user’s password, and check against the inserted
password• Difficult to implement
– Option3: Hashing• Hash the user’s password, store the hash, and create a new hash
based on the inserted password. Verify that they match.• Easy to implement, and mathematically impossible to construct
the password from the hashed value
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Software Design Decisions
• How should we control security?– Option3: Hashing (SHA-512)
• Can’t just store the user’s password• Need to store the user’s access level also• Therefore, store
hash(<access_level>+<password>)• then compute the four possible hashes based on the
current password that has been entered into the system and assign the user the correct access level
• Access Levels: None, Standard, Advanced, Experienced, Administrator
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Optimal Control Path
Experienced User
Administrator UserStandard User
Main GUI
Main Program User Login Main GUI Select File
Console GUI
mill()
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TranslateImage
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Main GUI
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Read Input File
• Convert the Gerber file to a TIFF (gerb2tiff.exe)• Convert the TIFF file to a PNG (convert.exe, Image Magick
suite)Runtime rt = Runtime.getRuntime();
pr = rt.exec(String toRun);• We did not want to have to write our own Gerber parser, so
we used the gerb2tiff program• Java will not natively handle TIFF files, so we used the convert
program– JAI library was deemed to add too much complexity to this
project
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Mill Procedure• mill(String fileName) procedure called• checkReady()
– Is the laser on?– Have any errors occurred?
• loadPreprocessedFile(String fileName)– If errors occur, exit gracefully to calling procedure which will handle the
outcome• loadSettings()
– Set how fast the XY head will move over areas where the laser will be on or off• traverseXY(int xy, int laser, int distance)
– int xy determines which MCU to connect with, laser determines whether the laser will be on or off and thus how fast to move the milling head, and the distance determines how far to go with this one command
– moveXY (int xy, int laser, int distance)• sends the actual commands to the respective microcontroller• returns a boolean to traverseXY(…) depending on whether the mill operation for that
movement command was a success or not
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Send and Receive Data
• Traverse the processed input file in an alternating line fashion
• Send the data to the machine, wait for an acknowledgement packet back before sending the next movement command
• If a line has nothing to be milled on it, move down until a line with something to be milled is found, the edge of the file, or the edge of the XY table is found
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Image Tiling•Idea: Split the image into smaller sections to reduce the extraneous travel of the milling head•Implemented along with a blank line skipalgorithm that allows quick travel throughlarge sparsely populated regions.
•Accomplished by loading the main full sized image first, grabbing sub sections•of this image and saving the location data of where to mill in a text file.
Blank Line
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Milestone Chart
Feb 21
Feb 28
Mar 7
Mar 14
Mar 24
Mar 28
Apr 4
Apr 11
Laser Cavity
Q Switch PS
XY Table Stepper PS
TEC PS
Software
Laser PS
XY Table Testing
Software Testing
Cleaning up
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Budget
• Software – free• Parts for XYZ table – $200• Laser setup
– Q-switch – $60 - $5000– 808nm Diodes – $600– Nd:YAG rod – $50– KTP(KD*P) – $30 to $100– Directing mirrors – $450– Lens – $600– Quarter wave plate – $200– Polarizer – $400
• Parts for Laser Power Supply – $200• Parts for TEC Power Supply – $75• Parts for Q switch Power Supply – $50• Parts for Stepper Power Supply – $30• Parts for Power Management Circuit – $50• Fume controller – $30
Total: $3100 to $8100
• Software – free• Parts for XYZ table – $200• Laser setup
– Q-switch – $512.95– 808nm Diodes – $486.99– Nd:YAG rod – $250– KTP(KD*P) – $43.22– Directing mirrors – $27.19– Lens – $420– Quarter wave plate – $74– Polarizer – $49
• Parts for Laser Power Supply – $400• Parts for TEC Power Supply – $35• Parts for Q switch Power Supply – $140• Parts for Stepper Power Supply – $30• Parts for Power Management Circuit – $70
Total: $2738.35
Estimate cost: Spent cost:
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Acknowledgment
• Special Thanks to the Laser Plasma Laboratories team in the CREOL department for the help in burn testing and laser diode calibration.
• Group 17 for there morale support.
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Questions?
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