TCS and IFO Properties

Dave Ottaway

For a lot of people !!!!!!LIGO Lab

Kavli Institute for Astrophysics and Space Research,

Massachusetts Institute of Technology

March ’05 LSC Meeting 2

Outline of Talk

The Questions Thermal Issues in LIGO 1 Optic The TCS system The static spatial offsets in the IFO The excess absorption in H1 Optics Conclusions

March ’05 LSC Meeting 3

Steady state effect of absorption on the optics

0.02 0.04 0.06 0.08 0.1 0.120

0.02

0.04

0.06

0.08

0.1

radius (m)

de

pth

(m

)

Temnperature Profile for 1 Watt Coating Absorbtion

1

2

3

4

5

6

0.02 0.04 0.06 0.08 0.1 0.120

0.02

0.04

0.06

0.08

0.1

radius (m)

de

pth

(m

)

Temnperature Profile for 1 Watt Substrate Absorbtion

1

1.5

2

2.5

OPDcoating/OPDsubstrate = 2.9 for surface reflection

OPDcoating/OPDsubstrate = 0.95 for optics transmission

Model does not include deformative effects of the coatings

0 0.02 0.04 0.06 0.08 0.1 0.12

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

radius (m)

OP

D (

um

)

Optical Path Difference in Transmission for 1 W absorption

CoatingSubstrate

0 0.02 0.04 0.06 0.08 0.1 0.12-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

radius (m)

OP

D (

um

)

Surface Distortion in for 1 W absorption

CoatingSubstrate

March ’05 LSC Meeting 4

Effect of Heating Optics

Effects are biggest when inner optics are heated ie Beamsplitter and Input Test Masses

Has minimal effect on Carrier power (stabilized by the arms)

Common heating (equal heating of the ITMs effects) sideband build-up and mode shape in the power recycling cavity

Differential heating effects AS_I level and phase noise coupling

March ’05 LSC Meeting 5

Initial LIGO TCS Concept

CO2 Laser

?Over-heat mask Under-heat mask Inhomogeneous mask

ZnSe Viewport

Over-heat pattern

Under-heat pattern

Raw Heating pattern

March ’05 LSC Meeting 6

Effect of TCS on Optics

0 0.02 0.04 0.06 0.08 0.1 0.12-0.1

-0.05

0

0.05

0.1

radial direction (m)

OP

D (

um

)

Correction Profile vs Rinner

0.040.050.060.07

• Initial TCS used binary masks

• Very successful for factor of 3 overheat

•Beyond this more improved masks are needed – Sub resolution structure

March ’05 LSC Meeting 7

Time Constants of TCS Heating

0 5000 10000 150000

0.5

1

1.5

2

2.5

3

3.5

4x 10

-5 Lensing vs Constant Annulus Heating

Time (s)

Th

erm

al L

en

s P

ow

er

(arb

. un

its)

VerticalHorizontal

0 1000 2000 3000 4000-6

-5

-4

-3

-2

-1

0x 10

-4 ITMX Lensing vs time for IFO cooldown

Time (s)

The

rmal

Len

s P

ower

(dio

ptre

/Wat

t on

MC

)

VerticalHorizontal

•Annulus heating has complicated time dependence

•Heat flow into the center

March ’05 LSC Meeting 8

Time Constant in Annulus Heating

•Reduction of TCS Power with time is due to heat flowing into the center of the optic which reduces TCS efficiency

•See talk by Stefan

March ’05 LSC Meeting 9

Effect on TCS Laser Noise on IFO performance

Predicted actuation agrees within 10% (ie experimental error)

Noise for 3nV circuit and 10 Watts Annulus heating

Thermal expansion of HR surface is the dominant noise term

102

103

104

10-19

10-18

10-17

Predicted Displacement Noise Due to TCS

Frequency (Hz)

Dis

pla

cem

en

t (m

/rtH

z)

SRDTCS Noise

March ’05 LSC Meeting 10

Overall TCS Performance

H1 achieves sideband build-up at ~ 2 watts

Cannot lock reliably without TCS at ~ 4 Watts input

Reduces oscillator phase noise sensitivity, which is dominant at higher frequencies

Increases sideband to maximum Does not have enough power to

correct H1 at 4 Watts input H1 show significant 1.064 um

absorption A nice servo for TCS (See

Stefan’s commissioning talk)

• Green curve (Without differential TCS)•Blue curve (With differential TCS)

March ’05 LSC Meeting 11

Livingston TCS Performance

Is not plagued by the same thermal issues as H1. No sign of 1.064 um heating NSPOB level increased from 150 – 330 Sideband power to dark port increase as NSPOB Optical Gains Increase (Not quite what you would expect)

» Darm ~ NSPOB0.8

» POB_I , POB_Q ~ NSPOB2

» Refl gain increases Results confirmed by FFT modeling Reduces phase noise sensitivity by 10 DC AS_I Level Reduced by a factor of 3 System becomes unstable when TCS reduces AS_I to zero

» This is not understood TCS runs open loop, no servo used Currently operating at 6 Watts of 1.064 micron input Summary provided by Valery Frolov

March ’05 LSC Meeting 12

Optimum power to correct static curvature errors

IFO ITMX ITMY

LHO 4K 35 52 27 60 82 60

LHO 2K 0 57 17 110

LLO 4K 22 53 39 83

• Experimental Data (Blue), Simple Curvature Model (Black) and Full FFT (Green)• Model results by Hiro, additional power required for BS ROC• Measurements assume a 15% loss from the calibration point to the power

March ’05 LSC Meeting 13

Optical Absorption in the IFOs

IFOs are originally designed as a point designed with 1.06um absorption needed to get to optimum operating point» 12mW in coating and 16 mW in substrate for 6 Watt input

» Substrate absorption ~ 4 ppm/cm, Coating absorption ~ 0.5 ppm

» Numbers from Ryan Lawrence’s PhD Thesis

H1 gets to the optimum operating point with ~ 2 Watts of power

L1 shows expected heating H2 show negligible 1.064 um heating

March ’05 LSC Meeting 14

Measurements to quantify absorption in H1

Significant power potentially absorbed in various optics

TCS servo to optimize heating power (Stefan B)

» Determine reduction in central heating required at each power level

» Sensitive to power absorbed in BS, ITM coatings and substrate

» Measures optimal absorption

G factor measurements (Rick S, Malik, Bill K and Keita)

» See talk by Rick Savage

Spot size measurements (Dave O and Joe B)

March ’05 LSC Meeting 15

Spot Size Measurement

AS Port Optics

Camera Spiricon Software

TCS Beam

RM

ITMY

ITMX

0 2 4 6 8 10 12 14 16 1865

70

75

80

85

90

95

Time (Minutes)

Wai

st S

ize

(arb

.)

Spot Size vs Cooling Time

TCS (Sag)

Fit

TCS X (Tan)

Fit

IFO Heat (Sag)

Fit

IFO Heat (Tan)

Fit

•Auxiliary have since been done

•Calibrated using TCS

March ’05 LSC Meeting 16

What are these measurements sensitive to ???

* Depends on exact location of heating

Mirror ITMX ITMY ETMX ETMY BS

Measurement No Coating/Substrate C S C S C C S,C

1 Xarm TCS 1 1.05 1

2 Yarm TCS 1 1.05

3 Xarm G factor 1 0.34 0.52

4 Yarm G factor 1 0.34 0.52

5 POB Spot Size 1*

6 POX Spot Size 1 1.05 0.25

7 POY Spot Size 1 1.05

March ’05 LSC Meeting 17

The Results so far

TCS optimal heating» 16 +/- 3 mW per W (Ypath), 43 +/-8 mW per W (Xpath)

G factor changes» 24 +/- 3 mW per W (Xarm), 15 +/- 5mW per W (Yarm)

Spot size changes » 12.6 +/- 1.6 mW per W (ITMY), 34mW +/- 5mW per W (ITMX)

H1 ITMX absorbs at the level of about 26 ppm Heating in the bulk cannot be eliminated New ITMX is being prepared See T050074-00-R

March ’05 LSC Meeting 18

Conclusions

A considerable amount of progress has on determining the spatial properties of the IFO and compensating errors using the TCS system

Significant amount of power is absorbed in either the H1 ITMX and ITMY is not pristine either

If this is not corrected ~ 10 Watts of TCS correction will be required to reach the SRD

New higher power TCS laser has been installed on the ITMX to enable the delay of the ITMX swap until after S5

March ’05 LSC Meeting 19

Time Constant in Annulus Heating

•Reduction of TCS Power with time is due to heat flowing into the center of the optic which reduces TCS efficiency

•See talk by Stefan