1

Thermal Headaches in Advanced LIGO Input Optics

Guido Mueller, Rupal Amin, David Guagliardo, David Tanner, and David Reitze

Physics Department

University of Florida

Gainesville, FL

LIGO-G010130-00-Z

2

Input Optics Functions

•RF Modulation

•Mode Cleaning

•Mode Matching

•Optical Isolation

•Distribution of Control Beams

•Self Diagnostics Conceptual layout of IO optical

components

Faraday Isolation

ModeMatching Telescopeinto ModeCleaner

Mode

Mode Matching and Beam Steering Telescope intoCore Optics

FaradayIsolation

ISC Wavefront Sensing

IFO Control to ISC

Intensity Stabilization

COC

to PSL

RFModulation

Stabilizationfrom ISC

Stabilizationto PSL

PSL

RFAM monitor

Cleaner

to steering mirrors

steeringmirrors

VariableAttenuator/Fast Shutter

Diagnostics

Parameter LIGO I Advanced LIGO

Laser Power 8.5 W 180 W (150 W)

Overall IO

Efficiency (TEM00)

75% 66%

Optical Isolation 70 dB (> 85 dB)

3

Advanced LIGO will operate at 180W CW powers - “presents some challenges”:

•Thermal Lensing --> Modal Degradation

= z = 1 + i

•Thermally induced birefringence

-FI- loss of isolation-EOM - spurious amplitude modulation

•Damage

•Other (nonlinear) effects (SHG, PR)

The Challenge

LiNbO3 at 30W:

5 x 5 x 40 mm LiNbO3 EOM - thermal lensing is:

i) severeii) position dependent

L P / 2 K dndT

EzME�

,~

4

Characterization of thermal lensing

50 W Nd:YLF

HRM

HRM HRM

Beam Dump

Power Meter

/2

/4

HRM

Glan Pol.

Lensing Measurement

HRM

Beam Dump

Power Meter

/2

/4

HRM

Glan Pol.

Sag Measurement

Beam Scan

DM

DM

NeNe

PD - Signal

PD -Ref.

Sample

Sample

= 1053 nm

z

Samples:

TGG: Litton [111] 10 mm diameter, 20 mm length

LiNbO3: Leysop, 5 x 5 x 40 mm

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Optical Path Difference Measurements

P=50 WAbsolute L (hot - cold): 10 mOPD (1/e intensity): ~ 100 nm 250 nm @ 125W

Theory: Hello-Vinet

6

Optical Path Difference Measurements

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Thermal Lens Magnitude (waves)

Tw

o-D

ime

nsi

on

al

Po

we

r C

ou

pli

ng

,

TEM00 with focus compensation

TEM00 without focus compensation

TEM02 without focus compensation

TEM04 without focus compensation

Mansell, et al., Appl. Opt., 2001

dxxxc aberratedmmaberratedx )()(),( *

yxnaberratedynaberratedymaberratedxmaberratedx cccc ),(),(),(),( **

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Propagation Measurements I

w(z)

0 500 1000 1500 20000.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

100 W - h

Laser/pol

Laser/pol/TGG

Laser only

Bea

msi

ze (

mm

)

Propagation Distance (mm)

0 500 1000 1500 20000.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2100 W - v

Laser/pol/TGG

Laser/pol

Laser only

Bea

msi

ze (

mm

)

Propagation Distance (mm)

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Propagation Measurements II

0 50 100 150 200

0

5

10

15

20

25

vert

hor

Fo

cal L

eng

th (

m)

Input Power (W)

fv= WP

m233

fh= WP

m174

Effective Thermal Lens

50 W

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Thermal Lensing in LiNbO3

EOM 1 EOM 2 EOM 3180 W

•KTP does work; 300 W CW power, 1064 nm (H. Injeyan, TRW); RTA should also work (lower loss tangent)

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E-O Modulation in Advanced LIGO

Alternative Method: Mach-Zehnder modulation --> architecture problem

PM 2 PM 3

f0

Im [V(t)]Re [V(t)]

SpectrumAnalyzer Optical

R=90%T=10%

R=10%T=90%

G

f0

PM 1

Prototype developed for initial LIGO detectors, but not well characterized >> R&D effort

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Power Independent Compensation of Thermal Lensing

...

),(

...

~

~

0

1

2

0

zMTEM

TEM

.........

...

...

),(//

/

25

2

23

23

2

2

2

2

1

zz

iz

i

z

zM

dndT

L P / 2 K

z = 1 + i

dndT

= absorption coefficient

K = thermal conductivity

......

~

~

2

0

0

1

TEM

TEM

M-1(, z)

dndT

12

0.0 0.2 0.4 0.6 0.8 1.0

0.80

0.82

0.84

0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

Rem

ain

ing

TE

M00

Separation Distance (m)

Thermal Lensing Compensation

Modeled using Melody

FI or EOM

Parameter TGG FK51

(m-1) 2 x 10-1 1 x 10-1

K (W/m K) 7.4 0.9

dn/dT (C-1) + 2 x 10-5 -6 x 10-6

Length (mm) 20 15.9

150 W

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Thermal Lensing Telescope

Similar to current LIGO Telescope• 2 mirror design (vacuum envelope constraints)• Accommodates wide range of mode matching parameters• All large (20 cm) optics

• in-situ adjustment with feedback

0.8

0.95

0.9

0.7

Dev. from Nom. Waist Position (m)

Wai

st S

ize

(cm

)

Wide Bandgap Glass

1064 nm

532 nm

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R&D Issues Still to be Faced

• Modulator Development: • RTA performance• MZ modulation

• Isolator Development:• Full FI system test (TCFI, EOT)• Possible thermal compensation (-dn/dT materials)

• Telescope Development:• in-situ mode matching adjustment