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eLIGO/advLIGO FI updateeLIGO/advLIGO FI update

Antonio Lucianetti, K.L. Dooley, R. Martin, L. F. Williams,

M.A. Arain, V. Quetschke, G. Mueller, D.B. Tanner, and D.H. Reitze

University of Florida, Gainesville, FL

Ligo-Virgo Meeting, Hannover, Oct. 2007G070675-00-R

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FI for eLIGOFI for eLIGO

1

Laser Mod FI

GW readout

IMC

OMC

● High isolation ratio (>30 dB)● Low beam drift (< 100 rad)● Weak thermal lens (residual │f│> 30 m)

25 W

Current iLIGO FI at Livingstonprovides an isolation ratio aslow as 13.6 dB

Refl

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eLIGO/advLIGO FI eLIGO/advLIGO FI configurationconfiguration

2

● Faraday Rotator - Two 22.50 TGG crystals with a reciprocal 67.50 QR

● Calcite wedge polarizers (superior to TFPs)

● Thermal lens compensation with - dn/dT material (deuterated dihydrogen phosphate, or ‘DKDP’)

Q R

W P TG GTG G

D K D P

TFP

R E FL

IS O

C W P C W P

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Problems we have Problems we have encounteredencountered

TGG and DKDP crystals: - surface damage - improper AR

coatings

SOLUTION: New vendor (NG)

Magnet

Diameter ~ 200 m

3

FI magnet ring failure

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Characterization of Characterization of individual TGGsindividual TGGs

yf it = 2E-08x6 - 2E-06x5 + 6E-05x4 - 0.0003x3 - 0.0311x2 + 0.827x + 17.26

16

17

18

19

20

21

22

23

24

25

26

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

TGG sleeve full turn [#]

TG

G r

ota

tio

n a

ng

le [

deg

]

●Incident laser power: 1 W

Result from 6th order polynomial fit:

Max TGG rotation angle (crystal #2): 24.03 deg +/- 0.01 deg

4

z

z

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Thermal lens created Thermal lens created by TGG and DKDPby TGG and DKDP

Telescope

Fiber laser beam(1-30 W)

DKDP or TGG

Focusing lens

Beam Scan

Thermal Lensing in 'x-direction'

-200-150-100

-500

50100150200

0 10 20 30 40

Power (W)

Fo

ca

Le

ng

th (

m)

TGG (Air)

DKDP (Air)

5

Thermal Lensing in 'y-direction'

-200-150-100-50

050

100150200

0 10 20 30 40

Power (W)

Fo

cal

Len

gth

(m

)

TGG (Air)

DKDP (Air)

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COMSOL Simulation COMSOL Simulation (radiation enabled on faces and (radiation enabled on faces and

edges)edges)

30 W incident powerTime from t = 0s to t = 60s with a line every 1s

Parameters: TGG radius = 10.3 mmLaser beam radius = 1.5 mm

Temperature in the center of the pumped face (point [0,0,0])

6

The time constants of thermal lensing are in the order of seconds

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30 W incident powerTime from t = 0s to t = 3600s (60min) with a line every 60s (1min)

Parameters: TGG radius = 10.3 mmLaser beam radius = 1.5 mm

Temperature in the center of the pumped face (point [0,0,0])7

COMSOL Simulation COMSOL Simulation (radiation enabled on faces and (radiation enabled on faces and

edges)edges)

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Faraday Isolator Faraday Isolator performance Isolation performance Isolation

ratio (CWPs)ratio (CWPs)

8

0

5

10

15

20

25

30

35

40

45

50

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time [min]

IR [

dB

]

DKDP between CWPs

DKDP after CWPs

● Decrease in isolation ratio under vacuum as time went on ● Could be recovered by < 2 degree rotation of waveplate

PL = 25Wp = 4*10-6 Torr

WP adjusted

IR of iLIGO FI (LLO)

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Faraday isolator Faraday isolator performance Effect of performance Effect of

vacuum vacuum

9

● PL = 25 W

● DKDP between CWPs

0

5

10

15

20

25

30

35

40

45

0 50 100 150 200

Time [min]

IR [

dB

]

in vacuum (p = 4*10^-6 Torr)

in air with chamber windows (p = 760 Torr)

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Faraday isolator Faraday isolator performance thermal performance thermal

drift (CWPs)drift (CWPs)

PL = 25Wp = 4*10-6 Torr

Result:Over the course of six hrs the horizontal and thevertical intrinsic drifts are < 50 microradians

FI

Refl beam thermal drift intrinsic to FI

-200

-150

-100

-50

0

50

100

150

0 100 200 300 400 500 600

time [min]

dri

ft [

mic

rora

dia

n]

horizontalvertical

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ELIGO FI ScheduleELIGO FI Schedule

LLO● Assembly, final test and measurements of the FI will be done in the clean optics lab at the LIGO Livingston Observatory ● Installation of the FI for LLO will start on Nov 13, 2007.● Integration and commissioning of the FI and Input Optics with PSL is planned to start on June 3, 2008.

LHO● Installation of the FI at LHO is planned to start in December 2007 or January 2008.● Integration and commissioning of the FI and Input Optics with PSL is planned to start on Feb. 19, 2008.

11

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ConclusionsConclusions

● Initial LIGO FI measurements reveal that isolation requirements for E-LIGO are very relaxed

→ 20 dB will work well ● Obtained 43 dB isolation ratio with CWPs in vacuum Decrease in isolation ratio under vacuum should be recovered by < 2 degree rotation of waveplate. Intrinsic thermal drift of the reflected beam was < 50 microradians for the horizontal and vertical axes

● Performance is expected to improve with Northrop Grumman crystals (TGG/DKDP) and new precision mount for DKDP with tip/tilt positioning