Recent developments in the LIGO Input Optics

(1)

Recent developments in the LIGO Input Optics

R. Adhikari ¹⁾ , J. Camp ²⁾ , P. Fritschel ¹⁾ , J. Heefner ²⁾ , B. Kells ²⁾ , N. Mavalvala ²⁾ , G. Mueller ³⁾ , D. Ouimette ²⁾ , D. Reitze ³⁾ ,

M. Rakhmanov ²⁾ , H. Rong ²⁾ , Q. Shu ³⁾ , D. Sigg ⁴⁾ , D. Tanner ³⁾ , S. Yoshida ³⁾ , M. Zucker ¹⁾

1) MIT

2) Caltech

3) University of Florida

4) LIGO Hanford, WA observatory

(2)

• IOO overview

• Mode Cleaner

• Mode Matching measurement

• Faraday Isolator

• Summary

Outline

(3)

requirement measurement

polarization 100:1 170:1

power loss by Faraday isolator*

5% 3%

RFAM at EOM**

(intensity)

1 x 10 ^-3 ~10 ^-4 Requirements

*coupling loss caused by thermal wavefront distortion.

** static RFAM

(4)

2 km 4 km Plane mirror transmittance 0.002 0.002 Curved mirror transmittance 1 x 10 ^-5 1 x 10 ^-5

Finess 1550 1550

Free spectral range 9.829 (MHz) 12.246 (MHz) Cavity full width half max 6.26 (kHz) 7.83 (kHz) Cavity optical half length 15.240 (m) 12.24 (m) Curved mirror radius of curvature 21.5 (m) 17.25 (m)

g = 1 – L/R factor 0.291 0.290

Waist size 1.818 (mm) 1.629 (mm)

Beam divergence 186 (µrad) 208 (µrad)

Mode cleaner

(5)

(6)

carrier

sideband

(7)

(8)

(9)

RESULTS

(10)

Thermal wavefront distortion in EOM

PSL beam size measurement

12-17-98 beam size change due to thermal lensingin EOT

0 0.1 0.2 0.3 0.4 0.5

0 2 4 6 8

power (W)

spot size (mm)

calculation a (m/W) = 2.2E-09

measured hor/ver average z0 (cm) = -29

Measured and calculated spot size of a cw, Nd:YAG beam transmitted through EOM Thermal lens before and after long exposure

 

  +

 

 



 +

≈

∆ w

r w

n r dT

dn k

L r P

OPL

th

abs

0 . 4

07741 . 0 )

(

₂

2

α

0 5 1 0 1 5 2 0 2 5

0 2 4 6 8 1 0 1 2

transmitted pow e r (W)

OPL change (nm)

after long exposure before long exposure OPL at w aist theory

Justin Mansell, private communication (1997) 1)

1)

(11)

f (MHz) @ 6 W note

26.7 5.94 x 10 ^-5 Mode Cleaner align ( Γ =0.1) 29.4 9.25 x 10 ^-5 Core optics align ( Γ =0.5) 68.8 1.75 x 10 ^-4 Recycling mirror align ( Γ =0.05) 35.5 1.38 x 10 ^-5 PSL pre-MC side band

40 1.55 x 10 ^-4 PSL AOM

RF amplitude modulation (intensity)

Residual intensity modulation caused by angular misalignment.

β

γ

EOM

polarizer

e ⁱ ^ω

^t

extraordinary

ordinary

cos β e ⁱ ^ω ^{t +} ^Γ ^sin ^Ω ^t

sin β e ⁱ ^ω ^t

cos β cos γ e ⁱ ^ω ^{t +} ^Γ ^sin ^Ω ^{t +} ^φo + sin β sin γ e ⁱ ^ω ^t

Measurement

( ): required modulation depth. Measurement was made at Γ=0.5 for 29.4

MHz and 68.8 MHz EOM, and at Γ=0.1 for 26.7 MHz EOM.

(12)

Faraday isolator

Thermal depolarization (single pass isolation)

single pass isolation in Faraday rotator

0.00E+00 1.00E-05 2.00E-05 3.00E-05 4.00E-05 5.00E-05

0 2 4 6 8 10

power (W)

single pass isolation

TGG only align at Pmax align at each P align at Pmin

N

S

TGG S

(13)

1/2 wave plate (HWP1)

polarizer (Pol1)

Faraday rotaotor (FR)

1/2 wave plate (HWP2)

to viewport polarizer(Pol2)

26.9 °

beam to core optics beam from core optics

Faraday isolator with ½ wave plate

0.00E+00 1.00E-03 2.00E-03 3.00E-03 4.00E-03 5.00E-03 6.00E-03

0 90 180 270 360

Angle of rotation by 1/2 w-plate (deg)

Depolarization

no FR

rotate FR 90 deg rotate FR 135 deg

Angle dependence

(14)

Fig.1 zero-order HWP and an analyzer cross-polarized to slightly elliptical output polarization.

s

¹

f

¹

θ

f

²

s

²

α

2θ+π/2+δ

E

ⁱⁿ

E

^out

x

y

F S

S F

S F F

S

F S F

S

Fig.2 Thermally induced birefringence in TGG

Birefringence in ½ w plate and TGG

(15)

OPL change at YAG waist (1.37 mm)

0 5 10 15 20

0 2 4 6 8 10 12 YAG power (W) optical path change (nm)

Measurement Theory

Thermal lens in Faraday rotator

Effective focal length

effective focal length due to thermal lensing in Faraday rotator

0 200 400 600 800 1000 1200 1400

0 5 10 15 20 25

transmitted YAG power (W)

effective focal length (m)

F from OPL change- power slope

F from OPL change measured at YAG spot size

X10

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Current status

• UF

Ø Bullseye detector tested on tabletop

• LHO 2-km interferometer

Ø All IOO components installed, aligned Ø Mode Cleaner locked

Visibility (reflection) 97%

Length adjustment 15.2396 (m) (0.4 mm short) Ø Faraday Isolator and Mode Matching telescope

aligned

• LLO

Ø Mechanical installation underway

Recent developments in the LIGO Input Optics

Recent developments in the LIGO Input Optics

R. Adhikari 1) , J. Camp 2) , P. Fritschel 1) , J. Heefner 2) , B. Kells 2) , N. Mavalvala 2) , G. Mueller 3) , D. Ouimette 2) , D. Reitze 3) ,

M. Rakhmanov 2) , H. Rong 2) , Q. Shu 3) , D. Sigg 4) , D. Tanner 3) , S. Yoshida 3) , M. Zucker 1)

1) MIT

2) Caltech

3) University of Florida

4) LIGO Hanford, WA observatory

• IOO overview

• Mode Cleaner

• Mode Matching measurement

• Faraday Isolator

• Summary

Outline

requirement measurement

polarization 100:1 170:1

power loss by Faraday isolator*

5% 3%

RFAM at EOM**

(intensity)

1 x 10 -3 ~10 -4 Requirements

*coupling loss caused by thermal wavefront distortion.

** static RFAM

2 km 4 km Plane mirror transmittance 0.002 0.002 Curved mirror transmittance 1 x 10 -5 1 x 10 -5

Finess 1550 1550

Free spectral range 9.829 (MHz) 12.246 (MHz) Cavity full width half max 6.26 (kHz) 7.83 (kHz) Cavity optical half length 15.240 (m) 12.24 (m) Curved mirror radius of curvature 21.5 (m) 17.25 (m)

g = 1 – L/R factor 0.291 0.290

Waist size 1.818 (mm) 1.629 (mm)

Beam divergence 186 (µrad) 208 (µrad)

Mode cleaner

carrier

sideband

RESULTS

Thermal wavefront distortion in EOM

PSL beam size measurement

12-17-98 beam size change due to thermal lensingin EOT

0 0.1 0.2 0.3 0.4 0.5

0 2 4 6 8

power (W)

spot size (mm)

Measured and calculated spot size of a cw, Nd:YAG beam transmitted through EOM Thermal lens before and after long exposure

 

  +

 

 



 +

≈

∆ w

r w

n r dT

dn k

L r P

OPL

0 . 4

07741 . 0 )

(

α

transmitted pow e r (W)

OPL change (nm)

after long exposure before long exposure OPL at w aist theory

Justin Mansell, private communication (1997) 1)

1)

f (MHz) @ 6 W note

26.7 5.94 x 10 -5 Mode Cleaner align ( Γ =0.1) 29.4 9.25 x 10 -5 Core optics align ( Γ =0.5) 68.8 1.75 x 10 -4 Recycling mirror align ( Γ =0.05) 35.5 1.38 x 10 -5 PSL pre-MC side band

40 1.55 x 10 -4 PSL AOM

RF amplitude modulation (intensity)

Residual intensity modulation caused by angular misalignment.

β

γ

EOM

polarizer

e i ω

extraordinary

ordinary

cos β e i ω t + Γ sin Ω t

sin β e i ω t

cos β cos γ e i ω t + Γ sin Ω t + φo + sin β sin γ e i ω t

Measurement

( ): required modulation depth. Measurement was made at Γ=0.5 for 29.4

R. Adhikari ¹⁾ , J. Camp ²⁾ , P. Fritschel ¹⁾ , J. Heefner ²⁾ , B. Kells ²⁾ , N. Mavalvala ²⁾ , G. Mueller ³⁾ , D. Ouimette ²⁾ , D. Reitze ³⁾ ,

M. Rakhmanov ²⁾ , H. Rong ²⁾ , Q. Shu ³⁾ , D. Sigg ⁴⁾ , D. Tanner ³⁾ , S. Yoshida ³⁾ , M. Zucker ¹⁾

1 x 10 ^-3 ~10 ^-4 Requirements

2 km 4 km Plane mirror transmittance 0.002 0.002 Curved mirror transmittance 1 x 10 ^-5 1 x 10 ^-5

26.7 5.94 x 10 ^-5 Mode Cleaner align ( Γ =0.1) 29.4 9.25 x 10 ^-5 Core optics align ( Γ =0.5) 68.8 1.75 x 10 ^-4 Recycling mirror align ( Γ =0.05) 35.5 1.38 x 10 ^-5 PSL pre-MC side band

40 1.55 x 10 ^-4 PSL AOM

e ⁱ ^ω

cos β e ⁱ ^ω ^{t +} ^Γ ^sin ^Ω ^t

sin β e ⁱ ^ω ^t

cos β cos γ e ⁱ ^ω ^{t +} ^Γ ^sin ^Ω ^{t +} ^φo + sin β sin γ e ⁱ ^ω ^t