©LZH

ZA

GEO 600 Laser Systemas in the optics lab of Callinstraße 38 at 12.08.2000

•LIGO-G000228-00-D

©LZH

ZA

New Features of GEO 600 Slave Laser

• Resonator spacer and base plate made of Invar (FeNi36 / 1.3912)– low thermal expansion 8x10-7 / K (average 20-50°C)

(thermal change of optical path length in air at const. pressure - 9x10-7 / K)

• Diode laser power monitor

©LZH

ZA

GEO 600 Slave Laser

©LZH

ZA

GEO 600 Slave Laser

©LZH

ZA

GEO 600 Slave Laser

©LZH

ZA

“Long Term” Stability

• Maximum power after two mirrors and an adjustable attenuator consisting of

a polarizer a half wave plate and a 2nd polarizer.

• Laser left untouched, attenuator varied for different purposes • 2 % / 1.5 % pump power drop observed over full 21 day period

©LZH

ZA

“Long Term” stability II(20 h preliminary)

0 180 360 540 720 900 10800,5

0,6

0,7

0,8

0,9

1,0

slav

e pi

ezo

leng

th in

crem

ent

[m

]

time [min]

All other acquired data stableto measurement resolution

– room temperature: 1 K

– pump power: 0.2 %

– output power : 1%

©LZH

ZA

Slave Intensity Noise Suppression

©LZH

ZA

Slave Intensity Noise SuppressionTransfer of Pump Current Modulation to Amplitude Modulation

102 103 104 105 106

-70

-60

-50

-40

-30

-20

ampl

itude

a. u

. [dB

]

102 103 104 105 106

-270

-180

-90

0

90

pha

se [d

eg]

frequency [Hz]

©LZH

ZA

Slave Intensity Noise SuppressionFull Open Loop Transferfunction of AM Servo (preliminary setup)

©LZH

ZA

Slave Intensity Noise SuppressionFirst Results (of preliminary setup)

©LZH

ZA

Power Scaling of End Pumped Nd:YAG

0 5 10 15 20 25 30 35 400

2

4

6

8

10

12

14

16

18

GEO Slave with Nd:YAG rods with undoped encaps first data taking second data taking after realingnment

outp

ut p

ower

[W]

pump power [W]

As ta n d a r d r o d s g o o d c o a t in g1 3 .5 W @ 2 x 1 7 W p u m p p o w e r.Bs ta n d a r d r o d s b a d c o t in g11 .5 W @ 2 x 1 7 W p u m p p o w e rCr o d s w ith u n d o p e d e n d c a p ss a m e c o a t in g a s in 1 5 W @ 2 x 2 0 W p u m p p o w e rBDe x p e c ta t io n s fo r r o d s w ith u n d o p e d e n d c a p sg o o d c o a t in gp ro b a b ly 1 7 W a t 2 x 2 0 W p u m pEr e d e s ig n o f c a v ity a n d p u m p o p t ic sm ig h t y ie ld 2 0 W

©LZH

ZA

Power Scaling of End Pumped Nd:YVO4

0 5 10 15 20 25 30 35 400

2

4

6

8

10

12

14

16

18

GEO slave with standard Nd:YVO4 "rods"

brewsterplates removed

outp

ut p

ower

[W]

pump power [W]

Advantages of Nd:YVO4 1)

• amplifies 1064 nm emission of Nd:YAG(? at what temperature difference ?)

• birerefingence na= 1.96 / nc= 2.17 no depolarization

• emission || = 25x10-19 cm-2 = 7x10-19 cm-2

polarized emission• large product of || sp (sp 90 s)

loss insensitive high gain lasers• 8 nm broad absorption @ 808 nm

low requirements on pump diodes

Disadvantage of Nd:YVO4 1)

• low pump intensity damage threshold58 W / mm2 @ 0.5 % doping29 W / mm2 @ 1.0 % dopingincreased by 50 % by undoped endcaps

1) Data from Y.-F. Chen, IEEE J. Q. E. 35(2), 234 (1999) / Tsunekane et. al. Elt. Lett. 32(1), 41 (1996) / VLOC, Casix, Castech web pages

©LZH

ZA

Problems of the slave

• Atmospheric pressure changes p dl/(l dp) 2.8x10-7 / hPa

– 50 hPa and 0.5 m 7 m

• Mirrors on single long range piezos tilt 10 rad / m

• Long range piezos have large low frequency resonances

©LZH

ZA

Possible Solutions

• Sophisticated piezo mountpre tension / damping / thick mirrorsmultiple piezos

• Thermal length actuator30 mm Al/FeNi36 0.5 m / K

pessimistic assumption: f 106 Hz / Hz1/2, fx-over 0.01 Hz

piezo: lRMS 10 nm

• Hermetically airproof resonatorconstant density of air nearly constant optical path length expansion dependent on spacer material only Suprainvar / Zerodur / ULE