Q09/2001

The GEO 600 Laser SystemLIGO-G010366-00-Z

V. Quetschke°, M. Kirchner°, I .Zawischa*, M. Brendel*,

C. Fallnich*, S. Nagano+, B. Willke°+, K. Danzmann°+,

and the GEO600 Team

*Laser Zentrum Hannover, Hollerithallee 8, D-30419 Hannover, Germany

°Universität Hannover, Institut für Atom- und Molekülphysik, Callinstraße 38, D-30167 Hannover, Germany

+Max-Planck-Institut für Gravitationsphysik, Albert-Einstein-Institut, Aussenstelle Hannover,

Callinstraße 38, D-30167 Hannover, Germany

Q09/2001

Scheme GEO600 PSL

m ode cleaners

in terfe rom eter

in jection locked laser

am pltitude contro l frequency contro l

Q09/2001

Scheme of the Injection Locked Laser System

Pound-Dreverlocking electr.

servo

EOMEOM

m aster oscillator

pum p diodes

slave laser

isolatoror

from Interferom eter

Q09/2001

Injection Locked Laser System

Q09/2001

Master: Monolithic Nd:YAG NPRO

• 800 mW single frequency

• RRO and intensity noise suppression (> 100 Hz) by electronic feedback

• Frequency control by– temperature

• 3 GHz/K (dc) • bandwidth 1 Hz

– piezo • 2 MHz/V• bdw. typ 50 kHz limited by mech.

resonances – pump power

• 1 MHz/mA (dc)• 1/f dependency f >100 Hz• bdw. 100 kHz• no observable beam pointing

• External EOM for fast phase control

808 nmlaser crystal

1064 nm

N d:YAG

PBS

diode laser

PZT

feedb. servo.

TEC

Q09/2001

Slave: Quasi monolithic Nd:YAG Laser

bow-tie ring with two end-pumped rods

• > 12 W, M2 < 1.1, DOP > 98%

• > 35 % optical efficiency

• 1 midrange piezo length actuator– 2.5 µm (2.5 GHz) / -15 to 300 V– max. Voltage -100 V to 500V – resonances > 50 kHz, – bandwidth 15-20 kHz– dc tilt typ. 10 µrad / µm

• Quasi monolithic design– no manually movable resonator parts– low thermal expansion spacer

Invar: = 8x10-7/K -> 225 MHz/K(air at 1000 hPa -> -250 MHz/K) (Alu: =24x10-6/K -> 6.7 GHz/K)

Q09/2001

Slave: Quasi monolithic Nd:YAG Laser

1 10 100 1000 1000010

-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

quasi monolithc slave relative to stabilized NPRO

calculated influence on system with 1 MHz locking range and 1 kHz servo

Fre

quen

cy F

luct

uatio

ns [

Hz/

Hz

-1/2]

Frequency [Hz]Slave influence on frequency noise

• comparable with free running master(not injection-locked)

• follows stabilized master

(when injection-locked)

Piezo range requirements (calculated):

• 25 MHz / K

• 80 MHz / mbar : 50 mbar p-p: 4 GHz

Deviation from center of locking range

• RMS 1 Hz -100 kHz: ca. 500 Hz which is 3x10-4 of locking range

Q09/2001

Short Term System Performance

• Locking range 1.6 MHz

• 94% visibility at first mode cleaner achieved

• No influence of slave to system frequency stability observable

• Amplitude prestabilization at detection band frequencies ...

Q09/2001

Out of Loop Measurement

Q09/2001

Modecleaner Frequency Noise

• The out-of-loop frequency noise at the first modecleaner: 10 mHz

Q09/2001

Autolock Slave to Master

• State (locked/unlocked) distinguished by output power

• Ramp slave cavity length to achieve transient injection lock

• Keep lock by switching from ramp to servo

• Typ. lock aquisition time 5 s (max. 20 s)

Q09/2001

Autolock Performance

0 2 4 6 8 10 12 14 16-8

-7

-6

-5

-4vo

ltag

e[V

]

au to lock perfom ance - set1

0 2 4 6 8 10 12 14 16-0.05

0

0.05

volta

ge

[V] SL error

0 2 4 6 8 10 12 14 16-2

0

2

4

volta

ge

[V]

tim e [sec]

SL PZT feedback

PD DC out

Q09/2001

Intensity Prestabilization

Q09/2001

Intensity Noise Control – inloop

100

101

102

103

104

105

frequency (H z)

10-9

10-8

10-7

10-6

10-5

10-4

RIN

(1/

Hz)

free running, in j.lockin loopanalyzer no ise @ C H 1 range 501m Vpk

10.08.01; H P-FFT:D C &G N D , 10 avg.; P reAm p:x100, low noise, 2H P@ 0,03H z; U _D C =-6,5V

Q09/2001

Intensity Noise Control - Out of loop

100

101

102

103

104

105

frequency (H z)

10-9

10-8

10-7

10-6

10-5

10-4

RIN

(1/

Hz)

free running, in j.lockout o f loop in tno iseanalyzer no ise @ C H 1 range 3,98 Vpk

10.08.01; H P-FFT: D C &G N D , 10 avg.; P reAm p: x100, low noise, 2H P@ 0,03H z; U _D C =-4,6 V