The GEO 600 Detector Andreas Freise and the GEO 600 Team University of Hannover May 20, 2002

The GEO 600 Detector

Andreas Freise and the GEO 600 Team

University of Hannover

May 20, 2002

May 20, 2002 Andreas Freise

Location of GEO 600

LIGO

ACIGA

TAMAVIRGO

GEO

East Arm 600 m

North Arm 600 m

the clean roomthe gallery in the central building

the central area

the trench with vacuum tube


GEO 600 - optical layout

Michelson Interferometer with Dual-Recycling

folded arms with an opticalpath length of 2400 m

Output Mode Cleaner

triangular 0.1 mring cavity

Laser

14 W

Mode Cleaners

triangular 8 m ringcavities


MichelsonInterferometer

Output Mode Cleaner

Laser

Mode Cleaners

Vacuum Enclosure

400 m3 volume / 4000 m2 surface600 m long tubes, 60 cm diameter2 m tall tanks with 1m diametertubes : 110-8 mbar main tanks : 510-8 mbar


Seismic Isolation

g e o p ho n z

g e o p ho n x

g e o p ho n y

PZT

rub b e r la ye r

fla ng e

b e llo w

x

yz

The mechanical structure insidevacuum tanks is mounted onthree Stacks:

Triple Pendulum Suspension


Monolithic Suspension

Silicate (Hydroxy- Catalysis) Bonding

Weld


Status May 2002 (I)

Michelson Interferometer

Laser

Mode Cleaners

final optics

test optics

Laser + Mode Cleaners complete

Power-Recycled Michelson with low finesse

two main mirrors with monolythic suspension


Slave

Master

Master

Slave

enter vacuum system

Laser System

Master Laser:

Nd:YAG NPRO (non-planar ring

oscillator) 800mW @ 1064 nm

Slave Laser:

Nd:YAG injection locked ring

cavity 14 W @ 1064nm less than 5% in higher

modes


Laser

Light Power


Output Mode Cleaner

Mode Cleaners

10 W 5 W

~ 5 kW

~ 50 mW

1 W

10 kW atBeam Splitter


Status May 2002 (II)


Laser

Mode Cleaners

2 W 1 W

~ 50 mW

200 W atBeam Splitter

Mode Cleaners:

Troughput 80% 72%

Finesse 2700 1900

Visibility 91% 92%

Power-Recycled Michelson:

MPR T=1.5%

Gain 200

Contrast 4000

MPR

final optics

test optics


Three types of control tasks:

1) Local control: damping of pendulum resonances, active seismic isolation, temperature control

2) Global control of longitudinal degrees of freedom of optical systems: length and frequency stabilisation

3) Global control of alignment of optical components: Automatic alignment system

Automated Control

control loops made of analog electronics

supervised by digital electronic(digital potentiometers, CMOSswitches, mico-controller, AD

converter)

controlled by distributed LabViewvirtual instruments

(digital bus, read ~1000 controlchannels, lock automation)


Length and Frequency Control


Output Mode Cleaner

Laser

Mode Cleaners

the laser frequency is locked to thelength of the first mode cleanerthe length of the first mode cleaneris locked to the length of the second

the now pre-stabilised laser frequency is locked to the common mode of the power-recycled Michelson interferometer

25 MHz13 MHz37 MHz

Laser Frequency Stabilisation:

no rigid reference cavity

laser is directly stabilised to suspended cavities

3 sequential Pound- Drever-Hall control loops

common mode of the power-recycled Michelson serves as frequency reference


Frequency Noise

Required frequency stability at the input of the final interferometer: 10 Hz/sqrt(Hz)


Mode Cleaners

Output Mode Cleaner

Michelson Length Control


Laser

15 MHz

10 MHz

Differential arm length:(gravitational wave signal)

heterodyne detection Schnupp modulation

Signal recycling control:

a separate modulation frequency

reflected beam from AR coating


Reaction Pendulum:

3 coil-magnet actuators at intermediate mass

Electrostatic actuation on test mass

Test Mass Actuators


Alignment Control (I)

DC: beam positions are defined by reference marks, spot position control, below 0.1 Hz

around the resonance frequencies of the suspension pendulums the beam follows the input beam from the laser bench, differential wave-front sensing, 0.1 Hz to 10 Hz

no active control at the expected signal frequencies, the two mode cleaners suppress geometry fluctuations by ~106


Alignment Control (II)

differential wave-front sensing

spot position control

4 degrees of freedom for MC 1

+4 for MC 2+4 for MI common mode+2 for MI differential mode+2 for signal recycling

16 + 32 = 48

Status May 2002: Complete (except for the not yet installed signal recycling mirror)


Data Acquisition

Data acquisition uses 3 Data Collecting Units (DCUs)with (in total) :

64 channels @ 16384 Hz

64 channels @ 512 Hz

~ 1000 channels @ 1Hz

Possible data rate:

600kB/sec

~ 50 GB/day


Data Storage and Transfer


Coincidence Run with LIGO

Engineering run 28.12.2001 - 14.01.2002

• 430 hours of continous data taking

• Duty cycle (> 10mins) ~ 75%

• 98% for the last 24h.

• Longest lock: 3h:38min

• ~ 0.9 TB of data recorded

0

10

20

30

40

50

60

70

80

90

100

31.12.01 02.01.02 04.01.02 06.01.02 08.01.02 10.01.02 12.01.02 14.01.02

Date

Pe

rce

nta

ge

of

time

in lo

ck

Daily overall duty cycles, maintenanceperiods not subtracted


Strain Sensitivity


Automated Control

Laser-mode-cleaner system with longitudinal control and auto alignment runs continuously since December 2000

Total time for relocking the injection locked laser and the two mode cleaners is typically < 40 sec

Continuous lock of the auto-aligned mode cleaner system: 48 hours

Locked 1200 m cavity without any re-alignment of the cavity mirrors for 36 hours

Continuous lock of the entire system: 10 hours

Documents

The GEO 600 Detector Andreas Freise and the GEO 600 Team University of Hannover May 20, 2002