The GEO 600 Detector Andreas Freise for the GEO 600 Team Max-Planck-Institute for Gravitational Physics University of Hannover May 20, 2002

May 20, 2002 Andreas Freise Network of Interferometric Detectors LIGO ACIGA TAMA VIRGO GEO

East Arm 600 m North Arm 600 m clean room gallery in the central building central area trench with vacuum tube

May 20, 2002 Andreas Freise GEO Optical Layout Michelson Interferometer with Dual-Recycling folded arms with an optical path length of 2400 m Output Mode Cleaner triangular ring cavity Laser 14 W Mode Cleaners 2 triangular ring cavities (8 m optical path length)

May 20, 2002 Andreas Freise GEO 600 Sensitivity broadband configuration narrowband configuration

May 20, 2002 Andreas Freise Michelson Interferometer Output Mode Cleaner Laser Mode Cleaners Vacuum Enclosure 400 m 3 volume / 4000 m 2 surface 600 m long tubes, 60 cm diameter 2 m tall tanks with 1 m diameter tubes :1  mbar main tanks : 5  mbar

May 20, 2002 Andreas Freise Seismic Isolation The mechanical structure inside each vacuum tank is mounted on three Stacks: Triple Pendulum Suspension

May 20, 2002 Andreas Freise Monolithic Suspension Silicate (Hydroxy- Catalysis) Bonding Weld

May 20, 2002 Andreas Freise 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

May 20, 2002 Andreas Freise Slave Master Slave entrance to vacuum system Laser System Master Laser: Nd:YAG NPRO (non-planar ring oscillator) 1064 nm Slave Laser: Nd:YAG injection-locked ring cavity nm less than 5% in higher modes

May 20, 2002 Andreas Freise Laser Light Power Michelson Interferometer Output Mode Cleaner Mode Cleaners 10 W 5 W ~ 5 kW ~ 4 mW (carrier) + ~ 100 mW (modulation sidebands) 1 W 10 kW at Beam Splitter

May 20, 2002 Andreas Freise Status May 2002 (II) Michelson Interferometer Laser Mode Cleaners 2 W 1 W ~ 50 mW 200 W at Beam Splitter Mode Cleaners: Troughput 80% 72% Finesse Visibility 96% 92% M PR final optics test optics

May 20, 2002 Andreas Freise Automated Control control loops made of analog electronics supervised by digital electronics controlled by distributed virtual instruments (LabView)

May 20, 2002 Andreas Freise Length and Frequency Control Michelson Interferometer Output Mode Cleaner Laser Mode Cleaners 25 MHz 13 MHz 37 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 Measured in-loop stability at the main interferometer input : Hz

May 20, 2002 Andreas Freise Mode Cleaners Output Mode Cleaner Michelson Length Control Michelson Interferometer Laser 15 MHz 10 MHz Differential arm length: (gravitational wave signal) heterodyne detection Schnupp modulation Signal-Recycling control: separate modulation frequency reflected beam from beam splitter AR coating

May 20, 2002 Andreas Freise Test Mass Actuators Reaction Pendulum: 3 coil-magnet actuators at intermediate mass Electrostatic actuation on test mass

May 20, 2002 Andreas Freise Alignment Control (I) differential wave-front sensing spot position control 4 degrees of freedom at MC 1 +4 at MC 2 +4 at MI (common mode) +2 at MI (differential mode) +2 at Signal-Recycling cavity = 36 Status May 2002: Complete (except for Signal- Recycling mirror)

May 20, 2002 Andreas Freise Alignment Control (II) Light on the main photo detector

May 20, 2002 Andreas Freise Data Acquisition Data acquisition uses 3 Data Collecting Units (DCUs) with (in total) : Hz Hz ~ Hz Possible data rate: 600kB/sec ~ 50 GB/day

May 20, 2002 Andreas Freise Daily overall duty cycles, maintenance periods not subtracted 430 hours of continuous data taking ~ 0.9 TB of data recorded Engineering run Coincidence Run with LIGO

May 20, 2002 Andreas Freise Detector Improvement (I) Detector characterisation groups analyse data from coincidence run Example: analysis of detector data for all times at which the Michelson interferometer left its normal operating point: 36 lock losses (on ) 9Not identified 7Acquisition failure 12Spike in laser channel 2Spot position event 2Stack movement 2Seismic event 2Manual alignment NoCause of loss of lock Checked wiring of the laser electronics, found and removed ground loops. duration of continuous locking of the mode cleaner section improved from ~4 hours to up to 100 hours

May 20, 2002 Andreas Freise Detector Improvement (II) Experimental optimisation period: electronics for Michelson servo loops are being completed Michelson automatic alignment is completed losses inside interferometer have been reduced (PR gain improved from 15 to 200) known problem with beam splitter suspension has been fixed sensitivity has been improved from /sqrt(Hz) to ~ 300 Hz

May 20, 2002 Andreas Freise Future steps Optimisation (Michelson) June 02 Coincidence run with LIGO (S1) July 02 Implementation of Signal-Recycling end of July 02 Optimisation (Dual-Recycling) Aug.-Oct. 02 Installation of final subsystems starting Nov. 02 Coincidence run with LIGO (S2) end of Nov. 02