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 TAMA VIRGO GEO

East Arm 600 m North Arm 600 m the clean room the gallery in the central building the central area the 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 0.1 m ring cavity Laser 14 W Mode Cleaners triangular 8 m ring cavities

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 1m diameter tubes :1  mbar main tanks : 5  mbar

May 20, 2002 Andreas Freise Seismic Isolation The mechanical structure inside vacuum tanks 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 enter 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 ~ 50 mW 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 91% 92% Power-Recycled Michelson: M PR T=1.5% Gain 200 Contrast 4000 M PR final optics test optics

May 20, 2002 Andreas Freise 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, CMOS switches, mico-controller, AD converter) controlled by distributed LabView virtual instruments (digital bus, read ~1000 control channels, lock automation)

May 20, 2002 Andreas Freise Length and Frequency Control Michelson Interferometer Output Mode Cleaner Laser Mode Cleaners the laser frequency is locked to the length of the first mode cleaner the length of the first mode cleaner is 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 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

May 20, 2002 Andreas Freise Frequency Noise Required frequency stability at the input of the final interferometer: 10  Hz/sqrt(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: a separate modulation frequency reflected beam from AR coating

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

May 20, 2002 Andreas Freise 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 ~10 6

May 20, 2002 Andreas Freise 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 = 48 Status May 2002: Complete (except for the not yet installed signal recycling mirror)

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 Data Storage and Transfer

May 20, 2002 Andreas Freise Coincidence Run with LIGO Engineering run hours of continous data taking Duty cycle (> 10mins) ~ 75% 98% for the last 24h. Longest lock: 3h:38min ~ 0.9 TB of data recorded Daily overall duty cycles, maintenance periods not subtracted

May 20, 2002 Andreas Freise Strain Sensitivity

May 20, 2002 Andreas Freise 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