GEO HF Limits/Goals/Options… Based on an meeting of the GEO team in early January in Hannover Harald Lück, Legnaro January 27th 2005

Thermal noise limitations in the kHz range

~Coating thermal noise silica ~Coating thermal noise silicon

GEO600 layout 7 kW 10W 5W detector

Changes needed to reach 1*10-23/Hz1/2 and a bandwidth of ~1-2 kHz Vacuum modest improvements (fix leaks, 2-4 additional pumps, incl. baking the tubes) Optics change to arm cavities with RSE , ~ 1-2 MW, maybe all reflective change to Sapphire or Silicon to cut down thermal noise require strong thermal compensation (prob. even for all reflective) require upgraded injection optics to handle power 200W Laser Control Likely to be very complex, due to optical configuration (esp. FP RSE), thermal problems digital controls to reduce commissioning time and ease filter design. ASI

Timescales Boundary conditions: need to take data with GEO for about 2 years @ current design sensitivity, (commissioning 2005, data taking 2006-2007) like to be online when LIGO is upgraded to adv. LIGO, i.e. ~2010-2013 -> 2 years (2008,2009) for upgrading GEO600 to GEO HF, incl. commissioning time/ noise hunting → Leaves no room for ambitious goals (e.g.diffractively coupled Sagnac with arm cavities @ few MW)

Possible way forward to ‘GEO-HF’ Continue to run GEO as it is, improving where possible GOAL: improved sensitivities 500Hz to 2kHz – aim 3 x 10-23/Hz at 1kHz – limited by coating/substrate thermal noise (magnetars, QNMs….) In parallel - design studies for technology towards advanced detectors to continue in the labs GEO-HF: reduce shot noise New SR mirror – tuneable bandwidth? Source tracking; in collaboration with VIRGO? Squeezing :No/some/full filtering for squeezing? Power increase of 2 to 4 times – new lower loss optics chain (Faradays/EOMs etc) To enable this digital control loops, thermal compensation (segmented heater), new calibration methods (that can better cope with changing interferometer responses) Continue applying for funds (MPG/PPARC) for VIRGO upgrade SR mirror incl. monolithic suspension stage Monolithic suspensions 200 W Laser contribute in designing control & locking loops

What can be reached with gradual GEO600 upgrades? Thermal noise: 3E-23/rt(Hz) with fused silica mirrors

What can be reached with gradual GEO600 upgrades? Thermal noise: 3E-23/rt(Hz) with fused silica mirrors ~2E-23/rt(Hz) with inboard and far silicon mirrors. better coatings -> ??? Shot noise: Current design 8E-23/rt(Hz)

What can be reached with gradual GEO600 upgrades? Thermal noise: 3E-23/rt(Hz) with fused silica mirrors ~2E-23/rt(Hz) with inboard and far silicon mirrors. better coatings -> ??? Shot noise: Current design 8E-23/rt(Hz) Power increase 4x -> 4E-23/rt(Hz) Narrow band operation (currently ~700Hz, BW/peak_sens~const) ca. 500Hz -> 3E-23/rt(Hz) ca. 200Hz -> 1E-23/rt(Hz) Squeezing: ???, depends on losses and squeezing achievable @ 1kHz, maybe factor 2, f-dependent squeezing???, R&D required (ongoing in Hannover)

Conclusions Upgrading GEO gradually is a promising path with limited risks to reach scientifically interesting sensitivity within the timeframe available