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

2. Thermal noise limitations in the kHz range

3. ~Coating thermal noise silica
~Coating thermal noise silicon

4. GEO600 layout
7 kW
10W 5W
detector

5. 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

6. Timescales
Boundary conditions:
need to take data with GEO for about 2 current design sensitivity, (commissioning 2005, data taking )
like to be online when LIGO is upgraded to adv. LIGO, i.e. ~
-> 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 few MW)

7. 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

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

10. 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)

12. 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 1kHz, maybe factor 2, f-dependent squeezing???, R&D required (ongoing in Hannover)

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