1. Nov 3, 2008 Detection System for AdV 1/8 Detection (DET) Subsystem for AdV  Main tasks and requirements for the subsystem  DC readout  Design for: the OMC, photodiodes, benches  Plan towards completion of the Design Benoit Mours (Subsystem Manager: Edwige Tournefier)

2. Nov 3, 2008 Detection System for AdV 2/8 Scope/Mains tasks of the DET subsystem DET main task: Convert the beams to digital signals Tasks:  Beam adaptation (telescope)  Output Mode Cleaner (OMC)  Photodiode, demodulations electronic, ADCs »Longitudinal control »Alignment controls  Beams diagnostic »Cameras »Phase Camera »Scanning Fabry-Perot  Optical benches »Layouts, Mechanic, Slow control  Optical setup for the squeezing of the light (future) Remark: Look at beams only after the Injection subsystem.

3. Nov 3, 2008 Detection System for AdV 3/8 Main Subsystem requirements From the Optical, Simulation & Design subsystem  New in AdV: »Signal recycling:  Requires additional control signals »Use of folded Degenerated Recycling Cavities  Change the suspended Bench layout From the ITF Sensing and Control subsystem (ISC)  Power and signal dynamic estimations Example: Typical total power values (VIR-NOT-068B-08) before the OMC in the Antisymetric Port (AP) beam  Demodulation frequencies The use of DC readout  The need to remove the sidebands with the OMC Avoid the introduction of technical noises  Back-scattering of light  Reduce the environmental noise (beam jitter, seismic/acoustic isolation…)  Electronic noise Be flexible enough to accommodate the commissioning needs

4. Nov 3, 2008 Detection System for AdV 4/8 New features for AdV: DC readout Main motivation: a smaller (~ 20%) shot noise Advantages for the technical noises for the “AP” beam:  Smaller coupling of technical noises at high frequency »No demodulation noise;. »No frequency noise due to the asymmetry of losses into the cavities – The frequency noise due to finesse asymmetry is the same as in the AC readout case.  Larger photodiodes can be used since no demodulation is needed. »Simpler alignment, reduced: power density, environmental noise from beam jitter, backscattering  No problem of reduced spatial overlap between the carrier and the sidebands Consequences on the detection system:  The sidebands should be removed by the Output Mode Cleaner (OMC)  New design  Need a clean (seismic isolation) ITF power noise measurement (POQR/POBS beam) DARM offset tuning:  This offset has to be kept well above the locking accuracy (~10 -15 m in Virgo)  The contribution of the contrast defect should be small enough  The offset should not be too high to keep the carrier power noise under control:  Baseline value:10 -11 m

5. Nov 3, 2008 Detection System for AdV 5/8 Photodiodes Design New modulation frequencies  New electronic required  Photo-detector equivalent to RC circuit  low pass filter »Typical values for Virgo photodiodes (d = 3 mm): R = 10 Ohms, C= 250pF  theoretical f c (-3dB) ~ 60MHz; Should be OK for the ~80MHz control signals Suspended Photodiodes  Motivations: »Back scattered light: evidence of limitations by ‘in air’ optics/ output window  Need to suspend the main optics/photodiodes »Other benefits: no ‘dust events’, noise due to photodiode motion wrt the beam reduced  Virgo+ ongoing work: »Preamplifier not vacuum compatible  Put the photodiode + protection (shutter) in air tanks »Installation date still TBD  AdV strategy will depend on the V+ experience  Quadrant Photodiodes + electronics to be checked

6. Nov 3, 2008 Detection System for AdV 6/8 OMC Design OMC specifications studied (VIR-NOT-071A-08)  A four “mirrors” monolithic ring cavity seems to be a good solution  Sidebands contribution less than 1% of the shot noise (SB2 filtering ~ 5.10 -3 )  The losses in the OMC are expected to be less than 1%.  Different AdV configuration investigated: Same length but different finesse requirement (VIR-NOT-071A-08): f sc <4.10 -7 ; use a faraday before the OMC or better seismic isolation, thanks to the SR cavity mirrors requirements R&D to study a Virgo like OMC with high finesse (500-1500)  To check that Thermal effects are not a problem »Absorption/ temperature control (  T=10 -3 o C) »Thermal lensing (f~20m)  To measure the birefringence

7. Nov 3, 2008 Detection System for AdV 7/8 Optical Benches Design The mirrors for the folded SR cavity need to be suspended  They provide also the main Detection Bench input telescope  The implementation of the suspension has to be studied »Level of isolation (see VIR-NOT-83A-08), »space issue, »mirrors controls systems, »bench local controls… Study the new layouts for the benches  Suspended and in air benches  Compatibility with future squeezed light injection? Define the mechanical improvement Study the cleanliness issue New pick-off benches?

8. Nov 3, 2008 Detection System for AdV 8/8 Plans towards completion of Design OMC  Complete the R&D on a monolithic OMC with high finesse  Freeze the OMC parameters once the AdV parameters confirmed Photodiodes under vacuum:  Continue to interact with the ISC group on the modulation frequencies  Continue the V+ preparation Benches layout  Study the SR cavity mirrors on the detection bench  Build the detailed list of photodiode and channels  Check the quadrants electronic  Study the mechanical changes of the bench  Provide new design for the benches  …