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)

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.

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

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 (~10-15m 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:10-11m

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 fc (-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

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): fsc <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 oC)» Thermal lensing (f~20m)

To measure the birefringence

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?

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 …