1. 1 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann New Quadrant Diodes New Quadrant Diodes Motivations & Requirements Status & Plans: see Nikhef talk

2. 2 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann The Frascati QD front end module

3. 3 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann New front end electronics - motivations No more spare parts + we want to install additional QD’s (Q52, Q1p2; 10 in total) Improvements Higher max. light power x 10 Presently 3 mW @ 1064 nm Lower electronics noise  3 Limited by preamplifier => Less noise in at all powers Lower offsets DC offset drifts caused problems Better geometrical configuration See Virgo CHRQ 008/2006 2 types of modules: High/Low power Reason: low noise + high power too difficult to realize in one module 2005 measurements Preamp noise Shot noise Photocurrent (A) Noise (A/rtHz)

4. 4 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann VSR1 alignment noise budget QD front end noise

5. 5 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Main requirements PropertyVirgo+ requiremt. Component spec Notes Electr. noise LP Electr. noise HP ≤ 2 pA/rtHz ≤ 6 pA/rtHz 5 pA/rtHz unknown total output noise, referred to the photocurrent of an individual QD element Photo current LP Photo current HP ≥ 1.5 mA ≥ 15 mA 1.5 mA 15 mA ? TBD the quadrant diode must support at least this total photo current Quant.effic. LP Quant.effic. HP ≥ 0.2 A/W 0.4 A/W 0.2 A/W responsitivity of the quadrant diode at 1064 nm CompatibilityCompatible with old modules (see CRQ) HP = high power modules (<= 30 mW) LP = low noise modules

6. 6 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Additional requirements (I) PropertyVirgo+ requirem. Component spec. Notes QD configuration “+” config.OKSee following slide QD size≥ 10 mm diameter 11 mm ΔP offs ≤ 200 nW/degree Offset drifts with temperature, in terms of equivalent incident power Crosstalk between channels: < 5% for optical excitation (6 MHz power mod.laser) RF gain matching < 1%2%for optical excitation RF phase matching < 10° for optical excitation

7. 7 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Comparison ‘X’ and ‘+’ configuration Relative sensitivity of X configuration Virgo QD’s are used in X configuration Same signal-to-noise-ratio as + config. Couplings Horizontal/vertical error signal couplings X config: couplings for h+v miscentering Misalignment sensitivity Strong horizontal or vertical misalignment: X config may give no error signal Conclusion For new QD front ends “+” configuration desirable vs.

8. 8 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Additional requirements (II) PropertyRequirem.spec.Notes 2 Omega suppression ≥ 30 dBSecond harmonic of modulation frequency Locally selectable RF atten. 0…40 dB Integrated DC gain switch Gain 1, 10 Saturation monitor DC output low pass filters LP filter (suppress >> 10 kHz) Use same output filters as in Nikhef demod. Boards. Keep output filtering option open. DC path whitening filters Double Zero 2Hz ± 2.5% Q=0.5±5% / Double Pole 20Hz ±2.5% Q=0.5±5% See following slide Diode windowsAR coated RF outputs50 Ohm, trough transformer

9. 9 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann DC signal whitening Whitening filter double zero @2 Hz, double pole @ 20 Hz? (-> similar to standard photodiode prefiltering) Whitening filter should be switcheable (jumper,...) DC signal spectrum (VSR1)

10. End

11. 11 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Geometrical specifications Geometry such that the front end holder can be re-used Front end support structure

12. 12 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Connector specifications connectors like on image

13. 13 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Anti-aliasing filters Presently 2 output filters in front end DC path simple poles 33 Hz & 85 Hz => Dephasing! Digital AA filters in readout chain possible? (To be verified) delay 6 msec DC filter + delay 6 msec AC filter + delay 6 msec (filter in demod. board) Frequency (Hz) Dephasing (degrees)

14. 14 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann CRQ referee additions 08/2006 Additional Requirements Cross-talk < 5% optical exitation RF gain/phase matching: < 1%/10° optical exitation Electronic isolation (ground not connected to bench) Geometrical/connection specifications Additional Functionalities RF saturation monitors for pre-amps (yel/red LEDs in front end) DC signal whitening (double zero at 2Hz, double pole at 20Hz) Less important features LEDs indicating DC signals (for initial quad alignment, done by hand) Separate connector and test-box (with BNC connectors) to inject/monitor RF signals (for on-site unit testing)

15. 15 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Diode material Important points Max. allowed laser power Quantum efficiency @ 1064 nm Diameter >= 10 mm InGaAs Quantum efficiency 0.7 A/W (up to 90%) Low bias voltage => high optical power possible High capacity but maybe OK with our low frequency? Large sized difficult custom fabrication possible (Ø 10 mm) Si Quantum efficiency at best 45% EG&G YAG 444-4 (180 V) 0.45 A/W large crosstalk? (GEO: 6 dB) Centronic QD 100-3T (15 V bias) 0.22 A/W IR enhanced (used at GEO) Centronic QD 100-4X (120 V) 0.43 A/W YAG enhanced

16. 16 2 nd Virgo+ review, Cascina 17/10/2007 H. Heitmann Noise sources ADC noise 2 uV/rtHz Preamplifier noise 5 pA/rtHz (1 quadrant element) typ. 50 nV/rtHz at front end output Demodulation board gain 200 10 uV/rtHz at ADC levelAC 80 nV/rtHz at ADC levelDC Conclusion DC signal below ADC noise level without pre-filtering