New Quadrant Diodes Motivations & Requirements Status & Plans: see Nikhef talk

1. New Quadrant DiodesMotivations & RequirementsStatus & Plans: see Nikhef talk

2. The Frascati QD front end module

3. 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 Shot noise Preamp noise Noise (A/rtHz) 2005 measurements Photocurrent (A)

4. VSR1 alignment noise budget QD front end noise

5. Main requirements HP = high power modules (<= 30 mW) LP = low noise modules

6. Additional requirements (I)

7. 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. Additional requirements (II)

9. 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. Geometrical specifications • Geometry such that the front end holder can be re-used Front end support structure

12. Connector specifications • connectors like on image

13. 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 Dephasing (degrees) AC filter + delay 6 msec (filter in demod. board) DC filter + delay 6 msec Frequency (Hz)

14. 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. 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. 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 level AC • 80 nV/rtHz at ADC level DC • Conclusion • DC signal below ADC noise level without pre-filtering