1 2 nd virgo+ review, cascina 17/10/2007 h. heitmann new quadrant diodes new quadrant diodes...

1 2nd Virgo+ review, Cascina 17/10/2007H. Heit mann

New Quadrant DiodesNew Quadrant Diodes

Motivations & Requirements

Status & Plans: see Nikhef talk


The Frascati QD front end moduleThe Frascati QD front end module


New front end electronics - motivationsNew front end electronics - motivations

No more spare parts+ we want to install additional QD’s (Q52, Q1p2; 10 in total)

ImprovementsHigher max. light power x 10

Presently 3 mW @ 1064 nm

Lower electronics noise 3Limited by preamplifier

=> Less noise in at all powersLower offsets

DC offset drifts caused problems

Better geometrical configuration

See Virgo CHRQ 008/2006

2 types of modules: High/Low powerReason: low noise + high power too difficult to realize in one module

2005 measurements

Preamp noise Shot noise

Photocurrent (A)

Nois

e (

A/r

tHz)


VSR1 alignment noise budgetVSR1 alignment noise budget

QD front end noise


Main requirementsMain requirements

Property Virgo+ requiremt.

Component spec

Notes

Electr. noise LP Electr. noise HP

≤ 2 pA/rtHz≤ 6 pA/rtHz

5 pA/rtHzunknown

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 mA15 mA ? TBD

the quadrant diode must support at least this total photo current

Quant.effic. LPQuant.effic. HP

≥ 0.2 A/W≥ 0.2 A/W

0.4 A/W0.2 A/W

responsitivity of the quadrant diode at 1064 nm

Compatibility Compatible with old modules (see CRQ)

HP = high power modules (<= 30 mW)LP = low noise modules


Additional requirements (I)Additional requirements (I)

Property Virgo+ requirem.

Component spec.

Notes

QD configuration

“+” config.

OK See following slide

QD size ≥ 10 mm diameter

11 mm

ΔPoffs ≤ 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


Comparison ‘X’ and ‘+’ configurationComparison ‘X’ and ‘+’ configuration

Relative sensitivity of X configurationVirgo QD’s are used in X configurationSame signal-to-noise-ratio as + config.

CouplingsHorizontal/vertical error signal couplingsX config: couplings for h+v miscentering

Misalignment sensitivityStrong horizontal or vertical misalignment:X config may give no error signal

ConclusionFor new QD front ends

“+” configuration desirable

vs.


Additional requirements (II)Additional requirements (II)

Property Requirem. spec. Notes

2 Omega suppression

≥ 30 dB Second harmonic of modulation frequency

Locally selectable RF atten.

0…40 dB

Integrated DC gain switch

Gain 1, 10

Saturation monitor

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 Pole20Hz ±2.5%Q=0.5±5%

See following slide

Diode windows AR coated

RF outputs 50 Ohm, trough transformer


DC signal whiteningDC 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)


Geometrical specificationsGeometrical specifications

Geometry such that the front end holder can be re-used

Front end support structure


Connector specificationsConnector specifications

connectors like on image


Anti-aliasing filters Anti-aliasing filters

Presently 2 output filters in front end DC pathsimple 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)

Dephasi

ng

(degre

es)


CRQ referee additions 08/2006CRQ referee additions 08/2006

Additional RequirementsCross-talk < 5%

optical exitationRF gain/phase matching: < 1%/10°

optical exitation Electronic isolation (ground not connected to bench) Geometrical/connection specifications

Additional FunctionalitiesRF saturation monitors for pre-amps (yel/red LEDs in front end)DC signal whitening (double zero at 2Hz, double pole at 20Hz)

Less important featuresLEDs 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)


Diode materialDiode material

Important pointsMax. allowed laser powerQuantum efficiency @ 1064 nmDiameter >= 10 mm

InGaAsQuantum efficiency 0.7 A/W (up to 90%)Low bias voltage

=> high optical power possibleHigh capacity

but maybe OK with our low frequency?Large sized difficult

custom fabrication possible (Ø 10 mm)

SiQuantum 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


Noise sourcesNoise sources

ADC noise2 uV/rtHz

Preamplifier noise5 pA/rtHz (1 quadrant element)typ. 50 nV/rtHz at front end output Demodulation board gain 200

10 uV/rtHz at ADC level AC80 nV/rtHz at ADC level DC

ConclusionDC signal below ADC noise level without pre-filtering

1 2 nd virgo+ review, cascina 17/10/2007 h. heitmann new quadrant diodes new quadrant diodes...

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