New Quadrant Diodes New Quadrant Diodes

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New Quadrant Diodes New Quadrant Diodes

Motivations & Requirements

Status & Plans: see Nikhef talk

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H. Heitmann

The Frascati QD front end module

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New front end electronics - motivations 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

2005 measurements

Preamp noise ^Sho^{t no} ise

Photocurrent (A)

Noise (A/rtHz)

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H. Heitmann

VSR1 alignment noise budget VSR1 alignment noise budget

QD front end noise

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Main requirements Main requirements

Property Virgo+

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

≥ 0.2 A/W 0.4 A/W

0.2 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

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H. Heitmann

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

ΔP_offs ≤ 200

nW/degre e

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

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Comparison ‘X’ and ‘+’ configuration 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.

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H. Heitmann

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 Pole 20Hz ±2.5%

Q=0.5±5%

See following slide

Diode windows AR coated

RF outputs 50 Ohm, trough transformer

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DC signal whitening 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)

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End

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Geometrical specifications Geometrical specifications

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

Front end support structure

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H. Heitmann

Connector specifications Connector specifications

connectors like on image

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Anti-aliasing filters 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)

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H. Heitmann

CRQ referee additions 08/2006 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)

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Diode material 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

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H. Heitmann

New Quadrant Diodes New Quadrant Diodes