1 ILIAS WG1 meeting, Hannover, 12.12.2005

Alignment electronics noise budget

● Sources of electronic noise● C7 electronic noise

● Electronic noise for optimized power● Some conclusions

2 ILIAS WG1 meeting, Hannover, 12.12.2005

Linear alignment setup

3 ILIAS WG1 meeting, Hannover, 12.12.2005

Quadrant photodiode

•type EG&G YAG 444

•sensitivity = 0.45 A/W

•DC power = 3 mWmax

•transimpedance = 2 k•Bias voltage = 180 V

4 ILIAS WG1 meeting, Hannover, 12.12.2005

QD electronics

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Quadrant diode box

5 ILIAS WG1 meeting, Hannover, 12.12.2005

Scheme of LA electronics

ADC noisePreamp. noise

Shot noise

Low-pass filter

AC: Gain 200

DC: Gain 1

diff. sig.

non-diff.sig.

Non-optimal treatment of DC signalsdominated by ADC noise(but were not foreseen as error signals)

VMEQD box

6 ILIAS WG1 meeting, Hannover, 12.12.2005

Noise measurements

after demodulator

quadrant diode AC output

Theoretical shot noise M. Mantovani

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7 ILIAS WG1 meeting, Hannover, 12.12.2005

Principles of calculation

Calculate electronic noise at each quadrant diodeAC and DC signals

Reconstruct error signalsUsing C7 matrix (not calibrated)

Pass through DSP correction filters

Obtain mirror motions through suspension transfer functionsLA loops closed (but gain not well known)

Suppose asymmetry (10, 1, 0.2 mm) => length noiseOnly cavity mirrors (PR, BS to be included)

Two cases1. C7

using measured QD DC powers

2. Optimized DC powers50% of saturation power

8 ILIAS WG1 meeting, Hannover, 12.12.2005

C7 matrix

ThetaX PR BS NI NE WI WEB2_q1_DC 2.5 -4.5 -6.4 15B5_q1_DC 10B2_q1_ACp -24 9.41 17.9 5.38B1p_q1_ACp 0.052 -0.108 0.0375 1 0.0729B7_q1_ACq 0.042 -0.035 0.375 -0.027B7_q2_ACq 0.042 -0.035 0.375 -0.027B8_q1_ACp -0.25 0.65 0.052 0.071B8_q1_ACq -0.25 -0.65 -0.052 -0.071

ThetaY PR BS NI NE WI WEB2_q1_DC 1B5_q1_DC 10B1p_q1_ACq 1B7_q1_ACp 0.33 0.36B7_q2_ACp 0.68 0.36B7_q2_ACq -0.36 -0.36B8_q1_ACp -0.46 -1 -0.36B8_q2_ACp 1

ThetaX has undergone second diagonalization => mixing of all signals

9 ILIAS WG1 meeting, Hannover, 12.12.2005

Electronics noise vs. C7 noise (WE tx)

10 ILIAS WG1 meeting, Hannover, 12.12.2005

Electronics noise vs. C7 noise (WE ty)

Pure DC signal

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Electronics noise vs. C7 noise (NE tx)

?

12 ILIAS WG1 meeting, Hannover, 12.12.2005

Electronics noise vs. C7 noise (NE ty)

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Electronics noise vs. C7 noise (NI tx)

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Electronics noise vs. C7 noise (NI ty)

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Electronics noise vs. C7 noise (BS tx)

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Electronics noise vs. C7 noise (BS ty)

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Electronics noise vs. C7 noise (PR tx)

18 ILIAS WG1 meeting, Hannover, 12.12.2005

Electronics noise vs. C7 noise (PR ty)

19 ILIAS WG1 meeting, Hannover, 12.12.2005

Total LA electronics noise (C7, calculated)

WE ty pure DC error signal => no extra noise vs. AC

WI under local controlSimulated WI LA curves for comparison

C7 noise not limited byLA electronics noise

(but: excess noise)

20 ILIAS WG1 meeting, Hannover, 12.12.2005

Influence of QD power

Can gain ~ factor 10by increasing QD powers

21 ILIAS WG1 meeting, Hannover, 12.12.2005

Noise budget (C7)

ADC noise (= DC noise)is not dominating, butclose => second diagonalization (tx) has spoiled signals by reintroducing DC signals everywhere ?

22 ILIAS WG1 meeting, Hannover, 12.12.2005

Influence of mirror centering (optimized powers)

Without optimized matrixnor optimized filters: => need LIGO centering precision (0.2 mm)

23 ILIAS WG1 meeting, Hannover, 12.12.2005

Conclusions: DC signals

DC signal not noisier than AC signalsAfter ADC: AC 50 DC 3 µV/rtHzDC has less electronic gain, but B2 DC signal seems very sensitiveThX: signal mixing (DC part everywhere) increases noise level

but still not noiser than pure AC signals

Other reasons for getting rid of DC signalsGet rid of laser technical noise at 6 MHz ?Seismic noise ?

24 ILIAS WG1 meeting, Hannover, 12.12.2005

Conclusions: extra noise

Extra noise on central mirrorsNot limited by electronic noise at 50 HzC7 observation:

NI ty injected noise into dark fringe=> filter roll-off had to be improved

Origin of extra noise- WI local control?- Diffused light?

same noise seen on B7, and on reconstr. signals using B7/B8

- QD miscentering?same noise seen in longitudinal noise (GV)

25 ILIAS WG1 meeting, Hannover, 12.12.2005

Conclusions: noise level

We can go quite far => LF design sensitivityusing present matrix and filters using DC signals

For this, we mustoptimize QD powercentering mirrors very well

For further improvements (10-15 Hz)Optimize correctors

10-20 Hz range difficult!

Optimize matrixUse InGaAs quadrant diodes?

higher quantum efficiencylower bias voltage => higher power

26 ILIAS WG1 meeting, Hannover, 12.12.2005

End

27 ILIAS WG1 meeting, Hannover, 12.12.2005

Contribution of mirrors (optim. powers)

NI ty filter difficult to improve (already optimized)

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Noise budget (optimized, 0.2 mm)

Still some effort neededat low frequencies

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Electronics noise vs. C7 noise (WI tx)

Local control

30 ILIAS WG1 meeting, Hannover, 12.12.2005

Electronics noise vs. C7 noise (WI ty)

Local control