1 ILIAS WG1 meeting, Hannover, Alignment electronics noise budget ● Sources of electronic noise ● C7 electronic noise ● Electronic noise for optimized power ● Some conclusions

2 ILIAS WG1 meeting, Hannover, Linear alignment setup

3 ILIAS WG1 meeting, Hannover, Quadrant photodiode type EG&G YAG 444 sensitivity = 0.45 A/W DC power = 3 mW max transimpedance = 2 k  Bias voltage = 180 V

4 ILIAS WG1 meeting, Hannover, QD electronics demodulator phase shifter Quadrant diode box

5 ILIAS WG1 meeting, Hannover, Scheme of LA electronics ADC noise Preamp. noise Shot noise Low-pass filter AC: Gain 200 DC: Gain 1 diff. sig. non-diff.sig. Non-optimal treatment of DC signals dominated by ADC noise (but were not foreseen as error signals) VME QD box

6 ILIAS WG1 meeting, Hannover, Noise measurements after demodulator quadrant diode AC output Theoretical shot noise M. Mantovani demodulator gain

7 ILIAS WG1 meeting, Hannover, Principles of calculation Calculate electronic noise at each quadrant diode AC and DC signals Reconstruct error signals Using C7 matrix (not calibrated) Pass through DSP correction filters Obtain mirror motions through suspension transfer functions LA loops closed (but gain not well known) Suppose asymmetry (10, 1, 0.2 mm) => length noise Only cavity mirrors (PR, BS to be included) Two cases 1. C7 using measured QD DC powers 2. Optimized DC powers 50% of saturation power

8 ILIAS WG1 meeting, Hannover, C7 matrix ThetaX PR BS NI NE WI WE B2_q1_DC B5_q1_DC 10 B2_q1_ACp B1p_q1_ACp B7_q1_ACq B7_q2_ACq B8_q1_ACp B8_q1_ACq ThetaY PR BS NI NE WI WE B2_q1_DC 1 B5_q1_DC 10 B1p_q1_ACq 1 B7_q1_ACp B7_q2_ACp B7_q2_ACq B8_q1_ACp B8_q2_ACp 1 ThetaX has undergone second diagonalization => mixing of all signals

9 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (WE tx)

10 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (WE ty) Pure DC signal

11 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (NE tx) ?

12 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (NE ty)

13 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (NI tx)

14 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (NI ty)

15 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (BS tx)

16 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (BS ty)

17 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (PR tx)

18 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (PR ty)

19 ILIAS WG1 meeting, Hannover, Total LA electronics noise (C7, calculated) WE ty pure DC error signal => no extra noise vs. AC WI under local control Simulated WI LA curves for comparison C7 noise not limited by LA electronics noise (but: excess noise)

20 ILIAS WG1 meeting, Hannover, Influence of QD power Can gain ~ factor 10 by increasing QD powers

21 ILIAS WG1 meeting, Hannover, Noise budget (C7) ADC noise (= DC noise) is not dominating, but close => second diagonalization (tx) has spoiled signals by reintroducing DC signals everywhere ?

22 ILIAS WG1 meeting, Hannover, Influence of mirror centering (optimized powers) Without optimized matrix nor optimized filters: => need LIGO centering precision (0.2 mm)

23 ILIAS WG1 meeting, Hannover, Conclusions: DC signals DC signal not noisier than AC signals After ADC: AC 50 DC 3 µV/rtHz DC has less electronic gain, but B2 DC signal seems very sensitive ThX: signal mixing (DC part everywhere) increases noise level but still not noiser than pure AC signals Other reasons for getting rid of DC signals Get rid of laser technical noise at 6 MHz ? Seismic noise ?

24 ILIAS WG1 meeting, Hannover, Conclusions: extra noise Extra noise on central mirrors Not limited by electronic noise at 50 Hz C7 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, Conclusions: noise level We can go quite far => LF design sensitivity using present matrix and filters using DC signals For this, we must optimize QD power centering mirrors very well For further improvements (10-15 Hz) Optimize correctors Hz range difficult! Optimize matrix Use InGaAs quadrant diodes? higher quantum efficiency lower bias voltage => higher power

26 ILIAS WG1 meeting, Hannover, End

27 ILIAS WG1 meeting, Hannover, Contribution of mirrors (optim. powers) NI ty filter difficult to improve (already optimized)

28 ILIAS WG1 meeting, Hannover, Noise budget (optimized, 0.2 mm) Still some effort needed at low frequencies

29 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (WI tx) Local control

30 ILIAS WG1 meeting, Hannover, Electronics noise vs. C7 noise (WI ty) Local control