NAOJ GW Elog Logbook

NAOJ GW Elog Logbook 3.2

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R&D (FilterCavity)

NaokiAritomi - 23:04, Thursday 24 October 2019 (1769) Get code to link to this report

IR locking accuracy

[Aritomi, Yuhang, Yaochin, Eleonora]

We measured IR error signal of filter cavity using BAB with TAMA PD which is same as CC1 PD in the reflection path from filter cavity. Pic. 1 shows IR error signal and IR transmission when filter cavity is scanned with AOM (setting is Pic. 2). Calculation method of calibration factor is same as entry 750.

Calibration:

peak-peak voltage of error signal: 26.2 mV

peak-peak time difference of error signal: 98 ms

slope = peak-peak voltage of error signal/peak-peak time difference of error signal = 26.2 mV/98 ms = 0.267 V/s

AOM scan frequency: 500 mHz

AOM deviation: 1 kHz

AOM scan speed for green: AOM deviation/AOM scan frequency = 2 kHz/s

AOM scan speed for IR: 2kHz/s /2 = 1 kHz/s

Calibration factor:

AOM scan speed for IR (Hz/s)/(2*slope(V/s)) = 1000(Hz/s)/(2*0.267(V/s)) = 1873 Hz/V

Note that factor of 2 in calibration factor is because slope of error signal on resonance is as twice as slope of peak-peak of error signal.

Then we measured spectrum of IR error signal when IR is locked on resonance and calculated rms (Pic.3). IR locking accuracy is 4.2 Hz which corresponds to 4.5 pm of locking accuracy. Pic. 4 shows squeezing degradation with this locking accuracy. In addition to mode mismatch, locking accuracy is also dominating. We need IR locking.

Images attached to this report

Comments related to this report

EleonoraCapocasa - 13:21, Sunday 27 October 2019 (1771)

Most of the RMS is accumualted below 10 Hz. We observed a correlation between the PDH error signal for IR (demodualtion of 15 Mhz sidebands) and the lock correction signal from RAMPEAUTO.

At the time of the measument we know the IR alignment was not good. This can be the cause of such behaviour. We should repeat this measurement in good alignment condition.