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kentaro.komori - 7:23 Tuesday 07 November 2023 (27516) Print this report
ITMX resonant frequency search (Quick report)

[Tanaka, M Yamamoto, Sato, Komori]

We initiated the frequency scanning procedure to search for the resonant frequencies of ITMX.
Initially, we confirmed that we can excite the drumhead mode at 23.7548 kHz, which has already been identified.
This confirmation was achieved through the measurement of the transfer function from K1:SEN-ITMX_L_OUTF_EXC to K1:MIR-AS_PDA1_RF17_I(Q)_OUT_DQ during FPMI RF locking.

For this round of testing, we are focusing on two vertical-01-like mechanical modes at 23.73 kHz and 24.52 kHz.
The choice is based on the observation that the beam spot position on ITMX shifts vertically but remains nearly centered horizontally, increasing the likelihood of successful sensing compared to other modes.

We have set the scanning frequency range from 23 kHz to 25.5 kHz and started the diferential excitation in the pitch direction.
The measurement is expected to continue until 7 am tomorrow, and I will verify that it concludes as planned around that time.

Comments to this report:
kentaro.komori - 7:51 Tuesday 07 November 2023 (27517) Print this report

The measurement has finished.
The results will be posted later.

I have restored the settings of the test input and the oplev local control, and I set the guardian state of the interferometer to be down.

kentaro.komori - 17:36 Tuesday 07 November 2023 (27530) Print this report

[Sato, Tanaka, Komori]

We targeted the two vertical-01-like modes, but we were unable to detect the excited peaks.

Figure 1 displays the transfer function results for the first half.
The highest peak corresponds to the drumhead mode, which was indeed excited despite our use of differential excitation.
The second highest peak appears to be random fluctuation without a clear signal (Figure 2).

Figures 3 and 4 present the results for the second half.
The presence of peak forests can be attributed to lockloss events, and we conducted two measurements to confirm that these peaks are not resonances.

Currently, we are contemplating whether the excitation phase is set correctly.
Surprisingly, we managed to excite the drumhead mode using differential excitation.
We compared the signal amplitude of the drumhead mode under common excitation (where the sign of the four coils is +1, +1, +1, +1) to that under differential excitation (+1, +1, -1, -1).
We observed that they were similar (Figure 5), suggesting that the excitation phase may exhibit some degree of randomness.
This could potentially be caused by stray capacitance in the circuits, among other factors.
It might be possible to adjust the phase by introducing additional low or high pass filters to mitigate the phase difference.

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kentaro.komori - 10:20 Tuesday 21 November 2023 (27688) Print this report

I attempted to identify additional resonances within the frequency range of 23.2 kHz to 24.2 kHz with PRFPMI.
However, due to instability in the interferometer, primarily caused by glitches in ETMY, I stopped the work temporarily.
I will resume the scan at the next available opportunity.

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