## Abstract
There seems to be three resonant modes at 23.756 kHz, 23.878 kHz, and 23.909 kHz in ITMY. However, the larger seismic motion may make the ringdown measurement difficult.
## What I did
At first, since it was difficult to keep the alignment by manual tuning due to large seismic motion, I fed back WFS signals in the DC region (< 0.1 Hz) to each setpoint of each suspension local control with OPLEV. Thanks to this, IFO alignments was kept for more than 2 hours without any manual tuning even though the seismic motion became larger.
Moreover, I aligned OSTM in order to send the light to OMC REFL QPDs. This time, I set the threshold value of the OMC protection by misaligning OSTM to 150 cnts in terms of OMMT2 TRANS PD (K1:OMC-OMMT2_TRANS_PDA1_DC_OUTPUT) so that OMC trans DCPD was protected if IFO got down.
In this state, I performed the scan for ITMY with narrower bandwith from 23.74 kHz to 23.84 kHz (100 Hz/1000 points). However, we found only one peak (23.756 kHz), which we already found yesterday, in this region (fig.1).
According to the previous scan performed in 2023 (JGWdoc), they found two peak at 23.87 kHz to 23.90 kHz. So I performed the scan with the same bandwidth from 23.84 kHz to 23.94 kHz. I succeeded in finding two more peaks at 23.878 kHz and at 23.909 kHz (fig.2). However, these peaks could be seen only in OMC REFL QPDs. Unfortunately, we added the DQ channels not for QPDs but for RFPDs...
Second, I tried to perform the ring down measurement for the 23.756 kHz mode with the QPD signal. However, the QPD signal flucuated largely because the power toward AS fluctuated largely due to large alignment flucuation of main IFO by larger seismic motion. Fig. 3 shows the timeseries of QPD signal during the ringdown measurement. As you can see, it seems to be difficult to see the ringdown behaviour. We need to wait for seismic motion becoming smaller or need other approach to evaluate Q values (by estimating from the linewidth of the peak?).
It become difficult to do Lock acquistion itself. And also, I'm afraid of snow and road frozon. So I gave up today's work.
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## Note
I (hope) restored the setup related ASC ({D,C}HARD_{P,Y}, {I,E}TM{X,Y}_TM_{LOCK, ISC2OPLEV}_INPUT).
I modified the filter bank related ASC ({D, C}HARD_{P, Y}) to implemented an integreater labeled "test_int" and gather some gain labeld "oo dB" in one FM.
