Summary:

Scanned the frequency of the PSL instead of the OMC PZT to measure the OMC finesse.

The idea is to inject into IMC servo (i.e. ultimately AOM) while the OMC pzt voltage was left close to the 00 mode resonance. We cannot do this very quick (1.6Hz pole in the VCO), unfortunately, but if the OMC length doesn't change much during the injection this is a good alternative to the PZT scan.

The analysis will come later.

What was done:

Injected into H1:IMC-L_EXC at 0.5Hz, 40000cts_pp. (At first we connected H1:LSC-EXTRA_AO_2_EXC to the EXCB on the IMC board to inject into the fast path , but we didn't have much range because of 1/10 attenuation in the EXC input. IMC_L was better).

H1:IMC-F_OUT_DQ calibration is 59.97dB Hz/cts (i.e. F_OUT is already pretty well calibrated in kHz).

This was measured by injecting at very low frequency (0.05Hz) so we can use the counter (H1:IMC-VCO_FREQUENCY) as our frequency readback. The dtt template used is /ligo/home/keita.kawabe/PSL_VCO_CAL_20230801.xml.

We used the single bounce beam from ITMY. ASC-AS_A and ASC-AS_B DC centering was turned on (DC3 and DC4). OMC ASC was on OMC QPDs.

We adjusted H1:OMC-PZT2_OFFSET to bring the OMC roughly to its 00 carrier resonance (1st attachment).

After everything was adjusted properly we left it from 11:30:50 to 11:31:15 local time (2023/08/01/18:30:50 - 18:31:15 UTC).

Just by looking at the close up (2nd attachment), the scan might have been a bit too fast, but not terribly so, as the transmission peaks in DCPD_SUM always rose faster than they fell regardless of the sign of e.g. the slope of the IMC_F_OUT_DQ.