craig.cahillane@LIGO.ORG - posted 16:27, Monday 13 March 2023 - last comment - 12:29, Tuesday 14 March 2023(67963)
DARM sensing plant comparison with DARM offset changes
On March 12, 2023 ran some DARM OLGs and and PCAL injections.
They are saved in /ligo/gitcommon/noise_recorder/data/darm_noise/20230312/
I set up DARMOffsetStep.py in labtuils to step the DARM offset three times such that we got 40, 20, and 10 mA on the DCPD SUM.
We stayed at each DARM offset for 15 minutes.
During those fifteen minutes, I did four injections (two DARM, two PCAL) to get a broadband DARM plant measurement.
I sorta missed on the timing of the injections, so I had to truncate the data a bit to avoid the glitch when you move the DARM offset, but the results are pretty clear:
The DARM optical gain scales pretty much exactly like sqrt(dcpd sum power).
If we think that more DARM offset light might help our homodyne angle or noise in some way, then maybe we can go for it.
There's no apparent change in the response around the DARM pole, which maybe we should have expected.
Non-image files attached to this report
Comments related to this report
Are the DC powers exactly 40, 20 and 10mA? Seems that the optical gain scaling is more like 1.5 and 0.63?
If we believe the homodyne angle to be 27° at 20mA, we would expect ratios of 1.50 and 0.61, respectively.
No, it was more exactly 40.58 mA 19.89 mA 10.15 mA plus minus around 0.02 mA for all.
This changes the prediction slightly to 1.52 and 0.62, respectively.