We were only about 2 and half hours into lock when I did this test due to our earthquake lockloss this morning.
I ran the
python auto_darm_offset_step.py
in /ligo/gitcommon/labutils/darm_offset_step
Starting at GPS 1404768828
See attached image.
Analysis to follow.
Returned DARM offset H1:OMC-READOUT_X0_OFFSET to 10.941038 (nominal) at 2024 Jul 11 21:47:58 UTC (GPS 1404769696)
DARM offset moves recorded to
data/darm_offset_steps_2024_Jul_11_21_33_30_UTC.txt
Here is the calculated Optical gain vs dcpd power and DARM offset vs optical gain as calculated by ligo/gitcommon/labutils/darm_offset_step/plot_darm_optical_gain_vs_dcpd_sum.py
The contrast defect is calculated from the height of the 410Hz PCAL line at each offset step in the output DCPD, and is 1.014 +/- 0.033 mW.
I added an additional plotting step to the code and it now makes this plot which shows us how the power at AS_C changes with the DARM offset power at the DCPDs. The slope of this graph tells us what fraction of the power is lost between the input to HAM6 (AS_C) and the DCPDs.
P_AS = 1.770*P_DCPD + 606.5mW
Where the second term is light that will be rejected by the OMC and that which gets through the OMC but is insensitive to DARM length changes.
The loss term between the anti-symmetric port and the DCPDs is 1/1.77 = 0.565