Today during lock I adjusted the demodulation phase of the SRC1 ASC loop to see if I could see improvement in DARM optical gain. Given that we are needing such a large SRCL1 offset to retune SRCL and adjust the DARM spring, it is worth considering if the SRC has alignment offsets that are affecting these parameters. AS A RF72 is the interferometric sensor for the SRC.

I stepped the four demod phases for the quadratures of the WFS and monitored kappa c and cavity pole. Looking at past locks it appears that both kappa c and the cavity pole change by about 2% during thermalization. I decided that a good metric of success would be witnessing changes in kappa c great or less than the usual 2% change of thermalization. I first increased the demod phases by about 30 degrees. Kappa c increased during this time by 2% only. To confirm, I undid the change in phase and saw no corresponding change in kappa c. I then decreased the demod phase from nominal by 30 degrees. I also saw no change in kappa c. I have reverted these changes.

I have attached a scope showing the various traces I mention during this test.

I think it's worth trying this test one more time after the IFO has thermalized and the kappa c has settled.

GPS start of test: 1367712405

GPS stop of test: 1367717069