Sheila, Evan, Rana, Eli, Kiwamu, Alexa
Today we were able to reduce the CARM offset from 800pm to 100pm. We made three major changes to acheive such an offset.
Transition Process from 800 pm to 400pm
To start,
With some TR buildup (approximately 1ct on LSC-X/Y_TR_A_LF_OUT),
With CARM on sqrt(TRX+TRY),
Transition Process from 400pm to 100pm
With all the settings as above, we bring the CARM offset to -3.2 (or ~150pm). At this point we transitioned the in-air TR PDs to the IR TR QPD_Bs. For reference, ASC-X/Y_TR_B_POW_NORM =1,1 and LSC-TR_X/Y_QPD_B_SUM_GAIN = 0.222, 0.175 respectively. Also, the QPD NSUM was about 400cts here. We continued to reduce the CARM offset to -4.5 cts (or ~80pm). At first,t the ASAIR_RF45_Q looked like a decent signal and responded well to a DIFF offset change. We turned on a servo for about 1.5min to ensure ASAIR was around zero (z servo -r LSC-ASAIR_A_RF45_Q_NORM_MON -g -11111 ALS-C_DIFF_PLL_CTRL_OFFSET). We measured ASAIR_RF45_Q/DARM_IN1 = 3e7 (at this point DARM_IN1 is just ALS DIFF signal). Note: we added a -160dB FM10 filter in LSC-ASAIR_A_RF45. Then the PD_DOF_MATRIX for ASAIR_RF45_Q is 3.3. So far, we were able to transition from ALS DIFF to RF DARM 50% of the way, and then we broke the lock. We started to reconsider whether we were actually in the linear range for RF DARM. Maybe we should be using AS45Q/SQRT(TRX) at this point? This requires a model change; however, this is already impleneted in the l1lsc.mdl that is in the SVN, so we could just copy that.
A little more ...
The farthest CARM offset we reached was -7 cts or ~60pm on sqrt(TRX+TRY) with the QPDs controlling CARM and ALS DIFF for DARM. Here we had 26 x single arm power, and REFL DC dropped from 80mW to ~75mW.
Some lock loss times for today:
Lock losses while transitioning DARM from ALS-DIFF to AS_AIR_45_Q:
06:01:40 UTC (28jan)
06:33:34
07:53:45