__Epics_Channel_Name______ __OLD_____ ___New___
C1:SUS-MC1_PIT_COMM 4.490900 3.246900
C1:SUS-MC1_YAW_COMM 0.105500 -0.912500
C1:SUS-MC2_PIT_COMM 3.809700 3.658600
C1:SUS-MC2_YAW_COMM -1.837100 -1.217100
C1:SUS-MC3_PIT_COMM -0.614200 -0.812200
C1:SUS-MC3_YAW_COMM -3.696800 -3.303800
While continuing our efforts to lock, we noticed the procedure failed at a point it had gotten past last night: turning on the bounce/roll filters in MICH, PRC, and SRC. We checked the MICH transfer function and noticed that the unity gain point was ~10 Hz, well below the bounce modes. We tried increasing the gain but found saturation, and Rob suggested that there could be misalignment on the AP table, which Steve worked on today. We went out and found two of the PDs (ASDD133 and AS166) to be badly misaligned probably due to a bumped optic upstream. We re-aligned.
Could not get past arm power of ~11 or so. I was suspicious of the transmon high-gain/low-gain PD handover, so I ran the matchTransMon scripts, but that did not help. I also removed the line in the cm_step script that increased the CM gain by 18dB at an arm power of 4. The gain of the CM servo will increase naturally as the power in the IFO builds up, so it may not be good to crank it right away. I tried several other CM gains, and watched the DARM loop, but still could not get past an arm power of ~10-11. I'm not sure what's wrong, but it may be that mysterious CM-servo/McWFS conspiracy, so we can try turning down the McWFS gain next time.
Last night, we put the IFO in FP Michelson configuration. We took transfer functions of CARM and DARM, first using CM excitations directly on the ETMs, and then using modulations of the laser frequency via MC excitation. We found that there was basically no coupling into DARM using the MC excitation, but that there was coherence in DARM using the ETM excitation. Therefore, I tuned the ETM common mode in the output matrix. I did this by taking transfer functions of PD1_Q with PD2_I (see attached plot). I changed the drdown_bang script to set C1:LSC-BTMTRX_14 0.98 and C1:LSC-BTMTRX_24 1.02.
I've plotted some transfer functions showing the response at POB DC to laser frequency (phase) noise. There are transfer functions for multiple CARM offsets. Basically, the transfer function looks like the DARM transfer function when the CARM is at zero offset, and is super-wonky elsewhere. POB-DC is not a good CARM signal for intermediate stages of lock acquisition in a dual-recycled interferometer. We should look into switching back to REFL-DC.