Abstract:
I recovered IMC with ASC.
To keep the beam axis to the IFO, I changed MCE trans QPD1 and QPD2 setpoints as follows:
QPD1P: No change
QPD2P: No change
QPD1Y: From 0.003 to -0.043
QPD2Y: From 0.006 to -0.062
ASC for IMC can be engaged but both pitch and yaw of IP1 PZT was saturated, so PZT offload inside the PSL is necessary.
Detail:
After changing the beam polarization from P to S, IMC lock can be recovered without any issues.
So, I started the recovery of IMC alignment.
What we would like to achieve this time is to compensate for the change in cavity axis due to the MCE shift of ~10.26 mm by adjusting the MCI and MCO alignments to -3.7 and +3.7 urad, respectively (klog37708), while keeping the beam axis aligned to the IFO.
So, QPD signals should be changed as follows:
IMMT1T QPD: no change to keep the beam spot on IMMT1.
MCET QPD1: no change in pitch and some change in yaw.
MCET QPD2: no change in pitch and some change in yaw.
To check how much amount we need to change the yaw setpoints of MCET QPD1 and QPD2, I moved the MCI and MCO suspension by 3.7 urad and measured the signal changes in MCE QPD1 and QPD2.
Following tables are the results:
| | MCET QPD1 | MCET QPD2 |
| MCI | 0.015 | 0.019 |
| MCO | -0.031 | -0.049 |
Our target is -3.7 urad for MCI and 3.7 urad for MCO, so QPD1 and QPD2 signals should be changed by -0.046 and -0.068, respectively.
Since the initial setpoints for QPD1Y and QPD2Y are 0.003 and 0.006, respectively, QPD setpoints should be -0.043 and -0.062.
After changing the QPD setpoints, I engaged the IMC ASC and all beam spots on QPDs can be controlled.
However, IP1 output is saturated and input beam axis cannot be aligned to the IMC axis, we need to offload the PZTs inside the PSL room.
In addition, MCI and MCO OpLevs are at the edge of linear range (or slightly off), so OpLev centering should be done at some point.
Figure 1 and 2 show the gigE camera image at IMC REFL and MCE trans, respectively for the reference.