[Elenna, Louis, + guidance from Sheila, Jenne, Keita, Camilla]

To investigate the POP clipping in 91549 we settled on a plan to pico in HAM3 while watching the POP pds and the ALS COMM beatnote. To do this we locked the x-arm in green and misaligned the y-arm. To get IR in HAM1 and on ISCT1 we set up single bounce using ITMX at 10W. 

We first had to adjust PM1 to get it centered on POP-X. This was done while locked on MICH dark. It took a while but we eventually got close enough for the POP-X centering to work. Once it did we offloaded the new positions onto the sliders. We rastered PM1 (pit, yaw) to demonstrate that we are hitting the maximum possible power on LSC-POP at the current alignment. We are getting predominantly 2f oscillations in POP-X but 1f in LSC-POP in both PIT and YAW, indicating that the beam is not completely well-centered on the LSC POP diode with the current upstream input alignment.

Once we had a reasonable beam on the POP pds and a reasonable COMM beatnote, we started pico's in the HAM3 POP path. We moved what felt like large distances in X without seeing any change in the POP pds or the COMM beatnote. We tried a bit in Y too but didn't go nearly as far. This was towards the end of the day so we reverted the pico positions (as much as we can trust them) and paused for the evening. We plan to continue pico'ing to better understand the clipping situation in the POP path.