Previous alogs: alog 64353, alog 64597. Robert, Dhruva, Hudson, Camilla, Vicky.
This morning Robert took more photos of HAM7 while we adjusted the ZM alignments. Robert turned off the VOPOS OSEMs during this. Started 2022-09-01 18:19:27UTC
| Start GPS time | State of ZMs | Power on OFI_PD_A (uW) |
| 1346091709 | (a) Aligned for IFO SQZ with SQZ on | 37 |
| 1346092048 | (b) Aligned as prev. 08/05 photos | 2.3 |
| 1346092659 | (c) Aligned for 08/26 "good" PD alignment ZM4(-188, 177) | 37 |
| 1346092983 | (c) Some PD clipping: ZM4(-600, 550) | 11 |
| 1346093371 | (c) More PD clipping: ZM4(-900, 850) | 0.3 |
| 1346093718 | (c) Optimal for no PD clipping*: ZM4(400, 50) | 44 |
| 1346094008 | (a) Original Aligned for IFO SQZ with SQZ off | 37 |
*actually got up to 45uW on PD at between photos with ZM4(-180,320) ZM5(-314,500), ZM6(772,790)
We should look at Robert's photos and plan to move the PD to minimize clipping when in chamber. Note that the beam won't be there when vented so we'll have to move the expected amount or set up a retro.. that latter wasn't good enough last time.
We were worried that this PD reflection is causing scatter in the IFO but Louis's scatter simulation alog 64666 estimated 0.81ppm in power injected back to the IFO. Keita pointed out this is a lower limit as the power seen at the OMC DCPDs will only be the in the same mode shape as the IFO beam. We expect ~0.7% OFI output going to HAM7 (4.5mW in HAM7 / 0.6W on ASC_AS_C) and a double pass of B:M5 is 10^-4 (1% BS transmission double passed). If 100% of light was reflected from the OFI_PD_A (unlikely) that would be 0.7ppm. So we think B:PD1/OFI_PD_A is not the main culprit. We are planning on confirming by repeating the scattering injections with different ZM alignments.