Shelia, TVo, Nutsinee, Alexei, Dan
Today we continued trying to align the beam into HAM6. The beam going into HAM6 leaking from the OFI was ~15mm too low on the SQZ apertures. To try and correct this we adjusted SR2 and SR3 pitch within the ranges we found yesterday (alog 41197) to avoid any OFI clipping. We were unable to find a suitable alignment that avoided the OFI clipping and pitched the beam up enough to make it through the center of the SQZ apertures.
The procedure was:
| SR3 slider value | SR2 aperture clipping points | Vertical offset as SQZ aperture (mm) |
| 500 | 270 and 620 | -17 |
| 600 | -540 and -70 | -12 |
| 800 | -1900 and -1480 | -10 |
| 1000 | -3290 and 2930 | -7 |
SR3 pitch of 1100 was causing clipping yesterday so we stopped here. We tried to improve on -7mm by pitching ZM2 but this railed before being able to sufficiently correct it. The beam going into HAM6 had an angle of 7mrad toward the SQZ aperture (The beam dropped ~5mm over ~68.6cm) which is too much for ZM2.
Shelia and Terry have gone back into HAM6 to look at alignment further.
We measured 5.5mW of light arriving in HAM6 heading towards the OMC in single bounce, and 3.4+/-0.1 uW arriving in HAM6 in the squeezer path, so the rejection ratio of the thin film polarizer at the output of the OFI is about 1600:1.
After the exercise that Daniel described above, we let SR3 pit at 600 on the slider (cage servo off), and 490 yaw, SR2 at -240.8 urad pitch, 3705 yaw, and zeroed the offsets on ZM2. Terry and I attempted to align the squeezer to this beam, to see if we can get in some measurements of the mode matching from the squeezer to the OMC before the HAM5 vent next week. In the end we didn't find the beam, but we have left ZM1 pitched with the adjustment screw most of the way in. We will undo this soon, so there is no need to re-center osems or worry about rubbing.