Sheila, Keita, Jennie, Camilla
After practicing with the damaged Fused Silica (FS) wedge, Sheila and I installed the new FS wedge. Labeled E1900361 S/N 07 Run# P20-378, 379. We noticed some dust/fiber on the FS after install (didn't inspect before) so Keita wiped with a clean swab. Photo's after cleaning are first and second attachments.
Yesterday 79351 we found indium foil between part (3) and (5) of the FS assembly D2000037 where the (6) screw contacts. Rodica reccommended we add a new piece of indium foil. Third photo attached.
Keita installed the FS holder ot the assembly and we adjusted roll by eye. We installed the assembly onto the OFI. We reinstalled the beamdump bar (never moved dumps on it but wiped them yesterday) and the baffle bar and baffle. Baffle was installed in the same location, touching the double thick beamdump. We then unlocked the OFI and reinstalled the nominal motion limiter screws.
We then transitioned to laser hazard, the retroflection of the aux beam looked good and we checked that SRM was in it's nominal position. No reason to go to SR2.
The beam through the OFI started very (50mm?) low and was hitting the fast shutter. We then adjusted the roll of the FS wedge assembly to correct for any pitch, it was hard to make fine adjustments and tightening the screw moved the beam. It was a little off in yaw. Keita has photos of the beam position.
We repeated yesterday's 79344 throughput power measurements with more laser power:
- Before OFI after SRM, 1) mean 9.627mW, stdev 198.1uW over 10sec 2) mean 9.862mW, stdev 289.6uW over 10sec 3) mean 9.901mW, stdev 287.8uW over 10sec
- SQZ beam power to ZM6: 1) mean 20.71uW stdev 367.3nW, Blocked/Background 200.1nW stdev 1.387nW, 2) mean 21.84uW stdev 481.9nW, Blocked/Background 251.1nW stdev 2.457nW, 3) mean 22.69uW stdev 548.6nW, Blocked/Background 228.9nW stdev 1.547nW,
- Input to HAM6 1) mean 11.10mW, stdev 306.4uW over 10sec 2) mean 11.10mW, stdev 268.0uW over 10sec 3) mean 11.50mW, stdev 270.3uW over 10sec
- Repeat before OFI after SRM @11:52PT (as laser power/polarization appears to be drifting), 1) mean 11.36mW, stdev 274.9uW over 10sec 2) mean 11.35mW, stdev 184.9uW over 10sec 3) mean 11.45mW, stdev 207.8uW over 10sec
- Repeat Input to HAM6 1) mean 11.49mW, stdev 255.6uW over 10sec 2) mean 11.46mW, stdev 217.1uW over 10sec 3) mean 11.55mW, stdev 195.4uW over 10sec
- Sheila will calculate the throughput and post in a comment.
The rejected beam to SQZ goes through ZM6 baffles, and around the middle of the HAM7 GV.
Sheila then headed to SR2 and checked that the beam was centered in pitch and yaw.
After taking IR photo, the beam position on the iris close to OM1 seems to be off by about ~2.75mm/2 radius from the center of the iris at 45 degrees angle, i.e. it's too low by ~1mm and to the +X direction in YAW by ~1mm. Look at the 1st picture looking at the iris from the direction of HAM5. There's no parralax though its more focused on visible light than IR.
1mm too low and 1mm to +X don't sound like a big deal, once we have the IFO we should be able to change the beam positions on SRM/OFI and SR2 to get back higher and to the -X if necessary. Remember that the iris was set using the beam we believe to reproduce the alignment before the second crator incident, and we have found that the beam was too high on OM1 using that beam. So the beam being too low on the iris could be a good thing. But we'll make sure that we can see the beam on ASC-AS_C.
The 2nd picture shows that the diameter of the iris hole is a tiny bit larger than 2.5mm but smaller than 3mm.
Roll adjustment of the fused silica wedge is not that easy at this level (1mm over maybe 2.5m? distance), a tiny rotation results in big change and loosening/tightening the set screw for the rotation seems to change the deflection. As far as we see the beam on ASC-AS_C we won't adjust the FS wedge further as this won't change the isolation/throughput etc. of the OFI.
Serial number of the original FS wedge is 001 according to Rodica.
From what Camilla wrote above, the new one we've just installed is S/N 007.
Not including the first measurement where the laser power was clearly lower, we calculated with attached:
Transmission: 99.82% with stdev 0.72%
Ratio rejected by TFP: 0.188% with stdev 0.004%
The sum of these is 100.01%, which is within the margin of error.
Tagging for EPO.