J. Oberling, P. King, R. Savage
This morning Peter continued to align the current FE laser, and ultimately got a pretty good looking beam out of it. The only problem is that it isn't 35W, but ~31W. Try as we might, we were unable to get more power out of the FE this morning. This beam was put through the 70W amplifier and after some quick alignment (no mode matching was done), we had 75.2W out (albeit questionable beam quality, Peter has the pictures from the WinCam). So even with power out of the FE down from nominal, we are still able to get >70W out of the 70W amplifier. 
At this point we needed to make a decision about whether or not to swap the FE. After some discussion among ourselves and with Daniel, we decided to continue on with the current FE laser; this means we are NOT swapping the FE laser. The main drivers for this decision were the current beam quality out of the FE (much improved by Peter's several hours of alignment work over the last couple days), and the fact that neither of the 3IFO FE lasers are swap-in ready.
This afternoon was spent checking the beam quality in various places to make sure we weren't fooling ourselves about the beam profile. Using the leakage beam from the 70W amp that is directed to the bullseye PD, Rick set up a rail so we could check the beam profile over a distance. Good news is that the beam shape remained constant, the only change was in its size (as expected). The bad news is that yes, the beam quality is questionable (as mentioned above, and not entirely surprising given that we have done no mode matching work for the 70W amp). Using this rail, Peter took the opportunity to measure the beam propagation out of the 70W amp. We then looked at the beam as it enters the PMC, and it didn't look right (had 2 peaks, was definitely not Gaussian. Unfortunately I don't have a picture of it); out of an abundance of caution we removed the ISS AOM to prevent any damage. We inspected some of the optics and found a few that showed evidence of contamination; AMP_WP04, AMP_M03, and L01. AMP_WP04 and AMP_M03 were simply dirty (and were therefore cleaned), but L01 had a damage spot almost dead center of the lens. This lens was of course replaced. Tomorrow we will continue working to recover the rest of the PSL, starting by confirming the beam quality at the PMC is improved after the lens swap and optic cleaning. Still to do (in no particular order, items in bold represent the bare-minimum required to get a beam into the IFO):
- Measure FE beam propagation
- Mode match FE to 70W amplifier
- Measure 70W beam propagation after mode matching
- Align beam to PMC
- Lock PMC
- Reinstall and align ISS AOM
- Mode match 70W amp to PMC
- Recover FSS and ISS
We currently plan on having a beam available to the IFO by Friday morning, and will need to use Tuesday maintenance days to continue tweaking the mode matching to improve PSL performance.
Attached are Wincam snap shots of the beam profile for the front end laser and the 70W amplifier output. The first image is of the output of the front end in its running condition. There is a small pedestal in the output. The output power was 31.2 W. The second image is when both banks of diodes are run at 45 A. In this case the pedestal is more obvious. Other images are of the 70 W amplifier output, taken at various distances from the amplifier. Clearly there is a ring in its output. This was done without moving the mode matching lenses, so it is possible that this could be removed by adjusting those. The output power of the amplifier is 75 W.In my above list I forgot to add: