It seems that the most important short-term task we have right now is to figure out what our PRC length is, and what our tolerance from nominal is. Gabriele and EricQ are going to work on that tomorrow. If our PRC is of a length that we can't do anything useful for full IFO locking, we need to open up and fix it sooner rather than later.
While we're in there, we need to also put a baffle on the back side of the PRM cage, to protect the OSEMs from stray light. Den and I discovered before Christmas that turning off the OSEM and OpLev damping to the PRM (while using the POP QPD for ASC) significantly reduced the power fluctuations in the PRC. We still had arm power fluctuations, but I believe those are likely because our ALS system can't hold an arm precisely at full resonance. So, putting a black glass baffle with ~2 inch aperture right up against the OSEMs should help a lot. This week, I'll ask Steve to make me a quickie to-scale cardboard version of the baffles that he has had cut, so I can try securing it to the dirty suspension cage that we have out. I will also check to make sure I have seen with my own eyes the baffles that I need, and copper wire to tie it to the cage.
Other, lower-priority things that we should do eventually:
* Steve, please find another razor beam dump for the WFS reflections - Rana and I used one of the ones that was there for reflection off the 2 inch lens in the MC refl path (replacing the aluminum dump that has been there for ages). We also need to label all of our razor dumps with their purpose, with a label on top, so we remember not to remove dumps that are actually in use.
* At some point, we should change the one remaining steering mirror in the main PSL path that is aluminum, to a steel Polaris ("Polanski" or "Polish") mount. For now, we should just make sure we have one handy. Hopefully this will help reduce the PMC transmission drift that we see.
* Steve, in the morning sometime this week, can you please do a test of the drift of the IOO QPDs? We'd like to see a trend that is maybe 30 or 60 minutes long of the QPD signals. First 10 minutes, all lights in IFO room off. Then, 10 minutes with the lights in the PSL on. Then, the rest of the time the PSL lights off. We want to see if these are hot enough to be causing a big temperature change in the PSL box, which may then be causing some optics to drift.
* QPD code in the simulink models (trans QPDs, but also OpLevs, and anywhere else we do normalization) needs to have anti-divide-by-zero protection. I'll take care of this, it should be a quick copy of what we have elsewhere in the simulink code.
* Note to self for the future, instead of doing a dither alignment for the ASS for the arms, we can use the IP POS and IP ANG, as well as end transmission QPD signals. However, for now, the ASS is working just fine.
* We want to go back to the idea of putting a lens into the in-vac IP ANG path, to avoid the clipping that Manasa and I were seeing tonight. We want something of order 2inch diameter, 1meter focal length. The material doesn't matter, but we do want it AR coated for 1064nm on both sides. We also need to make sure that we could use a fixed 2 inch in-vac mirror mount, or something, to hold this lens. If that won't work, we need to come up with another plan. Manasa is working on thinking about precisely what lens we want to buy for a nice guoy phase telescope for IPANG, so we'll buy a lens after she puts her conclusions in the elog.
* An idea for the MC spots plot that Rana had was to plot the beam tilt and translation, rather than the raw spot positions on the mirrors. The point of this would be to make it easier to see what the output beam from the MC looks like. For MC pointing, we should also think about what our actual tolerances are. The biggest thing is that we need to get through the Faraday without being too close to any edge, and also the REFL beam needs to come back through without clipping. For now, we're just visually checking that the POP beam and the REFL beam both look unclipped since we don't have access to good camera views of either side of the Faraday.