Adam Mullavey from LLO made some code to move the ETM and TMS in a spiral to scan for flashes in the arm. LLO has been using this for O4, and in terms of an automation step, this would be comparable to our Increase_Flashes state. Increase_Flashes is very simple in how it works - move one direction, one degree of freedom at a time, look for better cavity flashes, move the other way if they get worse. While this is reliable, it is very slow since we have to wait for one period of the quad between each step (20seconds) to ensure we dont miss a flash.

The last two days I spent some time converting Adam's state, Scan_Alignment, for use at LHO, adjusting thresholds and other parameters, and trying to improve on parts of it so it might work a bit more reliably. The most notable change I've made is to get data from the fast channel for the arm transmission, rather than collecting slow channel data. This seemed to help a bit, but this completely relies on nds calls that we've historically found not 100% reliable. I've also lowered minimum thresholds, thanks to the previous change. This allows it to start off from basically no light in the cavity and bring it up to a decent alignment.

After these changes it seems to really improve the flashes from a very misaligned starting point, but I'm not sure it's any faster than the Increase_Flashes state. In the attached example it took around 20-30 min to go from little to no light to a decent amount. I'm testing this without the PLL and PDH locked, so it's hard to say exactly how well aligned it is and how much better it can get. Next I'd like to take some time on a Tuesday to test with a PDH&PLL locked ALS, and compare it to the time it takes compared to Increase_Flashes for a very misaligned cavity and a barely misaligned cavity.

I've committed the changes I've made to ALS_ARM.py, ALS_YARM.py (both in common) to the SVN. This created a new state - SCAN_ALIGNMENT - that I'll keep there, but isn't in the state graph so it cannot be reached.