aLIGO LHO Logbook

H1 PSL (PSL)

jason.oberling@LIGO.ORG - posted 11:07, Tuesday 24 February 2015 - last comment - 12:57, Tuesday 24 February 2015(16887)

PSL FSS Maintenance

P. King, J. Oberling, J. Bartlett, E. Merilh

We realigned the FSS RefCav this morning. It was down around 0.7V on the FSS TPD. We aligned both mirrors of the input periscope in both pitch and yaw. Yaw alignment did not increase the RefCav TPD signal by much; most of the adjustmen was to pitch on both mirrors. We left the FSS TPD reading 1.56V and locked the adjustment screws on both periscope mirrors. We also found that the input periscope mirror mounts (they both mount to a ~1.5 inch diameter post that in turn is mounted to the PSL table itself) were a little loose. Peter was able to tighten both mounts by ~1/8 to ~1/4 of a turn on the big screws that mount the mirrors to the post. Will continue to monitor the FSS TPD to see if it continues to drift down.

We measured the laser power in 2 places after the alignment:

At the base of the FSS RefCav input periscope: 35.0 mW
After the Faraday isolator in the ALS path: 15.5 mW

We also measured the voltage on the FSS REFL PD when the RefCav was locked and unlocked:

RefCav unlocked: 280 mV
RefCav locked: 53 mW

Comments related to this report

peter.king@LIGO.ORG - 12:57, Tuesday 24 February 2015 (16889)PSL

Link

Luckily it seems that the reference cavity transmission signal in volts is one-tenth that of the transmitted
power in milliwatts.  As I recall ALS needs something like 10 mW in its beam path.  So if the reference cavity
transmission drops below 1 V, we should think about tweaking the alignment.