P. King, R. Savage, J. Oberling, D. Sigg

FSS RefCav Picomotor Mirror Mounts

At the request of the LHO commissioning team, today we installed 2 picomotor equipped mounts in the FSS RefCav path.  We replaced the mount for mirror M27 (immediately after the FSS EOM, 1st attachment) and for the upper periscope mirror (UPM, 2nd attachment).  We used M27 instead of the lower periscope mirror (LPM) because the LPM is too close to the RefCav; with this setup, M27 primarily changes beam position while the UPM primarily changes beam angle.  The 3rd attachment shows both new picomotor mounts.

The same driver (PICO D) that runs the picomotors for the PMC input mirrors (mirrors M06 and M07) had 2 empty channels, so we used these for the new RefCav picomotors.  As of now, channels 1 & 2 are for the PMC picomotor mirrors and channels 3 & 4 are for the RefCav; Daniel changed the displayed channel names on the picomotor control MEDM screen to reflect this.  To end, we confirmed that all picomotors functioned as expected, which they did.  When we left the enclosure the FSS RefCav TPD read ~4.1V, and the PMC was transmitting ~54.5W.  During the next maintenance window where we do not have an enclosure incursion, I will tweak the alignment into both the PMC and RefCav.

70W Amplifier Power Monitor PD

We had noticed some odd behavior with the 70W amp power monitor PD (the PD that the 70W amp power watchdog triggers off of).  When blocked directly at the PD aperture, the PSL Beckhoff software reports ~3W on this PD; when blocked farther away the reading is ~52W.  We suspected the cause to be room lights, so we added a tube with a RG850 (808nm pump light filter) screwed onto the end (4th attachment); this second RG850 was added to block more of the room light, as one wasn't quite enough.  This reduced the blocked reading to ~3W regardless of how far away the blockage occurred, with no degradation in the amount of power read by the PD when unblocked.