R. Short, J. Oberling

Continuing from the weekend.

First thing this morning Marc and Fernando turned off the 35.5MHz RF so we could swap the in-service EOM for the spare, as we had observed no beam distortions with the spare and having RF shouldn't change that.  We installed and aligned the spare and then moved on with recovering Amp1.  With the amp not being pumped we had 1.7W incident and 1.43W in transmission; after tweaking the alignment there was 1.55W in transmission (91.3% throughput, well above our 65% requirement).  We also preemptively turned the HWP on the High Power Attenuator (HPA) assembly after Amp1 to pass a minimum amount of power, so it was ready for Amp2 alignment checks.  We slowly increased the pump diode currents in 1A steps, keeping both diodes the same on the way up, and tweaked beam alignment into the amplifier at each step.  The power output by the amplifier was monitored with our roving 300W-capable water-cooled power meter.  The results:

To end we had power supply 1 @ 9.2A and power supply 2 @ 9.0A, to have most of our pump diodes monitors back at 100%; monitor for pump diode 3 (which is actually pump diode 1, the software is flipped; 3 and 4 are actually 1 and 2, with 1 and 2 actually being 3 and 4) is right below 90% while the rest are right below 100%, indicating pump diode 1 has seen the most degradation since install.  With these pumping currents we had 68.9W out of Amp1, so we aligned the beam onto the Amp1 power monitor PD and recalibrated it; we also recalibrated the NPRO power monitor PD as it turned out our original calibration was done with WP14 not fully optimized.  We then checked beam alignment up to Amp2, which all looked good.  We installed a temporary PBSC after M07 to check the polarization of the light incident on Amp2.  We turned the power in the Amp2 path up to ~3.55W (>5% of Amp1 output, to avoid the HPA causing any polarization weirdness).  PBSC transmission was measured at 0.47mW, and tweaking WP04 only got this down to 0.45mW, so polarization looked good.  We turned the power to ~1.71W in prep for Amp2 recovery, and measured the power transmitted through Amp2 with no pump light; this measured at 1.4W, a throughput of 81.9%.  At this point we broke for lunch.

After lunch we started recovering Amp2.  We didn't do any pre-alignment work, as our throughput was already higher than the 65% requirement so we started powering up Amp2 in the same way we did Amp1 (we stopped at 9.0A as that was where Amp2 was running before the NPRO swap).  The roving power meter was placed directly after L18, on the other side of the external shutter; we removed L18 on the off chance the laser power ablated any material from the power meter head.  We also pre-set the HPA after Amp2 to pass a minimum power in prep for alignment checks from Amp2 to the PMC.  Results of Amp2 recovery:

With Amp2 now mostly recovered (still had to increase the seed beam power, it was still at ~1.7W) we checked alignment between Amp2 and the PMC while we had low power in that path (L18 was reinstalled for this).  Everything here looked really good still.  We installed the cover onto the ISS AOM and the beam was nice and centered.  We then removed L18 again and reinstalled our roving power mete to increase the seed power into Amp2.  Ryan slowly increased the seed using the HPA after Amp1 while I watched all of the optical elements in the path with an IR viewer for any signs of early burn spots.  Everything went smoothly and at max Amp2 seed we have 141.3W out of Amp2.  We realigned the beam onto the Amp2 power monitor PD and recalibrated it in the Beckhoff software.  To finish for the day we closed the external shutter and turned on the power and PD watchdogs, as well as the NPRO noise eater.  The amplifiers are running overnight with the enclosure in Science Mode for more data gathering for glitches.  Tomorrow we will begin recovering the PSL stabilization systems.