R. Short, J. Oberling
This morning, we took the opportunity to fix up the alignments of the PSL PMC and FSS path before the observing run resumes. We started by tweaking the beam alignment into the PMC remotely using the two picomotor-controlled mirrors with the ISS off. After maximizing the PMC transmitted signal, we experimented with adjusting the pump diode currents in both amplifiers to improve the mode-matching into the PMC. Ultimately, we ended having increased both pump currents in AMP2 by 0.1A (from 8.7A to 8.8A).
- PMC TRANS Start: 106.2 W
- PMC TRANS End: 109.7 W
- PMC REFL Start: 19.8 W
- PMC REFL End: 15.8 W
Having improved PMC alignment, we then went into the PSL enclosure to touch up the FSS path alignment. We started with a power budget on the FSS path (done with the ISS on and both PSL Guardians paused):
- FSS In: 294.8 mW
- AOM In: 293.7 mW
- AOM Out (Single Pass): 206.2 mW
- Diffraction Efficiency: 69.4%
- AOM Out (Double Pass): 108.2 mW
- Diffraction Efficiency: 52.5%
- EOM Out: 109.5 mW
The most obvious issues appeared to be the single and double passes through the AOM. We adjusted the AOM in both pitch and yaw to improve single pass diffraction, and mirror M21 to improve double pass diffraction. Our results:
- AOM In: 297.9 W
- AOM Out (Single Pass): 215.1 mW
- Diffraction Efficiency: 72.5%
- AOM Out (Double Pass): 151.3 mW
- Diffraction Efficiency: 70.4%
Good improvements all around, although neither diffraction efficiency ended as high as after the last alignment (alog74346). During this adjustment period, the PMC kept unlocking periodically due to the temperature drifting. We tried turning the temploop on and off at different points to keep the PZT in the range we wanted it, but the PMC kept unlocking on us, causing this step to take longer than anticipated.
We then checked the alignment through the EOM; seeing it was good with no clipping and measuring 152 mW out, we locked the RefCav and started recovery of its alignment. Using the picomotor-controlled mirrors while watching the signal on the TPD:
- Start: 0.21 V
- End: 0.93 V
Next, we touched up the alignment onto the RefCav RFPD by adjusting mirror M25 and using a multimeter to watch the DC voltage:
- Start: 0.760 V
- End: 1.244 V
To finish off our activities in the enclosure, we measured the RefCav's visibility:
- Unlocked: 1.244 V
- Locked: 0.211 V
- Visibility: 83.0%
After leaving the enclosure, we resumed the PSL Guardians and are seeing that the PMC PZT signal is much more stable now that the temperature has stabilized, so the ISS is back on as well. I adjusted the ISS RefSignal to -1.95 to bring the diffracted power to just below 2.5%.
A rotation stage calibration will need to be done since the output power of the PMC has changed, but this will be done as a target of opportunity when the IMC can be unlocked in the coming days.
I did not get the chance to run quarterly tests on the PSL dust monitors, but otherwise, this work closes WP 11716.