J. Oberling, P. King
The swap of the NPRO is now complete. After needing the morning to figure out an AC problem in the PSL enclosure (as a result of Saturday's power outage), yesterday afternoon was spent trying to find better mode matching for the NPRO to the MOPA. Unfortunately, everything just made the beam profile worse. So this morning I returned to the configuration we had last Friday and we attempted to injection lock the HPO. The output power of the 35W FE was measured at 35.7 W.
We first checked the alignment through the HPO irises; some small vertical tweaks were necessary, we used mirrors M01 and M02 to preform the tweaks. The HPO was then brought online and we attempted to injection lock to the 35W FE. At first it didn't want to lock, so we looked at the PDH error signal. The error signal looked clean, so we realigned the beam onto the locking PD; this also did not help. Thinking we needed to improve the overlap between the FE and HPO beams, we performed slight tweaks to mirror M02 to improve the PDH error signal; this also didn't help. Peter happened to be messing with the RF summing box in the FE (for the 35.5 MHz RF for the PDH sidebands for injection and PMC locking), and we noticed the error signal got better. It still wouldn't lock, so Peter tried tightening the connectors on the summing box; lo and behold, it locked! We couldn't find any obvious issues with the cable or connector such as damage, so thinking that maybe we had a ground problem with the box Peter put a piece of Ameristat underneath the summing box. We then purposely broke the lock several times by tapping on the PSL table and the HPO box, and it relocked without issue every time.
Just to see where we were with the PMC, we opened the HPO external shutter and attempted to lock the PMC. It locked without issue, but definitely needs some tweaking; it's good that it locked so easily though. We left the PSL in this state to run overnight; the HPO was outputting 155.8 W. This completes the swap of the NPRO, now we need to recover the PSL subsystems. On the docket for tomorrow:
I'll update this alog with beam profile pictures tomorrow.