Yuhang, Aritomi, EleonoraP, and EleonoraC
On 5th of June 2019, we locked the filter cavity again after almost half a year we haven't done this. We checked several references including irises on the bench, target on the film of PR chamber, target on the film of BS chamber, the first and second target inside the filter cavity vacuum tube. To recover these checking points, we used pico-motors with almost no failures. But it seems there are still some problems with end mirror pico-motor. Also, we observed some large mirror motion after we moved pico-motor of BS. But it went back to static after several minutes.
The alignment is also done with the standard procedure. It is first to misalign input mirror and find filter cavity transmission. Then center it on the screen. Then bring back input mirror and make injection and reflection overlap. Finally, align end mirror to have TEM00 dominant. After the lock, change the control point of each mirror to see if the transmission goes up to maximize.
Power:
| Before AOM | 36.5mW |
| Before EOM | 212mW |
| Before MZ | 166mW |
| To filter cavity | 34mW |
| Before FC GR ref PD | 136uW |
Signal:
| FC tra PD | 4V |
| FC GR ref PD DC | 80mV |
| FC locking error signal | 260mV |
The demodulation phase for filter cavity locking is 65deg.
The setting of FC locking servo:
| Input attenuation | 3.6 |
| Gain 1 | 4.0 |
