Nic, Kiwamu
(Variable finesse technique turned out to be good to start)
Since I have been unsuccessful in locking the PRMI in the past two or three days, I wanted to try some other locking technique. We tried LLO's variable finesse technique (see LLO alog 11340) which seemed more reliable than randomly adjusting the gains and triggers. It turned out that it almost repeatably locks the initial low finesse PRMI. Very nice. We then fiddled with the MICH gain which needed some gain correction as we got rid of the offset in the MICH locking point.
POPAIR_B_LF fluctuated a lot presumably due to some misalignment in some optics. POPAIR_B_LF was about 20000 counts in average and ASAIR_B_LF stayed approximately 3000 counts in average. After 15 minutes or so, we lost the lock for some reason, we did not have a close look.
The attached is a video of ASAIR when the PRMI was in lock.
The final configuration (i.e. the MICH locked on a zero-offset point) is shown in the attached screenshot.
Also, we newly installed a 100 Hz low pass filter in POPAIR_B_LF because high frequency noise in POPAIR_B_LF saturated the BS actuator through the normalization.
When the simple Michelson is locked on a dark fringe, POPAIR_B_LF is typically 120 counts. So the recycling gain is (20000 counts) x (Tp 3%) / (120 counts) = 5 which seems too small. Clipping loss somewhere ?
For the records, with 60W in the L1 recycling cavity, without the BS baffles the BS drift in PRMI carrier lock was about 5 urad (see LLO entry 9920). This is the only H1 PRMI carrier lock collected so far, but the only drifts we see are ~0.5urad.