One of the difficulties of locking PRMI yesterday, according to Kiwamu, was that something was moving too much, so we started looking at optics, and in the process identified two OL problems, one for BS and the other for ITMY.

1. BS OL laser problem

Every 70 seconds, the beam coming to the AS port showed quick (as in 1 to a few Hz) jiggling motion mainly in YAW. This seems to be caused by intensity glitch of BS OL laser that takes place every 70 seconds, making a fake angle signal for BS, which is fed back to the BS by OL damping. The thing is that it's difficult to feed back to BS without BS OL damping.

Attached is the time series of the BS OL SUM (top left), BS OL YAW (bottom left) and PIT (bottom right) during the glitch.

For now, since the effect is mostly in YAW, Kiwamu disabled the OL damping for YAW, but we'd like to swap the laser.

2. ITMY OL problem

When you look at ITMY OL, it looks as if the optic is moving by 10 urad pp in YAW with a period of about 10 minutes , but nothing in BOSEMs and ISI sensors and such (second attachment), and we couldn't see that motion in the AS camera either. We convinced ourselves that the motion is not real.

We had a look at various temperature and some archane signals of PEM and FMCS but found nothing.  Maybe the laser itself is moving.

This is not a serious problem for now, but it should be fixed eventually.