Marc, Michael, and Yuhang

We have done a calibration for pointing loop with a new method. We move the locking point of pointing loop and check how much BS needs to compensate.

Pointing pitch:

we move pointing pitch, as attached figure 1 [1,0] subplot, from  -24 to -34 [counts]. Then we found BS pitch, as attached figure 1 [0,0] subplot, needs to move from 275.8 to 326.0 [counts] to compensate. Taking into account the calbration of oplev, we got  calibration factor for pointing loop on the base of BS.

The pointing precision was estimated by a RMS integral of pointing loop error signal spectra. We also found that high frequency spectrum can be better if we center beam on PSD, which is shown in attached figure 1 [0,1] and [1,1] subplots. However, the RMS of these two seneriaos are the same, which is reasonable since the dominating noise is at low frequency. In conclusion, we got pitch pointing precision as 0.43urad.

pitch pointing loop calibration factor 1.3 urad/count.

Pointing yaw:

We have done the pointing yaw calibration in the same manner with pointing pitch. The details can be found in attached figure 2. In conclusion, we got yaw pointing precision of 0.65urad.

yaw pointing loop calibration factor 1.5 urad/count.

Note: to take a quicker measurement, we have increased pointing loop gain by factors of 3 and 5 for pitch and yaw. So you can see the BS compensation finishes within 1 minute. We have also tested the spectrum of poiting pitch/yaw don't show difference when gains are increased.