sheila.dwyer@LIGO.ORG - posted 15:54, Wednesday 22 April 2015 - last comment - 12:47, Thursday 23 April 2015(18017)
PSL input power monitor calibration has changed
After the PSL periscope PZT swap, the periscope bottom mirror is a different high reflector. We are using the transmission through that optic to monitor the input power into the interferometer; since the transmission of the new optic seems to be a little higher than the old one our calibration of the power into the interferometer has been off since tuesday. We used to get a maximum power input of 22.7 Watts, after the swap our monitor reads a maximum power of something like 23.7 W. I adjusted the responsivity of the periscope PD, it used to be set to 0.35 and is now 0.311.
Next time someone is in the PSL it would be good to check this calibration using a power meter.
Actually, we didn't change the bottom periscope mirror. Rather, we placed what was the upper periscope mirror, the one actuated by a PZT stack, in the IO_MB_04 position, just downstream of the thin-film polarizers and just upstream of the bottom periscope mirror.
The original IO_MB_04 mirror was moved to the top of the periscope.
So the transmission through the bottom periscope mirror should have changed only slightly due to a small change in the incidence angle as we directed the beam to the upper newly-placed upper periscope mirror.
However, we didn't optimize the beam position on the power monitoring PD dowstream sampling the beam transmitted through the bottom periscope mirror.
We should have a look at this centering next time we are out in the Laser Room.