NAOJ GW Elog Logbook 3.2
[Aritomi, Eleonora P]
We found that green beam spot at trans is fluctuating (Mov 1) and drifting. So we measured oplev signal of each mirror. From Pic 1 we can see that END mirror is fluctuating at around 0.3Hz. We opened END mirror control loop and closed it again, but it didn't change. We also measured open and closed loop END spectrum (Pic 2,3). Open loop spectrum is similar to previous result. Anyway, since beam spot fluctuation is much faster than 0.3Hz, this is not due to END mirror fluctuation.
Mov 1 green beam spot at trans
Pic 1 time series of oplev signal
Pic 2 open loop END spectrum
Pic 3 closed loop END spectrum
Then we maximized IR reflection and could recover 00 flash once, but problem is that green alignment keeps drifting during IR alignment. Beam spot of green reflection at PR viewport is going away mainly in pitch direction and centering of trans beam by BS is also drifting. We're not sure the reason.
Both the open loop and close loop end mirror TF look fine to me. There is no oscillation at 0.3 Hz. Note that striptool used EPIC channels are sampled at 64 Hz, so the oscillation could be an artifact (down-coversion of higher frequency noise?) You can double-check with dataviewer.
From the movie of the transmitted beam it is not clear the frequncy of the oscillation but it likely to be from a steering mirror (BS or PR). It would be useful to take a spectrum of their motion.
I measured END oplev signal with dataviewer. The signal somehow oscillates at around 1.5Hz...
Beam spot fluctuation seems at several Hz. I measured PR and BS closed loop spectrum. This also looks fine.