No real progress.
Probably I spent a bit too much time realigning the beat-note optical path.
(what I did)
- Switched on a power supply which was supposed to give +/- 15V for the broadband beat-note PD.
The power supply had been somehow turned off.
- Realigned the beat-note path. When we installed the new EOM mount today, we moved some of the green steering mirrors to make a space.
So we had to realign the downstream of the beat-note path. After the realignment the DC output of the PD was about 120 mV and the signal level of the beat-note was at -20 dBm.
- Took noise spectrum of the beat-note with the arm cavity locked by the IR-PDH
The noise curve was almost the same as before (i.e. unknown high frequency white noise above 20 Hz and some low frequency noise which has structures at 1 and 3 Hz).
- Closed the ALS loop with the coarse sensor. But I was too lazy to go further more.
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Tomorrow I will try :
(1) Using the fine sensor.
(2) Noise budgeting with the fine sensor.
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