I started doing a scan of the Y arm cavity with IR with ALS enabled.
ALS servo tuning:
The servo tuning procedure is basically the same as described in elog 8831.
This time I had a stronger beat note(-14 dBm instead of -24 dBm of the last measurement) thanks to a better alignment.
Plot1 shows the Power spectrum of the BEATY_PHASE_OUT. The RMS is smaller by a factor of 2 (400Hz), corresponding to a residual motion of about 25 pm.
Offset setting avity scan
In order to give an offset linearly growing in time, I used the ezcastep script instead of giving the offset in OFFSETTER2. If the ramp time is long enough, it is not necessary to enable the 30mHz filter.
To span 2 FSR, I started from an offset of 450 and I gave a maximum value of 1600 with a delay of 0.2s between two consecutive steps.
I did a first scan with the cavity well aligned, basically to know the position of the 00 peaks and choose the best offset range (Plot2)
Then I misaligned the TT2, first in PITCH and yhen in YAW, in order to enhance the HOMs. (Plot3 and Plot4)
More investigation and measurements needed.