i tried a couple of things today to figure out what determines the low frequency noise level of the beat measurement.
I did the following steps, nevertheless the noise level didn't change:
- re-aligned everything starting with the PMC
- coupling into the cavities is >90%
- matched power levels in both paths to match power at RF photodetector
- re-positioned the RF photodiodes for locking the caviries
- added beam dumps for beams reflected from RF photodiodes
- optimized overlap of both beams on RF photodiode (beat)
- changed mixer from 7dbm model to 13dbm model
- removed cable going to DAQ from DC output of RCAV RF photodiode as it is causing ~36MHz oscillation of RF PD (even with no light)
- changed gains for both loops, ACAV and RCAV
- added first QPD at pick-off right in front of periscope into chamber for RCAV to check pointing
things to be checked tomorrow:
- power fluctuations of beams into both cavities
- power fluctuations of transmitted beam
- pointing of both beams (should also show up in power noise spectrum in transmission)
- measure TF of all loops with current setting for noise estimation
other things to change:
- move temp readout to VME based stuff
- rename VCO input monitor signal channel name
- remove PSL RT stuff from fb0 to see if networking problems are caused by that
- replace current cables for temp readout due to loose connection somewhere on table
- check ACAV RF photodiode
- change PID controller variable names in order to add other software loops like feedback from VCO input signal to RCAV temp setpoint. Right now we have already 4 software loops:
- feedback to laser for RCAV using FAST actuator signal
- temp ctrl for RCAV
- temp ctrl for ACAV
- feedback to laser temp for ACAV using VCO input signal (used to track ACAV temp tuning to match RCAV resonance)
|