This morning, the PMC couldn't be locked to the laser. The FSS servo was disabled during that time.
When the gain/ RF power were adjusted, PMC was locked to the laser, but the coupling efficiency dropped from 80% to 40%.
I try adjusting the mirror, but it's not the alignment problem because I couldn't increase the efficiency.
So after the noise budget party with Jan and Frank, I check if the EOM works looking at the error signal from mixer out. The laser frequency is scan at +/- 10V @ 100 Hz.
I'm not sure what is the corresponding freq span, but it must be less than 43 MHz(21.5 MHz x 2) because
three peaks of the signal could not be seen with +/- 10V span, so I use a voltage calibrator to slowly adjust the temperature and see the rest of the signals.
Nevertheless, the signals are there, so I try to lock the PMC again, and now the efficiency back to almost 80% again ( I have to re align again because of the earlier adjustment. The mixer out channel is monitored when I set the PMC gain to make sure there will be no oscillation.
I'm not sure what happen, loosen connectors, mode hopping in the laser, etc. I'll see if I can track this down , otherwise we could not have a stable locking system.