This week we have been working to tune the phase camera's phase locking loop and the camera exposure settings to enable us to image all the sidebands and carrier going from DRMI all the way up to full lock. The aim is too see how they may change in balance and shape. Unfortunately the only coincident times when the phase camera worked (nearly) as intended and we got a clean lock up to maximum power was Friday 1am PST before the run started and it was switched off, I was hoping to get a few powerups to compare before pulling it out on Tuesday.

https://lhocds.ligo-wa.caltech.edu/exports/powerup_odd.mp4

The above is a movie of the sidebands and carrier from left to right, carrier, +9, -9, -45, +45. Top row is phase and the bottom is the amplitude. I have applied a rolling average of 10 frames to the amplitude to stop it jittering around so much frame to frame. Each frame of the movie is ~20s. We start whilst acquiring DRMI and see the sidebands first appear and the carrier not very visible. We then reach resonance of the carrier. Next we see the powerup and the fields shifting from moving the spot positions. Shown in the bottom plot is the PSL and CO2X powers normalised. We also wanted to try pulsing CO2X on and off to see if we could see similar effects as we did before with the beam becoming more astigmatic and displaced, but with the new IFO alignment.

At around 25s seconds into the movie we see some odd shapes starting to emerge. The fields all become distorted and the signals oscillate around. This is not what is actually happening to the POP beam, at least I hope not. However it is also not a behaviour we have witnessed whilst using this phase camera previously, we had long stretches of DRMI time where this was not present. Our best guess is that phase lock became unstable, glitching maybe, with the increased power on the photodiode. Each frame in the movie is actually 10 frames averaged over 1s for each field, so it could be the glitch was large enough to distort each set of frames consistently. Which seems unlikely given the images of the fields change gradually over many frames. We weren't storing each individual frame to minmise the load on writing to the disk and also how much space was required, assuming we would leave it running over the weekend, so we can't go back and look. Although at the end of the movie it settles down to a constant shape which is odd. It doesn't really seem to match up with us changing the CO2 power, and I can't think of any reason why it would even effect the phase camera output like this.