Mitch, Corey, Anamaria, in spirit, and I installed the 6 nozzle baffles on the nozzles at the reduction flange by the ITMX optical levers (see photographs in Figure 1). We followed the LLO procedure and protected the viewports with the LLO pillow design. The baffles reduce the aperture of the viewports so we compared the red GigE and the green camera views before and after installation. I could not see a difference for these two camera views, but we were unable to check the Pcal-style camera. Also, while I could check that the optical lever laser came into the vacuum chamber through the center of the new viewport aperture, I could not check that the beam returning from ITMX exited through the center of the new aperture since the test mass safety cover blocked the beam.  However, I could see the photodiode through the viewport and it looked like there was a clear path from the test mass to the entire photodiode through the new aperture. Nevertheless,  we should check that there is a good optical lever signal after the test mass safety cover is removed.

The second page of Figure 1 shows a “before and after” comparison of the reduction flange from near the position of the beam spot on ITMX where the light is scattered and recombines. The reflections associated with the viewports/nozzles are mostly gone. There is a remaining annulus of reflected light around the cryo-baffle and we are considering a baffle for this. These beam-spot photos are illuminated with 940 nm light and taken with an IR-modified camera to better simulate the reflections of scattered main-beam light.

While the nozzle baffles may help, the damping of the cryobaffle was the main purpose of the incursion and was done afterwords so that the damping wasn't altered by the bumping of the cryobaffle during the nozzle baffle installation. Figure 2 shows the installed cryo-baffle dampers. To monitor the Q as I damped the baffle, I used a light “flashing” method similar to what had originally pointed to the cryobaffles as the source of scattering noise (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=55927): I set up a flashlight like an optical lever and counted the seconds that I could see the reflection vibrating at ~4 Hz after tapping the baffle. To damp the baffle I tried to minimize this decay time. I ended up inserting 4 dampers as shown in Figure 2. I checked that the final position of the cryo-baffle was within a mm or so of the “before” measurements, except that I gave an extra mm or two of clearance at the +Y eddy current damper, which had been almost touching (Figure 2).