Recently, I noticed that the mystery beam spot on the spool piece near HAM3 was much dimmer after the break this spring than in was before ( 85079) To see if this change may have been associated with the CP-Y move we made during the break, we swept through nearly the entire range of pitch and yaw (-300 to 300) while taking a video.  The linked video (https://www.youtube.com/watch?v=DIwnx13NzEU&ab_channel=RobertSchofieldLIGO)  shows the view from the MC2 camera viewport before the break and after the break. The drop in intensity over the break is quite obvious, but I can see no further change in intensity during the sweep. The sweep can be monitored in the video, both before the break and after, by the motion of the ghost beam spots on the ballast baffle below PR2 (on the center left of the image).  The CP move during the break was larger than these sweeps, so it is still possible that the move during the break was the source of the drop in intensity. 

However, another possibility is that the movement of the PR2 beamspot, and the reduction in clipping on the PR2 scraper baffle was the source of the drop in intensity.  The last pictures I took of the mystery beam spot before the break were in  January of 2025. After that, there were a series of moves of the PR2 beam spot and associated reductions in the intensity of the beam coming out the HAM3 viewport that were made in February of 2025 (82670, 82722, 82740, 82793), reducing the power in the beam that comes out of the viewport from about 17mW to about 3.5mW. The ”before” clip in the video below was made in December of 2024, when the HAM3 viewport beam was in the 17mW era, while the ”after” clip is at 3.5 mW, if we assume it is the same now as before the break (could be worth checking).  If the ”mystery” beam spot comes from the edge of the scraper baffle (see figure), then the PR2 spot moves might have reduced its intensity, by a factor of about 5 if it is proportional to the light at the viewport.

The figure shows that there is a spot on the edge of the scraper baffle (which is only there when laser light is present) that seemed to get dimmer when the mystery spot got dimmer. The diagram shows how the reflection/diffraction would light up the wall of the spool piece as seen in the photographs. The edge of the aperture would be lit by the beam that is clipped and especially by the beam reflected off of the baffle to the viewport and reflecting back to the baffle.