cheryl.vorvick@LIGO.ORG - posted 10:24, Saturday 02 March 2013 - last comment - 11:10, Saturday 02 March 2013(5634)
IO alignment irises on the PSL - beams were centered, but are not centered now
I installed irises on the PSL in January, and looked at them yesterday. I found that the beam coming from the PMC is about a beam diameter from center on it's alignment iris, and the transmitted beam from the bottom periscope mirror was also about a beam diameter from center. Attached is a drawing of the beam paths for these two irises, and where I found the beams.
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A possible explanation for the alignment drift might be that the shutdown of the PSL chilled water has caused some thermal motion either of the PSL table or some components on the table. I would expect some watercooled components are thermally anchored to the table so even small changes in termperature might cause some local deformation of the table surface. There may be large time constants associated with this.