Calum, Kate, Betsy

This week, we performed a series of First Contact cleaning tests on the old pilot optic ETM06 as a followup on the ring observed on the ETMy during green-arm resonance last month (alog 15928).

ETM06 has a very similar history to the installed LHO ETMs (ETM08, ETM12).  A FirstContact sheet which had the 2x 3" IAS windows was applied to ETM06 roughly 2 years ago.  After pulling the sheet this week, we observed the ring pattern, as seen on the ETMy.  Via cleaning we were able to remove a section of the ring, which implies the ring discoloration is not from etching.  Our other tests did not indicate there are any age correlations to the protective FirstContact sheets applied to optics.  Reminder - the LHO ETMs (ETMy 125ppm) have recently been measured to be low loss, so there is no current plan to further clean in-situ.

SYS/COC investigations to be continued...