Last Finesse measurement in air : ~ 17 000 the 20th of may (see logbook)

28th and 29th of august, we cleanned, with Loïc, mirrors S3 then P1 successively using only ultra pure water with the spin coater.

we measured the finesse after each cleaning by modulation technique and in both cases, F ~ 12 500 !!!

maybe the mirror surfaces have been covered by some hydrocarbure during the summer ?
or by an other contaminant which is difficult to clean with only water ?
we decided to clean the mirrors first with an isopropanol solution and then with ultra pure water and the spin coater.