lisa.barsotti@LIGO.ORG - posted 18:34, Friday 29 July 2011 - last comment - 19:11, Monday 01 August 2011(1128)
First attempt to clean the TRANSMON telescope primary mirror
Betsy, Lisa Betsy and I tried to clean the silver coated primary mirror (D1000075-v1) of the H2 OAT Transmon telescope. We did as follows: 1) Blow off the dust from the mirror 2) Soak the mirror (but not the surface) in DI water + 1% liquinox for about 10 minutes 3) Scrub the edge and the back with the soapy solution 4) Remove the soap with DI water At this point we noticed that the back surface and the barrel still had marks (I think they used a pencil or something similar to define the alignment reference lines before scribing them). So we decided to scrub with methanol to try to remove these lines. By doing that, we noticed that sticky brownish stuff remained attached to our wipes..(see picture). We locate the problem in the bevel at the edge of the coating. We continued to wipe down (kind of aggressively) until the wipes remained clean. So, we can summarize the procedure with: 5) Wipe down with methanol the barrels, in particular the bevel, and the back surface, until the wipes remained clean. 6) Sticky stuff were also present at the very edge of the surface. We removed them by wiping (more gently) with methanol We might have removed some pieces of the small area at the edge of the mirror where the coating was damaged. After that, we moved to the surface. We tried to remove some of the particles on the surface by wiping down with methanol, but very gently, as we worried that we could damage the coating. We are sure we removed at least one spot, which made us think that these spots are not inside the coating. However, we can't remove most of them. So, the message: we are ready to do an FTIR test on the substrate, to see how the cleaning went. About the surface, we removed the dust, but we didn't really remove the spots that are there (only a very small fraction), and it is really hard to judge if wiping down with methanol really helps. I brought Keita and Bram to look at the mirror, and we tried again, unsuccessfully, to attack some of the spots. By looking at the mirror with an inspection lamp showed greenish halos and thousands of spots all around the surface (those probably due to the coating itself). So, the plan is to go on with the FTIR test. For the surface, probably the best idea we had so far is to leave it as it is.
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Joe did the FTIR test on the substrate today. We focused on the back side of the optics were the (pencil?) marks are, a piece of the barrel, and the bevel all around the coating, which was the most dirty part. Results in 1-2 weeks.
Cheryl took pictures of the surface of the mirror. You can see a wide collection of scratches, bubbles and splatters on the surface. The tiny points are most likely imperfection of the coating itself. Some of the big splatters could be removed, but not easily.
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