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Message ID: 95     Entry time: Sun Aug 21 13:45:56 2016
Author: Gabriele 
Type: Optics 
Category: Daily Progress 
Subject: Wierd behavior of ring downs and Improved setup 

The last two ring downs I measured today showed a weird behavior of the lowest modes:

Although I'm not 100% sure, I suspect this is related to the fact that the beam reflected from the black glass was so close to the beam reflected by the disk that I could see interference.

So I broke vacuum and improved the setup, adding a peek washer below one edge of the black glass, to wedge it. In this way the reflection from the black glass is largely separated: it misses the upper periscope mirror and it is dumped on a black panel (together with the viewport reflection).

I realigned everything, installed back the disk and started pumping down at 1:30pm.

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