[Sudarshan, Gabriele]

To understand why intensity noise was worse than usual, we had a look again at the beam dumps we installed yesterday on the two beam coming out into IOT2R. 

After yesterday's realignment of the main beam, the two dumps were no more in a good position. To be more precise: the two beams coming into the enclosure are very close to the edge of the periscope upper mirror; one of the beams is hitting the bottom mirror in a reasonable position but was partially missing the beam dump; the other beam was hitting the edge of the mirror and the mount. Therefore, we moved the first beam dump to a better position, and we dumped the second beam before it hits the periscope bottom mirror. See attached picture

This improved the intensity noise, but we can still see a bit of 18 Hz peak.