Due to an apparent increase in noise when the cavity was well aligned, we (Bram and Matt) suspected that some of the 532nm light retro-reflected from the cavity was getting into the laser and causing problems.  To test this, we added a second faraday after the laser on the ALS table (ISCTEY) and realigned the beam.  This appears to have had the desired effect (see plots), but in the process we discovered that some work will be needed to understand the REFL RF photodector, as it seems to be overfilled and its alignment may change our noise floor.

We also found clear fringes in the cavity error signal (PDH_IMON) even with the ITM misaligned.  The fringe velocity is senstive to motion of the ASL table, and to the state of the HEPA fan on the table.  These fringes are only a few mV, but they may be a noise source and will need to be investigated further.