Evan, Kiwamu, Dan, Peter, Lisa

The goal for tonight was to relock the interferometer on DC readout, properly calibrate the spectrum (see  Kiwamu's entry  with today measurements), and in the process see if the  IO periscope PZT filters  had improved the beam jitter noise that we think is responsible for the bump around 100 Hz in the sensitivity.

The only other (known) change with respect to yesterday was the  new DARM filter  designed to give us better phase margin, with the goal (surprise!) of making the locking sequence more robust.

However, we soon realized that we had to retune the transition from ALS COMM to CARM (common mode board input 1 changed from -16 dB to -7 dB) as the current gains were totally wrong (meaning that corresponding OLTF were extremely marginal). We fixed the gains up to the transition to DARM on AS 45 Q, to discover that there was no chance of moving forward with the CARM TF we measured (Evan will post the offending TF later).  

Even if we believe the new DARM filters had little to do with the problem we were seeing, we decided to go back to the old DARM filters and the Guardian CODE which was running last night, as a sanity check. 

Still, we had to keep the low CARM gain to transition to transmission signals for CARM, then we made a couple of attempts to full lock, but we would lose lock before transitioning to AS 45 Q, this time because the DARM gain was wrong..

So, the message is that the problems we see are really easy to identify (loop oscillation, nonsense TFs) and we could keep fixing the locking sequence, but we don't want to make very radical changes in the gain/filter tuning at this time. Old DARM filters and Guardian code are running (as last night).