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Entry  Tue Oct 25 15:56:11 2016, gautam, Update, General, PRFPMI locked, arms loss improved PRFPMIlock_25Oct2016.pdfITMYwoes.png
    Reply  Tue Oct 25 18:07:28 2016, Koji, Update, General, PRFPMI locked, arms loss improved 
       Reply  Thu Oct 27 12:06:39 2016, gautam, Update, General, PRFPMI locked, arms loss improved PRG.pdf
          Reply  Thu Oct 27 13:48:20 2016, Koji, Update, General, PRFPMI locked, arms loss improved 
             Reply  Thu Oct 27 23:29:47 2016, ericq, Update, General, PRFPMI locked, arms loss improved TRY_REFL_2d.pngAS.pngREFL.pngseis_sub.pdf
                Reply  Fri Oct 28 01:44:48 2016, gautam, Update, General, PRFPMI model vs data studies 6x
                   Reply  Fri Oct 28 19:13:57 2016, rana, Update, General, PR gain 
Message ID: 12585     Entry time: Thu Oct 27 23:29:47 2016     In reply to: 12584     Reply to this: 12586
Author: ericq 
Type: Update 
Category: General 
Subject: PRFPMI locked, arms loss improved 

As Gautam mentioned, we had some success locking the PRFPMI last night. (SRM satellite box is still in surgery...)

Unsurprisingly, changing the loss/PRG/CARM finesse means we had to fiddle with the common mode servo parameters a little bit to get things to work. However, before too long, we achieved a first lock on the order of a few minutes. Not long afterwards, we had a nice half hour lock stretch where we could tune up the AO crossover and loop UGFs. The working locking script was committed to SVN. Really, no fundamentally new tactics were used, which is encouraging. (One thing I wondered about was whether a narrower CARM linewidth would still let our direct ALS->REFL11 handoff with no offset reduction work. Turns out it does)

However, the step where we increase the analog CARM gain isn't as bulletproof as it once had been. The light levels "sputter" in and out sometimes if the gain increases are too agressive, and can cause a lockloss. Maybe this is an effect of the narrower linewidth and injecting more ALS noise at high frequencies with the higher CARM bandwidth.

The spatial profiles of the light on the cameras is totally bananas. Here's AS and REFL.

As Koji suggested, here is a 2D histogram of TRY vs REFLDC. It appears that the visibility would max out at 75% or so at arm powers around 400. Indeed, we briefly saw powers that high, but as can be seen on the plot, we were usually a little under 300. Exploring the transmon QPD offset space didn't seem to have much effect here.

One thing that I hadn't looked at in previous locks is coherence with our ground seismometers. It would be cool to have more seismic feedforward, and looking at the frequency domain multiple coherence, it looks like we can win a lot between 1 and 20 Hz. I expected more of a win at 1Hz, though.

Attachment 4: seis_sub.pdf  47 kB  | Hide | Hide all
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