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Entry  Tue Oct 30 00:47:29 2007, rana, Other, IOO, MC Ringdowns tek00000.pngtek00001.pngtek00004.pngMC2ringdown.tar.gz
    Reply  Tue Oct 30 13:58:07 2007, ajw, Configuration, IOO, MC Ringdowns CavityRingdown.pngCavityRingdown.m
Message ID: 29     Entry time: Tue Oct 30 00:47:29 2007     Reply to this: 30
Author: rana 
Type: Other 
Category: IOO 
Subject: MC Ringdowns 
I did a bunch of MC ringdown measurements using the PD that Rob set up. The idea is to put a fast PD (PDA255)
looking at the transmission through MC2 after focusing by a fast lens. The input to the MC is turned off fast
by flipping the sign of the FSS (Andri Gretarsson's technique).

With the laptop sitting on the MC can, its easy to repeat many ringdowns fast:
- Turn off the MC autolocker. Relock the MC with only the acquisition settings; no boosts
  and no RGs. This makes it re-acquire fast. Turn the MC-WFS gain down to 0.001 so that
  it keeps it slowly aligned but does not drift off when you lose lock.

- Use low-ish gain on the FSS. 10 dB lower than nominal is fine.

- Setup the o'scope (100 MHz BW or greater) to do single shot trigger on the MC2 trans.

- Flip FSS sign.

- Quickly flip sign back and waggle common gain to get FSS to stop oscillating. MC
  should relock in seconds.

Clearly one can scriptify this all just by hooking up the scope to the ethernet port.

Attached are a bunch of PNG of the ringdowns as well as a tarball with the actual data. A sugar
napoleon to whomever can explain the 7 us period of the wiggle before the vent!
Attachment 1: tek00000.png  8 kB  | Hide | Hide all
Attachment 2: tek00001.png  8 kB  | Hide | Hide all
Attachment 3: tek00004.png  11 kB  | Hide | Hide all
Attachment 4: MC2ringdown.tar.gz  150 kB
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