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Wed Nov 21 14:31:41 2007
I `tweaked' the FSS path today. Here's what I did:
1) Shut down the FSS autolocker
2) Turn off FSS servo
3) Assume the beam coming back from the AOM is double-first-order, and don't make any changes large enough to lose it.
4) Tweak the alignment of these components to maximize the incident power on the RC reflected diode:
a) PBS before AOM
c) curved mirror after the AOM
5) Translate the AOM such that the beam moves away from the PZT, then when it levels off (no more power gains with movement),
move it back just a little bit so there's a teensy drop in power. This should but the beam as close to the edge as possible,
but whether or not it's the best place is still to be determined.
6) Lock the FSS, and align the mirrors into the frequency reference cavity.
After all this, the RC transmitted power went from .57 to .73 -- probably not a big enough change to account for the missing loop
gain, but we'll know more once the loop gets measured (after Alberto stops hogging the Agilent network analyzer).
Other possible routes include a systematic check of the upstream path (e.g., the Pockels cell) and just increasing the pickoff fraction for the FSS.