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Entry  Wed Jun 23 23:52:48 2010, tarac, Laser, RefCav, RefCav is locked and optimized 
    Reply  Thu Jun 24 09:37:16 2010, rana, Laser, RefCav, RefCav is locked and optimized 
Message ID: 174     Entry time: Wed Jun 23 23:52:48 2010     Reply to this: 175
Author: tarac 
Type: Laser 
Category: RefCav 
Subject: RefCav is locked and optimized 

I adjust the mode matching lenses and align the beam so that the transmitted power is ~97% of the input power. Actually I scan the beam and look at the reflected power. The reflected beam has power ~3%. The knobs on one of the periscope mirror acting weird. There's still thread (~ 4 or 5 turns, I guess) left but it seems to be very sensitive to my hand pressure when I rotate the knob, making fine adjustment rather hard .

Phase shift is adjusted by looking at the error signal. The laser is scan while the error signal from the fss servo mixer out is monitored. Feedback signals from the servo to EOM and laser must be removed.

RF power for RefCav is tuned. I assume that all sidebands' power will be reflected, and only power in the carrier will be transmitted, and to maximize the error signal's slope, we need Pcarrier/ Psideband ~ 2 [Black] .

So I measure the power of the incoming beam and adjust the RF power so that the transmitted beam's power is 1/2 of the input power. Another 1/2 of the input power will be the power of 2 sidebands that reflect back. 

 I use a photo diode to see the transmitted power and adjust the gain. The goal is to maximize the gain and have a stable transmitted power. However, the power still oscillates even when I decrease the gain, more than that and it loses lock. So I can only minimum the osicllation (You can see the beam spot pulsating on the monitor.)

All values are saved in the "startup.cmd" file.


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