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Entry  Sun Mar 28 20:05:33 2010, rana, Summary, PSL, FSS Work from Sunday: AOM/VCO level set wrong Untitled.png
    Reply  Sun Mar 28 20:51:31 2010, rana, Summary, PSL, FSS Work from Sunday: Cavity Suspension is Ridiculously Undamped! Untitled.png
       Reply  Sun Mar 28 23:17:46 2010, rana, Summary, PSL, FSS Work from Sunday: noise spec in2.png
          Reply  Sun Mar 28 23:47:47 2010, rana, Summary, PSL, FSS Work from Sunday: Open Loop Gain fssloop.pngsweep2.png
             Reply  Mon Mar 29 01:11:33 2010, rana, Summary, PSL, FSS Work from Sunday: RF Out Spectrum rfout.pngTEK00000.PNGTEK00001.PNGTEK00002.PNG
             Reply  Mon Mar 29 02:07:50 2010, Koji, Summary, PSL, FSS Work from Sunday: Open Loop Gain 
Message ID: 2720     Entry time: Sun Mar 28 20:05:33 2010     Reply to this: 2721
Author: rana 
Type: Summary 
Category: PSL 
Subject: FSS Work from Sunday: AOM/VCO level set wrong 

Just before working on the FSS today, I noticed that the VCO RF output level was set incorrectly.

This should ALWAYS be set so as to give the maximum power in the first order diffracted sideband. One should set this by maximizing the out of lock FSS RFPD DC level to max.

The value was at 2.8 on the VCOMODLEVEL slider. In the attached plot (taken with the FSS input disabled) you can see that this puts us in the regime where the output power to the FSS is first order sensitive to the amplitude noise on the electrical signal to the AOM. This is an untenable situation.

For adjusting the power level to the FSS, we must always use the lamba/2 plate between the AOM and the RC steering mirrors. This dumps power out to the side via a PBS just before the periscope.

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