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Entry  Thu Jul 21 11:49:29 2016, awade, DailyProgress, Mode matching, Beam measurement for MM into south cavity plot20160721_south_BeamMMForPMC.epsdata20160721_south_BeamMMForPMC.txt
    Reply  Thu Jul 21 12:30:15 2016, awade, DailyProgress, Mode matching, Beam measurement for MM into south cavity plot20160721_south_BeamMMForPMC_updated.eps
    Reply  Thu Jul 21 13:08:50 2016, awade, DailyProgress, Mode matching, Beam measurement for MM into south cavity 
Message ID: 1678     Entry time: Thu Jul 21 12:30:15 2016     In reply to: 1677
Author: awade 
Type: DailyProgress 
Category: Mode matching 
Subject: Beam measurement for MM into south cavity 

Correction: Wrong plot (at least the x-scale is wrong).  The updated one is attached.

Also the offset of the data from the laser head position is 2698 mm.


I placed a pair of lenses and a cylindrical lens in the path after the final EOM before the PMC location to provide a MM solution close to that of the PMC when we eventurally impliment this. The goal was 330 um waist.  The PMC base was bolted in position and with a quick alignment the cavity was scanned to see how well it will mode match when we install.  Visablity was found to be 84.4 % (with 1.000 V off resonance and a dip down to 156 mV on reflection).  All this is so that we have a fair idea of the MM solution and placement for later installation.

I took the PMC out today and took a proper beam profile referenced to the steering mirror just before the PMC.  Data and plot of fit are attached the fitted profile values were:

Horz. beam waist = 256.7996 um
Horz. beam waist position = 2635.8799 mm
Vert. beam waist = 211.6388 um
Vert. beam waist position = 2538.9972 mm
Mean beam waist = 234.2192 um
Mean beam waist position = 2587.4386 mm

However, looking at the plot it looks like the fit overshoots the actual measurments close to the waist.  It may be that the large distance measurments bias the measurment (and there are more of them). But the waist was definitly located closer to the reference point at which the PMC base was placed yesterday.  I haven't modeled it but I find a visablity of 84 % for a waist of 234 um hard to belive if the PMC cavity is designed for a 330 um.  For now it is probably ok to assume 330 um for this next modematching step.  

Next final MM to the south cavity. We expect that this should take to the end of today.


Attachment 1: plot20160721_south_BeamMMForPMC_updated.eps  134 kB  | Hide | Hide all
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