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Entry  Tue Apr 10 17:02:29 2012, Jenne, Update, IOO, Mode matching recollections and conclusions IMMT_positionSensitivity_plotted10Apr2012_LowRes.pngHistogram_20mmStDev_MMTmovesOnly_LowRes.pngHistogram_20mmStDev_MMTmovesAndTilts_LowRes.png
    Reply  Wed Apr 11 18:19:51 2012, Jenne, Update, IOO, Mode matching recollections and conclusions ModeMismatch_MMTpos_MMTang_MCw0_MCwz_change_LowRes.png
Message ID: 6516     Entry time: Tue Apr 10 17:02:29 2012     Reply to this: 6522
Author: Jenne 
Type: Update 
Category: IOO 
Subject: Mode matching recollections and conclusions 

...Mostly just recollections at this point.

I re-looked at the mode matching's sensitivity to misplaced optics.  Here is the plot that the original MMT code from 2010 spits out:

IMMT_positionSensitivity_plotted10Apr2012_LowRes.png

What this plot is telling us is that we should lose no more than 0.1% of mode matching "goodness" if we messed up the curved optic's positions by up to 2 cm.  If we can't place optics to within 2 cm, we might as well go back to optics kindergarten, because that's pretty lame.

UPDATE: Here is a histogram using the new code, which definitely includes the non-unity index of refraction for the transmissive optics and the Faraday.  The only optics which are permitted to move are the 2 curved optics, and they are allowed a stdev of 20mm.  Again, we shouldn't be doing worse than ~99% mode matching, even if we're 2cm off from the MMT positions that we measured with a ruler.  This histogram only has 300 iterations, since it takes quite a while (~0.5sec) to calculate each iteration.  Note this is mode overlap using the measured MC waist, propagated through optics, compared to the ideal arm mode.  This is completely ignoring the IPPOS measurements so far.

Histogram_20mmStDev_MMTmovesOnly_LowRes.png

 

UPDATE 2: Allowed 5 degrees of incident angle motion for both curved optics, which changes the astigmatism of the beam downstream.  Still, no big change from ~99% mode matching efficiency.  Again, this doesn't include any information from the IPPOS measurements.  3000 iterations this time around, since I didn't need my computer.  Curved optics still allowed to move back and forth by 2cm. 

Histogram_20mmStDev_MMTmovesAndTilts_LowRes.png 

More meditations and conclusions to follow...  currently running hist code to allow tilt of optics, to account for astigmatism changes also. 

Suresh and I are going to do some beam measurements tomorrow with the beamscanner, and then we will do a few measurements with the razor blade technique, to confirm that we're doing things okey dokey.

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