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Entry  Wed Feb 13 19:09:32 2013, yuta, Summary, General, possible explanations to oval REFL beam REFL_1044844506.bmp
    Reply  Wed Feb 13 19:30:45 2013, Koji, Summary, General, possible explanations to oval REFL beam 
       Reply  Wed Feb 13 19:41:07 2013, yuta, Summary, General, possible explanations to oval REFL beam 
    Reply  Wed Feb 13 22:09:26 2013, Jenne, Update, Alignment, REFL is not clipped 
       Reply  Thu Feb 14 00:10:12 2013, yuta, Summary, Alignment, REFL is not clipped 
          Reply  Thu Feb 14 10:42:41 2013, Jamie, Summary, Alignment, MMT, curved TTs does not explain beam ellipticity at Faraday T.pdfS.pdf
Message ID: 8084     Entry time: Thu Feb 14 10:42:41 2013     In reply to: 8082
Author: Jamie 
Type: Summary 
Category: Alignment 
Subject: MMT, curved TTs does not explain beam ellipticity at Faraday 

After using alamode to calculate the round-trip mode of the beam at the Faraday exit after retro-reflection form the PRM, I'm not able to blame the MMT and TT curvature for the beam ellipticity.

I assume an input waist at the mode cleaner of [0.00159, 0.00151] (in [T, S]).  Propagating this through the MMT to PRM, then retro-reflecting back with flat TTs I get

w_t/w_s = 0.9955,  e = 0.0045

If I give the TTs a -600 m curvature, I get:

w_t/w_s = 1.0419,  e = 0.0402

That's just a 4% ellipticity, which is certainly less than we see.  I would have to crank up the TT curvature to -100m or so to see an ellipticity of 20%.  We're seeing something that looks bigger than 50% to me.

Below are beam size through MMT + PRM retro-reflection, TT RoC = -600m:

 

T.pdfS.pdf

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