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Entry  Mon May 2 17:11:55 2016, rana, Update, COC, RC folding mirrors 
    Reply  Wed May 18 01:10:22 2016, gautam, Update, COC, Finesse modelling arms.pdfPRC.pdfSRC.pdfFinesse_model.zip
       Reply  Tue May 24 22:49:02 2016, gautam, Update, COC, Finesse modelling - mode overlap scans 9x
          Reply  Tue May 24 23:17:37 2016, ericq, Update, COC, Finesse modelling - mode overlap scans 
             Reply  Thu Jun 16 15:57:46 2016, gautam, Update, COC, Contrast as a function of RoC of ETMX contrastDefect.pdffinesseCode.zip
                Reply  Thu Jun 16 18:42:12 2016, rana, Update, COC, Contrast as a function of RoC of ETMX 
                   Reply  Thu Jun 16 23:02:57 2016, gautam, Update, COC, Contrast as a function of RoC of ETMX contrastDefect.pdf
                      Reply  Mon Jun 20 01:38:04 2016, rana, Update, COC, Contrast as a function of RoC of ETMX 
                         Reply  Mon Jun 20 18:07:15 2016, gautam, Update, COC, Contrast as a function of RoC of ETMX contrastDefectComparison.pdf
             Reply  Tue Jun 28 16:06:09 2016, gautam, Update, COC, RC folding mirrors - further checks C1_HOMcurves_Y.pdfC1_HOMcurves_DR.pdf
                Reply  Thu Jun 30 16:21:32 2016, gautam, Update, COC, Sideband HOMs resonating in arms image.jpegC1_HOMcurves_Y.pdfC1_HOMcurves_X.pdf
                Reply  Sat Aug 13 18:25:22 2016, gautam, Update, COC, RC folding mirrors - Numerical review PRX_consolidated.pdfSRX_consolidated.pdfGouy_PRC.pdfGouy_SRC.pdf
                   Reply  Tue Aug 16 11:51:43 2016, gautam, Update, COC, RC folding mirrors - Numerical review PRC_consolidated.pdfSRC_consolidated.pdfGouyPRC.pdfGouySRC.pdf
                      Reply  Tue Aug 16 16:38:00 2016, gautam, Update, COC, RC folding mirrors - Numerical review PRC_consolidated.pdfSRC_consolidated.pdfGouyPRC.pdfGouySRC.pdf
                         Reply  Wed Aug 17 14:37:36 2016, gautam, Update, COC, RC folding mirrors - Numerical review PRG.pdf
                            Reply  Wed Aug 17 16:28:46 2016, Koji, Update, COC, RC folding mirrors - Numerical review 
                            Reply  Mon Nov 21 15:34:24 2016, gautam, Update, COC, RC folding mirrors - updated specs Recycling_Mirrors_Specs_Nov2016.pdf
                               Reply  Thu Feb 23 10:59:53 2017, gautam, Update, COC, RC folding mirrors - coating optimization PR3_R_170222_2006.pdfPR3_123_TOnoise_170222_2203.pdfPR3_123_Layers_170222_2203.pdfPR3AR_R_170222_2258.pdfPR3AR_123_Layers_170222_2258.pdf
                                  Reply  Tue Mar 14 10:56:33 2017, gautam, Update, COC, RC folding mirrors - coating optimization PR3_R_170313_1701.pdfPR3AR_123_Layers_170313_1701.pdfPR3AR_R_170313_1752.pdfPR3AR_123_Layers_170313_1752.pdf
                                     Reply  Mon Apr 10 15:37:11 2017, gautam, Update, COC, RC folding mirrors - v3 of specs uploaded  8x
Message ID: 12631     Entry time: Mon Nov 21 15:34:24 2016     In reply to: 12417     Reply to this: 12847
Author: gautam 
Type: Update 
Category: COC 
Subject: RC folding mirrors - updated specs 

Following up on the discussion from last week's Wednesday meeting, two points were raised:

  1. How do we decide what number we want for the coating on the AR side for 532nm?
  2. Do we want to adjust T@1064nm on the HR side to extract a stronger POP beam?

With regards to the coating on the AR side, I've put in R<300ppm@1064nm and R<1000ppm@532nm on the AR side. On the HR side, we have T>97% @ 532nm (copied from the current PR3/SR3 spec), and T<50ppm @1064nm. What are the ghost beams we need to be worried about? 

  • Scattered light the AR side interfering with the main transmitted green beam possibly making our beat measurement noisier
    • With the above numbers, accounting for the fact that we ask for a 2 degree wedge on PR3, the first ghost beam from reflection on the AR side will have an angular separation from the main beam of ~7.6 degrees. So over the ~4m the green beam travels before reaching the PSL table, I think there is sufficient angular separation for us to catch this ghost and dump it. 
    • Moreover, the power in this first ghost beam will be ~30ppm relative to the main green beam. If we can get R<100ppm @532nm on the AR side, the number becomes 3ppm
  • Prompt reflection from the HR surface of PR3 scattering green light back into the arm cavity mode 
    • The current spec has T>97% @532nm. So 3% is promptly reflected at the HR side of PR3
    • I'm not sure how much of a problem this really will be - I couldn't find the reflectivities of PR2 and PRM @532nm (were these ever measured?)
    • In any case, if we can have T<50ppm @1064nm and R>99.9% @532nm, that would be better

So in conclusion, with the specs as they are now, I don't think the ALS noise performance is adversely affected. I have updated the spec to have the following numbers now.

HR side: T < 50ppm @1064nm, T>99.9% @532nm

AR side: R < 100ppm @1064nm and @532nm

 

As for the POP question, if we want to extract a stronger POP beam, we will have to relax the requirement on the transmission @1064nm on the HR side. But recall that the approach we are now considering is to replace only PR3, and flip PR2 back the right way around. Currently, POP is extracted at PR2, so if we want to stick with the idea of getting a new PR3 and extracting a stronger POP beam, there needs to be a major optical layout reshuffle in the BS/PRM chamber. Koji suggested that in the interest of keeping things moving along, we don't worry about POP for the time being...


Alternatively, if it turns out that the vendor can meet the specs for our second requirement (which requires 1.5% of lambda @632nm measurement precision to meet the 10+/-5km RoC tolerance on PR3), then we can ast for T<1000ppm @1064nm for the HR coating on PR2, and keep the coating specs on PR3 as above. 

 

Attached is a pdf with the specs updated to reflect all the above considerations...

Attachment 1: Recycling_Mirrors_Specs_Nov2016.pdf  300 kB  | Hide | Hide all
Recycling_Mirrors_Specs_Nov2016.pdf Recycling_Mirrors_Specs_Nov2016.pdf Recycling_Mirrors_Specs_Nov2016.pdf
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