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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: 12130     Entry time: Tue May 24 22:49:02 2016     In reply to: 12120     Reply to this: 12131
Author: gautam 
Type: Update 
Category: COC 
Subject: Finesse modelling - mode overlap scans 

Summary:

Having played around with a toy finesse model, I went about setting up a model in which the RC folding mirrors are not flipped. I then repeated the low-level tests detailed in the earlier elog, after which I ran a few spatial mode overlap analyses, the results of which are presented here. It remains to do a stability analysis.

Overview of model parameters (more details to follow):

  • PRC length = 6.7727m (chosen using l_{PRC} = (N+\frac{1}{2})\frac{c}{2f_1}, N=0 - I adjusted the position of the PRM to realize this length in the model, while leaving all the other vertex optics in the same positions as in elog 9590
  • SRC length = 5.4182 (chosen using l_{SRC} = M\frac{c}{2f_2} but not l_{SRC} = N\frac{c}{2f_1}, M and N being integers, for M=2 - as above, I adjusted the position of the SRM to realize this in the model, while leaving all other vertex optics in the same positions as in elog 9590. It remains to be verified if it is physically possible to realize these dimensions in vacuum without any beam clipping etc but I think it should be possible seeing as the PRM and SRM had to be moved by less than 2cm from their current positions..
  • For the losses, I used the most recent numbers we have where applicable, and put in generic 25ppm loss for all the folding mirrors/BS/AR surfaces of arm cavity mirrors/PRM/SRM. Arm round trip loss was equally distributed between ITMs and ETMs
  • Arm lengths used: L_X = 37.79m, L_Y = 37.81m
  • To set the "tunings" of the various mirrors, I played around with a few configurations to see where the various fields resonated - it turns out that for PRM, ITMX, ITMY, ETMX and ETMY, the "phase" in the .kat file can be set as 0. while that for the SRM can be set as 90. In the full L1/H1 interferometer .kat files, these are tuned even further to the (tenth?!) decimal place, but I think these values suffice for out purposes.

Results (general note: positive RoC in these plots mean a concave surface as seen by the beam):

  • Attachments #1, #2 and #3 reproduce the low-level tests performed earlier for this updated model - i.e. I look at the arm transmission with no PRM/SRM, circulating PRC power with no ETMs, and circulating SRC power with no ETMs. Everything looks consistent here... In Attachment #2, there is no legend, but the (almost overlapping) red and green lines are meant to denote the +f1 and +f2 sidebands.
  • Attachments #4 and #5 are a summary of the mode-overlap scans for the PRC and SRC. What I did was to vary the radius of curvature of the RC mirrors (finesse only allows you to vary Rcx and Rcy, so I varied both simultaneously) and calculate the mode overlap between the appropriate pairs of cavities (e.g. PRX and XARM) in the tangential and saggital planes. The take-away here is that there is ~5% mode-mismatch going from an RoC of 1000m to 300m. I've also indicated the sag corresponding to a given RoC - these are pretty tiny, I wonder if it is possible to realize a sag of 1um? I suppose it is given that I've regularly seen specs of surface roughness of lambda/10?
  • Attachment #6 shows the PRC gain (calculated as T_PRC * (transmitted arm power with PRM / transmitted arm power without PRM) as a function of the RoC of PR2 and PR3. As a sanity check, I repeated this calculation with lossless HR surfaces (but with nominal 25ppm losses for AR surfaces of ITMs, and BS etc), shown in Attachment #7. I think these make sense too...
  • Attachment #8 - in order to investigate possible mode mismatch between the arm modes due to different radii of curvature of the ETMs, I kept the ETMY RoC fixed at 57.6m and varied the ETMY RoC between 50m and 70m (here, I've plotted the mode matching efficiency as a function of the RoC of the ETM in the X and Y directions separately - the mode overlap is computed as \frac{1}{\sqrt{2}}(x^2 + y^2) where x and y denote the overlap in the tangential and saggital planes respectively. It would seem that we only lose at most a couple of percent even if the RoCs are mismatched by up to 10m...
  • Attachment #9 - .kat file and the various pykat scripts used to generate these plots...

Next step is to carry out a stability analysis...

Attachment 1: armTransmission.pdf  18 kB  | Hide | Hide all | Show all
armTransmission.pdf
Attachment 2: prcFSR.pdf  20 kB  | Hide | Hide all | Show all
prcFSR.pdf
Attachment 3: srcTransmission.pdf  18 kB  | Hide | Hide all | Show all
srcTransmission.pdf
Attachment 4: modeMatchPRX.pdf  630 kB  | Hide | Hide all | Show all
modeMatchPRX.pdf
Attachment 5: modeMatchSRX.pdf  635 kB  | Hide | Hide all | Show all
modeMatchSRX.pdf
Attachment 6: PRCgainScan.pdf  62 kB  | Show | Hide all | Show all
Attachment 7: PRCgainLossless.pdf  65 kB  | Hide | Hide all | Show all
PRCgainLossless.pdf
Attachment 8: armModeMatchScan.pdf  64 kB  | Hide | Hide all | Show all
armModeMatchScan.pdf
Attachment 9: Finesse_files.zip  11 kB
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