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40m Log |
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Mon May 2 17:11:55 2016, rana, Update, COC, RC folding mirrors
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Wed May 18 01:10:22 2016, gautam, Update, COC, Finesse modelling   
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Tue May 24 22:49:02 2016, gautam, Update, COC, Finesse modelling - mode overlap scans 9x
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Tue May 24 23:17:37 2016, ericq, Update, COC, Finesse modelling - mode overlap scans
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Thu Jun 16 15:57:46 2016, gautam, Update, COC, Contrast as a function of RoC of ETMX 
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Thu Jun 16 18:42:12 2016, rana, Update, COC, Contrast as a function of RoC of ETMX
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Thu Jun 16 23:02:57 2016, gautam, Update, COC, Contrast as a function of RoC of ETMX
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Mon Jun 20 01:38:04 2016, rana, Update, COC, Contrast as a function of RoC of ETMX
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Mon Jun 20 18:07:15 2016, gautam, Update, COC, Contrast as a function of RoC of ETMX
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Tue Jun 28 16:06:09 2016, gautam, Update, COC, RC folding mirrors - further checks 
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Thu Jun 30 16:21:32 2016, gautam, Update, COC, Sideband HOMs resonating in arms  
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Sat Aug 13 18:25:22 2016, gautam, Update, COC, RC folding mirrors - Numerical review   
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Tue Aug 16 11:51:43 2016, gautam, Update, COC, RC folding mirrors - Numerical review   
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Tue Aug 16 16:38:00 2016, gautam, Update, COC, RC folding mirrors - Numerical review   
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Wed Aug 17 14:37:36 2016, gautam, Update, COC, RC folding mirrors - Numerical review
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Wed Aug 17 16:28:46 2016, Koji, Update, COC, RC folding mirrors - Numerical review
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Mon Nov 21 15:34:24 2016, gautam, Update, COC, RC folding mirrors - updated specs
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Thu Feb 23 10:59:53 2017, gautam, Update, COC, RC folding mirrors - coating optimization    
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Tue Mar 14 10:56:33 2017, gautam, Update, COC, RC folding mirrors - coating optimization   
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Mon Apr 10 15:37:11 2017, gautam, Update, COC, RC folding mirrors - v3 of specs uploaded 8x
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Message ID: 12120
Entry time: Wed May 18 01:10:22 2016
In reply to: 12103
Reply to this: 12130
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Author: |
gautam |
Type: |
Update |
Category: |
COC |
Subject: |
Finesse modelling |
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I've been working on putting together a Finesse model for the current 40m configuration. The idea was to see if I could reproduce a model that is in agreement with what we have been seeing during the recent DRFPMI locks. With Antonio and EricQs help, I've been making slow progress in my forays into Finesse and pyKat. Here is a summary of what I have so far.
- Arm lengths were taken from some recent measurements done by yutaro and me
- Recycling cavity lengths were taken from Gabriele's elog 9590 - it is likely that the lengths I used have errors ~1cm - more on this later. Furthermore, I've tried to incorporate the flipped RC folding mirrors - the point being to see if I can recover, for example, a power recycling gain of ~7 which is what was observed for the recent DRFPMI locks.
- I used Yutaro's most recent arm loss numbers, and distributed it equally between ITM and ETM for modeling purposes.
- For all other optics, I assumed a generic loss number of 25ppm for each surface
Having put together the .kat file (code attached, but this is probably useless, the new model with RC folding mirrors the right way will be what is relevant), I was able to recover a power recycling gain of ~7.5. The arm transmission at full lock also matches the expected value (125*80uW ~ 10mW) based on a recent measurement I did while putting the X endtable together. I also tuned the arm losses to see (qualitatively) that the power recycling gain tracked this curve by Yutaro. EricQ suggested I do a few more checks:
- Set PRM reflectivity to 0, scan ETMs and look at the transmission - attachment #1 suggests the linewidth is as we expect
- Set ETM reflectivity to 0, scan PRM - attachment #2 suggests a Finesse of ~60 for the PRC which sounds about right
- Set ETM reflectivity to 0, scan SRM and verify that only the 55 MHz sidebands resonate - Attachment #3
Conclusion: It doesn't look like I've done anything crazy. So unless anyone thinks there are any further checks I should do on this "toy" model, I will start putting together the "correct" model - using RC folding mirrors that are oriented the right way, and using the "ideal" RC cavity lengths as detailed on this wiki page. The plan of action then is
- Evaluating the mode-matching integrals between the PRC and the arm cavities as a function of the radius of curvature of PR2 and PR3
- Same as above for the SRC
- PRC gain as a function of RoC of folding mirrors
- Mode overlap between the modes from the two arm cavities as a function of the RoC of the two ETMs (actually I guess we can fix RoC of ETMy and just vary RoC of ETMx).
Sidenote to self: It would be nice to consolidate the most recent cavity length measurements in one place sometime... |
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