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Entry  Wed Mar 30 19:43:33 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching 
    Reply  Wed Mar 30 19:54:19 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching laser_output_non_circular.png
       Reply  Wed Mar 30 20:08:34 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching Beam_Matching_02c_Vertical.pngBeam_Matching_02c_Horizontal.png
          Reply  Wed Mar 30 20:14:17 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching 
             Reply  Wed Mar 30 20:31:30 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching 
                Reply  Wed Mar 30 20:50:43 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching After_Faraday.pngAfter_Faraday_and_Rotated_Lens.png
                   Reply  Wed Mar 30 21:21:15 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching Oven_Lens_Solution_66mm.pngMatching_Into_Green_Oven_zoomed_out.pngMatching_Into_Green_Oven_zoomed_in.png
                      Reply  Thu Mar 31 02:59:49 2011, Koji, Configuration, Green Locking, The wonderful world of mode-matching 
                         Reply  Thu Mar 31 14:10:00 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching P3310028.JPGP3310029.JPG
                         Reply  Thu Mar 31 15:23:14 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching Zoomed_out_fitting01.pngZoomed_in_fitting01.png
                            Reply  Mon Apr 4 14:20:32 2011, Bryan, Configuration, Green Locking, The wonderful world of mode-matching Waist_Fits_from_laser.pngWaist_Fits_Bench_Position.png
Message ID: 4464     Entry time: Wed Mar 30 19:43:33 2011     Reply to this: 4465
Author: Bryan 
Type: Configuration 
Category: Green Locking 
Subject: The wonderful world of mode-matching 

Right. I've got a whole load of info and data and assorted musings I've been saving up and cogitating upon before dumping it into these hallowed e-pages. there's so much I'll probably turn it into a threaded entry rather than put everything in one massive page.

An overview of what's coming:

I started out using http://lhocds.ligo-wa.caltech.edu:8000/40m/Advanced_Techniques/Green_Locking?action=AttachFile&do=get&target=modematch_END.png as a reference for roughly what we want to achieve... and from http://nodus.ligo.caltech.edu:8080/40m/100730_093643/efficiency_waist_edit.png we need a waist of about 50um at the green oven. Everything else up to this point is pretty much negotiable and the only defining things that matter are getting the right waist at the doubling oven with enough available power and (after that point) having enough space on the bench to separate off the green beam and match it into the Y arm.

 

So…

Step 1: Measure the properties of the beam out of the laser. Really just need this for reference later because we'll be using more easily measurable points on the bench.


Step 2:
Insert a lens a few cm from the laser to produce a waist of about of a few 100um around the Faraday. Note that there's really quite a lot of freedom here as to where the FI has to be - on the X arm it's around columns 29/30 on the bench, but as long as we get something that works we can get it closer to the laser if we need to.


Step 3:
After inserting the FI need to measure the beam after it (there *will* be some distortion and the beam is non-circular to begin with)


Step 3b:
If beam is non-circular, make it circular.


Step 4:
Insert a lens to produce a 50um waist at the doubling oven position. This is around holes 7/8 on the X arm but again, we're free to change the position of the oven if we find a better solution. The optical set-up is a little bit tight near that side of the bench on the X end so we might want to try aiming for something a bit closer to the middle of the bench? Depends how the lenses work out, but if it fits on the X end it will fit on the Y end.

 
Oh... almost forgot. While I've been doing most of the grunt-work and heavy lifting - thanks go out to Suresh, Kiwamu, Koji, Steve and everyone else who's helped out with discussion of results and assorted assists to numerous to mention.

 

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