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Entry  Wed Jul 14 14:39:09 2010, Dmass, Laser, PSL, H1 NPRO Measured NPROWaist.pdf
    Reply  Thu Jul 15 15:41:40 2010, Dmass, Laser, PSL, H1 NPRO Measured 
       Reply  Fri Jul 16 18:54:57 2010, Dmass, Laser, PSL, H1 NPRO Measured H1ModeMSoln.pdf
          Reply  Sat Jul 17 01:41:20 2010, Koji, Laser, PSL, H1 NPRO Measured 
          Reply  Wed Jul 21 20:13:06 2010, Dmass, Laser, PSL, H1 NPRO Measured H1NPRO_AM.png
             Reply  Thu Jul 22 16:19:48 2010, Koji, Laser, PSL, H1 NPRO Measured 
             Reply  Fri Jul 23 00:45:46 2010, Dmass, Laser, PSL, H1 NPRO Measured 
                Reply  Tue Jul 27 00:10:20 2010, Dmass, Laser, PSL, PMC Calibrated PMCCtrl.pdf
             Reply  Tue Jul 27 19:04:35 2010, Dmass, Laser, PSL, H1 NPRO Measured NproPZTFMBode.pdf
                Reply  Wed Jul 28 19:51:10 2010, Dmass, Laser, PSL, H1 NPRO Measured IMG_0241.png
                   Reply  Fri Jul 30 16:48:11 2010, Dmass, Laser, PSL, H1 NPRO Measured 
                      Reply  Sun Aug 1 18:37:07 2010, Dmass, Laser, PSL, H1 NPRO Measured 
                   Reply  Mon Aug 2 00:46:13 2010, Dmass, Laser, PSL, H1 NPRO Measured Picture_2.png
    Reply  Mon Aug 2 22:23:36 2010, Dmass, Laser, PSL, H1 NPRO Measured H1MM2PMC.pdf
    Reply  Tue Aug 3 01:31:15 2010, Dmass, Laser, PSL, H1 NPRO Measured H1NPROWaist2.pdf
       Reply  Tue Aug 3 13:47:55 2010, Dmass, Laser, PSL, H1 NPRO Measured Npro2PMCmm.pdf
       Reply  Tue Aug 3 17:27:20 2010, Dmass, Laser, PSL, H1 NPRO Measured 
Message ID: 897     Entry time: Tue Aug 3 13:47:55 2010     In reply to: 896
Author: Dmass 
Type: Laser 
Category: PSL 
Subject: H1 NPRO Measured 

Quote:

I redid the NPRO measurement and got this:

 

This might explain some of the rediculousitude of my inability to get mode matching to make sense...

 This explains something. The chronological story (elog entries hyperlinked):

  1. I measured the waist of the NPRO (either I did it wrong, or it changed with temp/current)
  2. I calculated the mode matching for that waist, with 250mm and 200mm lenses
  3. I put them on the table in what I calculated to be the right spot
  4. I measured the waist of the input beam via the transmission through a steering mirror at the PMC waist
    1. It was grossly wrong
  5. I adjusted the mirrors by hand to give it the right waist (call these positions X1 and X2)
  6. I aligned into the PMC, and locked it, and noticed I only had about 25% transmission
  7. I measured the PMC waist
  8. I tried to adjust the lens positions by hand, hoping that my mode matching solution was sensitive to position / focal length errors.
    1. I moved the lenses by about a half inch in a few directions, realigning common/differential steering into the PMC each time
    2. I noticed no appreciable gain in any direction
    3. This is not surpising because I set the position of the lenses by forcing a 371 um waist at the PMC waist location
  9. I looked at the mode coming out of the laser, and on the PMC reflection
  10. I despaired that I might just not have much power in my TEM00
  11. I measured the beam profile after my first mode matching lens as a sanity check (250 mm focal length at 18 in) - plot at bottom of this elog
    1. I noticed that I couldn't get fits which were all that good - does this mean my M^2 is high?
  12. I redid the mode matching into the PMC with new lenses, aligned them into the PMC, locked it, and noticed a donut mode on REFL
    1. This is indicative of my mode matching being terrible
    2. I measured the waist with the wincamD at the PMC, it was WAY off (2mm instead of 370 um)
  13. I redid the beam waist measurement of the NPRO
    1. It looks drastically different
    2. I have changed both laser current slightly, and had feedback to the temperature
    3. I dont know if the above could cause that huge of a mode shift, or if it's just a somehow failed measurement with the wincamD. It's NOT a factor of 2.
    4. It had a funny mode shape (to be attached)
  14. I redid the mode matching with the new NPRO waist, and old lenses, and got the attached plot
    1. This is very similar to the first set of positions which I got moving the lenses by hand and using the wincamD, which leads me to believe the mode matching was roughly fine in the first place.
  15. I expect to find similar crappy (~25%) power transmission with this (old/new) mode matching solution and the "new" beam waist measurement, as I think I already did just this on the table
  16. If this is the case, I wonder if using a different laser is better...
  17. I was thinking of doing a cavity scan to see if there was a lot of "junk"
    1. If I do a cavity scan, will I see all the modal power? - that is to say, if I have a lot of higher order content, will it necessarily resonate in the cavity at some length
    2. Maybe what I'm asking is "do the resonant mode of the cavity form a complete basis for the HG laser polynomials?"
    3. Intuitively it seems like I could just get "unlucky" and have a lot of power in misc. mode which happen to not resonate strongly / at all in the cavity when my 00 is aligned perfectly - I'm half expecting someone to respond and let me know that this is not possible, and if I lock the cavity and align to 00, then scan, I have to see the higher order content I have in transmitted power.
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