User:Linh N Le/Notebook/2009/06/25

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To Do
11-6
 * Profile Evan's laser
 * Move stuff into the other lab
 * Get access to the other lab (key)
 * Play with the chemicals list some more (Need to talk to Andy about this)

Laser + new lab

 * Koch doesnt want me to take kochlab-daq2 to the new lab, so i will try to dig up an older computer to do so
 * We did set it up and took a look yesterday
 * The laser is 1.6W, Koch advises me to be extra careful with this laser
 * Also need Andy to tell me where the IR imaging cards are
 * Will try to use the CCD camera and labview to analyze the beam
 * We will try it at it's threshold power to for safety
 * Will then try with ND filters
 * Eventually we want to try it out at full power, but I'm afraid of melting ND filters
 * CCD Cam successfully installed on daq2

Laser Images

 * Currently, the laser has been running for ~20mins, which should be sufficient warm up time
 * I will trying to look at the laser with its power ~38mW
 * Note: Koch set it to 50mw, then before i left to get some optics it was 43mw, now its only saying 38mw
 * Will also place a ND3 filter in front of the CCD
 * Took a pic at 13in away, nd 3 filter, 8.65A, 11% .02W

Analysis

 * It has been almost a year since the last time I tried doing this, so I kinda forgot how I did it
 * Here are the notes from when I did it last year. They are on the private wiki so those w/o access can email me if they really want to read them
 * For the second photo, the max value is only 248, meaning that the photo is not saturated (255 is saturated according to me last year)
 * Following my old methods, multiply 248 by 1/e^2 = 33.5
 * pixles 220 and 476, distance of 256.
 * 256 times 5.6e-6 1.4e-3 meters
 * 1.4mm
 * We did it again at a further distance. got a worse pic and a smaller beam width?
 * Giving up, we tried beam expanders
 * The beam expanders did work a bit, but we were unsure how to image that beam
 * We tried the nightvision camera, but it was over saturated by the laser
 * End note: Koch feels that trying to beam profile is possible but much too time consuming
 * He wants to try to tweeze with the anyway
 * I wonder how we will know where the beam waist is w/o this data. I guess I do have 1 measurement of the beam diameter
 * Steve Koch 23:12, 25 June 2009 (EDT): Good point -- I thought I knew, but did some poking around and realized I know even less about lasers than I thought. I had been told previously that the beam waist is usually at the output coupling mirror, but now I'm not sure.  See: optical cavity configurations.  Then this picture confused me: beam diagram.  In any case, I think the practical answer is that once we beam expand, the imaged (virtual) beam waist is very far back in space -- many meters, I'd guess ... and thus it doesn't matter much.
 * Andy Maloney 00:00, 26 June 2009 (EDT): I agree with Koch about not really caring about the waist directly from the laser. However, if you really want to do it then I'd suggest kicking it 80's razor blade style. This is where you put a razor blade some distance from the laser and move it across the beam. At 86% and 33% of the total power of the beam, you have your 1/e2 values thus giving you the beam diameter. Do it again farther downstream and you can calculate the beam divergence.
 * Steve Koch 00:28, 26 June 2009 (EDT): Yeah that's a good idea. Linh was really good at the beam chopper, which is similar.  We probably picked the wrong thing to try first, though I was interested in the 2-D picture.  It'd be worth doing either of these things, except that I think days count a lot now.  You agree?


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