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Message ID: 1307     Entry time: Wed Feb 16 00:18:27 2011
Author: Zach 
Type: Laser 
Category: GYRO 
Subject: AOM set up, CCW and CW beams power-balanced @ ~80 mW 

 This evening, I set up the AOM double-pass and balanced the two beams going to the injection/extraction optics. This wasn't as simple as last time because I had to re-profile the beam and come up with a modematching solution. I've updated my recent "status" post to reflect the current status.

Here is the profile after the mirror leading into the AOM:


The beam was slightly elliptical and somewhat astigmatic (|z0x - z0y| ~ 10 cm). Using the average of x and y, I came up with a simple matching solution using an f = 100mm lens and the R = 30cm mirror we were using before. It puts the mirror roughly 30cm from the AOM, and the waist of about 124um near the center of the crystal. Here is the ABCD screenshot:


I was able to isolate the double-passed 1st-order beam with an overall efficiency of ~45% (i.e. single-pass efficiency of ~67%). This is slightly worse than before, but the output beams are very close together so it is difficult to know whether we actually had it better before at all. In any case, I balanced the beams heading toward the injection optics at about 80 mW apiece, which is more than what we were counting on already. There is still some power dumped just after the laser, so there is still room to step up the power a bit more should we need it. Here's a picture of the setup as it stands---I am holding an IR card to show where the two beams are going:




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