David Notebook: Difference between revisions

I've been aligning the 780 TA to a fiber so that the output will be single mode and Gaussian. This was more difficult than I hoped it would be, but all the problems in the end seemed to be from the having the wrong aspheres for the fiber launches. I'm only getting about 20-25% power through the fiber. Around 40% should be achievable, but I'm not really concerned about power as much as conversion efficiency at this point. There's about 50 mW just before the cavity with the chopper on, so there should be about 34 inside. After re-aligning the 780 beam, I'm getting just under 3 nW unchopped power at the photodiode, giving a conversion efficiency of about <math> 3.3*10^{-7} </math>. This is higher than without the fiber, but not the big jump I was hoping for. Adjusting the polarization of the 780 helped with 633 generation a little. I'm guessing the main problem at this point is that the 780 isn't fully overlapped with the 1064. 633 generation seems much more sensitive to the 780 alignment this time, which suggests the beam is smaller (a good thing). We previously had a 150 mm -C lens to focus the 780 into the cavity, which didn't seem the best choice given that there is about 400 mm of path from it to the middle of the cavity. I replaced it with a 400mm -B lens, but haven't checked the beam size. Next steps should be measuring the beam size and seeing what can be done to reduce it and ensure the beam is smaller than the 1064 or at least focuses in the middle of the cavity.