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David Notebook: Difference between revisions
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==Daily Log==
'''7/30/14'''
Josh says the 1064 beam is closer to 1200-1400 at the ends, so the 780 beam should be pretty good. I'm trying to measure the power of the 633 beam again but am having difficulty. I can see 633 in the mirror, both right after the diffraction grating and at the end of the PVC tube, but I'm not able to get a signal off the lock-in amplifier. I'm using the same settings as when I originally found the signal. There is a lot of noise and also this doesn't seem to change much when I take out the 633 bandpass filter which is surprising since 780 and 633 should be the only signal modulated at 500 Hz.
'''7/29/14'''
I tried a variety of lens combinations again for a telescope, and adjusted the lens positions over a large fraction of the focal distance of the second lens, but they all failed to collimate the beam at the wall (~20 feet) better than just the a-sphere by itself. I've decided to go with just a single lens for now and if this doesn't improve the 633 generation efficiency enough, I'll maybe switch to checking other variables like gas pressure. Calculating the proper focal length for the lens doesn't seem practical since there is about 34 cm of propagation distance before the lens (a distance over which the beam diverges a non-negligible amount) and then 20 cm after the lens before the beam enters the cavity. Finally the cavity mirror will also adjust the focus somewhat. I modeled this setup with a spare cavity mirror and just tried different lenses to see what works best. A focal length of 400mm was a good compromise, giving a beam size of around 930 at the start of the cavity, 630 in the middle, and 1075 at the end. While the 1064 is 810, this is actually only at the center and is somewhat larger at the front and back of the cavity--these sizes for the 780 beam might be alright then.
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