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David Notebook: Difference between revisions
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==Daily Log==
'''4/
Eventful last couple weeks. I finally ordered the new computers and Nick and I spent a productive day building them. We also won a SWAP auction for 30 monitors for only $375. Every computer in the lab will have 2 monitors minimum now. I spent a while writing a python program to calculate what lenses to put where to mode match a beam to the cavity (or to any shape). The orange laser was just so big by the time it got to the table it was hard to just eyeball it with lenses. I'll probably still make a few edits but I'll put the program up eventually---it worked great and the beam is pretty well focused through the cavity now.
I ordered a fast 2 GHz photodetector from Thorlabs--the DET025AL. Since the rep. rate of the orange laser is 100 MHz, I was hoping we'd see pretty high peak intensity on this, but so far I can't see any AC signal. I think maybe this one is just defective. In the meantime, I'm going to not try to detect individual spectral components and just the whole modulated beam. So no monochromator, just short pass filters to let through light under 800 nm. Using the same settings as when I did this for 780, I get fluctuations of around 75 mV out of the lock-in. Roughly 1 nW=1.77 V, so with only 10 mW incident on the cavity, it might be a little rough seeing a signal.
'''4/17/15'''
The beam quality is somewhat lacking with the orange laser, which makes it hard to match to the cavity mode--it's currently very poorly matched which is at least part of why I can't detect anything. It doesn't really behave as you'd expect when it's collimated. I checked how well it would focus--with a 40mm lens, I got to to about 30x60 micron diameter. The beam was about 5 mm before, so the diffraction limited spot should be closer to 10 microns. Still, we only need to focus to about 800 in the cavity, so no big deal hopefully. I'm vaguely trying to write a python thing so that I can say what initial beam I have and what I want to be and it tells me the best lenses to put where.
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