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Nick Brewer: Difference between revisions
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Today the cavity is working great. There were a few small peaks between the 0,0 peaks but they were small and I was able to get rid of them by adjusting the mirrors and mode matching lenses. Yesterday's problems might have been a laser issue due to the weather. This morning the humidity was 30%, I'm not sure what it was yesterday but I should keep an eye on how that affects how well the cavity is behaving.
I must have done the <math>I_r/I_{in}</math> measurement wrong on 5/21/14. Today I measured the same finesse that I got two days ago (~65.5%). I looked at the reflected signal before it went through the beam cube and got a similar measurement for <math>I_r/I_{in}</math> (5.4/7.02 = 0.769). I think the reflectivity needs to be measured once the temperature is optimized for green generation. When I did this I got <math>I_r/I_{in} = 0.239</math>, which accounts for a 106 mV noise the photodiode was seeing.
I redid the mode matching calculation with g=0.953, <math>R_{in}=0.0523</math>, and <math>I_r/I_{in} = 0.239</math>. With this numbers I get <math>m=0.759</math>. This is good because it means the cavity is mode matched pretty well, and also that the cavity must be pretty well impedance matched. If the impedance matching is perfect, I think the mode matching coefficient, m, is just <math>1-I_r/I_{in}</math>. In this case, <math>1-I_r/I_{in}=0.761</math>.
According to my Matlab program, we should expect 15.9% conversion efficiency. I was getting 10 mW of green for 65.5 mW of IR, which is 15.3%.
I also got a plastic 1" optics adaptor for the piezo we are using, so we can try that to see if it increases the resonant frequency at all.
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