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David Notebook: Difference between revisions
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==Daily Log==
'''7/17/14'''
I'm trying to calibrate the chopper/lock-in system to get better measurements of the 633 power and make sure our conversion efficiency numbers are accurate. I cut the power of the HeNe beam with irises to 20 nW as measured on the power meter (filters might have been better so that the intensity is reduced too, but I couldn't find a good combination to get the power I wanted. It probably won't matter since there is a lens in front of the photodiode anyway). However using the lock-in and my previous procedure to convert photodiode signals to power, I calculated only 1.25 nW.
Jared and I have both thought that the visible power meter head has been giving somewhat high values (10% or so), so I'm skeptical of it's readings. However, further investigation of the lock-in reveals it is supposed to always multiplies the output by an additional 10V, regardless of the settings. Page 21 of the manual alludes to this, but I couldn't find a full description. I measured this value as closer to 9 though--I used a function generator to send in a square wave at 500 Hz with a max amplitude of 2V and a min of 0V, similar to the type of signal the photodiode should send in. With the gain setting on the lock-in as "1V" or "1μA", the output was 9V. A 100 mV average value square wave gave 0.9V.
'''7/16/14'''
In addition to increasing absolute power of the 633 generated, we also want to improve the conversion efficiency. The 780 beam is larger than the 1064 in the cavity, so this will greatly limit efficiency. Maybe try a prism pair to reduce anisotropy or a fiber to make beam Gaussian? Power will be reduced, but efficiency should be higher.
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