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*Measure 780 power before and after cavity; see changes with cavity piezo▼
*Why is reflected 1064 signal fluctuating in power so much?
*What's wrong with the IR viewer?
==Daily Log==
▲'''Things to Do/Check'''
▲Measure 780 power before and after cavity; see changes with cavity piezo
'''6/13/14'''
We set up a diffraction grating over the past two days (G=1800; reflective in visible light region; borrowed from Saffman group), which gives better angular separation between wavelengths than the prism. Using the grating equation,
<math>Gm\lambda=sin(\alpha)+sin(\beta) </math>
(page 22 in Newport Diffraction Grating Handbook), 780nm and 633nm should be separated by about 18.6°. We overlapped a HeNe (λ=632.8 nm) with the 780 laser path, and then used this to figure out where the generated 633 should be. We set up a 1 inch flip mirror for viewing by eye and had the photodiode behind it. This worked very well and we were immediately able to see the 633 in the mirror, which was aided by the fact that it was much smaller than the 4 inch mirror we used before and we could set up the irises using the bright HeNe signal. We could still not see a definitive signal for 633 with the photodiode though, although we are confident we are hitting it or are extremely close. We mounted the photodiode on a translation stage, which we will try adjusting next.
▲make "V" shape with pvc pipes
There was scattered light getting to the photodiode , which is mostly 1064 or one of the generated sidebands, since there is an offset on the photodiode signal that changes while adjusting the 1064 beam power. At its worst, we saw 1-2 nW, and this dropped to a few tenths of a nW after better covering the photodiode. There was also a change in signal corresponding to ramping and locking the 1064 beam, even with the 780 off. The 780 also caused a slight offset on the photodiode, but a much weaker one than the 1064. We're going to try making a non-reflective container to put the photodiode in to get more isolation. Otherwise we'll go with a long path through PVC pipes, which shouldn't be too difficult using the HeNe.
▲make "N" shape with pvc pipes
The power fluctuations in the 780 TA are small and we don't think they are a problem beyond the difficulty they cause in detecting the 633 signal. We're going to ignore them for now and try to better isolate the 633 signal. We're switching out the prism for a diffraction grating and are going to use two
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