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David Notebook: Difference between revisions
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==Daily Log==
'''7/7/14'''
Installed a flip mirror for the HeNe, following Nick's advice. Switching between HeNe and 780 beams is much easier now and I am more confident in the alignment of the 780. Using a mirror as we have previously done, I was able to see 633 past the PVC pipe just before the lens, so it is almost certainly hitting the photodiode given that it is getting through the pipe and that I centered it on a photodiode with a lens using the HeNe as a guide. Still though, there is no clear change in signal between having the 780 on or off when locking the 1064. Josh, Deniz, and I tried to come up with explanations as to what could cause this and alternate methods to make the measurement (See Things to Try). We thought maybe a second order beam from the diffraction grating could be angularly close to the 633, but using the grating equation with G=1800 lines/mm, no second order diffracted light should exist above 475 nm, so that seems unlikely. Two 89 THz shifts and one 8.9 THz shift could produce light in the 630 nm range, but this would probably be a weaker signal than the .5 nW we are seeing.
'''7/4/14'''
It still seems that there is no difference in signal whether the 780 is blocked or unblocked, and there is a clear signal of around .5 nW when locking the 1064. The HeNe is not staying very well aligned--I hoped only a horizontal adjustment would be necessary, but it seems unscrewing it from the pedestal creates too much of a vertical change.
'''7/3/14'''
Had some difficulty with the 1064 beam today, see [[David_Notebook#1064_Laser_Notes|1064 laser notes]]. I also realized that even after getting the HeNe laser going through the cavity and hitting the diffraction grating, there was still a fair amount of play with the mirror walks which ultimately could move the beam at the photodiode by a couple inches. The generated 633 beam might be missing the detector then. I put two irises in the 780 beam path after the cavity and separated by a couple feet of path length. After lining up the iris to the 780 beam, I swapped in the HeNe and used its mirror walk (which is independent of the 780 path) to align through both irises and then put the photodiode and lens in this beam path. Hopefully the generated 633 beam will be overlapped with the HeNe path now and is hitting the photodiode. Maybe try using a very large diameter lens before the photodiode so there's more tolerance?
'''7/2/14'''
Decided to try propagating the beams across the lab instead of making a PVC maze in hopes of getting good spacial separation. We borrowed a breadboard from the optics lab and aligned the HeNe through a PVC pipe about 15 feet away from the diffraction grating. The beam then goes through a lens and onto the photodiode mounted on a translation stage. There is still a signal when locking the 1064 beam, even with the 780 blocked
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