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--[[User:Zjsimmons|Zjsimmons]] ([[User talk:Zjsimmons|talk]]) 22:13, 2 December 2014 (CST)
Spent much of the day messing with the Fabry-Perot cavity. I removed the cavity and checked to see what the beam looks like in the position of the cavity; it looks very similar to what my ABCD matrix script predicts if i remove the input coupler, so i am confident that my mode-matching is decent. I mentioned before that i did not see a Finesse above about 20, it turns out these were not the cavity resonances we were looking for. Nick suggested looking at more extreme orientations. I turned the cavity 90deg in its mount, i.e. rotated the whole can, and then searched for more peaks. Then i saw much sharper peaks, finesse>500. My leading theory is that when i glued the piezo back on, i must have glued it off-center. This led to the cavity resonance mode being at a weird angle and thus hard to find. Perhaps the crappy peaks we were seeing were etaloning between a cavity mirror and the windows? or some other cavity-like effect? Those peaks were very clean, we didn't see neighboring modes, they also benefited slightly from turning the polarization, two differences from what we see now.
Now the finesse looks like it's more like 500, 1.5GHz FSR cavity so about ~few MHz wide resonances, comparable linewidth to the laser. Also the cavity features are narrow enough that we can resolve the EOM sidebands. I stuck a cube in the beam path and now i can resolve corresponding dips in the reflection off the front of the cavity. Spent time tuning up the cavity mode-matching but was unable to kill a feature sitting on the side of the main peak.
Hopefully we can get the electronics all set up now that this cavity is working better.
--[[User:Zjsimmons|Zjsimmons]] ([[User talk:Zjsimmons|talk]]) 17:46, 1 December 2014 (CST)
Yikes, it's Dec, where has the semester gone. I have the "1030" Fabry-Perot that we have from QC set up. It doesn't look that great, but hopefully works well enough for us to set up the PDH electronics. Planning to work on that tomorrow.
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