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--[[User:Zjsimmons|Zjsimmons]] ([[User talk:Zjsimmons|talk]]) 13:18, 28 November 2014 (CST)
A few updates. I spent much of last week modifying/constructing a lockbox for the PDH set-up utilizing the ULE cavity. I feel like i was able to apply some lessons learned from the last time around to aid assembly this time, principally putting it in a larger box made it easier to put together. Unfortunately, the cavity has a fatal problem and will be returned. They mirror glass is oriented the wrong direction giving structure on transmission and acting like a grating. Hopefully in the meantime we can get something else working to at least let us set up some of the electronics. Toward that end, we're working on two fronts:
a) we're trying out a "1030nm" cavity borrowed from quantum computing. The cavity is about 101mm in length and contains an internal label: HHR-R1030 R=100mm 1030nm 99.9805%. This gives it a FSR of about 1.5GHz.
I could not see very good peaks with it earlier this week but it appears that the laser was at fault. I am seeing decent peaks now, although they are not great. Based on mirror reflectivity we would expect very high Finesse, >1000, more like 15000, using labled reflectivity:.999805. However this is for 1030nm, at 1055 it could be significantly lower. However even if it was only 99% (couldn't find a datasheet/know exactly what the mirrors are) at 1055, we'd still expect a finesse of ~300. I observe a finesse of more like 20. Could there be something wrong with the laser? 80MHz seems crazy wide for our laser linewidth. Or is the cavity reflectivity really only <90% at 1055nm? Or is there something i'm missing. Need to spend some more time messing with this cavity.
b) I'm planning to build a temporary stop-gap cavity out of invar or super-invar with the same dimensions as our ULE cavity. I figure this would hopefully allow us to move forward while minimizing time lost as we don't really know how long it will take to get the ULE cavity replaced.
--[[User:Zjsimmons|Zjsimmons]] ([[User talk:Zjsimmons|talk]]) 17:03, 13 November 2014 (CST)
This week has not been so productive in the lab.
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