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David Notebook: Difference between revisions
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==Daily Log==
'''1/20/14'''
I put an arrow on the backpolished E03 mirror pointing towards the side that was facing upwards in the packaging. I think this is the "back" side that is less well polished. The mirror didn't seem to help the signal strength though, and in fact made it worse. I flipped the mirror around too in case I got it in backwards, but I didn't notice any change. The problem now is probably that it is poorly impedance matched because the reflectivities are so different, which apparently is a thing. I'm seeing if Thorlab can make us a custom curved mirror (2 E03s would give a finesse of ~500) and I'm talking to Layertec about making a pair in the 2000-3000 range. We want the highest finesse we can get away with that will still be easy to lock and stay locked, but we're not sure what value that will end up being.
'''1/15/15'''
Zach and I both kept having trouble getting much transmitted signal and any reflected signals. We thought maybe we weren't mode matched well, but we'd both tried a few times and that didn't seem to be it. It was also possible that the laser linewidth was much bigger than the cavity linewidth. I made a python thing [https://wiki.physics.wisc.edu/yavuz/images/0/05/Cavity_coupling_efficiency.zip here] that calculates the power of an incident beam that is coupled into a cavity based on the spatial and frequency profiles. The cavity mirrors listed a selectivity of about 99.98%, which would give a finesse of around 8,000. The cavity linewidth is just the FSR/finesse, so it would be ~190 KHz, so with our ~500 KHz linewidth laser, and even very rough spatial coupling, we should still have been getting plenty of power. We thought maybe the radius of curvature of one of the mirrors was wrong, but we took out the cavity mirror and found that it focused a collimated beam at ~25 cm, which would give the correct R of 50cm. In retrospect this probably wouldn't have mattered as much as we thought--the spatial coupling curve is quite forgiving.
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