David Notebook: Difference between revisions

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/0/05index.php/File: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 16,000. The cavity linewidth is just the FSR/finesse, so it would be ~95 KHz, so with our ~500 KHz linewidth laser, and even very rough spatial coupling, we should still have been getting some 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.