Logan, Michael

We took out the Faraday isolator and set the beam profiler as a reference target. There was 2.7 mW incident. We set the Faraday isolator on a pedestal pillar and aligned it so that the beam profiler shape looks good, with no obvious HOM, and there is a decent amount of power, about 2.3 mW. Maybe not optimal transmission but good enough.

Then we checked the beam profile on the s-pol path. It is still doing that weird behaviour where ithe beam divergence coming out of the waist is about half the rate of beam convergence going into the waist, which applies to both the horizontal and vertical components. I don't know what is causing this, it doesn't seem to be the beam profiler since Hugo took it. I don't think it's anything to do with my Faraday technique since I just took it out of the box and I also did the Faraday for speed meter experiment and that is fine. There is one mode matching telescope before the PBS which seems a bit off centre but I feel like it's not enough to be causing the issue. The laser has a bit of difference between horizontal and vertical size but I think this was the same last time I did the OPO characterization. So I don't know what is causing the problem.

In some sense perhaps it is not important to find out either. That mode matching telescope was originally intended to make a 2.3mm collimated beam, so maybe we should just reset it to the original intention.