I am in the process of rebuilding the Mach Zehnder with the following goal:
I want the entire experiment to live inside one box, readout included. To this end I needed to compactify the Mach Zehnder somewhat.
In realigning the ovens, I looked closer at the crystal which was giving me problems before (the exact same behavior). When I look through it, I can see what looks like damage through the center of the crystal. This is consistent with the crazy behavior I get where aligning through the center of the crystal produces terrible beam profiles.
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I will proceed with the experiment, having to go with some funny alignment.