SED Machine Laser Alignment of Field Splitting Mirror
The sed machine simultaneously images a large 12' field of view with the rainbow camera, as well as a small 30" field with an integral field spectrograph. The 60" telescope has an angular scale of 64 µ/arcsecond. This means that the focal surface that the spectrograph subtends is less than 2 millimeters on a side. It's hard to find such a tiny little mirror that also covers the broad wavelength range of SEDM (0.37 µ - 0.92 µ). Instead I've designed the field to be picked off with a prism that operates in total internal reflection.
The prism has to be precisely aligned to be perpendicular to the optical axis of the telescope. Instead of relying on precision machining to align the prism (as I did for all other optics) the prism is aligned by hand. I use a UV-curing glass-to-metal epoxy which allows me to tweak the prism and then fix its position when I'm satisfied. I'm using a HeNe laser to align the prism as can be shown in the setup below.
The final result is that the prism is aligned to better than 1 arcminute (or better than 1 µ from one end of the prism to the other). Great!