Today I balanced the mirror, finished putting together the second photosensor, and finished my photosensor circuit box!
Upon Jamie's suggestion, I have used a translation stage to obtain calibration data points (voltage outputs relative to displacement) for the new photosensor and for the first photosensor.
I will plot these tomorrow morning (too hungry now > < )
Here is a photo of the inside of my circuit box! It is finally done! It is now enclosed in a nice aluminum casing ^ ^