Diagram of initial board drawing:
Meghan's amended drawing (with a few less background images, and my best attempt at explaining how the system works from current knowledge):
The reference and return photodiodes will convert the light signals they receive into current; from that current, we need information about what wavelengths of light were received. From searching basic information about photodiodes, they have a response parameter (speed/time) determined by the materials out of which they are made, which affects sensitivity in different wavelength regions. For example, PIN photodiodes are faster than P-N photodiodes.
This example PIN photodiode seems to be sensitive to IR and visible light, and has a parameter
Chris' comments Oct 24: Woo Hoo! Well done! As I look at this we can just use the beamsplitter to capture the outgoing light onto a photodiode at the top. We like (and have on hand) Hamamatsu 2281 photodiodes. They mount well in standard 1-inch mounting hardware.
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