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spherical aberration: I think this is less of an issue with a plano-convex lens, but we may have to measure it. CWS estimates it's about 1mm of image blur
How about this as a sensor: 
around $1000 from Digikey. We'd have to measure its QE relative to NIST diode. Also now that I think about it we will want a temperature sensor on it as well, and measure QE vs. temperature at red edge of response curve. He's the claimed response curve :
Notes from meeting on 6/9/2023 with Chris and Chuck
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