March 12, 2022
While successful, implementation of collimated beam projector to date has two issues: 1) dynamic range mismatch between monitor diode (wants nA of current) and astronomical instrument (100,000 electrons per pixel max), and 2) not directly monitoring beam at exit pupil, due to size mismatch.
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At 808 nm:
| angle (degrees) | Rp | Rs |
|---|---|---|
| 0 | 0.041365 | 0.041365 |
| 5 | 0.040948 | 0.041784 |
| 10 | 0.039693 | 0.043069 |
| 15 | 0.037593 | 0.045301 |
| 20 | 0.034640 | 0.048630 |
If angle of incidence is 10 degrees, reflected beam rotates by 20 degrees. If beam of diameter D rotates by theta, distance it must travel to not have incident and reflected overlap obeys tan(theta)=D/L so L/D=1/tan(theta)
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a 50 micron fiber needs to be 12*50 = 600 microns away from a pinhole to generate an f/12 beam.
Disperser
Say we want adjustable dispersion with Risley prism arrangement. At n1sin(theta1) = n2sin(theta2). For small angles we get 1.5*theta1=theta2. deflection is theta1-theta2 = theta1-1.5 theta1 = theta1 *(1-n(lambda)).
Using https://lightmachinery.com/optical-design-center/more-optical-design-tools/prism-designer/
| apex angle | incidence angle | 300 nm angle | 1100 nm angle | difference |
|---|---|---|---|---|
| 1 | 1 | 0.487 | 0.449 | 2.2 arcmin |
| 1 | 10 | 0.4981 | 0.4589 | 2.35 arcmin |
| 10 | 5 | 4.904 | 4.523 | 22.86 arcmin |
This wedge pair needs to be tilted relative to incident beam. Five degree wedge angle seems good, as a pair. That gives us variation from zero to around 30 arcmin. For any sensible focal plane array of 4K x 4K
References
Large optical wedge vendor, example: https://www.precisionoptical.com/precision-optics/optical-flats/unmounted-reference-flat/
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