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CVI laser makes UVFS 3 inch diameter wedge with 3 degree angle. Successive-reflection beams on same side emerge 6 degrees apart, with slight displacement. Sin(6 deg) = 0.1, so for 1m length the separation is 10cm = 4 inches. That's about right!. The Thor Labs rectangular beamsplitting wedge is 5 degree angle.
spherical aberration is tolerable as long as beam is slower than about f/8. If we design for f/10 then this ought to work well
Note that this is also somewhat dispersive, which is actually a plus.
Source needs to be on-axis for spherical reflector, otherwise we get off-axis aberrations (coma, in partticular).
Radius of spherical side of Plano-convex lens has to be 3 inches more than radius of meniscus lens. Maybe we just do away with that, and the whole thing is long?
Diffraction limit for 3 inch output beam is 1.3 arcsec at 500 nm. for 75mm footprint on reflector, and 2m focal length, f/number is 75/2000 = 27. So diffraction-limited spot at 500 nm is 0.5 microns * 27 = 12 microns. Good match to 10 micron pinhole.
If we eliminate the meniscus lens, the reflector only needs to be twice the beam size, or 6 inches in diameter.
We could bond a wedge to back of plano-convex lens to send second reflection off in a different direction.
It's also useful to move solar cell further back so its surface reflections don't bounce back from lens backside.
Purchases
Lambda optics 2 inch concave mirror blanks, polished both sides.
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