There are lot, depending on your requirements. Anyway you can try: i;#AW($+a
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1, Refractive: an achromatic as positive + plano-convex as negative; 7D4I>N'T
OR /j:-GJb*!u
2, Reflective: two parabolic mirrors; UQ2;Dg G%
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Both of them affer nice spherical aberration performance. Csm23QLsg)
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. ZQ~EaI9R
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Good luck.
