There are lot, depending on your requirements. Anyway you can try: HH'5kE0;d
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1, Refractive: an achromatic as positive + plano-convex as negative; d# q8-
OR ZVz`-hB
2, Reflective: two parabolic mirrors; }B2qtb3
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Both of them affer nice spherical aberration performance. `rI[
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. %1e{"_$O9
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Good luck.