There are lot, depending on your requirements. Anyway you can try: ]e"NJkcm
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1, Refractive: an achromatic as positive + plano-convex as negative; {H>iL
OR 5 !NPqka}.
2, Reflective: two parabolic mirrors; 2G'G45Q
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Both of them affer nice spherical aberration performance. oFIs,[Go
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. k2;8~LqF
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Good luck.