There are lot, depending on your requirements. Anyway you can try: ;E3>ay6m8
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1, Refractive: an achromatic as positive + plano-convex as negative; M$>1L
OR EkjN{$*
2, Reflective: two parabolic mirrors; 8L:ji,"
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Both of them affer nice spherical aberration performance. 1Y7Eajt-5
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. ]);%wy{Ho
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Good luck.