There are lot, depending on your requirements. Anyway you can try: [aM'
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1, Refractive: an achromatic as positive + plano-convex as negative; 2
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OR %::deV7
2, Reflective: two parabolic mirrors; d
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Both of them affer nice spherical aberration performance. hN_f h J
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. ;y~{+{{Ow
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Good luck.