There are lot, depending on your requirements. Anyway you can try: !4.VK-a9V%
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1, Refractive: an achromatic as positive + plano-convex as negative; 58[=.rzD
OR
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2, Reflective: two parabolic mirrors; FIMM\W
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Both of them affer nice spherical aberration performance. `T'[H/
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. WiU-syNh
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Good luck.