There are lot, depending on your requirements. Anyway you can try: GA(OK-WUd
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1, Refractive: an achromatic as positive + plano-convex as negative; -<]\l3E&J
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2, Reflective: two parabolic mirrors; ]!]`~ Z/
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Both of them affer nice spherical aberration performance. $xLEA\s
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. BvSdp6z9Iv
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Good luck.