There are lot, depending on your requirements. Anyway you can try: 1*]@1DJt
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1, Refractive: an achromatic as positive + plano-convex as negative; K~jN"ev
OR csms8J
2, Reflective: two parabolic mirrors; giu8EjzK
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Both of them affer nice spherical aberration performance. j?s+#t
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. J85Kgd1
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Good luck.