There are lot, depending on your requirements. Anyway you can try: jSpj6:@B
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1, Refractive: an achromatic as positive + plano-convex as negative; 0U7Gl9~
OR ^`!+7!
2, Reflective: two parabolic mirrors; *+*W# de.
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Both of them affer nice spherical aberration performance. _".h(
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. 8=$X hC
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Good luck.