There are lot, depending on your requirements. Anyway you can try: {&2aH>V/
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1, Refractive: an achromatic as positive + plano-convex as negative; woctnT%"Q/
OR 'l%b5:
2, Reflective: two parabolic mirrors; 7X
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Both of them affer nice spherical aberration performance. gEVN;G'B<=
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. }klET
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Good luck.