There are lot, depending on your requirements. Anyway you can try: 'X;cgAq8(
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1, Refractive: an achromatic as positive + plano-convex as negative; 'z ?Hv
OR wXIRn?z
2, Reflective: two parabolic mirrors; $G".PWc
eFG/!b<17
Both of them affer nice spherical aberration performance. {DRk{>K,
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. <T}^:2G|
O] @E8<?^
Good luck.