There are lot, depending on your requirements. Anyway you can try: 8}^R jMgI
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1, Refractive: an achromatic as positive + plano-convex as negative; t@Bl3Nt{
OR wUj#ACqB
2, Reflective: two parabolic mirrors; x e!([^l&
3 cb$g
Both of them affer nice spherical aberration performance. RdirEH*H
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w
Reminder: compute the laser beam density, ensure you have enough strong optical coating. GjfPba4>
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Good luck.