There are lot, depending on your requirements. Anyway you can try: W,oV$ s^
+w}%gps
1, Refractive: an achromatic as positive + plano-convex as negative; w!Lb;4x ?
OR ne~#{q
2, Reflective: two parabolic mirrors; -){^
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gdn,nL`dP
Both of them affer nice spherical aberration performance. 5>k~yaju/
Z.Y8 z#[xg
Reminder: compute the laser beam density, ensure you have enough strong optical coating. sVl:EVv
GISI8W^
Good luck.