There are lot, depending on your requirements. Anyway you can try: zf2]|]*xz
i mJ{wF
1, Refractive: an achromatic as positive + plano-convex as negative; m qtl0P0
OR [Ma&=2h
2, Reflective: two parabolic mirrors; |QxDjL<&t4
\!s0VEE
Both of them affer nice spherical aberration performance. # {!Qf\1M
9-)oA+$
Reminder: compute the laser beam density, ensure you have enough strong optical coating. B4&x?-0ZC
K3 "co1]u
Good luck.