There are lot, depending on your requirements. Anyway you can try: %FS;>;i?
\Da~p9T&
1, Refractive: an achromatic as positive + plano-convex as negative; FOp_[rR
OR 2u&c
&G
2, Reflective: two parabolic mirrors; #NF+UJYJ&'
7SHo%bA
Both of them affer nice spherical aberration performance. 7.|S>+Q
\UQ],+H
Reminder: compute the laser beam density, ensure you have enough strong optical coating. Qa?QbHc
y''V"Be
Good luck.