There are lot, depending on your requirements. Anyway you can try: fm(mO%
@~m=5C
1, Refractive: an achromatic as positive + plano-convex as negative; sU) TXL'_!
OR G(U 9rJ9
2, Reflective: two parabolic mirrors; qP~WEcH`[
%
v;e
Both of them affer nice spherical aberration performance. Tub1Sv>J
V]I:2k5
Reminder: compute the laser beam density, ensure you have enough strong optical coating. IDy_L;'`*
:J^qj AV
Good luck.