There are lot, depending on your requirements. Anyway you can try: [-0=ZKH?
"8$Muwm
1, Refractive: an achromatic as positive + plano-convex as negative; J4]tT pu"K
OR cd&sAK"
2, Reflective: two parabolic mirrors; 1f+z[ad&^
rDWwu'
Both of them affer nice spherical aberration performance. &s8vmUt
:bq${
Reminder: compute the laser beam density, ensure you have enough strong optical coating. OwN~-).%-
*kt|CXxAS8
Good luck.