There are lot, depending on your requirements. Anyway you can try: ^C;ULUn3
5B;;{GR
1, Refractive: an achromatic as positive + plano-convex as negative; JY$;m3h
OR l@>@2CB
2, Reflective: two parabolic mirrors; Lo}zT-F
C%"aj^u
Both of them affer nice spherical aberration performance. !~Kg_*IT
~P"o_b6,k
Reminder: compute the laser beam density, ensure you have enough strong optical coating. `Yyi;!+0
8#RL2)7Uy`
Good luck.