There are lot, depending on your requirements. Anyway you can try: K!]1oy'V
* C6a?]
1, Refractive: an achromatic as positive + plano-convex as negative; zBJ7(zh!
OR NbGV1q']
2, Reflective: two parabolic mirrors; y:h}z).
C,pJ`:P
Both of them affer nice spherical aberration performance. -atGlu2
OLvcivf
Reminder: compute the laser beam density, ensure you have enough strong optical coating. @;H,gEH^
]/B$br'O{?
Good luck.