There are lot, depending on your requirements. Anyway you can try: Es1Yx\/:
-49OE*uF
1, Refractive: an achromatic as positive + plano-convex as negative; ,Epg&)wC]
OR (',G
Ako
2, Reflective: two parabolic mirrors; 8&B{bS
HX?5O$<<N
Both of them affer nice spherical aberration performance. H"6:!;9,
ewD61Y8-
Reminder: compute the laser beam density, ensure you have enough strong optical coating. 76(&O
yin"+&<T
Good luck.