There are lot, depending on your requirements. Anyway you can try: %u{W7
2pHR_mrb
1, Refractive: an achromatic as positive + plano-convex as negative; Lju7,/UD
OR Y+%sBqo@
2, Reflective: two parabolic mirrors; n7aU<`U
j'%4{n
Both of them affer nice spherical aberration performance.
8Chj
w wB
W~T}@T:EN
Reminder: compute the laser beam density, ensure you have enough strong optical coating. U09.Y
;|%dY{L-
Good luck.