There are lot, depending on your requirements. Anyway you can try: G@KDRv
8@[S,[
1, Refractive: an achromatic as positive + plano-convex as negative; x2sKj"2?@
OR R<
L =&I
2, Reflective: two parabolic mirrors; G6.lRaPu"m
f^-ot@w
Both of them affer nice spherical aberration performance. mW$Oi++'d
7},oY""8
Reminder: compute the laser beam density, ensure you have enough strong optical coating. DcNp-X40I
k`;d_eW
Good luck.