There are lot, depending on your requirements. Anyway you can try: Q9>]@DrAx
$@kw>2
1, Refractive: an achromatic as positive + plano-convex as negative; U9 *2< c
OR 2oG|l!C
2, Reflective: two parabolic mirrors; |u;PU`^-z
KgWT&^t
Both of them affer nice spherical aberration performance. |=T<WU1$
ZG<!^tj
Reminder: compute the laser beam density, ensure you have enough strong optical coating. 'e64%t
odf^W
Good luck.