There are lot, depending on your requirements. Anyway you can try: QIw.`$H+
1a'JNe$
1, Refractive: an achromatic as positive + plano-convex as negative; @@5u{K
OR O$$N{
2, Reflective: two parabolic mirrors; 4?&=H
*H:
$^l=#tV
Both of them affer nice spherical aberration performance. -P?}
qy^j(
A@#dv2JzP
Reminder: compute the laser beam density, ensure you have enough strong optical coating. brFOQU?
MT*b+&1e
Good luck.