There are lot, depending on your requirements. Anyway you can try: /93z3o7D>
@o^$/AE?
1, Refractive: an achromatic as positive + plano-convex as negative; D_ ~;!^
OR '<uM\v^k
2, Reflective: two parabolic mirrors; $e--"@[Y
|B*B>P#
Both of them affer nice spherical aberration performance. jX(${j<
4\ *:Lc,-
Reminder: compute the laser beam density, ensure you have enough strong optical coating. Ldv,(ZV,<
=s]2?m
Good luck.