There are lot, depending on your requirements. Anyway you can try: tb,.f3;
\3K 6NA!L
1, Refractive: an achromatic as positive + plano-convex as negative; ^|}C!t+
OR zjgK78!<
2, Reflective: two parabolic mirrors; Wu)ATs}
+C7
1".i-
Both of them affer nice spherical aberration performance. aKs!*uo0H
Bc}<B:q%b
Reminder: compute the laser beam density, ensure you have enough strong optical coating. P
Y
+~,T2
>V(>2eD'S
Good luck.