There are lot, depending on your requirements. Anyway you can try: |y;}zQB-dH
\uqjs+
1, Refractive: an achromatic as positive + plano-convex as negative; F_iXd/
OR P9Yy9_a|x
2, Reflective: two parabolic mirrors; <#=N
m0S$
NL=|z=q
Both of them affer nice spherical aberration performance. : JzI>/
c .3ZXqpI;
Reminder: compute the laser beam density, ensure you have enough strong optical coating. $n^MD_1!
+y7;81ND
Good luck.