There are lot, depending on your requirements. Anyway you can try: !a~`Bs$'jr
".dZn6"mI
1, Refractive: an achromatic as positive + plano-convex as negative; 2c/Ys4/H4]
OR *Y@nVi
2, Reflective: two parabolic mirrors; J6<rX[
yZe
2<hpK!R
Both of them affer nice spherical aberration performance. X=C1/4wU
Tz9`uW~Mf
Reminder: compute the laser beam density, ensure you have enough strong optical coating. ?h!i0Rsm
\a+(=s(;
Good luck.