There are lot, depending on your requirements. Anyway you can try: gPo3jw o$
z'FpP
1, Refractive: an achromatic as positive + plano-convex as negative; Ju0W
OR Pjs
L{,
2, Reflective: two parabolic mirrors; R\^n2gK
8&g`Uy/b
Both of them affer nice spherical aberration performance. &jg..R
}m`+E+T4
Reminder: compute the laser beam density, ensure you have enough strong optical coating. WOv m%sX
%ut^ O
Good luck.