There are lot, depending on your requirements. Anyway you can try: $q}zW%
)Q:.1Hgl
1, Refractive: an achromatic as positive + plano-convex as negative; W8bh49
OR .
#+ N?D<
2, Reflective: two parabolic mirrors; H rMH
8\V
Both of them affer nice spherical aberration performance. O$
p
\L6kCY
Reminder: compute the laser beam density, ensure you have enough strong optical coating. ]'
ck!eG
g4p-$WyT8>
Good luck.