There are lot, depending on your requirements. Anyway you can try: hJk:&!M=T
KQw>6)
1, Refractive: an achromatic as positive + plano-convex as negative; =d:3]M^
OR u3wd~.
2, Reflective: two parabolic mirrors; Odh r=Hs
oJ"D5d,
Both of them affer nice spherical aberration performance. lq,]E/<&
zzW$F)X
Reminder: compute the laser beam density, ensure you have enough strong optical coating. 8ZCA
vEy
=9^}>u
Good luck.