There are lot, depending on your requirements. Anyway you can try: g~S>_~WL
k*\WzBTd
1, Refractive: an achromatic as positive + plano-convex as negative; ]3BTL7r
OR "@;q! B.qo
2, Reflective: two parabolic mirrors; )0
.gW
E;fYL]j/oZ
Both of them affer nice spherical aberration performance. Kzb&aOw
dw5.vXL`
Reminder: compute the laser beam density, ensure you have enough strong optical coating. }3!83~Qbx
By]XD~gcP
Good luck.