There are lot, depending on your requirements. Anyway you can try: +um
Ua
pkWJb!
1, Refractive: an achromatic as positive + plano-convex as negative; 'Xj9sAB
OR K)NB{8 _
2, Reflective: two parabolic mirrors; jUny&Alj
-M]NdgI
Both of them affer nice spherical aberration performance. %:61@<
l#40VHa?S
Reminder: compute the laser beam density, ensure you have enough strong optical coating. ahezDDR-.i
"J51\8G@@
Good luck.