There are lot, depending on your requirements. Anyway you can try: 7dZ!GX?\y
H#K|SSqY?
1, Refractive: an achromatic as positive + plano-convex as negative; ^gImb`<6-
OR we3t,?`rk7
2, Reflective: two parabolic mirrors; 10(N|2'q
wW~2]*n
Both of them affer nice spherical aberration performance. 4<|]k?@
t|%ul6{gz
Reminder: compute the laser beam density, ensure you have enough strong optical coating. |EunDb[Y
&/p9+gd
Good luck.