There are lot, depending on your requirements. Anyway you can try: }ykc
AK3U
X"Q\MLy
1, Refractive: an achromatic as positive + plano-convex as negative; t^g+nguz
OR wRe2sjM
2, Reflective: two parabolic mirrors; JYa3xeC;
3u1\zse
Both of them affer nice spherical aberration performance. (bGk=q=M
WTu1t]
Reminder: compute the laser beam density, ensure you have enough strong optical coating. y6 gaoj
GBGna3
Good luck.