There are lot, depending on your requirements. Anyway you can try: u37'~&o{U
8/i!' 0r\
1, Refractive: an achromatic as positive + plano-convex as negative; s2'yY(u/
OR Ne8Cgp
2, Reflective: two parabolic mirrors; 5R@
Cjqklb/
Both of them affer nice spherical aberration performance. /y _O4
l6YtEHNG
Reminder: compute the laser beam density, ensure you have enough strong optical coating. !%^^ \,
T (OW
Good luck.