There are lot, depending on your requirements. Anyway you can try: ^hZ0IM
wea-zN
1, Refractive: an achromatic as positive + plano-convex as negative; 3=aQG'B
OR zh8nc%X{
2, Reflective: two parabolic mirrors; [XEkz#{
x!5'`A!W%
Both of them affer nice spherical aberration performance. (|klSz_4LM
;$.J3!
Reminder: compute the laser beam density, ensure you have enough strong optical coating. S4Y&
(k5We!4[1
Good luck.