There are lot, depending on your requirements. Anyway you can try: t|q@~B
:
b^b@W^\hn
1, Refractive: an achromatic as positive + plano-convex as negative; #DjSS.iW
OR WVDkCo@
2, Reflective: two parabolic mirrors; @{16j#'R
Vg9nb
Both of them affer nice spherical aberration performance. Htd-E^/
x]o~ %h$
Reminder: compute the laser beam density, ensure you have enough strong optical coating. 5.!iVyN
kj_o I5<'
Good luck.