There are lot, depending on your requirements. Anyway you can try: S =5br
%+pF4f8]
1, Refractive: an achromatic as positive + plano-convex as negative; /Fj*sS8
OR tl6x@%\
2, Reflective: two parabolic mirrors; c)`=wDi
ew+>?a'&L
Both of them affer nice spherical aberration performance. D[p_uDIz
BbIg]E/G
Reminder: compute the laser beam density, ensure you have enough strong optical coating. F+<e9[
g:oB j6$
q
Good luck.