There are lot, depending on your requirements. Anyway you can try: g/frg(KF
}
m"':f
1, Refractive: an achromatic as positive + plano-convex as negative; T|,/C|L
OR Dn)B19b
2, Reflective: two parabolic mirrors; Id1de>:;
n&,X']z.
Both of them affer nice spherical aberration performance. P?^%i
k
t'[
Reminder: compute the laser beam density, ensure you have enough strong optical coating. %(|-+cLW+
[dFe-2u ,$
Good luck.