There are lot, depending on your requirements. Anyway you can try: s;1e0n
m*oc)x7'
1, Refractive: an achromatic as positive + plano-convex as negative; T3z(k
la
OR J8;Okzb!L
2, Reflective: two parabolic mirrors; tU:FX[&?R
i03gX<=*
Both of them affer nice spherical aberration performance. 85z;Zt0{
jBpVxv
Reminder: compute the laser beam density, ensure you have enough strong optical coating. h8=h >W-
/U*yw5
Good luck.