There are lot, depending on your requirements. Anyway you can try: Sb /?<$>
:5,~CtF5 `
1, Refractive: an achromatic as positive + plano-convex as negative; JM|HnyI
OR dX cbS<
2, Reflective: two parabolic mirrors; <&l$xn
z&amYwQcI
Both of them affer nice spherical aberration performance. j'z#V_S
7,+eG">0
Reminder: compute the laser beam density, ensure you have enough strong optical coating. .iRKuBM/
Op ar+|p\
Good luck.