There are lot, depending on your requirements. Anyway you can try:
25H=RTw
.Z9{\tj
1, Refractive: an achromatic as positive + plano-convex as negative; .`TDpi9OB
OR `D,mZj/b
2, Reflective: two parabolic mirrors; _7bQR7s
Sa 8T'%W
Both of them affer nice spherical aberration performance. AcQmY?
0/4"Jh$t
Reminder: compute the laser beam density, ensure you have enough strong optical coating. wpK[;
zEMZz$Y
Good luck.