There are lot, depending on your requirements. Anyway you can try: ?*dx=UI
j>M%?Tw
1, Refractive: an achromatic as positive + plano-convex as negative; mw%_yDZ{
OR 5qko`r@#
2, Reflective: two parabolic mirrors; D(GHkS*0q
+t6m>IBu
Both of them affer nice spherical aberration performance. Y'R1\Go-
tr+~@]I+
Reminder: compute the laser beam density, ensure you have enough strong optical coating. <C xet~x
&"0[7zgYQz
Good luck.