There are lot, depending on your requirements. Anyway you can try: %'$f ?y
MO[c0n%
1, Refractive: an achromatic as positive + plano-convex as negative; et@">D%;]
OR s;s0}Td_1
2, Reflective: two parabolic mirrors; YQN.Ohtv*F
}bZ
8-v
Both of them affer nice spherical aberration performance. |drf"lX<{
7`Qde!+C
Reminder: compute the laser beam density, ensure you have enough strong optical coating. JK[T]|G
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Good luck.