There are lot, depending on your requirements. Anyway you can try: HK%7g
MpOc
1, Refractive: an achromatic as positive + plano-convex as negative; !p/goqT~dY
OR Zb#u0Tq
2, Reflective: two parabolic mirrors; @PIp*[7oC
@'|~v<<WZ
Both of them affer nice spherical aberration performance. \}G^\p6?M
*=xr-!MEk
Reminder: compute the laser beam density, ensure you have enough strong optical coating. 4 H&#q>
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Good luck.