There are lot, depending on your requirements. Anyway you can try: <nvzNXql
'Lu d=u{
1, Refractive: an achromatic as positive + plano-convex as negative; `g}po%k
OR }'`iJb\
2, Reflective: two parabolic mirrors; R$m?aIN
~J:qG9|]}
Both of them affer nice spherical aberration performance. %/n#{;c#
a&z$4!wQB
Reminder: compute the laser beam density, ensure you have enough strong optical coating. 'w"hG$".
vJ?j#Ch
Good luck.