There are lot, depending on your requirements. Anyway you can try: ^y%8_r&
M`7[hr
1, Refractive: an achromatic as positive + plano-convex as negative; #K*p1}rf
OR @
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2, Reflective: two parabolic mirrors; C+>mehDC_G
A'Z!l20_
Both of them affer nice spherical aberration performance. h6bvUI+|h
JpZ_cb`<E'
Reminder: compute the laser beam density, ensure you have enough strong optical coating. Y]^*mc0fE
q(csZ\e=
Good luck.