There are lot, depending on your requirements. Anyway you can try: ?Fp2W+M
j
["7]EW\!:
1, Refractive: an achromatic as positive + plano-convex as negative; cf{rK`Ff^
OR :)g}x&A^$
2, Reflective: two parabolic mirrors; u`~,`z^{n
mi&mQQ
Both of them affer nice spherical aberration performance. *Al`QEW
2[QyH'"^E
Reminder: compute the laser beam density, ensure you have enough strong optical coating. N`xXH
U6K!FOND
Good luck.