There are lot, depending on your requirements. Anyway you can try: iSf%N>y'K
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1, Refractive: an achromatic as positive + plano-convex as negative; Fu{VO~w
OR HqV55o5f'
2, Reflective: two parabolic mirrors; hJ8&OCR }
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Both of them affer nice spherical aberration performance. no-";{c
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Reminder: compute the laser beam density, ensure you have enough strong optical coating. 83vZRQw
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Good luck.