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if we take a Gaussian beam whose waist occurs at the front focus of a positive lens, we will see that the Gaussian beam will have another waist at the back focus of the lens...

That seems to be in contradiction with what happens in geometrical optics: if we place a point source (diverging beam) at the front focus of a positive lens the beam will be perfectly collimated after the lens....there is no focusing whatsoever. But using a Gaussian beam we have a focusing at the back focal point....

Is my observation correct?

Thanks

fisico30

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# Gaussian beam and focusing versus geometrical optics

Can you offer guidance or do you also need help?

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