In the book "Fundamentals of Photonics", the form of the Gaussian beam is written as(adsbygoogle = window.adsbygoogle || []).push({});

[tex]I(\rho,z) = I_0 \left(\frac{W_0}{W(z)}\right)^2\exp\left[-\frac{2\rho^2}{W^2(z)}\right][/tex]

where [tex]\rho = \sqrt{x^2 + y^2}[/tex]

However, in some books (I forgot which one), the author use the following form

[tex]I(R) = I_0 \exp\left[-\frac{R^2W_0^2}{W^2}\right][/tex]

where

[tex]R = \rho/W_0, \qquad \rho=\sqrt{x^2+y^2}[/tex]

In the second expression, I don't know why there is no [tex]\left(W_0/W(z)\right)^2[/tex] in the amplitude and why he want to define R instead of using [tex]\rho[/tex] directly? And what about [tex]W_0[/tex] and [tex]W[/tex] in the second expression? Are they have some meaning as in the first one?

I forgot which book using such form, if you know any information, could you please tell me the title and author of the book? Thanks.

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# If this is Gaussian beam?

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