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From: "Bruno Luong" <b.luong@fogale.fr>
Newsgroups: comp.soft-sys.matlab
Subject: Re: fourier transform of gaussian beam to simulate far-field beam
Date: Fri, 9 May 2008 07:49:04 +0000 (UTC)
Organization: FOGALE nanotech
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"Jurgen Chan" <bigfoot84s@hotmail.com> wrote in message
<g00et4$q8p$1@fred.mathworks.com>...
> 
> i want to use the fraunhofer approximation method as such 
> to fourier transform my gaussian beam by using fftshift(fft
> (gaussian)).

The Fourier transform of the Gaussian can be computed by
hand (it is a Gaussian). No need for fft, where cares should
be taken for step side and radius as you have noticed.
 
> 
> Also, how should i normalize the F(vx,vy)? is it divide by 
> N^2 ?

It seems rather N. Also there mighty be an exception with a
DC term (0 order), so be careful. 

> By using the Parseual&#8217;s Theorem, the power of the initial 
> and farfield beam should be the same. but in my program, 
> the power of the initial beam and the farfield beam, they 
> are not equal.  
> 

Parseval? You could check the theorem with individual term
of the MATLAB fft. "help fft" for formula.

Bruno