Table_4_1_Circular_aperture.m

%Fresnel diffraction of a circular aperture% 
clear; %Clear all memory
%Defining the parameters
N=500;% Define the matrix size
lambda=0.633*10^-6;%Define wavelength in meters
z=0.02;%Propagation distance = 20 mm
r=10^-3;%Radius of aperture = 1 mm
wsamp=10*lambda;%sampling period or width
%Creating sampled space
    x=1:N;
    y=1:N;
    [X,Y]=meshgrid(x,y);%Sampling
    Rsamp=sqrt((X-N/2).^2+(Y-N/2).^2).*wsamp;%Define sampled radius
%Constructing the aperture
    A=ones(N,N);%Define matrix by assigning zeros to all pixels
    A(Rsamp>=r)=0;
% Calculating the Fresnel diffraction pattern
    PPF=exp(1i*pi/(lambda*z).*Rsamp.*Rsamp); %Calculate the parabolic phase factor
    A1=A.*PPF;%Multiply the circular aperture function with the parabolic phase factor
    E=abs(fftshift(fft2(fftshift(A1)))); %Calculate Fourier Transform
%Observation of the diffraction pattern
colormap(gray)%Display greyscale image
imagesc(E)%Display scaled image