I didnot find any error, when I run the code in my system (2015b)
clc;
clear all;
close all;
lambda=500e-9; k=(2*pi)/lambda; % wavelength of light in vaccuum
a=1e-6; b=1e-6; % dimensions of diffracting rectangular aperture
% a is along Z and b is along Y
Io=100.0; % relative intensity
R=1.0e-3; % distance of screen from aperture
Y=(-0.25e-2:1e-5:0.25e-2); Z=Y ; % coordinates of screen
beta=k*b*Y/(2*R*pi);alpha=k*a*Z./(2*R*pi); % intermediate variable
% diffracted intensity
for i=1:length(Y)
for j=1:length(Z)
I(i,j)=Io.*((sinc(alpha(j)).^2).*(sinc(beta(i))).^2);
end
end
%------------------------------------------------------------------------
figure(1)
imshow(I)
title('Fraunhofer Diffraction','fontsize',14)
fh = figure(1);
set(fh, 'color', 'white');
%------------------------------------------------------------------------
