% Close-up of first-order diffraction pattern of grating illuminated by% monochromatic light.  Shows the "defraction limit' caused by the finite% number of grooves, N.  The larger N, the narrower this pattern. % Tom O'Haver, March 2006clear% N = Number of grooves in grating (Try larger values of N if your computer is fast enough) N=300;format compactclfhold offstart=cputime;x=[0:.1:pi];  z=zeros(size(x));StartPLD=6.2;EndPLD=6.35;Increment=.002;intensity=zeros(1,2000);OPL=zeros(1,2000);k=1;figure(2);clf;for pld=StartPLD:Increment:EndPLD,  % path length difference in radians  z=zeros(size(x));  a=0;  for j=1:N,      y=sin(3.*x+a);     z=z+y;   % z is waveform (sine) resulting from superimposition     a=a+pld;  end  intensity(k)=sum(z.*z);  % calculates mean amplitude  OPL(k)=pld./(2*pi);  plot(OPL(1:k-1),intensity(1:k-1))  ylabel('Observed irradiance  (Mean-square of sum of all reflections)')xlabel('Pathlength difference between adjacent grooves, in wavelengths')title(['First-order diffraction pattern for grating with '  num2str(N)  ' grooves.'])  %drawnow  k=k+1;endhold offfigure(2)ElapsedTime=cputime-start