CGH mask computation for photolithography

Hi guys. So, I am learning how to make CGH masks. I have currently made masks for generating point image and line image at a specified distance from the mask. Now, I want to make a circular image but I am having trouble computing it's mask. I found this CGH mask pattern for a ring image, http://postimg.org/image/8omgkfuul/ but I don't know how to create the main (widest) fringe (the red circular ring). I have managed to do the point image mask http://postimg.org/image/sgvk9vso9/ Any help?? Regards

[Ali]

This is my code for generating the CGH mask for point image. How do I get the ring pattern?

 clc;
 clear all;

pixpitch=8e-6;
x=-3.068e-3:pixpitch:3.068e-3;    %length(x)=768
y=-4.096e-3:pixpitch:4.088e-3;    %length(y)=1024
lambda=0.4e-6;
z=0.1;
b=0;
H=zeros(length(x),length(y));
r=zeros(length(x),length(y));
phase=zeros(length(x),length(y));

for k=x    %for 768x1024 res
    c=0;
    b=b+1;
    for j=y    %for 768x1024 res
        c=c+1;
        r(b,c)=sqrt((k^2)+(j^2));
        H(b,c)=exp(1i*(pi*r(b,c).^2)/(lambda*z));
        phase(b,c)=angle(H(b,c));
    end
end

figure; imagesc(x,y,phase)

Rmax=(lambda*z)/(2*pixpitch);
[y2 x2] = meshgrid(y,x);
aprtr = sqrt((x2).^2+(y2).^2)<Rmax;
loc_diff_pat = phase.*aprtr;

figure; imagesc(x,y,loc_diff_pat)    % localised diffraction pattern

Answer 1

[Image Analyst]

If you want to create a circular mask, see the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F