How to find out the separation between to peaks of the azimuthally polarised beam at full width at half maximum?

hi, I have problem to find separation between two peaks at full width at half maximum, if you run following code you find figure(6) from that I have to find out separation between two peaks at full width at half maxumum

1. clear all;
2. clc;
3. close all;
4. [kx,ky]=meshgrid(-1:2/31:1,-1:2/31:1);
5. c=sqrt(kx.^2+ky.^2)<1;
6. N.A=0.5;
7. alp=asin(N.A);
8. k0=1/sin(alp);
10. kz=sqrt(k0.^2-(kx.^2+ky.^2));
11. GX=sqrt(k0./kz).*((k0*ky.^2+kz.*kx.^2)./(k0*(kx.^2+ky.^2)));
12. GY=sqrt(k0./kz).*((kz-k0).*kx.*ky)./(k0*(kx.^2+ky.^2));
13. GZ=-sqrt(k0./kz).*(kx/k0);
16. ph=(pi+atan2(kx,ky));
17. ph=rot90(ph,3).*c;
18. la=-sin(ph).*c;
20. lb=rot90(cos(ph).*c,3);
21. k=1024;
22. Ex=(la.*GX.*c+rot90(-lb.*GY.*c,3));
23. FEx=fftshift(fft2(Ex,k,k));
24. Ix=FEx.*conj(FEx);
26. Ey=(la.*GY.*c+rot90(lb.*GX.*c,3));
27. FEy=fftshift(fft2(Ey,k,k));
28. Iy=FEy.*conj(FEy);
30. Ez=(la.*GZ.*c+rot90(lb.*GZ.*c,3));
31. FEz=fftshift(fft2(Ez,k,k));
32. Iz=FEz.*conj(FEz);
34. I=Ix+Iy;
35. %figure(1)
36. %imagesc(I),colormap gray;axis image; axis off;
37. %figure(2)
38. %plot(I(16,:))
39. %figure(3)
40. %imagesc(Iz),colormap gray;axis image; axis off;
41. %figure(4)
42. %plot(Iz(16,:))
43. I1=Ix+Iy+Iz;
44. I0=max(max(I1(k/2,:)));
45. I1(k/2,:)=I1(k/2,:)/I0;
46. a=max(max(I1(k/2,:)))
47. %figure(5)
48. %imagesc(I),colormap gray;axis image; axis off;
49. figure(6)
50. plot(I1(k/2,:))
55. thanks in advanceabdul gaffar

[Walter Roberson]

It is easier on people if they can copy and paste your code without having to edit out the line numbers.