How to change the marking in colorbar?

How to change the colorbar marking uniformly?

clc;close all;clear all;

lambda=532

lambda = 532

w0 = 1;         % beam waist
z = 0;          % propagation distance
k = 2*pi/lambda; % wave number
l = 1;          % topological charge
x = linspace(-5*w0,5*w0,256);  % x-axis grid
y = linspace(-5*w0,5*w0,256);  % y-axis grid
[X,Y] = meshgrid(x,y);         % create meshgrid

R = sqrt(X.^2 + Y.^2);
phi = atan2(Y,X) + l*atan2(R,z);
u = exp(-(X.^2 + Y.^2)/w0^2) .* exp(1i*phi);

figure;
imagesc(x,y,angle(u));
colormap('hsv');
axis equal tight;
xlabel('x');
ylabel('y');
cb = colorbar;
cb.Ticks = [0  0.5  1];
cb.TickLabels = {'0',  'pi/2',  '2pi'};

Answer 1

[Walter Roberson]

lambda=532

lambda = 532

w0 = 1;         % beam waist
z = 0;          % propagation distance
k = 2*pi/lambda; % wave number
l = 1;          % topological charge
x = linspace(-5*w0,5*w0,256);  % x-axis grid
y = linspace(-5*w0,5*w0,256);  % y-axis grid
[X,Y] = meshgrid(x,y);         % create meshgrid

R = sqrt(X.^2 + Y.^2);
phi = atan2(Y,X) + l*atan2(R,z);
u = exp(-(X.^2 + Y.^2)/w0^2) .* exp(1i*phi);

figure;
angu = angle(u);
imagesc(x,y,angu);
colormap('hsv');
axis equal tight;
xlabel('x');
ylabel('y');

caxis

ans = 1×2

-3.1377 3.1377

[min(angu(:)), max(angu(:))]

ans = 1×2

-3.1377 3.1377

cb = colorbar;
cb.Ticks = [0  0.5  1];
cb.TickLabels = {'0',  'pi/2',  '2pi'};

Your actual data being drawn ranges from pretty much to . imagesc() leaves the data alone but changes the CLim (color axes limits) to match the actual range of data. You then ask for tick marks at the absolute positions 0, 0.5, and 1, rather than at some kind of relative position.

You also label with 0 to even though the values are to

I would suggest that what you want is

w0 = 1;         % beam waist
z = 0;          % propagation distance
k = 2*pi/lambda; % wave number
l = 1;          % topological charge
x = linspace(-5*w0,5*w0,256);  % x-axis grid
y = linspace(-5*w0,5*w0,256);  % y-axis grid
[X,Y] = meshgrid(x,y);         % create meshgrid

R = sqrt(X.^2 + Y.^2);
phi = atan2(Y,X) + l*atan2(R,z);
u = exp(-(X.^2 + Y.^2)/w0^2) .* exp(1i*phi);

figure;
angu = angle(u);
imagesc(x,y,angu);
colormap('hsv');
axis equal tight;
xlabel('x');
ylabel('y');

caxis([-pi pi])

cb = colorbar;
cb.Ticks = [-pi  0  pi];
cb.TickLabels = {'-\pi',  '0',  '\pi'};