# Plot DFT in wavelength for ultrashort pulse in MATLAB

I have a measured intensity cross-correlation signal that I want to plot in wavelength. I am new to FFT and I am using matlab. Here is exactly what I need it to look like

Here is what I have so far:

Im = load('Autocorrellation1.mat');

G = sum(Im.Image);

% sampling frequency in samples per meter
dx = 1e6;

c=3e8;

dt = 2/(dx*c);

Fs = 1/dt;

t = 0:dt:(dt*(length(G)-1));

plot(t,G)
axis tight
xlabel('time (s)')