changing to wavelength domain

% hello everyone i have a question : in my small code here, I drawn a Fourier transform function from time to frequency domain but what if I want the Fourier transform not in frequency , but in wavelength where wavelength=2*pi*c/frequency how can i change the scale in the Fourier transform from frequency to wavelength :
t=0:0.1:10;
P0=sqrt(9.6);
Ap=P0.*exp(-.05.*(t/3).^2);
figure
I=fftshift(fft(Ap));
S=I.^2;
plot(abs(S))
xlabel('normalized frequency')
ylabel('spectral intensity')