How to get vibrational Raman Spectra from Time-Frequency graph?

Hello everyone,

Recently I performed my first Pump-Probe experiment on a sample of cresyl-violet. Leaving out the experimental set up, what I got in output is a matrix whose elements are the Intensities of a single frequency at a single time (time delay between the pump and probe). The graph is:

The signal is clearly chirped, so after performing de-chirping what i obtain is an other matrix called "Signal". Now what i want to get is the Raman spectra. My tutor said me I have to perform a Fourier Transform, so what i did is:

for i=1:length(Lambda)
 Signal(i,:)=fft(Signal(i,:));
end

so for each wavelength, I should take the Fourier Transform of the vector and what I get is a complex number (ok I'm performing FFT so nothing strange) but if i plot both real and image part of Signal I get clearly wrong results. What i Should get is something like this:

Can you please help me?

Answer 1

[Kshitij Chhabra]

I understand that you are having a problem in visualizing the correct output on plotting the real part and the imaginary part obtained after doing the FFT.

To obtain the expected plot, you can try plotting the absolute values of Signal.

Documentation on Fourier Transform can be found here for your reference.