I'm so confused, and it would be nice if someone could clear my head, or at least direct me to suitable references.
Assume that I have two gaussian pulses with the same bandwidth in time, but for 2 different wavelengths. I'm going to handle them separatly- 2 separate graphs of one gaussian in time.
Both graphs are the same because they have the same bandwidth. Then, I use fft on each graph. Of course I'm going to have the same graphs after the fft- because I had the same graphs before.
Now, I want to creat the frequencies axis for each signal. In order to do that, I use the exact direction from matlab. df=1/T, T=N·dt. So the frequencies axis are also the same!
But how can it be if f=c/lambda? I'm talking about two different wave length, how is it possible that the both have the same spectrum of frequencies?
Further more, I don't understand what is the different between F and df and why is F=N·df. I do understand that T is the time in which I sample, dt=T/N. but that's it.