Hello All, Briefly on the exposition; I'm an undergraduate assistant to a professor. We contribute to the Muon g-2 experiment in Fermilab, designing and optimizing the magnetic-measurement equipment. As you might imagine I utilize the Fourier Transform often to analyze data. The data I'm analyzing is photo-current which comes from a laser of known power and is modulated by a magnetic field. The modulation by the magnetic field perturbs the plane of polarization in a well-defined manner (Faraday Rotation), resulting in a modulation of the intensity of photo-current and thus the voltage measured in our DAQ Assist box. I use LabView to analyze the data and thus use a proprietary "virtual instrument" in the program to do the FFT for me (obviously as the sheer amount of data would be overwhelming!). I understand the concept of an FFT, it being a mathematical tool to take a signal and decompose it into it's frequency domain and measure the strength of each frequency directly by their amplitude, as they contribute to the resultant "summed" signal. However what I need to understand is how to translate the amplitude of one of the frequencies (say 60 hz) into the amplitude for the magnetic field. In other words my professor wants me to be able to tell the magnetic field strength from the amplitudes present on our power spectrum. Now I have a few questions... i) Can this be done by simply analyzing one frequency and it's amplitude. My intuition says no as I would imagine the same strength magnetic field could produce different profiles for the power spectrum. However the way my professor puts it he makes it seem like he wants me to look and see "oh our 60 hz signal is at 1x10^-4, so that corresponds to a field of x Tesla" Well, I guess I don't have any more questions but if anyone could explain to me (or show me) how to go about calculating the strength of the magnetic field from the power spectrum that would be incredible.