Non-linearity and frequency shifts of nuclear magnetic spin-noise

We have systematically investigated the line shapes observed in proton nuclear spin-noise spectra which depend in a complex way on the properties of the resonance circuit, the number of spins present, transverse relaxation, inhomogeneous broadening, and radiation damping. Using highly sensitive high resolution probes these dependencies are investigated by way of high resolution 1H noise power NMR spectra of liquid samples. Significant deviations from intuitive expectations are observed. Simulations based on an adapted Nyquist noise equation are used to understand and interpret the experimental findings.