Nonperturbative broadening of paramagnetic resonance lines by transverse magnetic field gradients

We experimentally and theoretically study the broadening of paramagnetic resonance lines by transverse magnetic field gradients when a perturbative description is inadequate. The experiments are performed with an evanescent wave magnetometer using an octadecyltrichlorosilane-coated glass cell containing Rb-87 and N-2 buffer gas. We find that the transverse broadening of the resonance line is inversely proportional to the square root of the holding field. We also provide a quantitative theoretical explanation of the experimental results.