Magnetic field sensing using evanescent waves in the Kretschmann configuration

To verify the feasibility of magnetic field sensing based on the interaction between evanescent waves and magnetic thin films, we have investigated the polar magneto-optical Kerr effect of Co thin films with various thicknesses in the Kretschmann attenuated total reflection configuration. Because of the influence of the glass magneto-optical Faraday rotation under a polar magnetic field, a multi-step experimental method has been applied to measure the intrinsic magneto-optical Kerr rotations of the thin Co films as a function of the angle of incidence. The significant effects of the angle of incidence, the incident light polarization state and the film thickness on the polar Kerr rotations of magnetic thin films in the Kretschmann configuration have been clearly shown in our experiments. The analysis of the experimental results shows that the interaction between the evanescent wave and the magnetic thin film is the main source of the observed magneto-optical activity. On the basis of these results, we discuss the practicalities of the development of a magnetic field sensor based on an evanescent wave penetrating into the magnetic thin film in the Kretschmann configuration, which is a simple structure that is compatible with both optical fibers and integrated optical waveguides.