Probing evanescent modes from near-field optical microscopes:: propagation into anisotropic media

We describe how to probe the amplitude and polarization of the evanescent modes of light emanating from near-field scanning optical microscopes and Bethe–Bouwkamp holes by placing these structures near anisotropic dispersive media. Evanescent modes have different cut-offs for propagation inside the anisotropic medium as a function of the angles made by their wave vectors and the optic axes of the medium. The electromagnetic field mode amplitudes near the tip can be obtained by varying the orientation of the optic axes relative to the tip.