Abstract

An evanescent field is characterized by the complex wave vector. The real part corresponds to the propagating vector parallel to a dielectric surface which represents the pseudo-momentum of the evanescent field with a magnitude larger than the momentum in vacuum. The imaginary part represents the intensity gradient of the field and the penetration depth of its field nearly equals one wavelength. In microscopic viewpoint, the evanescent field can be regard as the field due to electric polarizations induced on the dielectric surface by the incident and the reflected fields. The spectroscopic study by using the evanescent field provides the understanding of the physical nature of a surface field. We present an experimental demonstration of the penetration depth, the pseudo-momentum and the excitation of the evanescent electromagnetic field at the dielectric surface by means of novel laser optical pumping spectroscopy of the Cs-D₂ line at 852.1 nm.

© 1995 IEEE