DIRECT-DETECTION OF EVANESCENT ELECTROMAGNETIC-WAVES AT A PLANAR DIELECTRIC SURFACE BY LASER ATOMIC SPECTROSCOPY

The penetration depth and pseudomomentum (wave vector) of evanescent e lectromagnetic waves are measured at a planar dielectric surface by me ans of laser spectroscopy using the Cs D-2 Lint with a wavelength of 8 52.1 nm. The same experimental setup is employed in all the experiment s. The first result shows a sharp, asymmetric absorption profile. whic h is explained in terms of the thin penetration depth, and the second shows an actual transfer of the pseudomomentum of the surface electrom agnetic mode to atoms via a resonance interaction. The measured penetr ation depth and pseudomomentum agree with the natural interpretation o f the complex wave number characterizing evanescent waves at a planar dielectric-vapor interface. Direct excitation of evanescent waves by e xcited Cs atoms has also been observed as atomic fluorescence emitted into the dielectric material at the angle of total internal reflection . The results are in good agreement with the theoretical predictions a nd exhibit the characteristics of excitation transfer or tunneling fro m Cs atoms into the surface mode.