Scattering and extinction of evanescent waves by small particles

Expressions have been obtained for the total cross sections for extinction and scattering of evanescent waves by small spherical particles. Due to the different structure of p- and s-polarized waves, cross sections for both e xtinction and scattering of p-polarised evanescent waves exceed those for s -polarised waves, as long as the Mie coefficients for magnetic multipoles a re smaller than those for electric multipoles for each multipolar order, i. e. for sufficiently small particles. The difference increases with the angl e of incidence of the totally reflected wave. The definition of cross secti ons for evanescent-wave excitation with variable intensity over the cross-s ectional area of the particle allows quantitative comparison with the case of plane-wave excitation. For example, within the dipole approximation the cross sections for plane-wave excitation lie between those for p- and s-pol arised evanescent-wave excitation, respectively. Due to the inhomogeneity o f the evanescent field higher multipole contributions are strongly enhanced as compared to plane-wave excitation and increase further with the angle o f incidence, resulting in corresponding changes in the scattering and extin ction spectra. These effects are demonstrated in the specific case of scatt ering of evanescent waves by small silver particles.