Spectral Properties of Near-Field Evanescent Waves Scattered From a Particulate Medium With Adjustable Boundaries

Within the accuracy of the first-order Born approximation, expressions are derived for the spectrum of near-zone evanescent waves, which scatter from a spatially deterministic particulate medium with semisoft edges. By assuming that the scattering potential of the medium suffices the multi-Gaussian profile, it is shown that the degree of red-shifted spectrum of scattered field can be modulated by changing the summation index and effective radius of the scatterer. Moreover, the spectral switch, which transforms from the red shifts to the blue shifts of the spectrum, can emerge when the effective radius is sufficiently small compared with the incident wavelength. In addition, the summation index is another factor influencing the degree of spectral switches of near-zone scattered fields. These results are of potential applications to the near-field biomedical imaging and determination of scattering potentials of tiny particles.