Abstract
Near-field scattering functions of small spheres are discussed and presented as a function of the distance from the scatterer. Although the total scattered energy defined by the angular integral of the scattering function does not depend on the distance from the particle, the scattering at any given angle in the near field does. In particular, apparent negative scattered energy flux values along the radius vector in given angular ranges are emphasized. The appearance of negative values was reported previously; however, they are shown here to reach any high normalized value, relative to the total scattering, depending mainly on the scatterer size, the distance from the scatterer, and the complex index of refraction. The negative values that were treated previously merely as numerical results are explained in terms of the Ricatti–Bessel-function asymptotic expansion. It is also shown that, excluding the scattering region near 90 deg, the physical significance of these high negative values in the near field is usually negligible relative to the overall field when the coherent interference with the incident wave is taken into account. In the far field the negative values disappear.
© 1989 Optical Society of America
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