The scattering direction and forward direction define a scattering plane. The orthonormal basis vectors, , are in direction of positive, and axes. The direction of propagation of the incident light defines axis, the forward direction.Īny point in object may be chosen as the origin of a rectangular coordinate system, where and axes are orthogonal to axis and to each other but otherwise arbitrary. This matrix is used to characterize angular distribution of scattered light.Ĭonsider object that is illuminated by a harmonic wave.
Particles can scatter and absorb more light that is geometrically incident upon them (corresponding efficiencies are greater than unity) if their sizes are comparable or smaller than the incident wavelength. Where is the object cross-sectional area projected onto a plane perpendicular to the incident beam (e.g. We may define efficiencies for extinction, scattering and absorption Īre extinction, absorption and scattering cross sections with dimensions of area. These energy flow rates are linearly dependent on incident wave intensity. Last term is a consequence of an interference between incident and scattered fields. Time averaged Poynting vector can be represented as (we omit here index for complex vectors and ) If object is embedded in nonabsorbing environment, is the rate at which energy is absorbed by object. If, energy is absorbed within the volume confined by surface. We construct imaginary closed surface around the object the net rate at which electromagnetic energy crosses this surface is Here we consider how to estimate energy scattered and absorbed by object. Consider arbitrary object illuminated by harmonic incident wave.įield in the medium surrounding the object can be represented as superposition of incident and scattered fields:
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