Effects of Interaction of Electromagnetic Waves in Complex Particles

The majority of natural materials (rocks, soil, wood, etc.) are inhomogeneous and have a complex structure. Very often they are conglomerates or aggregates, i.e. made of small grains stuck together. This is especially typical for planetary aerosols and all types of cosmic dust (interstellar, circumstellar, interplanetary, cometary, etc.). Cosmic dust, specifically, cometary will be the main test object for this paper. This is related to the fact that cosmic dust is usually studied through remote sensing, specifically through the study of electromagnetic waves it scatters and emits. Due to this, the field of light scattering by cosmic dust has always been at the frontier of the study of interaction of electromagnetic waves with non-spherical and inhomogeneous particles. It has inspired publication of the scholarly books by van de Hulst (1957), Schuerman (1980), Kokhanovsky (2001), Hovenier et al. (2004), Voshchinnikov (2004), Borghese et al. (2010), and Mishchenko et al. (2000, 2002, 2010) and numerous book chapters, e.g., Mukai (1989), Lien (1991), Gustafson (1999), Gustafson et al. (2001), Kolokolova et al. (2004a, b). To consider the scattering of electromagnetic waves by an object of complex structure, we will determine this object as a configuration of discrete finite constituents. They will be called inclusions in the case of inhomogeneous particles, or monomers in the case when they are constituent particles of an aggregate. Their volume is large enough that we may ignore their atomic structure and characterize their material by a specified complex refractive index, m=n+i┢, whose real part is responsible for the refraction and imaginary part for the absorption of the light by the material. The surrounding medium is assumed to be homogeneous, linear, isotropic, and, in the case of aggregates, non-absorbing. Although we discuss some approximations, our consideration is based on the Maxwell equations fully describing the interaction of the electromagnetic radiation with the material. The non-linear optical effects, non-elastic scattering, quickly-changing illumination and morphology of the scattering object are beyond the scope of our study. As mentioned above, our test example will be cosmic dust that typically can be presented as aggregates of submicron monomers. In the optical wavelengths they are good