Scattering by Oriented Spheroids R.V. MEHTA and J. M. PATEL Department of Physics, S. V. Regional College of Engg. & Tech., Surat-395007 (Received FebTliQT)' 3, 1977) ABSTRACT - Expressions for scattering and absorption cross sections of a cloud of particles oriented under external magnetic field are derived for the following cases (i) Electric vector of the incident plane polarized light oriented parallel to the symmetry axis of the spheroids (iii) Electric vector of the incident plane polarized light oriented pcipCD.dicular to the symmetry axis of the spheroids.Computations for r, as a function of orienting field are carried out for different ratio ofaxisofthespheroidsform= 1.47-0.Siandm= 1.47-0.1 i. 1. INTRODUCTION Study of scattering properties of partially oriented system is useful in several fields such as astrophysics [1] electro and magneto optical phenomenon [2, 3] flow optical properties [ 4] of dispersed systems etc. Intensity and polarization of light scattered at any angle by a cloud of particles, depend upon size, size distribution, shape, optical properties and orientation of the particles with respect to the scattering plane. Hence scattering and extinction cross sections of system are also functions of the above parameters. Thus if nature of variation of the scattering properties with the above parameters is studied theoretically it can be used with experimental data to determine certain characteristics of the scatterers. Earlier we have derived the depolarization factors and angular intensity functions for externally oriented dipolar spheroids [4, 5]. Here we extend this study for certain other scattering parameters of the particles with a view to determine the role of absorption in extinction observed from oriented system. We separate out here the absorption cross sections fromextinctioncrosssections. 2.THEORY When a light beam having four Stokes parameters L 10 L 20 L 30 and L 40 is incident on a single scatter, scattering is described by the following relation c· = ___!____ J a co Ja+ KR 2 Where k is the mean propagation censtant, R the distance of observation, Co and C' are the coherency matrix for the incident and the scattered beam is the scattering matrix and + denotes conjugate transpose. It has been shown earlier [4] that when a cloud of particles is oriented under an external field there exists particles with their mirror images, particles in the reciprocal position and mirror image of the reciprocal position. The matrices for the above positions are given by Jb = r Jll ] image t-J21 J22 J" = [Jaf Reciprocal position f = [Jb] r Mirror image of reciprocal position. T denotes transpose of the matrix. Intensity of the scattered beam is given by l=TrC and degree of polarization is given by P= 1 _ 41C"I {r,c ·t The resulting coherency matrix can be written as c· =-1-[JacoJa +JbcoJb +Jc coJc+ +JdcoJd+] k2R2 or if dn is the orientation distribution function C" = I,f[JiCo Ji + J dn where i = a,b,c,d. 1 =kR_2 X J {4I 10 + 2 (I + I 21I;1 )L 40 }dn J {4I 11I;2L zo + 2 (J 12J;1 + J 211;1 )L 3D }dn J {4Iz2I;IL3o + 2(IzJ;z + Itzi;I)Lzo}dn J {4I z 2I;2L4o + 2 (I +I 21I;1 )L 10 }dn