Optical properties of porous nonspherical particles


Here we compare the optical properties of porous nonspherical particles of two kinds:
  • layered spheroids and Chebyshev particles;

  • same shape homogeneous particles with an effective refractive index.

We calculate the dependence of the extinction and polarization cross-sections on a size parameter
and that of intensity and linear polarization of scattered light on the scattering angle.

We consider spheroidal particles with the aspect ratio a/b = 1.4
and Chebyshev particles with the shape parameters: n = 5, epsilon = 0.07, and n = 10, epsilon = 0.02.
The shape of the layers in a particle is the same.
The refractive index of the material is typical of astronomical silicate m = 1.7 + 0.03i.
The orientation angle between the symmetry axis of the particles and the wavevector of incident radiation is alpha = 45 deg.

The scatterers are divided in 3 groups:
    weakly porous (the ratio of vacuum to material volume in a particle is equal to P=0.1),
    moderately porous (P=0.5) and
    essentially porous (P=0.9).
Links provide access to PDF files with computed optical properties.

For each considered value of porosity P, we give first 8 figures on 1 page that show the dependence of the dimesionless extinction (Qext) and linear polarization (Qpol) cross-sections particles on their difraction parameter xv = 2 pi rv / lambda, where rv is the radius of a sphere which volume is equal to that of a nonspherical particle, lambda is the wavelength of incident radiation. Then we give 23 pages of figures showing variations of scattered light intensity (actually F11/g) and linear polarization degree (-F21/F11) with changes of the scattering angle theta for different values of xv. So, we have 24 pages with 8 figures for each of three porosity value P=0.1, 0.5, 0.9 (all together 672 figures).

The figures show tha optical properties of 2, 4, 8, 16, 32 and 64-layered particles (thin lines) as well as the same shape homogeneous particles with the effective refractive index derived from Maxwell-Garnett, inverse Maxwell-Garnett è Bruggeman rules (thick lines).

To compute these properties of the layered and homogeneous nonspherical particles we used our new code based on the SVM method with a spherical basis.
For more comments see the paper by A.A. Vinokurov, V.G. Farafonov and V.B.Il'in, Separation of variables method for multilayered nonspherical particles, JQSRT, 110, 1356--1368, 2009 (available here).

The work was supported by the RFBR grant 07-02-00831.