Muñoz et al., 2000

We have measured the scattering matrix as a function of the scattering angle of randomly oriented particles of a Mg-rich olivine sample and a ground piece of Allende meteorite as cometary analogues using lasers at two wavelengths (442 nm and 633 nm). The elements of the scattering matrix, Fij , depend on the scattering angle, the wavelength of the laser light, and on the size, shape and refractive index of the particles. The sample of olivine has been prepared so that four different size distributions were obtained, and results for these size distributions are presented. The element ratio −F12/F11, which in our case equals the degree of linear polarization for unpolarized incident light, is of particular interest, since it can be compared directly with observations e.g. for comets and asteroids. This ratio shows negative values at angles close to the backward direction for Allende meteorite and olivine particles at both wavelengths. Such negative polarization has been observed for many objects in the solar system. Our data have been compared with polarization data of comets and asteroids. We conclude that differences in the maximum polarization observed for different comets can be due to differences in the size distributions and/or the color of cometary dust particles.