Polarized‐light scattering studies of marine Chlorella

Abstract

This paper compares results of rigorous calculations of light scattering by a distribution of coated spheres with the measured light scattering of marine Chlorella. The elastic scattering properties of any organism are described completely by the 16‐element scattering matrix that gives all the intensity and polarization information as a function of angle. Fitting the angular dependence of several matrix elements affords a much more stringent test of scattering calculations than does fitting only one, such as the phase function or linear polarization. The added requirements of this test significantly narrow the range of acceptable optical models and thereby permit better characterization of the scattering medium. Measurements of several elements of the scattering matrix of laboratory cultures of Chlorella were obtained with a scanning polarization‐modulation nephelometer. The results for these elements were best fit by calculations based on a model of a Gaussian distribution of spheres with a relative complex refractive index of 1.08(±0.005)−0.05 i (±0.005) and a 60‐nm coating of index1.13(±0.005)−0.04 i (±0.005) to approximate the cell membrane. Good agreement was obtained for only a very narrow range of particle parameters. Experimental results were broken into spherical and nonspherical contributions to evaluate the effects of nonsphericity.