Research On Diffuse Backscattering Of Polarized Light From Highly Scattering Media

The diffuse backscattered polarized lights from highly scattering media generate peculiar spatial intensity distributions, which depend on the physical properties of the media. The parameters of the media can be determined by analyzing these polarized diffuse backscattering patterns. The research on the diffuse backscattering of polarized light from highly scattering media is a basic method for the multiple polarized light scattering and very significant for us to understand the propagation process of the polarized light in turbid media. In this dissertation, we investigate the diffuse backscattering of polarized light from highly scattering media in-depth by means of the theories, computer simulations and optical experiments.In Chapter 1, we introduce the background of this subject and review the investigations of the diffuse backscattering of polarized light from highly scattering media. The main research contents of this dissertation are stated.In Chapter 2, we present the relations between the electromagnetic fields of the polarized light and the Stokes vectors, and the experimental measurement methods for the Stokes vectors. The transfer theories and the Monte Carlo simulations of the light propagation in turbid media are detailed after a brief introduction for single scattering and multiple scattering theories.In Chapter 3, we firstly establish the physical model of the diffuse backscattering of polarized light from highly scattering media. Then, we detail the double scattering theory and the multiple scattering theory of the diffuse backscattering based on the incoherent light assumption. From the two theories, the effective Mueller matrix of the diffuse backscattering of polarized light from highly scattering media is obtained analytically. A Fourier analysis method for the effective Mueller matrixes is firstly proposed, which is able to extract whole information of the Mueller matrix patterns.In Chapter 4, we establish the vector Monte Carlo (VMC) simulation model of the diffusebackscattering of polarized light from mono-disperse polystyrene suspensions and depict the algorithm flow. The VMC program to trace the propagation process of polarized light in highly scattering media is realized independently. The effective Mueller matrixes are simulated for the suspensions with different diameter spheres. The reasons for the influence of the particle size on the effective Mueller matrixes are discussed by the Mie theory. After conducting the Fourier analysis method on the effective Mueller matrixes, the reduced diffuse backscattering Mueller matrixes are calculated for the first time. Then, we reconstruct the effective Mueller matrixes from the reduced diffuse backscattering Mueller matrixes. The reconstructed patterns are coincident with the ones directly simulated by the VMC. It proves that the symmetry and correlation of the effective Mueller matrixes is correct and Fourier analysis method is effective to extract whole information of the Mueller matrix patterns.In Chapter 5, a novel experimental setup is established for the diffuse backscattering of polarized light from highly scattering media. In our setup, a laterally incident laser beam is reflected onto the surfaces of media by a small mirror so that the patterns can be directly imaged without an intermediate image plane. As a result, our patterns are more precise than other research groups. The diffuse backscattering patterns of linear polarized light from the polystyrene suspensions with different diameter spheres are recorded. In a co-polarized diffuse backscattering pattern which is normalized by the pattern size, the ratio of 4th and 2nd order Fourier coefficients increases linearly with the intensity sampling radius. After a linear fitting, we find the slope rate is a monotonic function of the particle diameter and especially shows a very nice linearity over a wide range of 200-2500nm. Experiments show good agreement with the simulation results. Finally, we compare the new experimental setup and the previous ones, and analyze the effect factors on the e...