On Characteristics Of Light Scattering By Inhomogeneous Particles And Measurement Of Refractive Index Profile

For many practical applications such as combustion, environmental control, fluid mechanics, and chemical reaction, we need to measure the properties of particles such as size and refractive index-temperature ratio quickly and precisely. A technique based on light scattering has proved its importance over time. This paper is devoted to the research on light scattering of inhomogeneous particles and the measurement of refractive index profile. Some valuable results are obtained and summarized as follows:1. Scattering coefficients are derived in detail of an infinite inhomogeneous cylinder illuminated normally by plane waves. On the basis of the improved algorithm of light scattering of plane waves by multilayered spheres, an efficient numerical procedure for computing the scattering coefficients of a multilayered cylinder is presented. Compared with the previous algorithms, computations for scattering field in our code are extended to fairly large parameters, up to 10~4 and 10~6 in number of layers, and computational time is shorted to a few seconds at most. The algorithm can also be used to the simulation of different fields for absorbing or transparent cylinders illuminated by different wave bands.2. Light scattering theory is investigated of plane waves by a radially stratified tilted cylinder. An efficient numerical algorithm for computing the scattering coefficients of a radially stratified tilted cylinder is discussed. On the computer of on Intel Pentium 4, CPU 2.93GHz and 512M Memory, computations for scattering field in our code are extended to fairly large parameters, up to more than 10~4 and a few millions in number of layers, and computational time is shorted than the previous algorithms . The capabilities of our code depend also on the memory of computer. The algorithm can also be used for absorbing or nonabsorbing cylinders in different electromagnetic wave bands.3. Using Lorenz-Mie theory, geometrical optics approximation and Debye series, characteristics of rainbow for inhomogeneous particles are discussed. The results show that for some refractive index, the intensity distribution near rainbow angles is the interference of different orders of rainbow. Each order rainbow can be separated and reconstructed from the interference intensity distribution, using Low or band pass filtering and IFFT. At last, the multiple first order rainbows of layered cylinders are presented, which supplies more information in particle sizing. 4. Scattering intensity distributions of rainbows are simulated for inhomogeneous particles with different refractive index profile using Lorenz-Mie theory and Debye series. The results show that the scattering intensity distributions depend closely on refractive index profile. The relation of the positions of Airy peaks to each order rainbow with the refractive index profile is simulated and discussed. Based on the above relations, refractive index profile is reversed by least square methods with high precision. The experimental setup is introduced, and some simple measuring results are given and compared with theoretical ones.5. Scattering characteristics are studied of inhomogeneous cylinders immersed in an absorbing medium illuminated normally by plane waves. Scattering and extinction cross sections are derived, and the efficient algorithm is presented. Scattering matrix is simulated and discussed.