Polarimetric Light Scattering Characterization Of Individual Aerosol Particles

The optical properties of aerosol particles depend on their chemical composition,size,shape,and internal structure.Scattered light detection technology is widely used for the measurement of the species,concentration,and size distribution of atmospheric particles.The polarization of light plays an important role in the detection and research of aerosol particles.The light scattering polarization properties of particles can be expressed by the Mueller matrix(4×4 matrix,determined by the particle size,shape,and refractive index),which relates the polarization information of the scattered light and the value of the Mueller matrix element to the polarization state of the excitation light.In this paper,the characteristics of the light scattering Mueller matrix of aerosol single particles are calculated and analyzed for the two linear polarization excitation lights with their polarization directions perpendicular to each other,and compared with the preliminary experimental results.In this paper,using T-matrix differential scattering cross section calculation method for single particle scattered light,a calculation code for the integrated scattering cross-section intensity of a scattered light detector corresponding to a certain range of acquisition solid angles is compiled.The code can help to obtain the response of detectors to the scattered light at different positions and sizes for spherical or axisymmetric particles having different equivalent diameters and refractive indices.The scattered light response intensity of the detector with several scattering polar angles was calculated.The influence of particle size,refractive index and shape feature(aspect ratio)on the Mueller matrix element and polarization intensity factor(Pf)is investigated.The results show that the difference in the scattering intensity of the polarized light of two linear polarizations whose polarization directions are perpendicular to each other is proportional to the Muller matrix element Z12.Z12 fluctuates around the zero point with the change of the particle size,and the matrix element Z11 corresponding to the total scattered light intensity increases rapidly with the increase of the particle size.As the aspect ratio of non-spherical particles increases,the magnitude of Z12 changes tends to increase,which reflects the difference between spherical and non-spherical particles.Changes in the refractive index will lead to changes in Z12,but do not show obvious regularity.Using the aerodynamic particle size measuring device,the Z12 and Pf values corresponding to the polarized incident light are obtained for several spherical,cubic and elongated particles in the diameter range of 0.91 to 1.19?m.The analysis shows that the values Z12 and Pf of cubic particle is almost the same as the spherical particle,but the long particle has obvious difference.The measurement method of the Muller matrix element Z12 and Pf and its ability to distinguish the long and spherical particles are shown.