Analysis And Experiment Of Particle Extinction Cross Section Based On Optical Interference

The optical properties of aerosol particles affect us not only in atmospheric environmental pollution,but also in many fields such as atmospheric science,national security,medicine and manufacturing.The extinction cross-section of particles is an important parameter to evaluate the optical properties of aerosols.Further research on the extinction cross sections of aerosol particles from different sources and compositions can help understand the impact of solar and earth radiation,and provide scientific basis for studying the impact of climate change.Firstly,this paper analyzes the optical properties of particles.Based on Mie theory and Tmatrix,the effects of equivalent radius,shape and transverse and longitudinal ratio on the extinction cross sections of water droplets,silica.(standard quartz crystal),dust and calcium carbonate(wall ash)particles at 532 nm are studied.The results indicate that the extinction crosssection of cylindrical particles varies more significantly than that of ellipsoidal particles in a larger particle size range.When the equivalent radius is 2 μm,the extinction cross sections of calcium carbonate and dust particles with different shapes and transverse and longitudinal ratios range from 25 to 29 μm2.For the equivalent radius of Marine dust particles from 0.7 to 1.4 μm,the extinction cross sections of ellipsoidal particles with different transverse and longitudinal ratios at the same radius vary more than those of cylindrical particles.For spherical particles,the higher the complex refractive index,the greater the relative scattering intensity of calcium carbonate particles.For non-spherical particles,the relative scattering intensity of ellipsoidal particles tends to increase around 100°,while that of cylindrical particles tends to be gentle.Secondly,the coaxial interference system is selected as the experimental device.The attenuation of the original beam caused by the interaction between the incident wave and the particle is used to measure the extinction cross section of aerosol particles,and the standard particle is used for experimental verification.In this system,the incident light source is a continuous semiconductor laser with wavelength of 532 nm,the pixel size of CMOS sensor is 2.5 μm,the system magnification is 8.9 times,and the minimum particle resolution is 2.46 μm.The sensor subtracts and filters the background of the collected photos to obtain a particle contrast interferogram,thereby obtaining the attenuation of the incident wave.Besides,the extinction cross section of particles can be obtained by fitting the envelope of the integral curve obtained by integrating the interference ring from the center to the edge.Different extraction methods are compared.The results show that the ring method has higher accuracy.The standard spherical silica particles with radius of 2.5 μm and 5 μm are selected for verification experiments.The normalized comparison between experimental and theoretical values of standard particles showed that the normalized extinction cross section of silica particles with radius of 2.5 μm is 1.0383.The normalized results of extinction cross sections with radius of 5 μm is 0.91244,respectively.The errors are both within 10%,which verifies the accuracy of particle extinction cross sections measured by interference system.In order to verify the effectiveness of the outfield experiment of the system,the interference images of dust,water droplets,and wall ash particles are processed to obtain the measured extinction cross-section values of the particles.To verify the accuracy of the measurement values,holographic reconstruction is used to obtain the transverse to longitudinal ratio and equivalent radius of the captured particles,and T-matrix simulation is used to calculate the extinction crosssection of each particle.By comparing and analyzing the results of measured values and simulated reproduction values,it was found that the error of most particles remained stable within 20%,mainly due to interference from the system and external environment,as well as the limitations of extinction cross-section processing and reproduction methods.On this basis,holographic reconstruction and T-matrix are used to statistically analyze the distribution and extinction cross-section of dust,and water droplet particles in different transverse to longitudinal ratios and equivalent radius captured in the external field.