| Compared with conventional visible light detection and infrared detection,polarization detection technology has the advantages of multi-dimensional information,strong fog permeability and less interference by background light sources.It is widely used in the fields of optical remote sensing,lidar,laser ranging,laser communication and atmospheric environment monitoring.In practical applications,aerosol particles,suspended particles,gas molecules and other scattering media in the atmosphere will affect the transmission characteristics of polarized light waves.Polarized light waves has obvious depolarization due to scattering,which greatly affects the test results.However,when the polarized light wave is transmitting in the atmosphere,its polarization characteristics are regularly related to the optical properties of atmospheric particles.By analyzing this law,we can not only make corresponding compensation in the detection system,but also deduce the relevant optical information in complex weather.Therefore,the study of depolarization characteristics of narrow pulse laser transmission in the atmosphere has become one of the key problems to be solved in the development of optical remote sensing,laser radar,atmospheric environmental monitoring and other fields.Aiming at the depolarization problem of 1064 nm narrow pulse laser propagation in the atmosphere,the following works are carried out in this paper:In theory,the concept of polarized light and the characterization method of polarized state are summarized.Through the derivation of Mie scattering theory formula,the optical properties of four common aerosol particles are numerically calculated.On this basis,the scattering characteristics of aerosol particles are further discussed.Then based on Monte Carlo algorithm and Mie single scattering model,the Monte Carlo model of multiple scattering depolarization of narrow pulse laser is established,and the multiple scattering process of photon in scattering medium is simulated.The influence of particle number concentration,transmission distance,particle radius and polarization state of incident light on the depolarization degree of forward scattering light is calculated and analyzed.In the experiment,aiming at the problem of polarization measurement of narrow pulse laser,a polarization measurement system with high-speed real-time response is improved.The semi physical method is adopted,and the smoke particles with two effective particle sizes are taken as typical research objects.Under the irradiation of 1064 nm narrow pulse laser,the depolarization degree data of forward scattered light with different particle number concentration,transmission distance,particle radius and polarization state of incident light are obtained,and the experimental data are analyzed in detail.The results of this study show that the increase of particle number concentration,transmission distance and particle radius will increase the probability of multiple scattering of photons in the medium,resulting in obvious beam depolarization.The depolarization degrees of the incident light with different polarization states are all increased.The circularly polarized light has better polarization retention than the linearly polarized light,and when the particle size in the medium changes,the circularly polarized light also shows certain insensitivity in the transmission process.At the same time,the polarization maintaining ability of elliptically polarized light is stronger than that of linearly polarized light and weaker than that of circularly polarized light.The difference in depolarization characteristics of elliptically polarized light mainly comes from the ellipticity angle.The research results of this paper can not only provide theoretical reference for the application of narrow pulse polarized laser in the fields of optical remote sensing,lidar,laser ranging and laser communication,but also provide data support and theoretical guidance for the development of narrow pulse polarized laser equipment. |
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