| Aerosol particles such as rain,smoke and haze are the main interference sources of pulsed electromagnetic/laser signals.Through the absorption and scattering of pulsed signals,these interference sources will cause the intensity attenuation and waveform distortion of pulsed signals,which will seriously affect the transmission of pulsed signals.It is of great scientific significance and application value to study the scattering and transmission characteristics of aerosol particles on pulsed electromagnetic/laser,which will provide a key basis for applications such as laser communication,laser detection,and laser fuze anti-smog interference.In actual measurement,it is difficult to extract accurate shape information of ultrashort pulses.Rectangular,Gaussian,Hyperbolic secant,Lorentzian and other models are commonly used models to approximately describe the envelope shape of ultrashort pulses.The scattering and transmission characteristics of different models of pulsed lasers in particles and particle groups is an important research topic.In this paper,a corresponding study is carried out on the scattering and transmission characteristics of ultrashort pulses(here,femtosecond pulses are mainly analyzed)by spherical particles(take aerosol as an example).The main research contents of the paper include:1.Based on the Generalized Lorenz-Mie theory and the Fourier transform theorem,the theoretical derivation of the interaction between pulsed laser with arbitrary spatial envelope and spherical particles is given.And through the MATLAB platform,the numerical programming for the analysis of the scattering characteristics of spherical particles under the incidence of Rectangular,Gaussian,Hyperbolic secant,and Lorentzian pulsed lasers is realized.On this basis,(1)the scattering characteristics of different types of pulses,such as hyperbolic secant,rectangular,Lorentzian,Gaussian,etc.,on aerosol particles are analyzed in detail.The effects of particle size,pulse width and other parameters on scattering efficiency,extinction efficiency,backscattering efficiency,phase function distribution and other scattering properties were studied.The results show that,compared with the continuous laser,the oscillation of the scattering characteristic spectrum and the extinction characteristic spectrum of the particles becomes weaker under the incident pulsed laser,and the smaller the pulse width,the better the curve smoothness.The absorption spectrum of the particles is insensitive to the type and pulse width of the laser pulse.By comparison,it is found that under the incidence of different types of pulsed lasers such as rectangular,Lorentzian,Gaussian,etc.with the same pulse width,the overall change trend of the scattering characteristic curves of aerosol particles is the same,and the difference in scattering characteristics becomes larger when the pulse width is smaller.(2)The variation of the optical properties of aerosol particles with the particle size,scattering angle,beam order,beam half-cone angle and pulse width under the axial incidence of pulsed Bessel beam was analyzed.In terms of scattering efficiency and backscattering efficiency,as the beam order and half cone angle increase,the overall value decreases greatly.The difference of the scattering characteristic spectrum under different pulse widths also increases with the increase of beam order and half cone angle.(3)The transformation of the internal field distribution characteristics of the Gaussian plane pulse wave incident aerosol particles with the complex refractive index,particle size and pulse width of the particles is preliminarily simulated.2.Based on the transmission theory of ultrashort pulsed beams in discrete random media,the transmission characteristics of ultrashort pulsed beams in complex atmospheric environment are studied by using the Two-Frequency Mutual Coherence Function.Based on the assumption of single scattering,the transient Mie scattering theory is used to analyze the extinction characteristics of aerosol particles on pulsed beams.On this basis,the characteristics of broadening and time delay of pulsed beams with different pulse widths in aerosols are analyzed under the conditions of different spectral distributions and different concentrations of aerosol particles.The results show that with the increase of transmission distance,the laser transmittance decreases exponentially,and the characteristics of pulse broadening,peak time delay in transmission are closely related to pulse width,transmission distance,particle number density and particle size. |
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