Investigation of a vortex beam-based inversion method for aerosol particle size distribution

Vortex light is a type of structured light with a spiral phase distribution. Owing to its unique orbital angular momentum and spiral phase, a new scattering mechanism might emerge when vortex light interacts with atmospheric aerosols. Unlike the existing 3β+2α aerosol particle size distribution (APSD) inversion method, vortex light is utilized instead of the traditional Gaussian beam, and a vortex beam-based 6β+6α regularization algorithm at a single wavelength is proposed to achieve the inversion of the APSD. First, on the basis of generalized Lorenz–Mie theory (GLMT), the aerosol scattering characteristics of vortex light are simulated and analyzed, and the sensitivities of aerosol particles to different types of vortex light are obtained. On this basis, a novel vortex beam-based APSD inversion method is presented. The core idea of this method is that the aerosol backscattering coefficients and extinction coefficients of vortex light with different topological charge L are employed as the optical inputs of the regularization algorithm, and the genetic algorithm is combined to solve the optimal configuration and the corresponding optimal combination of vortex light, thus realizing the rapid iterative inversion of the APSD. Second, taking urban industrial-type aerosols as an example, the simulated APSDs are investigated in detail under different configurations and combinations, and comparisons with the given APSD and error analysis results show that the optimal APSD inversion result can be achieved under the optimal configuration of 6β+6α, and the optimal combination of vortex light of L = 0, 2, 3, 4, 5, and 7. Last, the volume concentration distributions of three typical types of tropospheric aerosols were inverted by the 6β+6α configuration, and the inversion errors were evaluated in terms of the aerosol volume concentration, number concentration, effective radius, and mean radius. The noise effects were also controlled within ±20%, ± 40%, ± 28%, and ±15% under 15% random noise. The results revealed the feasibility and universality of the proposed 6β+6α configuration for APSD inversion, which provides an important theoretical basis for the development and application of vortex light lidar in the atmospheric field.