Optical Trapping And 3D Manipulation Of Aerosol Particles In Air Based On Photophoretic Force

Aerosol particles are one of the major components of air pollution.A large heterogeneity exists among the aerosol particles due to the wide range of sources and the series of rapid physico-chemical evolution processes occuring in the atmospheric environment.In order to reveal the formation mechanism of atmospheric particulate matter and accurately infer the source of pollutants,it is necessary to develop in-situ analysis methods for single suspended aerosol particles.Laser trapping provides an important tool for in situ analysis of single particles for its significant advantages of being non-contact,non-destructive,and low-cost.Laser trapping-assisted in-situ spectroscopy has shown considerable application prospects in single particle analysis in air.In thoes methods,the stability and manipulation accuracy of laser trapping have a great influence on the sensitivity and measurement accuracy of single particle analysis.In order to achieve stable trapping and three-dimensional precise manipulation of particles,the following work has been done in this thesis:Firstly,a single aerosol particle capture system was constructed using a size-tunable hollow beam.It is found that the aerosol particles can be stably trapped for several hours in both vertical and horizontal trapping configurations.In addition,the position of a large number of trapped aerosol particles was observed,and it was found that the trapped aerosol particles were inside and close the hollow beam ring.Furthermore,combining with the theory of photophoretic force,we analyzed the force mechanism of particles experiencing in the hollow light field,which lays a foundation for the manipulation of particles.Secondly,one-dimensional manipulation of aerosol particles along the laser output direction(z plane)was achieved by adjusting the size of the hollow beam in both vertical and horizontal devices.And the manipulation accuracy is in micron-level.Then,employing a a wedge-shaped prism in the the hollow beam trapping setup,we realized particle rotation by rotating the wedge-shaped prism.The force exerting on the trapped aerosol particles during the rotation process was analyzed.Combing the above two ways,three-dimensional manipulation of aerosol particles is achieved.Finally,the aerosol sampling device was improved by sputtering carbon black ethanol aqueous solution with Gaussian light.Through the statistics of the particle size trapped in the hollow beam trap and the Gaussian beam trap,the screening ability of the Gaussian beam trap for particles of different sizes is proved.The resulting accumulated modal particles were further captured and manipulated with a hollow beam,and the trapped particles was analyzed using laser-induced breakdown spectroscopy.An excellent reproducibility is achieved,proving that the proposed particle trapping and three-dimensional manipulation method can be used in a single particle analysis.In all,three-dimensional opticla manipulation of individual aerosol particles in both vertical and horizontal directions is realized,and the accumulation modal particles were studied in combination with LIBS.This work provides a useful method for non-contact,non-destructive in situ analysis of individual aerosol particles.