Trapping And Manipulation Of Suspended Particles In Air Based On Bessel Beam With Adjustable Size

In recent years,the air pollution in China cities has become increasingly serious,and the atmospheric particulate(atmospheric aerosols)are the most important pollutants affecting air quality,so the study of suspended particulates in the air has become a hot spot of widespread concern.Particle can be suspended in low-altitude for a long time because of its light weight and small size,and it also absorbs various toxic substances emitted by the industry and produces new particles and secondary pollutants which seriously endanger the health of people.The development of real-time on-line detection techniques for individual particle components will not only help to reveal the formation mechanism of atmospheric particle and accurately infer the source of pollutants.It can also provide a theoretical basis and technical support for the formulation of corresponding prevention and control strategies and governance schemes.In view of this,our research group put forward the idea of on-line detection of single particle by laser capture and laser in-situ spectroscopy.Among them,the key problem is how to improve the stability and control accuracy of particle laser capture.In order to solve this problem,the following work has been done in this paper:Firstly,we built horizontal and vertical laser capture system.On this basis,we study the light field distribution and the influence of regularity for absorption particles’ in capture efficiency and stability.The results show that Bessel beam have higher capture stability than Gaussian beams.The regular particles cannot be trapped in horizontal laser trapping system,and the regular and irregular particles can be captured in a vertical trapping system.This study is a guiding significance to the selection of laser capture devices for different types of particles.Then we propose a method of generating High-order Bessel beam by cross-phase modulation(XPM)caused by thermally induced nonlinearity.The modulation law of the pump beam on the High-order Bessel beam size is studied theoretically and experimentally.The experimental results show that the High-order Bessel beam size varies linearly with the pump power.This method lays a foundation for stable capture and accurate control of airborne suspended particle.Finally,the size tunable High-order Bessel beam is used for capturing and manipulation the absorbing particles in air.Theoretically,we analyzed the mechanism of the force at the different capture positions in the convergent High-order Bessel beam field.Experimentally,by trapping and manipulation graphite particles with sizes ranging from 1 μm to 40 μm,it is found that all these irregular graphite particles can be stably captured by our trapping device for several hours,and we also found that the movement of the particles can be precisely controlled in the millimeter range by adjusting the size of the Bessel beam.In this study,we used the High-order Bessel beam to capture absorbing particles in air,which effectively improves the stability of capture.We first proposed to manipulate the particles by changing the size of the hollow beam,and accurate manipulation of particles in the millimeter range.Compared with the traditional control of particles by changing the laser power or changing the spatial position of the captured light,there are two advantages in our method: firstly,the optical damage caused by the traditional laser power-controlled particles is avoided,secondly,the influence of aberration caused by changing the spatial position of the captured light on the moving accuracy of the control particle is overcome.This study lays a foundation for in-situ on-line study of single suspended particles in air.