Research On Optical Trapping Characteristics Of Absorbing Particles In Liquid

In 1986,Askin invented the single-beam optical tweezers technology to capture and manipulate micro-biological particles by focusing Gaussian beam.Since then,the door of micromanipulation has been opened.For more than 40 years,optical tweezers technology has been an indispensable tool in biology,physical chemistry and condensed matter physics.Optical tweezers technology mainly includes two types.One is based on gradient force and scattering force.Such optical tweezers technology can achieve the control of particles with high refractive index.The other method is based on photophoresis force,generally capture the light-absorbing particles in media,which has a wide application prospect in medicine,pharmacology,atmospheric science and planetary motion.At present,optical tweezers for absorbing particles are mainly used to capture and transport the particles in air,but the research on controlling the absorbing particles in liquid is still at two-dimensional level.The main difficulty in controlling strongly light absorbing particles in the liquid is that the side illuminated by light will absorb more energy,thus it will induce positive photophoretic force,which pushes the particle away from the light source and fail to achieve stable capture.Aiming at the research status of absorbing particles in liquid,this paper proposes an optical trapping technique for absorbing particles in liquid which based on photophoresis force.The stress of the particles is derived and analyzed in theory,and we solve the magnitude of FΔα type photophoretic force.By designing a set of two-way real-time monitoring optical tweezers system,we realize the 3-D trap and axial displacement of absorbing particles in liquid,with the fluorescence temperature field of trapped particle taking and the data’s processing.This paper provides a non-contact and high-precision control method which can achieve three-dimensional capture and axial position control of strongly absorbing particles,and which provides the possibility for studying the unique characteristics of absorbent particles i liquid media.The following researches are mainly carried out:1.The conventional optical tweezers technology based on radiation pressure and gradient force is not suitable for the capture of highly absorbing particles.This paper proposes the optical tweezers technology scheme for the capture of highly absorbent particles which based on optical photophoretic force,and deduces the theoretical formula.Then,based on Thorlabs’ cage optical components,a set of spatial optical tweezers system was designed and built.The system was used to capture and control single absorbent particles in the liquid environment in 3d.By changing the light power,the displacement control of particles along the beam propagation direction is realized,and the control precision can reach nm level.2.We designed and built a side-bottom dual-view field real-time observation system to realize simultaneous observation of the trapped absorbing particles from the side and the bottom view.The design of side fluorescence excitation module was improved and the fluorescence temperature data of absorbent particles captured in liquid environment were record.3.In order to research the experiment results of trapped absorbing particles when we use different objective to construct various degrees of focus,the objective lens in the optical tweezers system was replaced by 3D modeling and 3D printing technology.The axial displacement distance of particles was widened,and the relationship between optical power,axial displacement and optical trap force were explored.