Research On Trapping And Characteristic Of Absorbing Particles Based On Optical Fiber Tweezer

Optical tweezers is a novel technique for non-contact particle manipulation with the interaction between light beam and particle.It has been widely used in chemistry,biology,physics and other fields.Generally,optical tweezers is to trap strong light transmittance and high refractive index particles with radiation pressure and gradient force,such as biological cells,biological macromolecules and colloidal particles.In recent years,optical tweezers based on photophoresis force has been received much attention of researchers.This optical tweezers is usually used to trap absorbing(opaque)particles,such as dust particles,metal particles,graphite sheets and other new light-absorbing materials.In this paper,we propose and realize trapping and manipulating absorbing particles in liquid environment with optical fiber tweezers.This work not only expands the application field of optical fiber tweezers,but also provides a new theory and feasible method for the absorbing particles trapping and manipulation in liquid environment.Firstly,the development of optical tweezers was briefly introduced in this paper,and then we introduce the characteristics and applications of traditional optical tweezers and optical fiber tweezers.Based on the difference of the trapping mechanism,we discuss the characteristics and development of optical tweezers based on radiation pressure and gradient force and photophoresis force in detailed.Finally,we list the applications of optical tweezers in biology and other fields.Secondly,we introduce photophoresis first and then introduce the principle and characteristics of ?T-type photophoresis force which dominated by the temperature and ??-type photophoresis force which dominated by the thermal accommodation coefficient.We detailedly derive the formula of ?T-type photophoresis force and,especially,??-type photophoresis force and provide theoretical support for the following experimental design.We study the pure liquid glycerol and find that the thermodynamic property is perfectly fit the ??-type photophoretic force.On the basis of these properties we demonstrate trapping of absorbing particles in pure liquid glycerol with ??-type photophoretic force.On this basis,we introduce an annular core fiber optical tweezers with integrating a high refractive index silica microsphere on the annular core fiber end facet and trap the absorbing particles in pure liquid glycerol.We measure the temperature distribution around trapping particles by using the fluorescence dye method and calculate ??-type photophoretic forces tendency.The simulated results were in agreement with the experimental results which are proved that the absorbing particles were trapped by ??-type photophoresis force.It is reasonable and reliable for trapping absorbing particles in glycerol by ring core optical tweezers.Finally,we introduce a seven-core fiber optical tweezers with integrating a high refractive silica microsphere on the seven-core fiber end facet.Light is injected into two cores of the seven-core fiber and form double beam cross light field which is used to trap and manipulate absorbing particles in pure liquid glycerol.Then we transport absorbing particles along two-dimensional which is based on adjusting the output power of two laser beams.Light is injected into three cores of the seven-core fiber,and after the transparent microsphere,the laser beams converge to form a three-beam cross light field.By adjusting the output light power of the laser beams,the three-dimensional transport of particles in the light field is successfully achieved.