Theoretical And Experimental Investigation Of The Influence Factors Of Stiffness Of Optical Tweezers

Optical tweezers is a technique for trapping and manipulating micro particles based on the mechanical effects of light.This technique has been widely applied to the fields of physics,chemistry and life sciences because of its low damage,non-mechanical contact,wide range of manipulated objects,high-precision measurement of micro-force and micro-displacement,etc.Among the many characteristics of optical tweezers,high-precision measurement of micro-force is an important basis for the application.Focused on mechanical properties of optical tweezers,the research in this thesis covers the following aspects:1.The impact of particle's size and refractive index,numerical aperture of an objective lens and polarization state of light field on optical trap stiffness of optical tweezers are theoretically investigated with the T matrix method in electromagnetic scattering model.These theoretical research works,will provide theoretical guidance and reference for the experimental investigation of the influence factors of optical trap stiffness of optical tweezers.2.An optical tweezers system with the function of generating and switching multi-polarized light fields is designed and built.This system is designed with modular design,which is compact and stable in structure,and convenient for switching and adjustment.The function,parameters and selection basis of each device in each module are given in detail,which provides an experimental basis for calibrating optical trap stiffness of optical tweezers.3.The impact of polarization state of light field,particle's size,particle's refractive index and laser power on optical trap stiffness of optical tweezers are experimentally investigated with quadrant photodiode detector tracking the displacement of Brownian motion of particles and power spectral density method calibrating the stiffness of optical tweezers.The three-dimensional optical trap stiffness of cylindrical vector beam(radially polarized beam,azimuthally polarized beam)and Gaussian beam(linearly polarized beam,circularly polarized beam)for trapping different sizes silica beads are compared and investigated.These experimental research works provide reference for the practical application of optical tweezers.