Analyses For Trapping Force To Micro-particles In Gauss Beam

Optical tweezers use the forces exerted by a strongly focused beam of light to capture and manipulate micro-particles ranging in size from tens of nanometers to tens of micrometers, or can trap the micro-particles near the focus. Because of optical tweezers can non-contact and no invasion operate active cells, it have become an important tool for research in the fields of biology, physical chemistry and medicine.In present, there are two theoretical modes for calculation of the trapping force: Ray-Optics Model (RO) and Electromagnetic Model (EM). In this paper, the optical trapping forces exerting on the Mie particles by using the RO model and the Rayleigh particles based on EM Model are calculated quantitatively. According to the calculation results, the relationship between the optical trapping force and some parameters, including refractive index, radius of the particle, beam waist, laser wave-length, laser power, absorption coefficient of microscopic particles and so on, are discussed. These conclusions are useful for choosing parameters in experiments.This paper is consisted of six chapters. In chapter one, we introduce the researching history, researching background and the researching progress of optical tweezers. The research actuality and application of optical tweezers in domestic and overseas are also introduced. In chapter two, the rudimental principles of the laser trapping technique, including radiation pressure, scattering force, gradient force and optical trap, are analyzed.In chapter three, the character of laser, fundamental-mode Gaussian beam and high-order Gaussian beam are analyzed. In chapter four, the optical trapping forces exerting on Mie particles and Rayleigh particles are calculated, the results show the relationship between the optical trapping force and some parameters of instrument. We also simply introduce the T-matrix method for calculating optical trapping force. In chapter five, we briefly introduce the single-beam optical trap system and discuss the question of choosing the major components of instrument. In chapter six, we give the conclusion of this paper and prospect future of optical tweezers.