Transverse Force Of Rayleigh Particles In The Optical Field

Optical tweezers is the optical potential basing on the interaction between the scattering force and the gradient force , and can control micro-particles ranging in size from tens of nanometers to tens of micrometers. As the Optical tweezers has the characteristics of non-contact and no invasion, and becomes the important implement of the biology science and promotes the interaction and the development between the physics and biology.The expression of the minimum particle radius for Zero-order Bessel beams capture was deduced through the electromagnetism model ,and the transverse forces and potential depths were calculated for Rayleigh particles in Zero-order Bessel ,Gaussian and Laguerre-Gaussian beams respectively . We calculate the theoretical conditions of the Rayleigh particles stably captured and discuss the relationships of the experiment parameters, the characteristics of the particles and the conditions of surrounding medium to the transverse force. Through the calculations on the Rayleigh particles in Zero-order Bessel, Gaussian and Laguerre-Gaussian beams, the conclusion can be obtained that the transverse force and the potential depth increase with the decreasing of the laser wavelength, decrease with the decline of the comparative refractive index and increase with decline of the optical waist radius. The intensity gradient distributing has the most influences on the ability of capturing, and the bigger optical intensity can create deeper potential and more stable capture. The optical intensity gradient of Zero-order Besssel beam and Laguerre-Gaussian beams are both bigger than the Gaussian beam intensity gradient. So Zero-order Besssel beam and Laguerre-Gaussian can produce deeper potential well, and overtake the influences of Brownian motion to capture the Rayleigh-particles.This thesis is consisted of three chapters. In the first chapter, the researching history, researching background and the researching progress of optical tweezers are presented. In chapter two, the principles of the laser trapping technique are analyzed, and the gradient force and scattering forces are generally introduced. In chapter three, the transverse forces and potential depths exerting to a Rayleigh particles in Bessel and Gaussian and Laguerre-Gaussian beams are calculated. The relations between the optical trapping force and the main parameters of the system are discussed.