The Propagation Characteristics Of Some Special Laser Beams And Their Applications In Optical Tweezers

Optical tweezers are useful tools in the fields of biology and physics in investigating cells, macromolecules, metal nanoparticles and so on. The setup of optical tweezers usually uses the fundamental Gaussian beams to manipulate the particles. But recently, researchers have found that some kinds of special laser beam also could be used in optical tweezers. Special methods of manipulation could be realized, or the trapping property would be improved with the use of the special laser beam. The purpose of this dissertation is to investigate the application of some special laser beams in optical tweezers, or to find some new special beam which may offer improvement to optical tweezers.The applications of Lorentz Gaussian beam and circular Airy beam on optical tweezers by numerical calculation are investigated in this dissertation. Some new kind of special laser beams which could be used in optical tweezers are also proposed in theory. Moreover, the holographic optical tweezers is constructed in our lab, the multiple optical tweezers are realized in experiment. The results of our investigate will be helpful in the use of the optical tweezers in different area.In chapter1, the development, the research status and the principle of the optical tweezers are reviewed. The study about the use of the special laser beam in optical tweezers, such as optical vortex, the Bessel beam, the Airy beam, and multiple beam array, is introduced in this chapter.In chapter2, the radiation force of highly focused Lorentz Gaussian beam on a Rayleigh particle is analyzed. Through numerical calculation and the analysis of the trapping stability, we find that the particle can be stably trapped by highly focused Lorentz Gaussian beam, and the trapping range will be more larger compared with the fundamental Gaussian beam.In chapter3, the radiation force of circular Airy beam on a Rayleigh particle is analyzed. Through numerical calculation and the analysis of the trapping stability, we find that the particle can be stably trapped at different positions along the beam axis, and the particles with different refractive indices can be simultaneously trapped by circular Airy beam. Because of the abruptly autofocusing property, the optical trapping with circular Airy beam will be more stable.In chapter4, the setup of optical Airy transform is introduced. Through the numerical simulation of the optical Airy transform of different beams. We find that this setup can be used to generate and control the Airy beam, and a new kind of beam with curve trajectory is obtained through the Airy transform of flat-topped Gaussian beam. In chapter5, the propagation characteristics of the circular Airy beam with optical vortices is investigated. It is found that the abruptly autofocusing property will be enhanced by imposing a single vortex in circular Airy beams. When two opposite vortices are imposed, the intensity in the focal region will increase greatly, because the vortices will collide and annihilate.In chapter6, the setup of holographic optical tweezers in our lab is introduced. We have realized the multiple optical tweezers through the method of computer generated hologram. Then we propose another method, phase Fresnel lens method, to improve the trapping efficiency of the multiple optical tweezers.