Optical Trapping Of A Single And Multiple Rayleigh Particles

Optical trapping and manipulation of little particles is based onmechanical effect of light. It has wide applications in fields of lifesciences due to the advantages of non-contact and no damage.Centered on theory and research of optical trapping, thefollowing works are completed in the thesis: the first chapter simplydescribes the principle of optical trapping and introduces some novelresearch developments about near-field trapping and array trapping. Thesecond chapter introduces three kinds of the vector diffraction theory,including the vector angular spectrum theory, the vectorRayleigh-Sommerfeld diffraction integral and Richard-Wolf vectordiffraction integral. The formulas for optical trapping force exerted onRayleigh particles are also derived. A theoretical model of near-fieldtrapping Rayleigh particles with high and low refractive indices isproposed in the third chapter. A double-ring-shaped vector beam isemployed to be incident on a subwavelength Fresnel zone plate andthree-dimensional subwavelength bright and dark spots are generated inthe near field which can be used to trap Rayleigh particles with high andlow refractive indices, respectively. The fourth chapter presents another model of spot array simultaneously trapping multiple particles.Subwavelength spot array is formed on the optical axis due to theinterference of two counter-propagating vector beams, which can be usedto trap multiple Rayleigh particles at the same time. Conclusions andprospects are in the last chapter.The innovations in this thesis are that:(1) in the near-fieldtrapping model, a subwavelength Fresnel zone plate, which has particularfocusing properties, is employed to generate tight focused spots in thenear field. The effect on the diffraction field distribution by thepolarization state is also considered. It’s achieved to respectively trap twotypes of particles with different refractive indices in this one model.(2) inthe array trapping model, the effects on the diffraction field distributionby phase difference, numerical aperture of lens and distance between twoadjacent zones of diffraction optical element are discussed. Differentkinds of subwavelength spot array are generated, which cansimultaneously trap multiple particles.