Optical Pulling Force And Lateral Force In Structured Background

The exchange of momentum during the light-matter interaction directly lead to the change of the object's momentum,which exhibits the optical force effect.The optical force effect is a direct manifestation of the connection between the momentum of the light field and that of the object.The related research of optical force aims to understand the lightmatter interaction and to manipulate the object by non-mechanical means.In recent years,the tractor beam and optical lateral force,which have received extensive attention,provide new dimensions for optical manipulation and imply rich momentum exchange processes during light-material interactions.In this paper,we focus on the optical pulling force and optical lateral force of micro-nanometer scaled objects in the structured background: We study the possibility of optical pulling force in photonic crystal background and further analysis the physical mechanism behind it;We study the optical lateral force and the reverse of lateral force for a chiral sphere located at air-water interface.We study the optical force on the sphere with different size and refractive index inside the evanescent mode excited by photonic crystal waveguide,further we analysis the mechanical of optical force in this situation.In the case of weak scattering,the optical pulling force act on the scatterer is dominated by the gradient force of the light field.While the sphere will be pushed along the beam axis when the scatterer's scattering force is not negligible.Thereby,the sorting of two types of particles,strong scattering and weak scattering,is realized.Based on the characteristic which evanescent mode could be curved with the bend of the photonic crystal structure,we could drag the particle along a curved path.We built a periodic photonic crystal background which supports the self-collimation mode and discusses and analyze the optical pulling force of the scatterer inside the channel.Interestingly,we found that the pulling force here is mainly contributed by the intensity gradient force originating from the localized field inside the object and proposed a new mechanism of optical pulling force which is the self-induced backaction.Further,the bandwidth characteristics of the traction force,the dependence on the incident angle,and the robustness to the random disturbance of the structure are discussed.Based on the self-recovery characteristics of photonic crystal self-collimation mode,the scheme of simultaneous traction of multiple objects is discussed.A photonic crystal waveguide that supports dual mode is designed to exert an optical pulling force to a scatterer.From the view of mode conversion,we discuss the mechanism of mode conversion leading to the enhancement of forward momentum which enables optical pulling following the momentum conservation.It has also been analyzed that the reflective portion adversely affects optical traction.We do analysis this could be realized in a wide frequency as this system is not resonance dependent.Further,the topological photonic is introduced to build the one-way channel which also supports dual mode.This could weaken the adverse effects of the reflective portion,and more efficiently achieving optical traction of the object.Optical force model of a chiral sphere at the air-water interface is established,we study the optical lateral force and its reverse effect on a chiral Mie particle under oblique incidence.By discussing the distribution of the Poynting vector,we present an intuitive explanation which the transverse deviation of linear momentum will lead to the optical lateral force and the reverse effect.The effects of the incident angle,the incident polarization,the sphere size effect,and the chirality parameters on the optical lateral force and its reversal effect are calculated and discussed in detail.Two cases of chirality unevenness are also discussed,and it is found that the chirality unevenness,in this case,has little effect on optical lateral force and lateral force reversal.Optical pulling force and lateral force provide new degrees of freedom for optical manipulation,which greatly enrich the function and application range of optical manipulation technology,and also reveal the mechanism of light-matter interaction.The research of this thesis has important value for the theory and application of optical manipulation.