The Research On Optical Radiation Forces

Optical radiation forces attract more and more attention recently. Optical tweezers and optical lift are important studies in the research of optical radiation forces. Because optical tweezers can move cells without broken, it is now wildly used in gene fusion, rearrange and cooling atoms. Optical lift was discovered one year ago. It is soon arouse attention by researchers and has a lot meaning in solar sails and micro machines etcIn the first part, we investigate the effect of primary spherical aberration and astigmatism on radiation forces of Raleigh particles, when radial polarized beam is focused by a high numerical-aperture system based on Richards-Wolf vector diffraction method. The research results show that when changing the primary spherical aberration and astigmatism, influences not only reflect on the magnitude of the radiation forces, but also reflect on the balance position and the valid area. These changes caused by positive and negative primary spherical aberration are not always in the same patterns, for the positive spherical aberration make the forward direction gradient forces increases at first and then decreases while this trend also happens on the backward direction gradient forces with negative primary spherical aberration. Under different conditions, the degree of primary spherical aberration will also change and we can make use of it to reduce these influences.In this forth chapter, we employed angular spectrum theory to study the radiation forces on a transparent plate illuminated by a Gaussian beam under geometric optics model. Unlike optic traps, it is depends only on the deference of light pressure to produce the optical lift. The influences of waist radius, transparent plate location and inclination angle are investigated and the distributions of forces are illustrated in longitudinal and transverse components. The numerical results show that if we choose the appropriate parameters there will be enough transverse forces to conquer the gravity force to move the plate upwards. We can also construct a type of angular spectrum which can produce more forces and in turn to derive this type of beam.Then we employ ray-optic (RO) model to study the torque on a specially shaped micro object produced by a vortex beam. Based on conservation of momentum and orbital angular momentum, the formulas for the torque along x, y and z direction are derived. The numerical calculation is given to show the dependence of the optical torques on the inclination angle of the micro object. It is shown that the torque is dependent upon both the light momentum and orbital angular momentum (OAM) of the incident vortex beam. We can control the rotation of the micro object by modulating the topological charge of the incident light beam. Moreover we can make the micro object stop. These results seem important, and may find applications in micro machines and other high-precision instruments.In the end, we investigate on the optical radiation forces and stability upon a triangular prism with the undersides of obtuse triangle under geometric optics model. According to the law of conservation of momentum, the expressions of the optical radiation forces and torque are derived. The distributions of radiation forces and torque are obtained after numerical calculations taken with varying values of rotation angle. The research results show that the triangular prism can get stable uplift under some rotation angles. If the optical power strong enough, the uplift forces can conquer the gravity force to move the triangular prism upwards.These results obtained in this paper provides a theoretical basis for future optical manipulation of objects.