Study Of Radiation Trapping Force On A Particle For Optical Tweezers

The radiation trapping forces acting on a particle in the optical tweezers system are studied. An introduction of the optical tweezers technology and its applications is presented, and also an analysis of the character of the Gaussian beam and its focusing through lens. Based on a discussion of the momentum conservation of electromagnetic fields, expressions of the radiation trapping forces on a one-layered or multilayered spherical particle in the optical tweezers system are derived by using the generalized Lorenz-Mie theory(GLMT), and for the former, the influences on the axial and transverse radiation trapping forces of such parameters as its radius and refractive index and the beam waist radius and power of the Gaussian beam are analyzed, and a numerical simulation is also made of the radiation trapping forces on a one-layered spherical particle when its size is comparable with the wavelength. About two-layered absorbing particles, there is a discussion as to the influences on trapping forces of their absorbing coefficients, relative refractive indexes and thickness of the two layers. A comparison of the computational results with those by the ray optics and Rayleigh models in the literatures shows that the particle size analyzed theoretically and computed numerically in the thesis can be extended to the size regimes of ray optics and Rayleigh models.