| The technology of optical tweezers has been developed and applied extensively in the fields of biology, physics, chemistry, and so on, but its development is limited by some factors, such as the size of high N.A. objective and the optical diffraction limit. The technology of near-field optical tweezers has overcome the limitations of the conventional optical tweezers in the different aspects. It has broken through the diffraction limit, and may catch the nano-scale particles.The study includes the principle of optical tweezers, the near-field optical theory, development of near-field optical tweezers technology, the finite difference time domain method(FDTD) theory, as well as the design of the experiment platform for near-field trapping in the focus evanescent field.First, introduce the principle of optical tweezers in detail, explain the process of optical tweezers trapping from different aspects, such as optical momentum, optical pressure, gradient force, scattering power and so on. And give details of development of the theory and experiment about the near-field optical tweezers.Secondly, introduce the basic principles of finite difference time domain method(FDTD), Yee cell and basic equations of FDTD. Basing on the theory of optical tweezers, do a simulation of evanescent field which have a total reflection internally using two-dimensional FDTD method. We discuss the radialization stress of the micron particles, using three-dimensional FDTD method.Finally, we attempt to design a experiment platform for near-field trapping in the focus evanescent field, based on the theoretical analysis and numerical simulation.Near-field optical tweezers technology can significantly reduce the size of trapped particles, and realize nano-capture, because of near-field optical evanescent field attenuating sharply along with the distance. In the field of nanotechnology, it becomes another higher precision instrument for biology, chemistry, physics and so on.
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