Metamaterial Optical Tweezers In The Visible Wavelength Regime

Optical tweezers are used to trap particles with optically-focused beam. However, the size of high power microobjective and optical diffraction limit have a negative effect on the further development of traditional optical tweezers system. Researchers invent the metamaterial optical tweezers based on metamaterial with Nanotechnology. Compared with traditional optical tweezers, the new optical tweezers are small and easy-to-integrate. They attract full attention of related researchers because it is capable of breaking out optical diffraction limit and trapping nano-sized particles. The present research investigates metamaterial optical tweezers system theoretically. It introduces the fundamental theory of optical tweezers and three physical models used to manipulate optical force which are ray optic model, Rayleigh scattering model and electromagnetic model. In the thesis, theoretical simulation of metamaterial optical tweezers system and numerical calculation of optical force are based on the electromagnetic model.Previously, metamaterial optical tweezers can trap a nanoparticle through3D optical trapping produced by Surface Plasmon Resonance (SPR), which requires light to incident at specific angle. However, most of metamaterial optical tweezers are not active in visible wavelength regime. Besides, visible light plays an important role in biomedical detection with naked-eye. As a new kind of metamaterial, fishnet metamaterial is easy to be fabricated and the normal incident light can activate SPR. Meanwhile, the change of its geometry structure could make it work in visible wavelength regime. As a result, the metamaterial optical tweezers working in the visible regime are introduced based on fishnet metatmaterial.This study presents Finite-Difference Time-Domain (FDTD) in detail and it is applied to calculate electromagnetic distribution of metamaterial. Electromagnetic properties of metameterial obtained from the calculation is helpful for sifting out fishnet metatmaterial that works in visible wavelength regime. Additionally, we also made the nano-sized sample near the surface of fishnet metatmaterial and calculated the electromagnetic distribution. Based on law of conservation of momentum, the optical force on the sample was received. The study concludes that fishnet metatmaterial optical tweezers can trap nano-sized samples in visible wavelength regime in theory. Simulation shows that it is suitable for optical trapping of nanoscale particles at illumination intensity of1mW/μm2. The metamaterial optical tweezers have advantages of small size, low power and less strict demands for technique, etc. It is easy to activate light source system.