Imaging Technique By Using Optical Second Harmonic Generation And The Investigation Of Spin Dynamics In Low Dimensional Semiconductor System

In the area of spintronics, the injection and detection, the transport, and the coherent manipulation of spin polarization are challengeable problems. Among these challenges, the injection and detection of spin is a very important one because it is the first step. Optical injections of spins in non-magnetic semiconductors by using polarized lasers are feasible methods, and the optical detections by the transmittance, polarization rotation, photoluminescence and optical nonlinearity are also widely used. The Optical injection and detection method takes no contacts, low noise, and have high spatial and time resolution.There are three chapters in this thesis. in the first chapter, we made a summary about the development, content and classification of the semiconductor spintronics, especially about the theoretic and experimental results of the injection and detection of spins in non-magnetic semiconductors.The second chapter is mainly about the spin current in semiconductors, including the theoretic predictions and the experimental detections from literature. The prediction concerns the non-dissipative spin current, the intrinsic spin current, the split of the spin wave packet, and the quantum spin Hall effect; the detections include the split of the spin wave packet with and without external fields, the optical injection of spins, the quantum spin Hall effect in HgTe, et al. Our experiments about optical spin injection and detection base on these works.The third chapter descripts the experiments of our works about the spin detection. Firstly, we calculate the direction and distribution of the spin polarization injected by a single linear polarized laser; then we calculate the second harmonic generation in the existence of magnetic and electric dipoles in GaAs crystal, we deduced that the intensities of the effective magnetic and electric field can be measured by the second harmonic generation of left and right circular polarized lasers; and at last we constructed an pump-probe second harmonic generation set-ups and successfully imaged the spatial distributions of the effective magnetic and electric field. We made an conclusion that the second harmonic generation, which is very sensitive to the magnetic and electric field, can be used for the detection of the spin and charges in semiconductors.The forth chapter is the last chapter, in which we measured the enhanced SHG and third-order nonlinearity of ZnO nano-materials, include the ZnO nano-rod arrays, the ZnO microcrystalline films, and the ZnTiO composite films.