Excited-State Nonlinear Refractive Dynamics In Semiconductor Materials

Semiconductor materials can be used as rectifier, photovoltaic cell, infrared detector, luminescent materials and have potential applications in areas of laser protection, optical storage and optical information processing. Study of optical nonlinear dynamics of semiconductor materials is of great actual significance. This dissertation mainly studies the optical nonlinear dynamics of several organic and inorganic semiconductor materials, including the case of degenerate and nondegenerate. The main research works are listed below:We use degenerate pump-probe 4f imaging technique to investigate the excited-state nonlinear refraction in an organic semiconductor C60/toluene solution at 532nm. Based on the five-level model and with the help of the known lifetime of the energy level, we obtained the absorptive cross sections and determined the magnitude and sign of refractive coefficient of the first excited singlet state and the first excited triplet state simultaneously. The stimulated Rayleigh-wing scattering induced two-beam coupling theory is employed to interpret the energy transfer in toluene. By numerical simulation, we obtained the Kerr refractive index and reorientational relaxation time of the molecule. The contribution of two-beam coupling in toluene to the nonlinearity of the solution is also discussed.Based on the theory of excited states refraction with three-level model, we use the degenerate pump-probe 4f imaging technique to study the single excited state slow-recovery nonlinear dynamics in an organic semiconductor PbPc(CP)4/DMF solution. Firstly, we employ a double 4f coherent imaging system to investigate optical nonlinearity in PbPc(CP)4/DMF at wavelengths from 500 to 600nm. We qualitatively interpret the dispersion relation for nonlinear absorption coefficients and nonlinear refractive indexes which shows an exponential increase with respect to the wavelength. We use a simplified singlet state three-level model to explain the slow-recovery response of nonlinear dynamics in PbPc(CP)4. By numerical simulation, we obtained the absorptive cross-section and refractive coefficient of the first singlet excited state respectively. The results of nonlinear dymaics for DMF exhibit an intensity-dependent pure Kerr effect. Additional nanosecond and picosecond Z-scan experiments are conducted to verify the exactness of the singlet-state three-level model.We expand the PO (phase object) pump-probe technique to the nondegenerate field and use it to study the large free-carrier nonlinear refraction in ZnO and ZnS single crystals. We use the theory of optical nonlinearity for free-carrier to study the quick-recovery large free-carrier refraction in ZnO and pure free-carrier refraction in ZnS. By numerical simulation based on nondegenerate pump-probe theory, we obtain the nondegenerate two-photon absorption coefficient, free-carrier lifetime, free-carrier absorptive cross-section and refractive coefficient of ZnO and ZnS at different probe wavelengths respectively. We propose a fast free-carrier recombination process to interpret the large difference between the free-carrier lifetime, which is determined by free-carrier absorption and free-carrier refraction respectively. Furthermore, we analysed the dispersion relation of free-carrier absorptive cross-section and refractive coefficient in ZnO and ZnS respectively.We use the nondegenerate PO pump-probe technique to investigate the bound-electron and free-carrier nonlinear refraction in ZnSe and CdS single crystal. Based on the theory of optical nonlinearity for bound electron and free carrier, we study the competition of bound electronic Kerr effect and free-carrier refraction in ZnSe. Moreover, we analyse the free-carrier refraction and strong bound electronic Kerr effect in CdS. By numerical simulation based on the nondegenerate pump-probe theory, we obtain nondegenerate two-photon absorption coefficient, nondegenerate bound electronic Kerr refractive index, free-carrier lifetime, free-carrier absorptive cross-section and refractive coefficient of ZnSe and CdS at different wavelengths respectively. We interpret the large bound electronic Kerr effect in CdS induced by its narrow band gap. The experimental results between ZnSe and CdS are compared with each other detailedly.