Research On The Nonlinear Optics In Quantum Wells

As a new subject nonlinear optics is associated with the foundational and applied studies. After the invention of the laser, nonlinear optics is developed quickly in theories and experiments. Many nonlinear optical phenomena have been observed. With the further study on the theories and experiments, many nonlinear optical effects have been applied widely in many scientific fields.After the essence of all kinds of nonlinear optical phenomena has been known through long-range theoretical and experimental studies, nowadays our researches are being focused on searching and composing the nonlinear optical materials with special function. The ideal nonlinear optical materials require very large nonlinear optical susceptibility, small threshold power and very fast response time. A large number of researches have shown that the low dimensional semiconductor materials are one of the ideal nonlinear optical materials. With the progress of crystal growth technology, many low dimensional quantum systems with different dimensions and sizes can be fabricated. So the nonlinear optical effects in the low dimensional semiconductor materials, such as quantum wells, quantum wires and quantum dots, become an important research content in nonlinear optical fields.In the first chapter of the dissertation, the research background, the fundamental conception and the method have been introduced, and the recent research achievements of nonlinear optics in the low dimensional semiconductor materials have been summarized also.In the second chapter, the refractive index changes in V-shaped quantum wells are studied. Firstly, under effective-mass approximation, we solve the Schrodinger equation to get the expressions of the wave functions and eigenenergy of the electron in the V-shaped quantum well system. The expressions of the total refractive index changes have been derived in the V-shaped quantum by using compact-density-matrix approach and iterative method. We also use GaAs/AlGaAs V-shaped quantum well to find out how the refractive index changes. The results show that the third-order refractive index changes can not be ignored, comparing with the linear refractive index change. Because the value of nonlinear refractive index change has a opposite sign to the value of the linear one, it creates the linear refractive index change decreasing. Another result is that the total refractive index change will raise with electron density increasing or incident intensity decreasing.In the third chapter, polaron effects on the third-harmonic generation in square wells are investigated. The analytic expression of the third-harmonic generation coefficient is derived by using the compact-density-matrix approach and iterative method and the expressions...