Nonlinear Optical Properties Of Two-dimensional Quantum Systems

Since the realization of the strong optical source, nonliner optical phenomena whichcan not be observed before could be observed by scientists. Thus a new brand subjectappears, namely nonlinear optics. Since second harmonic generation was frst realized ex-perimentally in1960, nonlinear optics has obtained great achievement in basic theoreticalresearch, new indentity of nonlinear optical efect, and application as well as explore ofnew nonlinear crystal after ffty-years development. Especially along with development ofnano-technology, some new materials are emerging. Studying the nonlinear optical prop-erties of these new materials will contribute to realization of new concepts and devices.With the rapid advancement of new science and technology, technology for opticscommunications, quantum computer and quantum communications and so on greatlycontribute to development and progress of human society. Human society are on the wayto high-speed and information. To solve some problems arisen in the process of socialdevelopment, some present electronic devices must be replaced by some new devices,such more-rapid, more special, smaller, more environment-friendly. Some very urgentproblems are arisen in the course of social development, one of which is to develop theoptical devices with more efcient and high-speed. Some previous studies have shownthat man-made nano-materials could meet what we study in the feld of nonlinear optics.These low-dimensional semiconductor materials show some advanced properties over bigbulk materials, such size-quantum efect, big nonlinear optical parameters and so on.So it is practically signifcant to study these materials for solving some practical socialproblems. This thesis is based on compact density-matrix. Some detailed investigationsof nonlinear optical properties have been performed for GaAs/AlxGa1xAs. Somediscussion have also carried out about efect of structures parameters of quantum ringon nonlinear optical properties as well as external feld efect. The thesis is divided in tothe following5chapters.The frst chapter is introduction. First, we mainly introduces the research felds anddevelopment process of the nonlinear optics and of quantum ring, application felds ofthe low dimensional semiconductor quantum dots, secondly, we mainly introduces themain contents, and the last part we mainly introduced the theory research methods used.In the second chapter, Optical properties of a two-dimensional quantum ring with pseudopotential in the presence of an external magnetic feld and magnetic fux havebeen theoretically investigated. Our results show that both of the pseudopotentialand magnetic feld can afect the third nonlinear susceptibility and oscillator strength.In addition, we found that the oscillator strength and the absolute value of theresonant peak of the linear, non-linear and total absorption coefcient demonstratesthe Aharonov-Bohm oscillation with magnetic fux, moreover, changes in confnementpotential can infuence the Aharonov-Bohm oscillation in peak. While the resonant peakvalue of the linear, non-linear and total refractive index changes decreases as magneticfux increases.In the third chapter, We have studied the nonlinear optical absorption and thenonlinear optical rectifcation of an exciton in a nanoring in the presence of magnetic fux.Calculations results show that one can control properties of nonlinear optical absorptionand nonlinear optical rectifcation of a nanoring by tuning outer and inner radius.Moreover, we fnd that nonlinear optical properties of a nanoring can be modulated bythe magnetic fux through nanoring.In the fourth chapter, We investigate the linear and nonlinear optical propertiesof a donor impurity confned by a two-dimensional pseudoharmonic potential bothincluding harmonic dot and antidot potentials in the presence of a strong magnetic feld.Calculations are made by using the perturbation method and the compact density-matrixapproach within the efective-mass approximation. Based on the computed energies andwave functions, the linear, third-order nonlinear and total optical absorption coefcientsas well as the refractive index changes have been examined. The results are presented asa function of the incident photon energy for the diferent values of the chemical potentialof the electron gas and the zero point of the pseudoharmonic potential. The results showthat the optical properties of a donor impurity in a two-dimensional pseudoharmonic QDare strongly afected by the zero point of the pseudoharmonic potential，the chemicalpotential of the electron gas and the Coulomb interaction.In the last chapter, summary of the paper and the main results are given, furtherresearch are also mentioned.