Nonlinear Optics In Cylindrical Parabolic Quantum Wires,,,cubical And Parabolic Quantum Dots

As a new subject nonlinear optics associated with the foundational and applied stud-ies. After the invention of the laser, nonlinear optics is developed quickly in theories andexperiments. Many nonlinear optical phenomena have been observed. With the furtherstudy on the theories and experiments, many nonlinear optical e?ects have been appliedwidely in many scientific fields.With the fast development of the scientific technology, optical communication andinformation processing are more and more important for the progress both in the econ-omy and in the society. Nowadays, the human society has been developing towards aninformation one. Therefore, in the future information society, in order to satisfy the de-mand of high-speed transmitting, processing, and circulating large-capacity information,the development of new nonlinear optical materials with good optical switching, opti-cal computing and optical transmitting properties for hybrid-type optoelectronic deviceinstead of electronic devices has become an important research topic. Many scientific re-searches have shown that the synthetic low-dimensional semiconductor materials are oneof the ideal nonlinear optical materials which can meet the above requirements. For onereason, due to the quantum confinement e?ect in such low-dimensional semiconductormaterials, the nonlinear optical parameters such as nonlinear optical absorption, nonlin-ear optical refractive index and so on can be strengthened significantly. For the other,the low-dimensional semiconductor materials are with fast response time. Therefore, theresearches for the nonlinear optical properties in low-dimensional semiconductor materialshave important practical significance.In the first chapter of my dissertation, a brief history of the development, the researchbackground and recent research achievement of nonlinear optics have been summarized,the specific method adopted has been introduced in detail, and the main contents of thisdissertation have been summarized brie?y.In the second chapter, the nonlinear optical rectification (OR) in cubical quantumdots(CQDs) is studied. The potential model of CQDs is introduced, the eigenfunctionsand eigenenergies of the electron in the conduction bands are presented by quantummechanics principles with the e?ective-mass approximation, and the analytical expressionof the nonlinear OR coe?cient is derived using the compact density matrix approach anditerative method. Finally, numerical calculations for the typical GaAs/AlAs CQDs areperformed, and the dependence of the OR coe?cient on the applied electric field,the length of CQDs andθangle is analyzed in detail. The numerical results show that theOR coe?cient obtained in CQDs is 2～3 orders higher than that in parabolic quantumdots systems. Therefore, it is expected that an optimum system will be achieved bychoosing appropriate values of electric field and the length of CQDs to obtain a strongerχ0(2 ).In the third chapter, the third harmonic generation (THG) in spherical quantumdot(QD) in the presence of electric and magnetic fields is studied. First, the analyti-cal expression of the THG coe?cientχ(33ω) is derived using the compact density matrixapproach and iterative method. And The potential model of QD is introduced, the eigen-functions and eigenenergies of the electron in the conduction bands are presented byquantum mechanics principles with the e?ective-mass approximation. Finally, numericalcalculations for the typical GaAs/AlGaAs spherical QD is performed, the dependenceof THG coe?cient in spherical QD on the radius of QD, the external electric field andmagnetic field on the THG coe?cient is analyzed in detail, respectively. The numericalresults reveal that we choose an optimized the radius of QD, applied electric field andmagnetic field, we can get a very high value of the THG.In the fourth chapter, we have derived the analytical expressions of the absorptioncoe?cients and refractive index changes for a cylindrical quantum wire by using thecompact density matrix approach. Numerical calculations show that the linear changesin the absorption coe?cients and refractive index are not related to the incident opticalintensity, whereas the incident optical intensity has a great in?uence on the third-ordernonlinear change, and the total changes in the absorption coe?cients and refractive indexwill be reduced as the incident optical intensity increases. Moreover, we find that boththe applying electric fields and the parabolic confinement frequency have a great in?uenceon the linear and nonlinear changes in the absorption coe?cient and refractive index dueto quantum confinement e?ect. Thus, not only the linear term but also the nonlinearterm should be considered in calculating the optical characteristic in quantum wire.In the last chapter, the main contents and conclusions of this thesis have been sum-marized.