Second-Order And Third-Order Nonlinear Optical Properties In Micro Nano Systems

In recent years,the rapid development of crystal growth technologies（such as molecular beam epitaxy,liquid phase epitaxy and chemical vapor deposition）has made it possible to prepare semiconductor nanostructures of various sizes.These structures are interesting because the movement of charge carriers can be limited in one,two and three dimensions,and the energy levels of electrons are quantized in the direction of restriction,which provides the possibility to effectively control the physical properties of these structures.The nonlinear optical properties of low-dimensional semiconductor structures have attracted extensive attention due to their potential applications in electronic and optoelectronic devices.Quantum dots（QDs）are the most ideal low-dimensional nanomaterials.The size of quantum dots in all directions of three-dimensional space varies from a few nanometers to hundreds of nanometers,and the movement of electrons in them will be restricted in three directions.Therefore,compared with superlattices,quantum wells and quantum wires,the quantum confinement effect will be more obvious,and the nonlinear optical effect will be significantly enhanced.Therefore,the nonlinear optical properties in QDs systems have attracted extensive attention.In this paper,the nonlinear optical properties in QDs systems under different limiting potentials have been studied as follows:（1）Effects of hydrostatic pressure,temperature and Al-concentration on optical rectification（OR）of GaAs/Ga_1-xAl_xAs spherical QDs under a like-Hellmann potential are discussed in detail.The solution of Schr?dinger equation is adopting Nikiforov–Uvarov（NU）method.Using the compact density-matrix approach,an analytical expression of the OR coefficient can be obtained.The result of the calculation illuminates that hydrostatic pressure,temperature,Al-concentration and the radius of the QDs can make an impact on the energy level interval,dipole moment matrix elements,effective mass and other factors,so that the peak value of OR coefficient and resonance peak changing under the action of these factors.Furthermore,the potential depth have a bearing on the OR coefficient.（2）The simultaneous effects of hydrostatic pressure,temperature and Al-concentration on the second-harmonic generation（SHG）coefficient for GaAs/Ga_1-xAl_xAs tuned QDs under parabolic-inverse squared potential plus the modified Gaussian potential in a perpendicular magnetic field are studied in detail.The analytical expression of the SHG coefficient can be obtained using the density matrix theory and iterative method.The numerical results of GaAs/Ga_1-xAl_xAs tuned QDs are given.The result of calculation illuminates that the applied magnetic field,Al-concentration,hydrostatic pressure,temperature and the harmonic confinement frequency can make an impact on energy level interval,the product of matrix elements,transition frequency and other factors so that the peak value of SHG coefficient and resonance peak changing under the action of these factors.（3）In this work,third-harmonic generation（THG）of GaAs/Ga_1-xAl_xAs spherical QDs affected by like-Deng–Fan–Eckart（DFE）potential are carefully analyzed for different applied tuning parameters（pressure,temperature and Al-concentration）.The eigensolutions of the radial Schr?dinger equation are obtained using NU method within the effective mass approximation.The results show that the energies and dipole matrix elements are strongly dependent on like-DFE potential parameters and applied tuning factors.Moreover,we find that these parameters have a significant effect on the position and magnitude of resonant peak of THG coefficient.