Nonlinear Optical Properties Of An Anisotropic QD And A Nanolayer QD

Nonlinear optics is an new important branch subject of modern optics, the develop-ment of which is beneft from the appearance of the laser. When the laser is incident onthe medium, the new optical phenomena can be observed because of the high strengthoptical feld of the laser. However, the linear optical theory used to describe the ordinaryoptics is no longer applicable to these new phenomenon. So the nonlinear optics is intro-duced. Since the strong light incidents to the media, the response can often described byexpressing the polarization as a power series in the feld strength. This the physical originfor the new optical phenomena. The basic theory of nonlinear optics has been greatlybroaden and deeply studies after50-years development. Up to now, based on nonlinearoptical theory, many new nonlinear efects have been discovered, and a great contributionhas been made to get the new optical nonlinear materials.The emergence of new materials is the sign of social progress. The development ofhuman society is entering the information and high-speed. We eagerly need new materialto appear, which is more high-speed, more economical, more environmental protection,compared with classic material, especially on the optical device. With the advance ofnano-technology, the fabrication technology of low dimensional semiconductor materialshas gradually matured up. Much attention has put on the studied of quantum well, quan-tum wires and quantum dot. Quantum dot, due to the restriction on three dimensionaland strong quantum size efect, has been the favour for researchers. A large number ofstudies have shown that that quantum dot is the most ideal one of materials to realize thehigh efciency, the high-speed operation. In this paper, we chooses ellipsoidal quantumdot, anisotropic quantum dot, and nano-layer structure quantum dot as the research ob-jects. Moreover, we fully expounds the nonlinear optical theory and the great potentialapplication of the quantum dots with the efects of the applied feld (applied electric feldand magnetic feld). This paper is divided into fve parts as follows:The fst chapter is introduction. In this part, we introduced general concept of low-dimensional semiconductor, and mainly summarized the knowledge of quantum dots andthe application in various relevant areas. Also, we have introduced the research course ofthe nonlinear optical properties in quantum dots. At last, the theory research methodsused in this paper is mainly introduced, and the research results of this paper is briefysummarized.In the second chapter, we have performed theoretical calculation of second-order non- linear optical rectifcation (OR) coefcient in a typical GaAs/AlGaAs QD with ellipsoidalconfnement potential in the presence of an impurity and an applied electric feld. Usingan appropriate coordinate transformation and the perturbation theory, we have investi-gated the OR coefcient as a function of incident photon energy. Calculation results showthat the values of OR coefcient increase with an increase of applied electric feld. How-ever, the values decrease with increases in confnement strength and ellipticity constant.Additionally, the presence of a donor impurity shifts the OR coefcient peak positions tohigher energies (blueshift), contrary to that of an acceptor impurity.In the third chapter, the linear and nonlinear optical properties in a three-dimensionalanisotropic quantum dot subjected to a uniform magnetic feld directed with respect tothe z axis have been investigated within the compact-density matrix formalism and theiterative method. The dependence of the linear and nonlinear optical properties on char-acteristic frequency of the parabolic potential, on the magnetic feld and on the incidentoptical intensity is detailedly studied. Moreover, take into account the position-dependentefective mass, the dependence of the linear and nonlinear optical properties on the dotradius is investigated. The results show that the optical absorption coefcients (ACs) andrefractive index (RI) changes of the anisotropic quantum dot (QD) have strongly afectedby these factors, and the position efect also plays an important role in the optical ACsand RI changes of the anisotropic QD because of its efect on the size quantization.In the fourth chapter, the linear and nonlinear optical properties in sphericalnanolayer quantum system subjected to a uniform applied electric feld directed withrespect to the z axis have been theoretically investigated within the compact-densitymatrix formalism and the iterative method. In the framework of given approximationsand considering the boundary conditions, the expressions of the energy spectrum andcorresponding wave functions have been obtained. The dependence of the optical ACSand RI changes on the core radius R1, on the inner radii of the clad R2, and on theapplied electric feld F has been investigated. The results show that the optical absorp-tion coefcients (ACs) and refractive index (RI) changes of the nanospherical layer havestrongly afected by these factors. And also, one can obtain a blue or red shift by tuningthe core radius, the inner radii of the clad and the applied electric feld. Engineering theelectric structure of materials by means of these physical quantities, ofers the possibilityof tailoring the energy spectrum to produce desirable nonlinear optical properties.In the ffth chapter, summarizes the paper and shows the main results of our research.And also, some defciencies are pointed out and the further research are mentioned.