Optical nonlinearities in three-level asymmetric semiconductor quantum wells (QW) are analyzed (optical rectification, second harmonic generation (SHG)). The influence of permanent dipole moments on SHG conversion efficiency for various QW structures is investigated. It is found that as the pump photon wavelength increases so does the relative importance of the permanent dipole moments, provided the QW is resonant.
Optical nonlinearities in three-level asymmetric semiconductor quantum wells (QW) are analyzed (optical rectification, second harmonic generation (SHG)). The influence of permanent dipole moments on SHG conversion efficiency for various QW structures is investigated. It is found that as the pump photon wavelength increases so does the relative importance of the permanent dipole moments, provided the QW is resonant.
The influence of permanent dipole moments of quantized states on intersubband second harmonic generation based on quantum-interference induced transparency in semiconductor quantum wells is explored using the harmonic balance method. The permanent moments are found to be quite important: they affect the transparency condition, especially at larger pump intensities. Hence, both the conversion efficiency and the optimal interaction path length change significantly when accounting for the permanent moments, and the conversion efficiency is reduced.
Some interesting features of the intrinsic optical bistability, based on intersubband transitions in asymmetric semiconductor quantum wells, are analyzed within the two-level model. In particular, the excitation-induced levels shifting, on which the bistability relies, is found to be significantly influenced by the exchange-correlation potential, thus requiring self-consistent modeling-the simple charge separation dipole model is not accurate enough. The optical influence of the permanent dipole moment, characterizing bound states in asymmetric quantum wells, is also analyzed. This is found to have some beneficial and some adverse consequences on bistability, both of which may be quite important in realistic structures.>
Abstract In this paper, the effects of external electric, magnetic and non-resonant intense laser fields on the nonlinear optical rectification (NOR), second-harmonic (SH), and third-harmonic (TH) generation in a GaAs quantum well with asymmetrical Gaussian potential are theoretically investigated. Firstly, the energy eigenvalues and eigenfunctions of a single electron confined in the structure are obtained by using the diagonalization method within the framework of the effective-mass and parabolic band approaches. Then, using these energy eigenvalues and eigenfunctions, expressions derived within the compact density matrix approximation has been employed to calculate the coefficients of the nonlinear optical response in the structure. The obtained simulation results show that the influence of the external fields leads to significant changes in the coefficients of nonlinear optical rectification, second and third harmonic generation in the system. As a result, it has been seen that the amplitude and position of the peaks of nonlinear optical rectification, second and third harmonic coefficients can be controlled by changing the applied external fields.
The nonlinear optical properties of semiconductor heterostructures, such as GaAsAl/GaAs alloys, are studied with analytic and numerical methods on the basis of quantum mechanics. Particularly, second and third-order nonlinear optical properties of quantum wells described by the various types of confining potentials are considered within the density matrix formalism. We consider a Pöschl-Teller type potential which has been rarely considered in this area. It has a tunable asymmetry parameter, making it a good candidate to investigate the effect of the asymmetry on the nonlinear optical properties. The calculated nonlinear quantities include nonlinear absorption coefficient, second-harmonic generation, optical rectification, third-harmonic generation and the intensity-dependent refractive index. The effects of the DC electric field on the corresponding nonlinearities are also studied. The results are in good agreement with the results obtained in other types of quantum wells, such as square and parabolic quantum wells. The effects of the Coulomb interaction among the electrons on the nonlinear intersubband absorption are considered within the rotating wave approximation. The result is applied to a Si-delta-doped, square quantum well in which the Coulomb interaction among the electrons are relatively important, since there has been no work on the nonlinear absorption spectrum of the Si-\delta-doped quantum well. The results are found to be new and interesting, especially when a DC electric field is included in the calculations.
Recently, there has been an increasing interest in nonlinear optical properties of semiconductor quantum well structures, because of their relevance for studying practical applications and as a probe for the electronic structure of mesoscopic media. In this paper, the nonlinear electro-optic effects in special asymmetric quantum wells are studied. Because of this kind of quantum well is more approximate a practical quantum well between the conduction band and valence band, and it can be realized very easily in experiment. The analytical expressions of electro-optic coefficient have been derived by compact density-matrix approach and the numerical results were presented for GaAs/AlGaAs asymmetric quantum wells. The shape of the quantum well varying with the parameter a and the parameter V_0 were plotted. It is found that the asymmetry of the quantum wells enhances with the increase of parameter a. On the contrary, the asymmetry of the quantum wells decreases with the increase of the parameter V_0. The maximum values of the electro-optic coefficient varying with the parameter a and the parameter V_0 were plotted. The numerical results show the electro-optic coefficient enhances with the increases of the parameter a and the decrease of the parameter V_0. Therefore, it is found that the electro-optic coefficient increases with the enhancement of the quantum wells' asymmetry. The electro-optic coefficient as a function of the photon energy with different values of parameter a and different values of parameter V_0 were also plotted. It can be observed that there are three peak values in the figures, respectively. And it is obvious that the larger the asymmetry of quantum wells is, the bigger the peak value is. It can be seen that with the increase of the asymmetry of quantum well, the peaks move to the low energy side. Moreover, the electro-optic coefficient obtained in this special quantum well is as large as 10~(-6) m/V. With the advances of nanofabrication technology recently, it is possible to fabricate such semiconductor quantum wells and it is possible for us to get better nonlinear materials in experiments.
The effects of a static electric field on the nonlinear optical rectification, second- and third-harmonic generation in a quantum well described by Morse potential are theoretically investigated. Analytical expressions for the optical coefficients due to intersubband optical transitions with an applied electric field are extracted from the compact-density matrix approach and iterative scheme. Numerical results presented for a typical GaAs quantum well reveal the feasibility of control of optical transitions between the size-quantized subbands. In addition, we have to emphasize the fact that the optical response of the system is remarkably sensitive to the electric field and structural range parameter.