In this work optical properties of two dimensional quantum well structures are studied. Variational calculation of the eigenstates in an isolated quantum well structure with and without the external electrical field is presented. At weak fields a quadratic Stark shift is found whose magnitude depends strongly on the finite well depth. It is observed that under external electrical field, the asymmetries due to lack of inversion symmetry leads to higher order nonlinear optical effects such as second order optical polarization and second order optical susceptibility.
In this work optical properties of two dimensional quantum well structures are studied. Variational calculation of the eigenstates in an isolated quantum well structure with and without the external electrical field is presented. At weak fields a quadratic Stark shift is found whose magnitude depends strongly on the finite well depth. It is observed that under external electrical field, the asymmetries due to lack of inversion symmetry leads to higher order nonlinear optical effects such as second order optical polarization and second order optical susceptibility.
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.
It has recently been shown that the dipole matrix elements between subbands in semiconductor quantum wells are extremely large.1 Third-order nonlinear susceptibilities are proportional to the fourth power of these matrix elements. Large nonlinearities have thus been predicted for these systems, in particular an intensity-dependent index of refraction suitable for use in all-optical logic elements.1 Second-order nonlinearities vanish identically in symmetric wells, suggesting the use of asymmetrically graded quantum wells for quadratic interactions.2 External bias electric fields also break the inversion symmetry, resulting in Stark shifts and large quadratic susceptibilities whose sign depends on the direction of the applied field. The magnitude of the nonlinearity depends on the carrier density, the dc bias field, and the detuning of the fundamental and second harmonic frequencies from resonances.
The effects of external applied fields on the electron-related optical nonlinear properties in a short-range bottomless exponential potential quantum well are investigated. The potential profile behaves as inverse square root in the vicinity of the origin and vanishes exponentially toward infinity, supporting a finite number of bound states whose energies and wave functions are determined within the effective-mass approximation. The linear, third-order nonlinear and total optical absorption coefficients (TOACs) as well as the coefficient of relative refractive index changes (RRICs) of the system are calculated from the expressions derived in the framework of the compact density matrix approach. The results obtained after numerical calculations show that with the effect of the static electric and magnetic fields (high-frequency THz laser field), the resonant peak position of the optical response shifts toward higher (lower) energies and the magnitude of the peak increases.
In this study, the effects of external electric, magnetic, and non-resonant intense laser fields on the optical absorption properties of a GaAs/Al0.30Ga0.70As single quantum well were theoretically investigated. The electronic structure was obtained by solving the one-dimensional Schrödinger equation within the effective mass approximation using the finite difference method, and the transition energy, dipole matrix element, and linear optical absorption spectra were compared under different field conditions. The results show that electric and magnetic fields produce limited but systematic shifts in the optical absorption resonance. In contrast, the non-resonant intense laser field modifies the effective well potential and leads to a more pronounced and nonmonotonic change in the transition energy and absorption spectrum. Under combined-field conditions, the optical resonance can be tuned depending on the applied field parameters. These findings indicate that the optical absorption response of GaAs/Al0.30Ga0.70As quantum wells can be controllably modified by external fields and that the investigated structure provides a theoretically meaningful model for field-controlled optoelectronic applications.
Abstract In this present study, the effects of electric, magnetic, and non-resonant intense laser field (ILF) on the linear, third-order nonlinear, and total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs) of GaAs quantum well, having Hulthen confinement potential, were theoretically investigated. In addition, the dependence of the nonlinear optical properties in the structure on the optical intensity of incident photon and the inverse relaxation time was also calculated. To do this research, firstly the energy eigenvalues and eigenfunctions of the structure were calculated by using the effective mass and envelope function approaches. By using these calculated subband energy levels and wave functions belonging to these levels, the nonlinear optical properties of the system were obtained via the iterative method, within the compact density matrix approach framework. The obtained numerical results show that the optical properties of the considered system depend on the externally applied fields. With the applied external electric and magnetic field, the peak positions of TOACs and RRICs shift to higher energies, and the peak magnitudes increase. The high-frequency ILF applied to the structure shifts the peak positions of TOACs and RRICs initially towards higher energies and then towards lower energies and their peak sizes increase. These results show that the optical properties of the system can be adjusted purposively by changing the magnitude of applied external fields.
. In this study, the effects of a non-resonant intense laser field and the Al-concentration on the optical rectification, second and third harmonic generation in asymmetric double quantum well are investigated within the compact density matrix approach theoretically. The results show that the intense laser field and the Al-concentration lead to significant changes in the coefficients of nonlinear optical rectification, second and third harmonic generations. Keywords: Asymmetric double quantum well, Nonlinear optical rectification, Second and third harmonic generations, Intense laser field Özet. Bu çalışmada, asimetrik çift kuantum kuyusunun doğrusal olmayan optik düzeltme, ikinci ve üçüncü harmonikleri üzerine Al-konsantrasyonu ve rezonans olmayan yoğun lazer alanının etkisi kompakt yoğunluk matris yaklaşımı kullanılarak teorik olarak incelenmiştir. Sonuçlar, yoğun lazer alanı ve Al-konsantrasyonun doğrusal olmayan optik düzeltme, ikinci ve üçüncü harmonikler üzerine önemli değişmelere neden olduğunu göstermektedir.