Nonlinear Optical Rectification,Second and Third Harmonic Generations in Square-Step and Graded-Step Quantum Wells under Intense Laser Field

For square-step quantum wells(SSQWs) and graded-step quantum wells(GSQWs), the nonlinear optical rectification(NOR), second harmonic generation(SHG) and third harmonic generation(THG) coefficients under an intense laser field(ILF) are analyzed. The found results indicate that ILF can ensure a vital influence on the shape and height of the confined potential profile of both SSQWs and GSQWs, and alterations of the dipole moment matrix elements and the energy levels are adhered on the profile of the confined potential. According to the results, the potential profile and height of the GSQWs are affected more significantly by ILF intensity compared to SSQWs. These results indicate that NOR, SHG and THG coefficients of SSQWs and GSQWs may be calibrated in a preferred energy range and the magnitude of the resonance peak(RP) by tuning the ILF parameter. It is feasible to classify blue or red shifts in RP locations of NOR, SHG and THG coefficients by varying the ILF parameter. Our results can be useful in investigating new ways of manipulating the opto-electronic properties of semiconductor QW devices.     

Electronic and Optical Properties of a Lens Shaped Quantum Dot under Magnetic Field: Second and Third-Harmonic Generation

In the present work, we have studied electronic and optical properties of a lens-shaped quantum dot under an external magnetic field. For this goal, we have calculated the energy levels and wave functions using the finite element method(FEM) for different values of magnetic field. We have also studied effect of magnetic field on second harmonic generation(SHG) and third-harmonic generation(THG) in the lens-shaped quantum dot. In this regard, we have obtained an analytic expression for the SHG and THG by a compact density matrix approach and an iterative procedure. According to the obtained results, it is found that the presence of the magnetic field affects the symmetry of the system. The SHG and THG are decreased with increasing the magnetic field. The magnetic field has a great influence on the energy levels, wave functions, the SHG and THG in a lens shaped quantum dot.     

Electronic and Optical Properties of a Lens Shaped Quantum Dot under Magnetic Field：Second and Third-Harmonic Generation

In the present work, we have studied electronic and optical properties of a lens-shaped quantum dot under an external magnetic field. For this goal, we have calculated the energy levels and wave functions using the finite element method (FEM) for different values of magnetic field. We have also studied effect of magnetic field on second harmonic generation (SHG) and third-harmonic generation (THG) in the lens-shaped quantum dot. In this regard, we have obtained an analytic expression for the SHG and THG by a compact density matrix approach and an iterative procedure. According to the obtained results, it is found that the presence of the magnetic field affects the symmetry of the system. The SHG and THG are decreased with increasing the magnetic field. The magnetic field has a great influence on the energy levels, wave functions, the SHG and THG in a lens shaped quantum dot.     

Electron-related optical responses in triple δ-doped quantum wells

A detailed theoretical study on the electron-related optical responses in triple δ-doped GaAs quantum wells in the presence of non-resonant, monochromatic intense laser field is presented. For this purpose, we first obtained the bound subband energy levels and their corresponding envelope wave functions of the structure for different central doping concentrations within the effective-mass approximation. Then, we calculate the effect of the non-resonant intense laser field on the optical properties of this structure using the compact-density-matrix approach via the iterative method. We found that the optical absorption coefficients and refractive index changes in the triple δ-doped GaAs quantum well can be modulated by changing the central doping concentration and the intensity of the non-resonant, monochromatic laser field. In addition, it is shown that a sufficiently intense laser field suppresses the multiple quantum well configuration towards a single potential well one and the optical response becomes practically independent of the δ-doping concentration.     

Anisotropic optical absorption in quantum well wires induced by high-frequency laser fields

The subband structure and optical properties of a cylindrical quantum well wire under intense non-resonant laser field are investigated by taking into account the correct dressing effect for the confinement potential. The energy levels and wave functions are calculated within the effective mass- approximation using a finite element method. It is found that the absorption coefficient and the saturation intensity are strongly affected by the laser amplitude and frequency as well as by the incident light polarization. As a key result, a large anisotropy in the linear and nonlinear optical absorptions for very intense laser field is predicted. These effects can be useful for the design of polarization sensitive devices.     

Third harmonic generation in quantum dot with Rashba spin orbit interaction

Here we have investigated the influence of magnetic field and confinement potential on nonlinear optical property, third harmonic generation (THG) of a parabolically confinement quantum dot in the presence of Rashba spin orbit interaction. We have used density matrix formulation for obtaining optical properties within the effective mass approximation. The results are presented as a function of confining potential, magnetic field, Rashba spin orbit interaction strength and photon energy. Our results indicate that an increase of Rashba spin orbit interaction coefficient produces strong effect on the peak positions of THG. The role of confinement strength and spin orbit interaction strength as control parameters on THG have been demonstrated.     

Nonlinear optical properties of asymmetric n-type double <Emphasis Type="Italic">δ</Emphasis>-doped GaAs quantum well under intense laser field

The effect of non-resonant intense laser field on the intersubband-related optical absorption coefficient and refractive index change in the asymmetric n-type double δ-doped GaAs quantum well is theoretically investigated. The confined energy levels and corresponding wave functions of this structure are calculated by solving the Schrödinger equation in the laser-dressed confinement potential within the framework of effective mass approximation. The optical responses are reported as a function of the δ-doped impurities density and the applied non-resonant intense laser field. Additionally, the calculated results also reveal that the non-resonant intense laser field can be used as a way to control the electronic and optical properties of the low dimensional semiconductor nano-structures.     

Electronic and optical properties of asymmetric GaAs double quantum dots in intense laser fields

In the present work, we investigated the effect of an intense non-resonant laser field on the electronic structure and the nonlinear optical properties (the light absorption, the optical rectification) of a GaAs asymmetric double quantum dot under a strong probe field excitation. The calculations were performed within the compact-density matrix formalism under the steady state conditions with the use of the effective mass approximation. The obtained results show that: (i) the electronic structure and, consequently, the optical properties are sensitive to the dressed potential; (ii) the changes in the incident light polarisation lead to blue or redshifts in the intraband optical absorption spectrum; (iii) for specific values of the structure parameters and under an intense laser illumination, the asymmetric double quantum dots can be a good candidate for NOR emission of THz radiation.     

Density of states in a cylindrical GaAs/AlxGa1−xAs quantum well wire under tilted laser field

Within the effective-mass approximation the subband electronic levels and density of states in a semiconductor quantum well wire under tilted laser field are investigated. The energies and wave functions are obtained using a finite element method, which accurately takes into account the laser-dressed confinement potential. The density of states obtained in a Green's function formalism is uniformly blueshifted under the laser's axial field whereas the transverse component induces an additional non-uniform increase of the subband levels. Our results confirm that the tilted laser field destroys the cylindrical symmetry of the quantum confinement potential and breaks down the electronic states' degeneracy. Axial and transversal effects of the non-resonant laser field on the density of states compete, bringing the attention to a supplementary degree of freedom for controlling the optoelectronic properties: the angle between the polarization direction of the laser and the quantum well wire axis.     

Laser-induced reshaping of the density of impurity states in GaAs/AlGaAs nanowires

The binding energy of shallow-donor impurities in a cylindrical quantum well wire irradiated by an intense non-resonant laser field is calculated within the effective mass approximation by using a variational procedure. Accurate laser-dressing effects are considered for both the confinement potential of the wire and the Coulomb potential of the impurity. The computation of the ground state subband energy eigenfunctions for different laser field intensities is based on a bidimensional finite element method. Important changes of the electron probability density under intense laser field conditions are predicted. The study reveals that the laser field compete with the quantum confinement and breaks down the degeneracy of states for donors symmetrically positioned within the nanostructure. A proper analysis of the density of impurity states is found to be essential for controlling the optical emission related to shallow donors in semiconductor quantum wires.     

Effects of hydrostatic pressure and temperature on the nonlinear optical properties of semiparabolic plus semi-inverse squared quantum wells

In this study, the effects of hydrostatic pressure and temperature on nonlinear optical rectification(OR), second-harmonic generation(SHG), third-harmonic generation(THG) and the linear,nonlinear, and total optical absorption coefficients(OACs) of a semiparabolic plus semi-inverse squared quantum well(QW) are theoretically investigated. The results show that hydrostatic pressure and temperature have significant effects on the optical properties of semiparabolic plus semi-inverse squared QWs, and that the energy levels and magnitudes of the resonant peaks of OR, SHG, THG, and the total OACs vary according to the shape of the limiting potential, the hydrostatic pressure, and the temperature. It is easily seen that the peak positions of the resonant peaks of OR, SHG, THG, and the total OACs in the semiparabolic plus semi-inverse squared QW show a red shift with increasing hydrostatic pressure, but a blue shift with increasing temperature. Therefore, the magnitude and position of the resonant peaks of OR, SHG, THG,and the total OACs can be adjusted by changing the hydrostatic pressure and the temperature,which promise a new degree of freedom in the tunability of various electro-optical devices.     

Electron-related nonlinear optical properties of cylindrical quantum dot with the Rosen-Morse axial potential

We present a theoretical study on the effects of intense laser field(ILF) and static electric field on the linear and nonlinear optical properties of a cylindrical quantum dot with Rosen-Morse axial potential under the framework of effective mass and parabolic band approximations. This study also takes into account the effects of the structure parameters(η, V_1, and R). The analytical expressions of the linear, third-order nonlinear and total optical absorption coefficients(TOACs)and the relative refractive index changes(RRICs) are obtained by using the compact-densitymatrix approach. The results of numerical calculations show that the resonant peak position of the TOACs and RRICs shifts towards lower energies and the magnitude of the peak increases with the effect of the static electric field and ILF. In addition, it is observed that while the resonant energies of the TOACs and RRICs of system shift towards the higher(lower) energies with the enhancement of η, V_1, they decrease with the augmentation of R. Thus, the findings of this study show that the optical properties of the structure can be adjusted by changing the magnitude of structure parameters and applied external fields.     

Nonlinear optical rectification and the second and third harmonic generation in Pöschl–Teller quantum well under the intense laser field

In this work, the effect of a non-resonant intense laser field on the optical rectification and second and third harmonic generation in a Pöschl–Teller quantum well is theoretically investigated. In this regard, the coefficients of nonlinear optical rectification and second and third harmonic generation are obtained by using the compact-density matrix approach and an iterative method. Different values of the asymmetry parameters of the Pöschl–Teller potential as well as intense laser field strength have been considered. Numerical results presented for a typical GaAs quantum wells show that higher-order optical effects are considerably sensitive to intense laser field and can be adjusted by a correct choice of asymmetry parameters of the potential.     

Linear and nonlinear intersubband optical absorption in a disk-shaped quantum dot with a parabolic potential plus an inverse squared potential in a static magnetic field

The linear and nonlinear optical absorption in a disk-shaped quantum dot (DSQD) with parabolic potential plus an inverse squared potential in the presence of a static magnetic field are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. The energy levels and the wave functions of an electron in the DSQD are obtained by using the effective mass approximation. Numerical calculations are presented for typical GaAs/AlAs DSQD. It is found that the optical absorption coefficients are strongly affected not only by a static magnetic field, but also by the strength of external field, the confinement frequency and the incident optical intensity.     

Third-harmonic generation in cylindrical parabolic quantum wires with static magnetic fields

The third-harmonic generation (THG) and its conversion efficiency in Al_xGa_1-xAs/GaAs cylindrical parabolic quantum wires with static magnetic fields are studied in detail. The calculated results show that the parabolic confining potential and the static magnetic field have evident influence on the THG and its conversion efficiency. In addition, the conversion efficiency of the THG is also related to the input optical intensity. It is noted that very high conversion efficiency of the THG can be obtained by increasing properly the input optical intensity and choosing an optimized parabolic confining potential and applied static magnetic field.     

Plasmon-Assisted Phase-Matched Second- and Third-Harmonic Generation in Single-Negative Heterostructures

Dispersion relations of surface plasmon polaritons （SPPs） in sandwiched optical systems are studied. The system is actually a kind of SPP waveguides, with two kinds of single negative material （SNG） as core and cladding layers, respectively. Since both TM and TE polarized SPPs can be excited in the structure, the dispersion of SPPs becomes more abundant and leads to colorful nonlinear opticM properties. The authors demonstrate the effective phase-matched second and third-harmonic generation （SHG, THG） assisted by the coupled SPPs. A cascaded second-order nonlinear process can Mso be achieved in the structure when the thickness of the core layer is properly selected, leading to the simultaneous SHG and THG. Further investigations show that much easier phase-matching can be fulfilled in the SNG waveguide array. Our results would be of potential use for surface-enhanced frequency conversion device such as light emitters or lasers.     

Investigation on high efficiency temporal phase modulated broadband second harmonic laser

In this paper, it is the first time to experimentally demonstrate the second harmonic generation (SHG) of temporal phase modulated broadband laser. The SHG conversion efficiency and the characteristic of SHG spectrum are investigated in detail and the relation between SHG conversion efficiency and incident fundamental light intensity is obtained. The highest efficiency of nearly 70% is achieved at the fundamental pulse intensity of 1.6 GW/cm². The experimental results show that the SHG spectrum widths under high and low intensity are both half of the incident fundamental lights, and don’t result in the spectrum narrowing. The obtained results are very useful for operation at the second harmonic wavelength in inertial confinement fusion (ICF) laser facility.     

Intense laser effects on the optical properties of asymmetric GaAs double quantum dots under applied electric field

We investigated the combined effects of a non-resonant intense laser field and a static electric field on the electronic structure and the nonlinear optical properties (absorption, optical rectification) of a GaAs asymmetric double quantum dot under a strong probe field excitation. The calculations were performed within the compact density-matrix formalism under steady state conditions using the effective mass approximation. Our results show that: (i) the electronic structure and optical properties are sensitive to the dressed potential; (ii) under applied electric fields, an increase of the laser intensity induces a redshift of the optical absorption and rectification spectra; (iii) the augment of the electric field strength leads to a blueshift of the spectra; (iv) for high electric fields the optical spectra show a shoulder-like feature, related with the occurrence of an anti-crossing between the two first excited levels.     

由变反镜耦合输出的卡塞格林非稳腔激光技术研究

讨论了变反镜参数和由变反镜耦合输出的卡塞格林非稳腔参数的相互关系以及它们对激光光束特性的影响。在此理论基础上，设计了Ｎｄ：ＹＡＧＱ形状高功率高光束质量的激光系统，获得了脉冲能量为１．４ＪＥＭ００模，脉宽１０ｎｓ，重复频率１０ｐｐｓ，束散度达到衍射极限的１．１倍，其倍频效率及混频效率分别为６０％和３０％。