Effect Of Laser Field Research Articles

Modification of droplet morphology and arc oscillation by magnetic field in laser-MIG hybrid welding

In this paper, we presented the morphological characteristics of droplet and arc during alternating magnetic field assisted laser-MIG welding. High speed camera was used to map the effect of magnetic intensity and frequency on droplet transfer and arc shape. Results revealed that the magnetic field indeed modified droplet morphologies and hence pointing direction. This appearance was mainly attributed to the centrifugal force during droplet spinning and resultantly reduced effective potential energy (mechanism I). Moreover, combined effect of laser and magnetic field induced a regularly altered axial asymmetry of arc along the welding direction. Cause of this arc oscillation was due to “particle packing effect” in one side during laser-MIG welding (mechanism II). At last, the optimum magnetic field parameters during the laser-MIG parameters (2000 W, 150A and 1.1 m/min) was concluded as B(mT)f(Hz)≤0.8 and f(Hz)>12t0.

Effect of pulsed magnetic field on electron acceleration due to plasma wave generated by plane polarised laser

Electron acceleration due to plasma wakefield generated by plane polarised laser field in the presence of pulsed magnetic field has been investigated. Laser propagation is considered in transverse direction to the plasma wave. The electron gets trapped in the plasma wakefield and excited in the combined effect of plasma and laser fields. The pulsed magnetic field induces a resonant effect and contributes to additional gain in the electron energy. Laser, plasma and applied magnetic field parameters are optimized to achieve high energy gain.

A quantum model for photoemission from metal surfaces and its comparison with the three-step model and Fowler–DuBridge model

This paper studies a quantum mechanical model for photoemission from a metal surface due to the excitation of laser electric fields, which was developed by solving the time-dependent Schrödinger equation exactly. The quantum model includes the effects of laser fields (wavelength and intensity), properties of metals (Fermi energy and work function including Schottky effect), and the applied dc field on the cathode surface. Shorter wavelength lasers can induce more photoemission from electron initial energy levels further below the Fermi level and, therefore, yield larger quantum efficiency (QE). The dc field increases QE, but it is found to have a greater impact on lasers with wavelengths close to the threshold (i.e., the corresponding photon energy is the same as the cathode work function) than on shorter wavelength lasers. The quantum model is compared with existing classical models, i.e., the three-step model, the Fowler–DuBridge model, and the Monte Carlo simulation based on the three-step model. Even though with very different settings and assumptions, it is found that the scaling of QE of the quantum model agrees well with other models for low intensity laser fields. When the laser field increases, QE increases with the laser field strength in the longer laser wavelength range due to the increased contributions from multiphoton absorption processes.

Interferences driven by the few-cycle laser field in the photodetachment of Cl− ion

The time-dependent semiclassical theory is extended to study the photodetachment of negative ions with outer p-state electrons. The photodetachment cross section of Cl− ion is specially studied exposed to a few-cycle laser field. Considering the influence of laser field effects, the photodetachment cross section is found to oscillate complicatedly with increasing laser intensity and frequency. We demonstrate that different types of closed orbit have different impacts on the interference structures in the photodetachment cross section. Detailed analysis of the t-ti map of the detached electron reveals a remarkably correlation with the initial phase in the laser field. Additionally, the profiles of photodetachment cross section show strong dependence on the optical cycle number N in the laser field, indicating that it is an important parameter for controlling the photodetachment of negative ion. The method adopted in this work is universal, and can be applied to study the photodetachment of other halide negative ions in the laser field, such as F− ion, Br− ion, etc This work provides a new method for the experimentalists to coherent control of the photodetachment process of negative ion using a few-cycle laser field.

Sub-optical-cycle electron dynamics of NO molecules: the effect of strong laser field and Coulomb field

The sub-cycle bound- and free-electron dynamics and the Coulomb effect during the strong field ionization of NO molecules are studied by using a combination of phase-controlled two-color femtosecond laser fields and photoelectron imaging. The AC–Stark effect and ponderomotive potential is identified and tracked by measuring the energy shift of phase-dependent photoelectron spectra under different asymmetric laser fields. The Coulomb effects of molecules during ionization are studied by measuring the energy-dependent phase change and the cusp-like transverse-momentum distributions of the ionized electrons. The results show an obvious sub-cycle time scale response of ionized electrons in NO molecular ionization. The present method provides new ways to measure the electronic dynamics of molecules in strong field ionization.

Effects of inhomogeneous laser field in time and space on the generation of broad spectral continuum and ultrashort attosecond pulse

The inhomogeneous effects of laser field in time and space on the generations of high-order harmonic spectra and attosecond pulses from He atom have been investigated with the assistance of the frequency-chirping technique and the metallic nanostructure. We find that in different combinations of chirps and spatial inhomogeneous effects, not only can the harmonic cutoff be extended, but the single harmonic emission peak (HEP) can also be selected to contribute to the spectral continuum. In detail, with the combinations of (i) symmetric chirp in frequency and positive inhomogeneous effect in space or (ii) asymmetric down chirp in frequency and negative inhomogeneous effect in space, two broad spectral continua with bandwidths of 496 eV and 480 eV can be obtained. Further, by properly adding IR or UV controlling pulse, the harmonic emission efficiency can be enhanced by several orders of magnitude. The enhancement of harmonic yield from adding UV pulse is higher than that from adding IR pulse. Moreover, the difference of harmonic enhancement between UV combined field and IR combined field is much more obvious at lower controlling laser intensity. Through analyzing the ionization probability, we find that the higher enhancement of harmonic yield from UV combined field is because of UV-resonance-enhancement-ionization between the ground state and the excited state of He atom. Finally, by properly superposing some harmonics, a number of attosecond pulses with pulse durations of 45 as can be obtained.

Studies on the nonlinear optical properties of two-step GaAs/Ga1−xAlxAs quantum well

In this paper, the numerical computation for the absorption coefficient and the relative refractive index change, considering the third order correction nonlinear optical properties, is reported. This study was performed for a symmetric two-step GaAs/Ga1−xAlxAs quantum well, subjected to a constant electric field applied along the growth direction z, and an in-plane constant magnetic field B. We also consider the intense laser field effect, characterized through the laser-dressing parameter α0. The electronic structure computation was obtained by working under the effective mass approximation and the Schödinger equation was solved by diagonalization procedure. The optical properties are calculated by using the well-established compact density matrix formalism expressions for the nonlinear optical properties of interest. In general, we found that the structural parameters, as the step-like potential or the central barrier, permit the resonant peak and the amplitude design. We also found that the system becomes more sensitive to electric than to magnetic field, and finally that the intense, non-resonant, laser field can strongly change the optical properties of interest. Our results indicate that the implementation of the step-like potential profile, experimentally feasible, enhance the optical properties of interest, that falls within the THz electromagnetic range, and can be used to design a photodetector, or even can be used for quantum cascade lasers design.

Binding energy of excitons in an infinitely deep spherical quantum dot under intense THz laser field

We study the effects of intense THz laser field on the ground-state binding energy of heavy hole excitons confined in GaAs spherical quantum dots. The calculation is performed using the variational method in the framework of the single band effective mass theory. Our results show that (i) the laser electric field lowers the binding energy for all quantum dot radii, making the exciton clustered near the centre of the dot, (ii) the binding energy is mainly due to the dressed potential making the kinetic part insensitive to the field and (iii) the behaviour of the exciton, under the approximations used, can be modelled by a unique set of plots, depending on the material only via its excitonic units.

Effects of Laser Field on Excitonics States of Spherical Quantum Dots with Different Confinements

In this paper, we have studied the effect of intense laser field on excitonic states of excitons confined in spherical quantum dots by means of variational technique within the effective mass approximation. The results show that the exciton binding energy depends on the laser field parameter and quantum dot radii. And the laser field lowers total energy (E), kinetic energy (T) , coulombic potential (Vc) and the binding energy of exciton for all confinements and for any material used.

Impurity-modulated optical response of a disc-shaped quantum dot subjected to laser radiation

We report the optical properties of a laser-driven two-dimensional quantum dot with a hydrogenic impurity exposed to a magnetic field. The effective mass approximation is used to bring out the effect of an intense laser field, resulting in dressed Coulomb and confinement potentials, on the one-electron energy levels and wave functions. The results obtained suggest that the action of the laser field leads to crucial changes in the energy spectra of the system and the impurity binding energy. Furthermore, the position and the height of the resonant peaks of the absorption coefficients and refractive index changes depend strongly not only on the geometrical confinement strength but also on the magnetic field and laser radiation through the “laser-dressed” potential.

Effective tuning of isotropic and anisotropic properties of quantum dots and rings by external fields

Abstract The combined effects of intense THz laser field, magnetic field and in-plane electric field on electronic states and intraband optical properties of single isotropic quantum dots and rings are investigated using the non-perturbative Floquet theory in the high-frequency limit. Here we show that the change of the electric field direction for fixed values of intense THz laser field parameter can recover the degeneracy of the excited states and the dipole-allowed transition intensities in a quantum dot. Additionally, it is shown that in isotropic quantum rings the intense THz laser and the in-plane electric field create unusual Aharonov-Bohm oscillations. For fixed values of the intense THz laser field parameter, the amplitudes of Aharonov-Bohm oscillations can be effectively tuned by changing the electric field direction. Furthermore, for fixed values of the electric field strength and the laser field parameter the intraband optical properties can be effectively tuned by changing the electric field direction. Therefore, it can be asserted that circular quantum dots or circular rings in the intense THz laser field are equivalent to anisotropic quantum dots or rings respectively, and the electric field direction effectively tunes the single-electron energy spectrum and intraband optical properties of these structures.

The effect of intense laser field on the nonlinear optical features in asymmetric multiple step and inverse V-shaped multiple step quantum wells

For asymmetric multiple step quantum wells (AMS QWs) and asymmetric inverse V-shaped multiple step quantum wells (AIVSMS QWs), the nonlinear optical features, such as the nonlinear optical rectification (NOR), the second harmonic generation (SHG) and the third harmonic generation (THG) coefficients are analyzed as according on the intense laser field (ILF). The found consequences indicate that the ILF parameter confirms a vital influence on the shape and height of the confined potential profile of both AMS QWs and AIVSMS QWs, and the 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 AIVSMS QWs compared to AMS QWs were affected differently from ILF intensity. These results indicate that NOR, SHG, and THG coefficient of AMS QWs and AIVSMS QWs may be regulated in a preferred energy range and the magnitude of the resonance peak (RP) by tuning the ILF parameter. By varying the ILF parameter, it is feasible to classify blue or red shifts in RP locations of NOR, SHG and THG coefficients. Our results can be valuable in investigating new ways of manipulating the opto-electronic properties of semiconductor QW devices.Highlights•The electro-optical properties of AMS QWs and AIVSMS QWs vary by increasing ILF.•The change of AIVSMS QWs compared to AMS QWs is more affected by ILF.•NOR, SHG, and THG coefficients change with rising ILF.•RP spectrums show blue or red shifts as according to ILF.

Theoretical suggestions of resonant tunneling diodes and laser field effects on their current-voltage characteristics

Abstract Several resonance-tunneling diodes are modelled for a fixed resonance energy. The theoretically suggested diodes are classified according to their local potentials differed by the doping concentrations. The electronic properties of the diodes are explored in the framework of numerical calculations. In addition, the laser field effects on the latter properties are reported. They show that the laser field application enriches the functionality of these devices in applications.

Effect of the High-Frequency Laser Radiation on the Nonlinear Optical Properties of n-Type Double δ-Doped GaAs Quantum Wells.

In the present work, the effect of non-resonant intense laser field on the nonlinear optical rectification and second and third harmonic generation of n-type double δ-doped GaAs quantum well is studied in detail. The energy eigenvalues and eigenfunctions of this structure are calculated within the framework of effective mass and envelope function approximations. Analytic formulas for the coefficients of nonlinear optical rectification and second and third harmonic generation are obtained using the compact-density matrix approach (CDMA) and iterative method. Based on this model, our obtained numerical results are reported as a function of incident photon energy for several values of non-resonant intense laser field. The results show that the coefficients of nonlinear optical rectification and second and third harmonic generation are strongly affected by the non-resonant intense laser field.

Intense laser field effect on [formula omitted] molecular complex localized in semiconductor quantum wells

D2+ molecular ion in a semiconductor quantum well under laser-field radiation by using finite elements method within the effective mass approximation is theoretically studied. The effects of the laser radiation, donor-donor separation, and quantum well width on the D2+ total energy and the D2+ binding energy corresponding to the second ionization process D2+→D++D++e- are analyzed. We show that the laser-field radiation modifies significantly the equilibrium length and the dissociation energy of a D2+- complex in a quantum well. Our results in the limit cases are in good agreement with those previously reported for a single donor impurity D0.

High-order harmonic generation with a single-color mid-infrared laser field by frequency-chirping

By numerically solving the time-dependent Schrödinger equation for helium atoms in a single mid-infrared laser field, we explore the frequency-chirping effect of laser field on high-order harmonic and isolated attosecond pulse generation. One or two ultrabroad supercontinuum harmonic plateaus can be controlled through modulating the laser field frequency by a small time-dependent signal. Under the best chirping condition, an ultrashort 2.2 as pulse can be obtained by Fourier transformation with the bandwidth of 782 eV. Furthermore, we explain the harmonic generation physical mechanisms by classical ionizing and returning energy maps and time–frequency analyzes.

Intense laser-induced electronic and optical properties in double finite oscillator potential

ABSTRACTIn the present paper, a theoretically study of the non-resonant laser field effect on the optical response, such as nonlinear optical rectification (NOR), second (SHG) and third harmonic generation (THG) coefficients in double finite oscillator potential (DFO) quantum wells is performed in the framework of the effective mass approximation. The obtained results reveal that, energy states and optical response is significantly affected by the non-resonant intense laser field (ILF) intensity and symmetry of the structure. Also it was found that the laser field is more effective on the optical response in the DFO potential when the asymmetric character of the confinement potential is strong. Thus, the NOR, SHG and THG coefficients with designated values can be obtained by using a properly adjusted ILF intensity and symmetry parameter of confinement potential.

α decay in intense laser fields: Calculations using realistic nuclear potentials

We calculate the effect of intense laser fields on nuclear alpha decay processes, using realistic and quantitative nuclear potentials. We show that alpha decay rates can indeed be modified by strong laser fields to some finite extent. We also predict that alpha decays with lower decay energies are relatively easier to be modified than those with higher decay energies, due to longer tunneling paths for the laser field to act on. Furthermore, we predict that modifications to angle-resolved penetrability are easier to achieve than modifications to angle-integrated penetrability.

Hydrogenic donor impurities in -doped cylindrical quantum dots under intense laser field

A theoretical study of the effects of non-resonant intense laser field on the donor impurity binding energy in a cylindrical quantum dot with -doped axial potential is performed in the framework of the effective mass approximation. The obtained results indicate that, 2D impurity concentration and intense laser field intensity have a significant effect on the impurity binding energy and energy levels of electrons in the cylindrical quantum dots with -type axial potential.

Effect of Intense Laser Field in Gaussian Quantum Well With Position‐Dependent Effective Mass

In this paper, the effects of the intense laser field (ILF) and position dependent mass (PDM) on the electronic structure in a Gaussian quantum well are theoretically deduced by using the diagonalization method for obtaining energy levels and corresponding wave functions. We find that, in the case of narrow PDM distribution, the dependence of the energy levels on the effective length of the electron mass distribution becomes more apparent, and the evolution of the dressed mass with ILF is significant. Given this feature, it is more meaningful to take into consideration the PDM of the electron in the low dimensional semiconductor heterostructures under the ILF.