Presence Of Strong Laser Field Research Articles

Deuterium-tritium fusion process in strong laser fields: Semiclassical simulation

In this paper, we investigate the deuterium-tritium (DT) fusion process in the presence of strong laser fields with a semiclassical (SC) method. In this model, two nuclei with a given incident kinetic energy that closely approach each other are simulated by tracing the classical Newtonian trajectories in the combined Coulomb repulsive potentials and laser fields. At the nearest position or classical turning point, quantum tunneling through the Coulomb barrier emerges, and its penetrability is estimated with the Wentzel-Kramers-Brillouin formula. Nuclear fusion occurs after the tunneling, and the total fusion cross section takes the Gamow form. We find that the tunneling penetrability can be enhanced dramatically because the nuclei can closely approach each other due to the quiver motion of the charged nuclei driven by the intense laser fields. We then calculate the DT fusion section for a wide range of laser parameters according to various incident nuclei kinetic energies and obtain the phase diagrams for the enhanced DT fusion. We compare our SC results with the quantum results of the Kramers-Henneberger approximation and the Volkov state approximation.

Ellipticity dependence of nonperturbative harmonic generation in few-layer MoS2

High-order harmonic generation in solid state materials is viewed as a means of studying strong field nonperturbative physics. Researching ellipticity dependence can help understand the dynamics of electron–hole pairs in the presence of strong laser field. In this work, ellipticity dependence of high harmonic generation in few layer MoS2 is experimentally investigated with a midinfrared laser centered at 3.9 um. We irradiate monolayer, bilayer and trilayer MoS2 with intense mid-infrared light to generate non-perturbative harmonics up to 11th order. We find that the normalized yield of each harmonic descends in a form of Gaussian-like profile as increasing the ellipticity of driving pulse. It is astonishing to see that ellipticity dependence of monolayer, bilayer and trilayer MoS2 follows the same rules. We ascribe this similarity to the same deviation distance of electron–hole pairs in three sets of samples. Meanwhile, the higher the harmonic order is, the more sensitive it is to ellipticity, which shows agreement with gas-phase harmonics. To explain the phenomena, we explore the role of intraband and interband dynamics with multiband semiconductor Bloch equations, which helps to delve deeper into ultrafast and strong-field features of MoS2.

Relativistic electron scattering from freely movable proton/ in the presence of strong laser field**Project supported by the National Natural Science Foundation of China (Grant Nos. 11774131, 91850114, 11604119, and 11627807).

We have investigated the electron scattering from the freely movable spin-1/2 particle in the presence of a linearly polarized laser field in the first Born approximation. The laser-dressed state of electrons is described by a time-dependent wave function which is derived from a perturbation treatment. With the aids of numerical simulations, we explore the dependencies of the differential cross section on the laser field intensity as well as the electron-impact energy. Due to the mobility of the target, the differential cross section of this process is smaller than that of Mott scattering.

The Lagrangian formulation of strong-field quantum electrodynamics in a plasma

The Lagrangian formulation of the scalar and spinor quantum electrodynamics in the presence of strong laser fields in a plasma medium is considered. We include the plasma influence in the free Lagrangian analogously to the “Furry picture” and obtain coupled equations of motion for the plasma particles and for the laser propagation. We demonstrate that the strong-field wave (i.e., the laser) satisfies a massive dispersion relation and obtain self-consistently the effective mass of the laser photons. The Lagrangian formulation derived in this paper is the basis for the cross sections calculation of quantum processes taking place in the presence of a plasma.

Dynamics of intersubband transitions in triangular quantum wells due to static magnetic and laser fields

We study dynamics of intersubband and bound–continuum transitions of the electron bound in the conduction band of triangular quantum wells interacting with perpendicular static magnetic field in the presence of strong monochromatic laser field. We use non-perturbative Floquet theory and finite differential method to study the influence of static magnetic field on quantum well (QW) system in the presence of strong laser field. We show that the system dynamics gets modified due to the perpendicular magnetic field. The sensitivity to the ratio of strengths of magnetic and laser field intensity (Bs/I) of the state populations is studied.

Modifications of laser field assisted intersubband transitions in the coupled quantum wells due to static electric field

AbstractWe consider the electron bound in the conduction band of a coupled asymmetric double quantum well (ADQW) interacting with static as well as strong monochromatic field in terahertz (THz) region. We use non‐perturbative Floquet theory to study the static field and quantum well (QW) system in the presence of strong laser fields. We show that the intersubband dynamics gets modified due to the static field. The sensitivity to the ratio of strengths of static and laser field (Es/E0) of the state populations can be used in various optoelectronic device applications.

Mott scattering of polarized electrons in a strong laser field

We present analytical and numerical results of the relativistic calculation of the transition matrix element $S_{fi}$ and differential cross section for Mott scattering of initially polarized Dirac particles (electrons) in the presence of strong laser field with linear polarization. We use exact Dirac-Volkov wave functions to describe the dressed electrons and the collision process is treated in the first Born approximation. The influence of the laser field on the degree of polarization of the scattered electron is reported.

Correlated multielectron systems in strong laser fields: A multiconfiguration time-dependent Hartree-Fock approach

The multiconfiguration time-dependent Hartree-Fock approach for the description of correlated few-electron dynamics in the presence of strong laser fields is introduced and a comprehensive description of the method is given. Total ionization and electron spectra for the ground and first excited ionic channels are calculated for one-dimensional model systems with up to six active electrons. Strong correlation effects are found in the shape of photoelectron peaks and the dependence of ionization on molecule size.

Non-Markovian evolution of the density operator in the presence of strong laser fields

We present an accurate, efficient, and flexible method for propagating spatially distributed density matrices in anharmonic potentials interacting with solvent and strong fields. The method is based on the Nakajima–Zwanzig projection operator formalism with a correlated reference state of the bath that takes memory effects and initial/final correlations to second order in the system–bath interaction into account. A key feature of the method proposed is a special parametrization of the bath spectral density leading to a set of coupled equations for primary and N auxiliary density matrices. These coupled master equations can be solved numerically by representing the density operator in eigenrepresentation or on a coordinate space grid, using the Fourier method to calculate the action of the kinetic and potential energy operators, and a combination of split operator and Cayley implicit method to compute the time evolution. The key advantages of the method are: (1) The system potential may consist of any number of electronic states, either bound or dissociative. (2) The cost for arbitrarily long solvent memories is equal to only N+1 times that of propagating a Markovian density matrix. (3) The method can treat explicitly time-dependent system Hamiltonians nonperturbatively, making the method applicable to strong field spectroscopy, photodissociation, and coherent control in a solvent surrounding. (4) The method is not restricted to special forms of system–bath interactions. Choosing as an illustrative example the asymmetric two-level system, we compare our numerical results with full path-integral results and we show the importance of initial correlations and the effects of strong fields onto the relaxation. Contrary to a Markovian theory, our method incorporates memory effects, correlations in the initial and final state, and effects of strong fields onto the relaxation; and is yet much more effective than path integral calculations. It is thus well-suited to study chemical systems interacting with femtosecond short laser pulses, where the conditions for a Markovian theory are often violated.

Ramsey interference in strongly driven Rydberg systems

We have studied the evolution of regular and ``dark'' radial wave packets under the influence of two coherent, temporally separated 100 fs laser pulses. The atomic states are probed by ramped-field ionization. The final state populations exhibit Ramsey oscillations with periods ranging from 2.6--1000 fs as a function of the delay between the two pulses. This time-domain bound-state interferometry reveals several new aspects of the dynamic evolution of wave packets in the presence of strong laser fields. Lowest order perturbation theory is inadequate to describe wave packet formations, even at the lowest intensities studied.

Resonant scattering in the presence of strong laser fields

Resonant scattering in the presence of strong laser fields is investigated by solving numerically the one-dimensional Schrodinger equation. It is shown that at high intensities of radiation one can observe new effects in free-free transitions like, for instance, the splitting and overlapping of the scattering resonances. The relation of these phenomena to multiphoton ionisation processes is also discussed. The Schrodinger equation is solved by applying the approach proposed by Jung and Taylor [1] or by Varro and Ehlotzky [34]. It is also shown how the second approach can be generalised in order to treat more complicated problems like for instance the relativistic processes.

Intensity effects in free-free transitions in the presence of strong laser fields.

Le phenomene de «commutation des pics» peut se produire dans les transitions libre-libre d'electrons en presence de champs laser intenses, d'apres l'analyse numerique exacte de l'equation de Schrodinger 1D

Field coherence in laser-assisted charged-particle scattering

The problem of charged-particle scattering in the presence of strong laser fields is investigated within a treatment in which the effect of the assisting field is included exactly, to all orders. Two laser field models are considered: 1) the model of a purely coherent field and 2) that of a field with well-stabilized amplitude and fluctuating phase (phase diffusion model, PDM). The scattering cross-sections are numerically investigated for selected but representative values of the parameters of the problem. Differential and total cross-sections are evaluated as functions of the scattering angles, the incident energy, the field coherence and intensity and the number of exchanged photons. The band width of the PDM field is found to affect significantly the scattering parameters, especially in the case of differential cross-sections and of high intensities. As compared to the purely monochromatic (SM) field, the PDM field is found to exhibit oscillations of smaller amplitudes with a tendency to a smooth behaviour with increasing band width, photon multiplicity and intensity. The PDM cross-sections are generally slightly larger than the SM ones. For the first time are reported calculations of the total cross-sectionsvs. the intensity with a sufficiently large density of points to resolve accurately the oscillatory structure of the high-intensity portion of the cross-sections. A consequence ensuing from the exact treatment of the laser field is that the field coherence properties too are treated exactly, at least within the given laser models, and it is expected to be of importance beyond the particular problem treated here, especially when nonresonant processes are concerned.

Resonant non-linear spectroscopy in strong fields

A method is presented to describe multiple resonant non-linear spectra in the presence of strong laser fields. The Liouville equation for the density operator of the molecular system is transformed to a time-independent linear equation system. This can be easily solved rigorously by numerical methods or, after partitioning into a strong-field part and a perturbation, the solution can be obtained analytically by a novel perturbative approach. The results account for power broadening. Rabi splitting of signals, and power-induced extra resonances, the latter being related to the pure dephasing-induced resonances in the weak-field limit. The method can be applied to a large number of multiple resonant non-linear spectroscopies, especially CARS, CSRS, coherent Rayleigh scattering and sum- or difference-frequency generation.