Superstrong Laser Fields Research Articles

Ionization of a single hydrogen-like atom by laser pulse of near-atomic strength

The dynamics of high-harmonic generation and atom ionization by a strong and superstrong laser field are studied. In contrast to many earlier works, the present theory does not impose limitations on the laser field’s strength. We solve the nonrelativistic problem of a single hydrogen-like atom’s ionization from the ground state by a short laser pulse of subatomic, atomic, and superatomic field strength. Within the framework of the proposed method, we investigated the matrix elements of the ionization transition and revealed its substantially nonlinear dependence on the laser field strength. Both ionization and recombination processes are taken into account. The proposed method enables us to take into account the arbitrary order multiphoton ionization processes.

Experimental study of nuclear processes in the presence of superstrong fields of a picosecond laser plasma

Nuclear processes in the presence of the superstrong laser fields of a picosecond laser plasma are experimentally studied at a radiation intensity of 2 × 1018 W/cm2 on a Neodim laser setup with a power of 10 TW. Experimental data regarding neutron generation on the surface of a deuterated target (CD2)n owing to the thermonuclear fusion 2H(d,n)3He and the neutron generation on the Be target due to the photonuclear reaction 9Be(γ,n)2α are presented. Neutron yields Yn of 106 and 103 per 4π sr per laser pulse are obtained for the (CD2)n and Be targets, respectively. The alpha-particle yield is measured for the first time in the neutron-free thermonuclear reactions 11B + H → 34He in the laser plasma on the surface of the composite B + (CH2)n targets. The alpha-particle yield is 103 per 4π sr per laser pulse.

Quantum dynamics of relativistic electrons

A new implementation of the split-operator method for calculating the time-evolution of Dirac wave functions is presented. With the help of self-adaptive numerical grids we are able to study the dynamics of an initially free electronic Dirac wave packet under the influence of an ultra-intense laser pulse and its scattering at a highly charged ion. Furthermore, we provide the necessary tools for constructing the Dirac ground state wave function of any single-electron ion and demonstrate them for hydrogenic oxygen. Bound Dirac dynamics in a super-strong laser field is finally investigated.

Interference Dynamics of Hydrogen Atoms in High-FrequencyDichromatic Laser Fields

We investigate the ionization and high-order harmonic generation of ahydrogen atom in high-frequency (several atomic units) super strong (upto several tens of atomic units) dichromatic laser fields. An effectiveiterative method in the framework of high-frequency Floquet theory is usedin the calculations. We have considered two kinds of dichromatic laserfield, i.e. 1ω-2ω and 1ω-3ω. We find that, in boththe cases, the ionization and high-order harmonic generation show evidentdependence on the relative phase and strength of the additional harmonicfield. The dynamical origin of these interference effects is also discussed.

Floquet study of ionization and high-order harmonic generation for a hydrogen atom in high-frequency laser fields

In this paper, we investigate the dynamics of a hydrogen atom in high-frequency (several atomic units) super strong (up to several tens of atomic units) laser fields within the high frequency Floquet theory framework. The ionization rate, ionization spectrum, angular distribution and high-order harmonic generation are all investigated. Our studies reveal the universal behavior of the total ionization rate, excess-photon ionization spectrum and angular distribution of the ionization rate in the stabilization regime, and achieve a deep insight into the dynamics of high-order harmonic generation in the stabilization regime.

The influence of the spatial inhomogeneity of the field on the nonlinear-optical response of an atom

The theory of the interaction of a centrosymmetric atom with a superstrong spatially inhomogeneous laser field is developed. This theory employs the two-level approximation to describe the dynamics of spatially nonlocal interactions related to variations in the populations of the levels. We propose a model that includes spatially nonlocal interactions, such as magnetic-dipole and quadrupole interactions and interactions due to the gradient of the ponderomotive potential of the field. We consider the interaction of a homogeneous medium of centrosymmetric atoms with a superstrong laser field, which is represented as a superposition of two plane-wave ultrashort pulses propagating at some angle with respect to each other. Perturbation theory, which is valid for the fields of moderate intensity, is developed for the atomic response. The results of numerical simulations are compared with the predictions of this perturbation theory. The specific features of the nonlinear-optical response of an atom in a superstrong field are investigated. The angular distribution of the second- and third-harmonic emission is calculated in the constant-field approximation for different polarisations of the incident field.

Relativistic theory of atom-laser interactions at very high laser intensities

The high-frequency approximation of Kristic and Mittleman is considered in detail as a basis for the relativistic theory of atom-laser interactions. The properties of the 3D potentials are discussed. Within a one-dimensional model similar to that employed by Kylstra, Ermolaev, and Joachain in ab initio calculations on the time-dependent Dirac equation, the electron mass-shift due to dressing by a superstrong laser field is investigated. In the full domain of the laser parameters, the frequency ω and the peak field strength ℰ0, the 1D bound states exhibit remarkable features. The numerical calculations show the existence of a very wide intermediate range of the field strengths where, in the zeroth order of the high-frequency approximation, the binding is stabilized by the field.

'Progress-P' laser facility with chirped-pulse amplification in neodymium glass

A Nd:YLF/Nd:glass laser facility with chirped-pulse amplification capable of generating pulses with a duration of 1.5 ps and a power up to 30 TW at the wavelength of 1053 nm was investigated. The facility consists of a initial laser system, producing a chirped pulse with an energy up to ~1 J, a main three-stage rod amplifying channel with a 85-mm aperture of the output stage, a pulse compressor based on 210 mm × 420 mm diffraction gratings, and a focusing axial parabolic mirror (with an aperture ratio of 1:11). Optimisation of the parameters of the laser facility allowed us to generate an output laser beam with an angular divergence close to the diffraction limit and an intensity up to ~1019 W cm-2 . Laser radiation with such parameters can be employed in experiments on the interaction of superstrong laser fields with matter.

Interaction of an atom with superstrong laser fields

A theory of atomic interaction with a superstrong laser field has been developed. The specific feature of the suggested theory is that its small parameter is the interaction between the atom and the solenoidal part of the external field, whereas its interaction with the potential part is accurately taken into account. It follows from the reported investigation that, in calculating the interaction of atoms with superstrong fields, one must abandon calculations of multipole moments of transitions between unperturbed atomic levels, and calculate instead the atomic response, which comprises multipole moments of all orders and depends on the instantaneous field magnitude. The results are compared with calculations based on the perturbation theory in terms of the interaction Hamiltonian.

An atom in a superstrong laser field

The consistent analytical theory of multiphoton ionization in a superstrong laser field is developed. The corresponding initial problem for the Schrodinger equation is reduced to the initial problem for the pair of integro-differential equations. The appropriate asymptotic technique is derived and the leading asymptotic term of the solution is obtained. It is shown, that the atomic stabilization is present under fairly general conditions. The possibility of population revivals is also shown.

The evolution of molecular wave packet in superstrong laser fields

In this note wc numerically simulate the wave packet evolution of H2 + in superstrong laser fields with the multiple electronic-states model. The result is that the evolution process of H2 + wave packet is mainly determined by the laser frequency. For the high-frequency fields H2 + wave packet extends out of the interaction region step by step. However, the H2 + wave packet is quickly dissociated in low-frequency fields. In addition, the molecular stabilization effect can be characterized at the intensity of 8 × 1015 W/cm2 for the low-frequency field ω1.

Interaction of superstrong laser fields with matter: Hypotheses, effects, and applications

A review of research results in physics of superstrong laser fields is given. It includes an analysis of the nonlinear atom response in superstrong optical fields and a discussion of the properties of a femtosecond laser-produced plasma. A description of new experiments on high-order harmonic generation, plasma wake field excitation by intense laser pulses, and ultrashort pulse self-channeling due to ionization is presented.

ELECTRON IMPACT PROCESSES IN SUPER-INTENSE LASER FIELDS

We discuss the motion of an electron in a classical electromagnetic wave, including ponderomotive force effects. To describe electron impact stimulated reactions under the action of superstrong laser field we formulate instant-impact approximation. We demonstrate how it can be applied to calculate hard electron-nuclear processes for obtaining the reaction rates for such effects as trident pair production, hard X-ray generation, electrostimulated nuclear fission, and both ions and nuclei excitation by electron impact in the laser field.

Hard x-ray generation in laser field of relativistic intensity

X-ray production stimulated by electron-ion collisions in superstrong laser fields is described theoretically in the framework of instant impact approximation. The results are compared with the corresponding experimental data.

Intense-field scattering and capture of an electron by a model atom

We have solved numerically the time-dependent Schr\odinger equation for an electron in a superstrong laser field while it undergoes a collision with a model one-dimensional hydrogen atom. We show that a certain fraction of the electron can be trapped by the atom in superstrong fields. This trapped portion has a dichotomous spatial probability distribution, corresponding to an effective excitation of Kramers-Henneberger field-dressed states, which is quite resistant against subsequent detachment. By varying the incoming electron's kinetic energy these states can be selectively excited.