Dmitry A. Telnov

Sub-cycle Oscillations in Virtual States Brought to Light

Understanding and controlling the dynamic evolution of electrons in matter is among the most fundamental goals of attosecond science. While the most exotic behaviors can be found in complex systems, fast electron dynamics can be studied at the fundamental level in atomic systems, using moderately intense (≲103 W/cm2) lasers to control the electronic structure in proof-of-principle experiments. Here, we probe the transient changes in the absorption of an isolated attosecond extreme ultraviolet (XUV) pulse by helium atoms in the presence of a delayed, few-cycle near infrared (NIR) laser pulse, which uncovers absorption structures corresponding to laser-induced “virtual” intermediate states in the two-color two-photon (XUV+NIR) and three-photon (XUV+NIR+NIR) absorption process. These previously unobserved absorption structures are modulated on half-cycle (~1.3 fs) and quarter-cycle (~0.6 fs) timescales, resulting from quantum optical interference in the laser-driven atom.

Floquet formulation of time-dependent density functional theory

Abstract We present a generalized Floquet formulation of time-dependent density functional theory for nonperturbative treatment of both bound-bound and bound-free multiphoton transitions of many-electron systems in intense monochromatic laser fields. It is shown that the time-dependent Kohn-Sham equations can be converted into an equivalent time-independent infinite-dimensional non-Hermitian Floquet Hamiltonian eigenvalue problem. We introduce the notion of complex density and present a procedure for extracting the partial ionization rates from individual electron orbitals. The method is illustrated by a case study of multiphoton ionization of He in both weak and strong fields.

Dual-kinetic-balance approach to the Dirac equation for axially symmetric systems: Application to static and time-dependent fields

Dual kinetic balance (DKB) technique was previously developed to eliminate spurious states in the finite-basis-set-based solution of the Dirac equation in central fields. In the present paper, it is extended to the Dirac equation for systems with axial symmetry. The efficiency of the method is demonstrated by the calculation of the energy spectra of hydrogenlike ions in presence of static uniform electric or magnetic fields. In addition, the DKB basis set is implemented to solve the time-dependent Dirac equation making use of the split-operator technique. The excitation and ionization probabilities for the hydrogenlike argon and tin ions exposed to laser pulses are evaluated.

Exploration of the origin of anomalous dependence for near-threshold harmonics in on the ellipticity of driving laser fields

The anomalous dependence of near-threshold harmonics in the molecular ion on the ellipticity of the driving near-infrared laser field is studied theoretically based on accurate solution of the time-dependent Schrodinger equation in prolate spheroidal coordinates with the help of the generalized pseudospectral method. For these harmonics, the maximum radiation energy corresponds to a non-zero ellipticity of the driving field. Our analysis reveals that the origin of the phenomenon lies in the near-resonant excitation of π-symmetry molecular orbitals. The excited states responsible for the anomalous ellipticity dependence of different near-threshold harmonics are identified. The effect is confirmed at the equilibrium internuclear separation R = 2 a.u. as well as for stretched molecules at R = 3 a.u.

The Coulomb glory effect in collisions of antiprotons with heavy nuclei: relativistic theory

Collisions of antiprotons with bare uranium nuclei are studied for scattering angles near 180° in the framework of relativistic theory. The Coulomb glory phenomenon is investigated at antiproton energies in the range 100 eV–2.5 keV. The vacuum polarization effect and the anomalous magnetic moment of the antiproton are taken into account. Estimations of possible influence of such effects as radiative recombination and antiproton annihilation are given.

Electron angular distributions after above-threshold multiphoton detachment of by 1064 nm radiation

We present a non-perturbative Floquet calculation of the electron angular distributions and partial widths for multiphoton above-threshold detachment of by 1064 nm radiation. When a beam of ions is used as a target, the angular distributions in the frame where the ions are at rest can be extracted from the energy (angle-integrated) distributions in the laboratory frame. The experiments measuring the electron angular distributions are now in progress. Our calculation procedure consists of the following elements. (i) Determination of the resonance wavefunction and complex quasienergy by means of the non-Hermitian Floquet Hamiltonian formalism. The Floquet Hamiltonian is discretized by the complex-scaling generalized pseudospectral technique recently developed (by Wang and co-workers). (ii) Calculation of the angular distribution and partial widths based on an exact integral formula. The calculations were performed for the linearly polarized laser field with the wavelength 1064 nm and several intensities in the range - . With the increase of the number of photons absorbed above the threshold, the angular distributions become more stretched along the field direction manifesting, however, a few additional maxima. Besides the numerical data for the angular distributions we also present the coefficients of expansion on the basis of Legendre polynomials.

Investigation of the characteristic properties of high-order harmonic spectrum in atoms using Bohmian trajectories

We study the electron quantum dynamics of high harmonic generation (HHG) processes of atomic hydrogen under intense near infrared (NIR) laser fields by means of the De Broglie–Bohms framework of Bohmian mechanics. The proposed accurate 3D numerical scheme is utilized to discuss the mechanism of the multiple plateau generation and the cut-off extension, as the main characteristic features of HHG spectrum. One-color (1600 nm) and two-color (1600 nm + 800 nm) laser fields with different time delays are used to investigate the effect of pulse shape on electron dynamics and HHG process. The presented results on Bohmian trajectories and their energy content, along with the analysis of the emission time period of different groups of trajectories, provide a comprehensive and fresh electron dynamical picture and uncover novel mechanisms of the HHG processes and power spectra.

Time-dependent generalized pseudospectral method for accurate treatment of multiphoton processes of diatomic molecules in intense laser fields

Article history: We present a numerical method based on the generalized pseudospectral discretization in prolate spheroidal coordinates and split-operator time propagation. The method has been applied for the study of multiphoton processes of H + and N2 diatomic molecules in intense laser fields. It proves very accurate while using only moderate computer resources.

High-order above-threshold multiphoton detachment of H − : time-dependent non-Hermitian Floquet approach

We present a nonperturbative quantum study of high-order above-threshold detachment of H− in intense laser fields using an accurate one-electron model potential and a new time-dependent non-Hermitian Floquet approach. Detailed exploration of the electron energy and angular distributions is pursued for the laser field intensities 1010–1011 W cm−2 and wavelength 10.6 µm. In accordance with semiclassical predictions, the electron energy spectrum exhibits a plateau region in the higher energy part. Transformation of the electron angular distributions in the plateau region is discussed. The computational method involves the complex-scaling generalized pseudospectral (CSGPS) spatial discretization of the Hamiltonian and non-Hermitian time propagation of the time-evolution operator by means of the split-operator technique in the energy representation. The approach is designed for effective treatment of multiphoton processes in very intense and/or low-frequency laser fields, which are generally more difficult to treat using the conventional time-independent Floquet matrix techniques.

Multiphoton above-threshold detachment by intense laser pulses: a new adiabatic approach

We present a new adiabatic approach for non-perturbative treatment of multiphoton above-threshold detachment (ATD) in intense laser pulses. The electron energy distributions for the pulse detachment are expressed via the detachment transition amplitudes in the monochromatic fields, and the latter are calculated with the help of the adiabatic theory based on the smallness of the laser frequency compared with the electron affinity or ionization potential. The theory is applied to the first study of the pulse shape effects on the multiphoton ATD of the negative ion H- by 10.6 mu m radiation. Two pulse shapes are considered: a Gaussian pulse and a square pulse with smooth edges. We present the angle-resolved as well as angle-integrated ATD electron energy distributions. They contain oscillatory satellite structures to the main peaks due to interference of the electrons detached on the rising and falling edges of the pulse. Simple analytical formulae describing these subpeak structures are also presented.