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In the strong-field ionization of atomic and molecular systems, the photoelectron is exposed to the long-range Coulomb force which is neglected in the standard theories based on the strong-field approximation (SFA). We introduce an ansatz which takes into account the Coulomb effects and at the same time is as simple as the standard SFA. Our Coulomb distorted plane wave-Volkov approximation provides analytical expressions for the relevant matrix elements. We also present a generalization of this approximation taking into account first-order term of an expansion in the atomic potential. Similarly as in the standard improved SFA, this generalized approximation describes well the rescattering plateau and the cutoff observed in the photoelectron spectra. Our new approximation is illustrated with numerical examples of strong-field ionization of the hydrogen atom exposed to linearly and circularly polarized laser pulses. The spectra obtained are slightly flatten in comparison with the SFA spectra and this effect is stronger for shorter laser wavelengths. [ABSTRACT FROM AUTHOR]

Radiation produced in high-order harmonic generation (HHG) process can be utilized to generate attosecond pulses. According to the semi-classical theory of HHG, the maximum emitted photon energy is I P + 3. 1 7 U P . The ionization potential ( I P) and ponderomotive energy ( U P) , play important roles in the generated photon energy; therefore, choosing the material and field for HHG is important. Here, investigating the probability of ionization of material in laser and plasmonic field for HHG is important. The ionization probability of noble gases atoms and ions was investigated. Using Ammosov–Delone–Krainov (ADK) model formulas, the parameters for ions and atoms were determined. The results show that helium is the most suitable noble gas atom for HHG in both fields. After ionizing the atoms, the ionization potential increases significantly, and the ionization probability also decreases. Then, ions are better than their corresponding atoms for HHG. Among noble gas atoms and ions, the helium ion is the most suitable for HHG. In addition, the plasmonic field increases the ponderomotive energy and decreases the probability of ionization for all atoms, as shown by the simulation. Then, extreme ultraviolet (XUV) high-energy photon can be efficiently generated using noble gas ions. [ABSTRACT FROM AUTHOR]

We report computations for the quantum dynamics and spectra of the iodine atom in the ground state () subjected to a strong laser field at wavenumbers in the range of CO laser emission. The computations include the hyperfine structure of the magnetic dipole transitions between the fine structure levels (and) of the iodine atom near cm−1 important for the iodine atom laser and for the kinetic spectroscopy of iodine atoms generated in infrared multiphoton excitation and dissociation of organic iodides, where simultaneous high time and frequency resolution including hyperfine structure can be achieved, that is only limited by the Heisenberg uncertainty principle. Accurate numerical results from calculations with the URIMIR package are compared with estimates from perturbation theory and they agree well. Possibilities for experimental tests of the theoretical predictions are outlined and the URIMIR package is included in an appendix of supplementary material. [ABSTRACT FROM AUTHOR]

What are the final size and velocity limits of electronic data processing and magnetic information storage areas, and how can we approach these boundaries questions and the understanding and control of microscopic electron motion along with many scientific studies have led to the birth and progress of Attosecond Science. The progress of ultrafast laser technology in recent years, the interaction process between the matter and the intense field play a key role in understanding how energy and charge are carried in atoms as well as in more complex solid and molecular systems. This review study will focus on the basic concepts and experimental tools that allow to observe and control the atomic scale motion of electrons in real time, understand the theoretical models that are critical for combining experimental observability with microscopic variables, and the expected technological effects. For this purpose, the role of nano and attosecond technologies in atomic and molecular physics, and condensed matter physics will be investigated and local literature sources will be presented about several important and recent current application areas of attosecond pulses. [ABSTRACT FROM AUTHOR]

By numerically solving the two-dimensional time-dependent Schrödinger equation, we investigate the strong-field photoelectron holography (SFPH) for different atomic and molecular targets. The results show that the photoelectron hologram is capable of providing structural information-the phase of scattering amplitude. In our calculations, the holographic pattern shifts with the target, indicating the phase difference between various targets. However, for the near-forward scattering, the phases of scattering amplitude for different targets are similar and thus no structural information has been retrieved in the previous works on near-forward scattering hologram. We suggest to use the backward scattering photoelectron hologram to extract this type of structural information. This paves a significant step towards time-resolved imaging of molecular structure and dynamics with the concept of SFPH. [ABSTRACT FROM AUTHOR]

Ionization of molecules in strong femtosecond laser fields is a key process for understanding a variety of strong-field molecular physical phenomena. In this study, we performed an experimental study on strong-field ionization and dissociation of three linear triatomic molecules, CO 2 , CS 2 , and OCS, using time-of-flight mass spectrometer. We measured the yield of different parent ions and various fragment ions as a function of laser intensity in the range of 2.0 × 10 13 W/cm 2 to 8.0 × 10 14 W/cm 2 , in both 800-nm and 400-nm strong laser fields. The mechanism of strong-field single and double ionization, as well as fragmentation, was discussed based on the experimental results. In addition, the angular distributions of fragment ions were obtained. The results show the anisotropic distributions in the formation of highly charged atomic fragment ions, which may be attributed to the alignment of the molecules in strong laser fields before dissociation. [ABSTRACT FROM AUTHOR]

Through the numerical solution of the 3D time-dependent Schrödinger equation, the two-dimensional photoelectron energy spectra (PES) of argon have been calculated, showing good accordance with the experimental measurements. Further analysis on the TDSE calculated data and comparison of PES under linearly and circularly polarized laser pulses demonstrated that the forward rescattering of the recolliding electron is mainly responsible for the appearance of the low energy structure (LES) in the PES. It is further revealed that the LES is correlated with the high angular momenta ( l = 8 – 13 ) of the photoelectron. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present a 3D quantum approach for studying the atom–laser interaction. [•] Sine-DVR and split-operator propagator are used for economizing computational time. [•] Our calculated electron spectrum has good agreement with experimental result. [•] The ATI spectra have studied in linearly and circularly polarized lights. [Copyright &y& Elsevier]

The nonlinear scattering of a laser pulse off spherical nanoclusters with free electrons and with a diffuse surface is examined in the collisionless hydrodynamics approximation in the framework of perturbation theory with respect to the laser pulse intensity, as well as of the steady-state approximation. In a previous publication [S.V. Fomichev and W. Becker, Phys. Rev. A 81, 063201 (2010)] we reported the full nonlinear hydrodynamic model of forced collective electron motion confined to a cluster with diffuse surface and introduced two different perturbation theories corresponding to different laser intensity regimes. In the current paper, in the framework of this hydrodynamic model we focus on the properties of plasmon resonance-enhanced third-harmonic generation in a spherical cluster and its dependence on the shape of its diffuse surface whose role increases for nonlinear processes. At the same time, the quadrupole second-harmonic generation in a spherical cluster is also inspected as a necessary intermediate step. Both cold metal clusters in vacuum or in a dielectric surrounding and hot laser-heated and laser-ionized clusters are considered within the same approach for a wide range of the fundamental laser frequency. Nonlinear laser excitation of the dipole plasmon Mie resonance in spherical clusters, as well as of other respective multipole plasmon resonances is investigated analytically and numerically in detail (position, width, and strength) versus the cluster-surface diffuseness, the outer ionization degree in charged clusters, the electron-density diffuseness, and their interplay. Under certain conditions, depending on the various cluster parameters, different secondary nonlinear resonances are found. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We propose a physical mechanism based on breakdown of the Born-Oppenheimer approximation to rationalize the ultrafast hydrogen migration in strong laser driven isomerization reactions. A three nuclei (proton, donor, and acceptor) model is employed to develop a three step solution scheme. The proton-donor Coulomb repulsion is shown to be responsible for the high proton mobility. We identify a proton tunneling process and use the Keldysh-Faisal-Reiss theory to calculate the tunneling probability. The effect of laser parameters (intensity, frequency, polarization, and pulse duration) has been studied and found to be consistent with recent experiments. [ABSTRACT FROM AUTHOR]

A theory describing above-threshold ionization of atoms and ions in a strong electromagnetic field is presented. It is based on the widely known strong field approximation and incorporates the Coulomb interaction between the photoelectron and the nucleus using the method of complex classical trajectories. A central result of the theory is the Coulomb-corrected ionization amplitude whose evaluation requires little extra numerical effort. By comparing our predictions with the results of ab initio numerical solutions for two examples we show that the new theory provides a significant improvement of the Coulomb-free strong field approximation. For the case of above-threshold ionization in elliptically polarized fields a comparison with available experimental data is also presented. [ABSTRACT FROM AUTHOR]

We investigate the laser-wavelength dependence of high-order above-threshold ionization and high-order harmonic generation rates. For both processes we have found pronounced enhancements in the spectra for those wavelengths for which the channel-closing condition is satisfied. These enhancements are explained in two complementary ways. One is in terms of the constructive interference of a large number of long quantum orbits, while the second interpretation is based on threshold anomalies. There are two types of these enhancements, which leave very different footprints in the spectra. When the ground-state parity of the atom changes, the two types are interchanged. [ABSTRACT FROM AUTHOR]

Abstract: The elimination of H2 + from alkyl iodides under strong (up to 5×1015 Wcm−2) laser irradiation is studied by means of time-of-flight mass spectrometry. The study has been performed by using 60fs (λ =800nm) and 35ps (λ =1064, 532, 355 and 266nm) laser pulses. It is concluded that the H2 + ions are ejected from ionic states via Coulomb explosion processes. The molecular rearrangement leading to H2 + formation is attributed to a tunneling process through a H transfer barrier. For the case of methyl iodide, about 10% of the doubly charged parent ions undergo molecular rearrangement. From a comparison of the H2 +/H+ ion yield ratio of the studied molecules, it turns out that the H2 + formation from H atoms bonded to a terminal carbon atom is more efficient than that arising from H atoms bonded to central C atoms of the molecular chain. [Copyright &y& Elsevier]

Abstract: We analyze the laser ellipticity dependence of n-photon differential cross sections for electron–atom scattering in an intense elliptically polarized laser field. We show that there exist two plateau-like structures in the dependence of on n for any ellipticity, including for the case of circular polarization. We present numerical predictions for e–H scattering in a CO2-laser field and an analytical description of the plateau features in terms of the rescattering scenario. [Copyright &y& Elsevier]

By numerically solving the time-dependent Schrödinger equation, we theoretically investigate the holographic structure of the multiple-returning rescattering recorded in the photoelectron momentum distribution. In the orthogonally polarized two-color fields, we show that the interference patterns periodically oscillate with the relative phase. Tracing the relative phase where the oscillation minimizes, we find that the dependences of the phase on the parallel momentum for the first-returning and the second-returning rescattering holographic interferences are different. With the quantum-orbit model, we demonstrated that the difference is related to the ionization and rescattering times of the electron. Moreover, we show that the influence of the Coulomb interaction on the oscillation of both the first-returning rescattering and the second-returning rescattering holographic interferences can be ignored. This suggests us that the temporal characteristics of the electron can be resolved by analyzing the relative phase's dependence of the multiple-returning holographic interference. [ABSTRACT FROM AUTHOR]

We calculate the photoelectron momentum distributions (PMDs) from strong-field above-threshold ionization of Ar in the co-linearly polarized two-color laser fields consisting a strong fundamental component and a much weaker second harmonic by solving the time-dependent Schrödinger equation. Utilizing the recently introduced phase-of-the-phase (PP) spectroscopy, we analyze the relative phase dependence of the PMDs of the recollision electrons and the jumps in the PP spectroscopy are observed. With the semi-classical model, we demonstrate that the phase jumps originate from the competition between the orbits where recollision occurs at different returnings. Thus, the relative contribution of the multiple-returning recollision orbits is unambiguously identified with the PP spectroscopy. Additionally, we show that the relative contribution of the multiple-returning recollision orbits depends on the laser wavelength and ellipticity. In elliptically polarized laser field, the yield of the high-energy photoelectrons favors the contribution of the second-returning recollision orbits. In 1600-nm laser field, the PP spectroscopy indicates that the relative contribution of multiple-returning recollision orbits is strongly sensitive to the electron energy. [ABSTRACT FROM AUTHOR]