emilpersson's ati [29 articles]

Abstract

In conditions where the interaction between an atom and a short high-frequency extreme ultraviolet laser pulse is a perturbation, we show that a simple theoretical approach, based on Coulomb-Volkov-type states, can make reliable predictions for ionization. To avoid any additional approximation, we consider here a standard case: the ionization of hydrogen atoms initially in their ground state. For any field parameter, we show that the method provides accurate energy spectra of ejected electrons, including many above threshold ionization peaks, as long ...

Abstract

Using a semiclassical rescattering model, the momentum distributions of recoil ions from laser induced single and double ionization are obtained. Not only in the case of double ionization but also in the case of single ionization, the distributions of the momentum parallel to the polarization direction of the laser field show a double-hump structure as a consequence of the rescattering. By comparing with experimental data we find that, as the intensity of the laser decreases, the rescattering ionization mechanism of the ...

Abstract

In this paper, the quasistatic model is extended to describe the double ionization of helium in an intense linearly polarized field, yielding insight into the two-electron correlation effect in the ionization dynamics. Our numerical calculations reproduce the excessive double ionization and the photoelectron spectra observed experimentally both quantitatively and qualitatively. Moreover, it is shown that the classical collisional trajectories are the main source of the double ionization in the knee regime where the double ionization yield is much higher than that ...

Abstract

We report calculations of energy- and angle-resolved photoelectron distribution of F − irradiated by a linearly strong short infrared pulse, performed by evaluating the photoelectron ejection probability in the framework of a modified Keldysh theory, taking into account the temporal behavior of the pulse and the spatial inhomogeneity of the laser intensity. Results of the calculations are compared with the measurements of the photoelectron angular distribution recently appearing in the literature. The oscillations found in the experimental data are ...

Abstract

We solve the three-dimensional time-dependent Schrodinger equation for a three-cycle circularly polarized laser pulse interacting with an atom. The photoelectron momentum distributions show counterintuitive shifts, similar to those observed in a recent experiment (Eckle et al 2008 Science 322 1525). The physical origin of the shifts is examined by a detailed investigation of the wave packet after the pulse. We show that the shifts arise as a consequence of an intimate interplay between the external field and the binding potential, and ...

Abstract

We investigate the photodetachment process in the negative fluorine ion in a strong linearly polarized laser field. Angle-resolved momentum distributions of photoelectrons are measured with the use of an imaging technique for a wide range of laser frequencies and peak intensities. The nonmonotonic structure recorded in photoelectron spectra is interpreted in terms of the quantum interference effect predicted by a Keldysh-like theory. In particular, the dependence of the interference term on the laser parameters is used to explain the origin of ...

Abstract

Numerical calculations of photodetachment of F − irradiated by a linearly polarized strong short infrared pulse have been performed by evaluating the photoelectron ejection probability in the framework of a Keldysh-type approach modified to account for the temporal behavior of the pulse. The results of the calculations are in good agreement with measurements of energy spectra recently appearing in literature, and show features that may be explained in terms of quantum interferences in time domain. ...

Abstract

Using numerical solutions of a time-dependent Schrödinger equation for a hydrogen atom in a linearly polarized few-cycle laser field, we calculate the left-right photoelectron kinetic-energy spectra measured by two opposing detectors placed along the laser polarization vector, with laser focus in the center. The fastest electrons show huge asymmetries strongly dependent on the laser carrier-envelope (CE) phase which confirms the recent theoretical results [D. B. Milosevic et al. , Opt. Express 11 , 1418 (2003)], obtained from a modified ...

Abstract

Electron-momentum distributions for above-threshold ionization of argon in a few-cycle, linearly polarized laser pulse are investigated. Spectral features characteristic of multiphoton as well as tunneling ionization coexist over a range of the Keldysh parameter γ in the transition regime γ ∼1 . Surprisingly, the simple strong-field approximation (SFA) is capable of reproducing the key features of the two-dimensional momentum distributions found in the full solution of the time-dependent Schrödinger equation, despite the fact that SFA is known to ...

Abstract

The single ionization of an He atom by intense linearly polarized laser field in the tunneling regime is studied by S -matrix theory. When only the first term of the expansion of the S matrix is considered and time, spatial distribution, and fluctuation of the laser pulse are taken into account, the obtained momentum distribution in the polarization direction of laser field is consistent with the semiclassical calculation, which only considers tunneling and the interaction between the free ...

Abstract

We present high resolution photoelectron energy spectra of noble gas atoms from high intensity above-threshold ionization (ATI) at midinfrared wavelengths. An unexpected structure at the very low-energy portion of the spectra, in striking contrast to the prediction of the simple-man theory, has been revealed. A semiclassical model calculation is able to reproduce the experimental feature and suggests the prominent role of the Coulomb interaction of the outgoing electron with the parent ion in producing the peculiar structure in long wavelength ATI ...

Abstract

Electron emission for single ionization of Ne by 25 fs, 1.0   PW/cm 2 laser pulses at 800 nm has been investigated in a kinematically complete experiment using a “reaction microscope.” Mapping the complete final state momentum space with high resolution, a distinct local minimum is observed at P e ∥ =0 , where P e ∥ is the electron momentum parallel to the laser polarization. Whereas tunneling theory predicts a maximum at zero momentum, our findings are in good ...

Abstract

A generalized strong-field approximation is formulated to describe atoms interacting with intense laser fields. We apply it to determine angular distributions of electrons in above-threshold ionization (ATI). The theory treats the effects of an electron rescattering from its parent ion core in a systematic perturbation series. Probability amplitudes for ionization are interpreted in terms of quasiclassical electron trajectories. We demonstrate that contributions from the direct tunneling processes in the absence of rescattering are not sufficient to describe the observed ATI spectra. ...

Abstract

10.1126/science.108836 ...

Abstract

We have experimentally determined the harmonic-generation cutoff as a function of the laser intensity in neon using an intense, short-pulse Ti:sapphire laser. The experimental cutoff is lower than that obtained in single-atom calculations. Using a simple quantum-mechanical approach to harmonic generation valid at high intensity, we show that the difference is due to the effect of propagation. ...

Abstract

In the long-wavelength limit, above-threshold ionization (ATI) is primarily the result of the interaction of a newly freed electron with the laser field. Classical physics requires that linearly and circularly polarized light produce very different ATI spectra. Measurements performed using both linearly and circularly polarized, picosecond, 10- μ m pulses confirm these conclusions. ...

Abstract

The analytic expressions for the probabilities of tunnel ionization of atoms and atomic ions and for the energy and angular electron spectra in a strong low-frequency electromagnetic field are obtained. The adiabatic approximation of quantum mechanics is used. The cases of linear and circular polarization of the field are considered. ...

Abstract

The authors report above-threshold ionisation in krypton irradiated by a two-colour radiation field ( lambda 1=1064 nm, lambda 2=532 nm), where the phase difference between the two colours can be precisely controlled. The ionisation rate depends not only on intensity but also on the relative phase between the two lasers, as do the relative intensities and widths of the electron spectral peaks. ...

Abstract

A simplified form of multiphoton and tunneling ionization is applied to the problem of ionization of atoms by a bichromatic field consisting of the coherent superposition of a fundamental field and its second harmonic: E ( t )=0.5[ E 1 exp(- i ω t )+ E 2 exp(-2 i ω t )]+c.c. This superposition possesses a polar asymmetric average of the cube of the field, 〈 E 3 〉=3/8( E 1 2* E 2 + E 1 2 ...

Abstract

Exact non-Born-Oppenheimer numerical solutions of the time-dependent Schrödinger equation for the 1D H 2 + molecule in an intense, two-color ( ω +2 ω ) laser field have been obtained. Both electron and proton kinetic energy spectra show spatial, correlated, asymmetric distributions. The calculated spectra exhibit the same unusual correlations as in experiments, in which both positively charged nuclear fragments and negatively charged photoelectrons were preferentially emitted in the same direction. The above asymmetries of photoemission of ...

Abstract

We present a review of work that has been done during the last 10 years on atomic scattering and reaction processes in bichromatic laser fields. Of particular interest will be the case where the field is composed of two components of commensurate frequencies, usually consisting of a fundamental component ω and one of its low harmonics 2ω or 3ω. These two components are in general out of phase by an angle . The above processes are then investigated as a ...

Abstract

We present calculations of ionization rates, angular distributions, and above-threshold-ionization spectra for a hydrogen atom in a strong, two-color laser field. The two lasers are first- and second-harmonic fields with the same intensity and a constant relative phase difference between them. At longer wavelengths (1064 nm) and higher intensities (> 10 13 W/ cm 2 ), there is clear evidence in the phase dependence of the ionization rates that ionization takes place primarily through tunneling. Even though the total ionization ...

Abstract

Abstract  Classical analysis and quantum-mechanical studies of the energy spectra of photoelectrons have been carried out for above-threshold ionization of atoms in a two-color laser field of the first and third (n = 3) harmonics. Numerical computations show that the boundary of direct ionization plateau corresponds to the electron energy E ≈ 3.56 $$U_p_1 $$ , while the boundary of rescattering plateau corresponds to the electron energy E ≈ 16.62 $$U_p_1 $$ for the two-color field of fundamental frequency and ...

Abstract

The interaction between an atom and a short laser pulse is studied in the case where both photon energies are smaller than the ionization potential and perturbation conditions prevail. Under these conditions, a full numerical solution of the time-dependent Schrödinger equation for a hydrogen atom initially in its ground state shows that secondary peaks show up in the above-threshold ionization (ATI) spectrum. We introduce here an easy-to-implement approximation that sheds light on these features. This approach, which is based on Coulomb-Volkov-type ...

Abstract

During strong-field multiphoton ionization, a wave packet is formed each time the laser field passes its maximum value. Within the first laser period after ionization there is a significant probability that the electron will return to the vicinity of the ion with very high kinetic energy. High-harmonic generation, multiphoton two-electron ejection, and very high energy above-threshold-ionization electrons are all conssequences of this electron-ion interaction. One important parameter which determines the strength of these effects is the rate at which the wave ...

Abstract

The very pronounced intensity-dependent enhancements of groups of peaks of high-order above-threshold-ionization spectra of rare-gas atoms are investigated using an improved version of the strong-field approximation, which realistically models the respective atom. Two types of enhancements are found and explained in terms of constructive interference of the contributions of a large number of long quantum orbits. The first type is observed for intensities slightly below channel closings. Its intensity dependence is comparatively smooth and it is generated by comparatively few (of ...

Abstract

We present a method for the accurate calculation of above-threshold ionization (ATI) spectra of single active electron systems. The technique involves the expansion of the radial wavefunction onto a set of B-spline functions. Results of ATI in hydrogen are presented and particular features of the spectra are discussed. A detailed study of the sensitivity of the results to the critical parameters is given to emphasize the importance of the necessity of a high degree of convergence in such calculations. Finally, we ...