Strong-field Ionization Of Atoms Research Articles

On the role of the Coulomb potential in strong field atomic ionization dynamics

In this paper, we present a model aimed at exploring the role of the Coulomb potential in the mechanism of ionization of atomic hydrogen exposed to a strong low frequency pulsed laser field. Our approach is based on the solution of the time-dependent Schrödinger equation in momentum space. Although we are in a frequency and intensity regime where tunnelling is expected to dominate, our results indicate that the atomic structure associated to the Coulomb potential plays a significant role for low energy ejected electrons.

X-Ray Microprobe of Orbital Alignment in Strong-Field Ionized Atoms

We have developed a synchrotron-based, time-resolved x-ray microprobe to investigate optical strong-field processes at intermediate intensities (10(14) - 10(15) W/cm2). This quantum-state specific probe has enabled the direct observation of orbital alignment in the residual ion produced by strong-field ionization of krypton atoms via resonant, polarized x-ray absorption. We found strong alignment to persist for a period long compared to the spin-orbit coupling time scale (6.2 fs). The observed degree of alignment can be explained by models that incorporate spin-orbit coupling. The methodology is applicable to a wide range of problems.

Strong-field ionization of atoms and molecules: The two-term saddle-point method

We derive an analytical formula for the ionization rate of neutral atoms and molecules in a strong monochromatic field. Our model is based on the strong-field approximation with transition amplitudes calculated by an extended saddle-point method. We show that the present two-term saddle-point method reproduces even complicated structures in angular resolved photoelectron spectra.

Quantum control and quantum control landscapes using intense shaped femtosecond pulses

A hitherto not considered physical mechanism of quantum control with intense shaped femtosecond laser pulses is investigated. Phase modulated pulses are used to exert control on the strong-field ionization of potassium atoms. We use a sinusoidal phase modulation function to manipulate the intensity of the Autler–Townes (AT) components in the photoelectron spectrum. The effect of all sine parameters is studied systematically. In addition, controllability is investigated using parameterized pulse shapes to generate a two-dimensional quantum control landscape. Our results show that the selective population of dressed states is the underlying strong-field physical mechanism. Due to its robustness with respect to the laser parameters, the selective dressed state population is an important general control mechanism.

Strong-field ionization of diatomic molecules and companion atoms: Strong-field approximation and tunneling theory including nuclear motion

We present a detailed comparison of strong-field ionization of diatomic molecules and their companion atoms with nearly equal ionization potentials. We perform calculations in the length and velocity gauge formulations of the molecular strong-field approximation and with the molecular tunneling theory, and in both cases we consider effects of nuclear motion. A comparison of our results with experimental data shows that the length gauge strong-field approximation gives the most reliable predictions.

Super strong field ionization of atoms by 1019 W cm−2, 10 Hz laser pulses

We report on the optical field ionization of rare gases (argon, krypton and xenon) by > 1019 W cm−2 laser pulses whose electric field well exceeds the Coulombic binding field in strength. Charge states as high as Ar16+, Kr19+, and Xe26+ have been observed, which correspond to He-like argon, Cl-like krypton and Ni-like xenon, respectively. The extension of the laser system to petawatt peak powers is described.

Strong field atomic ionization: origin of high-energy structures in photoelectron spectra.

Two distinct interpretations have been proposed to account for conspicuous enhancements of the ionization peaks in the high energy part of above-threshold ionization spectra. One of them ascribes the enhancement to a multiphoton resonance involving an excited state, while other analysis performed for zero-range model potential link it to "channel closings, " i.e., to the change in the number of photons needed to ionize the atom when the laser intensity increases. We report the results of model calculations that confirm the existence of a resonant process in atoms and shed light on why short-range potential models can mimic the experimental observations.

Super strong field ionization of atoms by 10 19 W cm −2 , 10 Hz laser pulses

Super strong field ionization of atoms by 10 19 W cm −2 , 10 Hz laser pulses

Direct and indirect pathways in strong field atomic ionization dynamics.

With the help of a suitably chosen momentum-space analysis, we study some of the basic mechanisms governing the physics of the processes occurring when atoms are submitted to intense infrared laser pulses, with peak intensities 10(14) W cm(-2)</=I(max)</=10(15) W cm(-2). This intensity range is especially interesting because two highly nonlinear atomic processes, namely, above threshold ionization and high-order harmonic generation, take place with significant probabilities. Several issues regarding the dynamics of these processes are resolved, with special attention devoted to the mechanism leading to the ejection of the photoelectrons in this intensity range.

Coherent control of strong-field two-pulse ionization of Rydberg atoms

Strong-field ionization of Rydberg atoms is investigated in its dependence on phase features of the initial coherent population of Rydberg levels. In the case of a resonance between Rydberg levels and some lower-energy atomic level (V-type transitions), this dependence is shown to be very strong: by a proper choice of the initial population an atom can be made either completely or very little ionized by a strong laser pulse. It is shown that phase features of the initial coherent population of Rydberg levels and the ionization yield can be efficiently controlled in a scheme of ionization by two strong laser pulses with a varying delay time between them.

Strong-field laser ionization of alkali atoms using two-dimensional cylindrical and three-dimensional Cartesian time-dependent Hartree–Fock theory

The time-dependent Schrodinger equation is solved directly for an alkali atom subject to an arbitrarily strong electromagnetic field. Two methods are compared. A tridiagonal finite-difference method is used to solve Schrodinger’s equation on a two-dimensional (2D) cylindrical coordinate lattice, while a finite-element method using odd-order B splines is used to solve Schrodinger’s equation on a three-dimensional (3D) Cartesian coordinate lattice. Multiphoton ionization cross sections are extracted from 2D cylindrical calculations for hydrogen and lithium and then compared with previous perturbation theory results. Single-photon ionization probabilities are compared from 2D cylindrical and 3D Cartesian calculations for hydrogen.

Strong-field high-frequency approximation to the multiphoton ionization of hydrogen

The strong-field multiphoton ionization of atoms is considered and a theoretical approach dealing nonperturbatively with the radiation field formulated. The general computational scheme is the conventional perturbation theory, but the intermediate states are dressed by the field. We present in detail a method to dress the continuum states and to study the dipole transitions within the continuum. In the high-frequency domain, the proposed procedure rapidly converges over a wide range of field intensity and offers an interesting framework for calculating ionization rates for arbitrary numbers of absorbed (above-threshold) photons and field polarization.

Phase space approach to above threshold ionization

Phase space averaging method of classical mechanics is applied to the study of strong field ionization of atoms (ATI). The photoelectron spectra calculated by this simple method exhibit the main features of the spectra observed in numerous experiments. This approach provides a novel insight into the strong field processes and is the only one so far which can be applicable for intensities above 1014 W/cm2.

Strong-field multiphoton ionization of hydrogen. TheS-matrix treatment of the elementary process

A theoretical model is presented to treat the elementary act of strong-field multiphoton ionization of atoms when the electron continuum final-state distribution is important. It is based on theS-matrix formalism and treats the final-state electron-radiation interaction in an essentially nonperturbative way. Selected numerical calculations concern the ionization of hydrogen atoms and include differential and total cross-sections of several multiphoton channels as a function of the laser intensity. Good, qualitative agreement with the experimental observations is found for values of the field intensity which are not critical with respect to the simplifications adopted in constructing the theoretical model. It applies particularly to the use of an ideal model for the laser field. Significant departure from observations is instead found when the implications of the ideal laser model play a critical role, as occurs at channel inversion and suppression. It is concluded that the theoretical treatment to be completely satisfactory needs essentially to incorporate a more realistic laser model such as a multimode one.

Strong-field laser ionization of model atoms

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text M. S. Pindzola and C. Bottcher, "Strong-field laser ionization of model atoms," J. Opt. Soc. Am. B 4, 752-753 (1987) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article