2,067 research outputs found
Wave-packet propagation based calculation of above-threshold ionization in the x-ray regime
We investigate the multi-photon process of above-threshold ionization for the
light elements hydrogen, carbon, nitrogen and oxygen in the hard x-ray regime.
Numerical challenges are discussed and by comparing Hartree-Fock-Slater
calculations to configuration-interaction-singles results we justify the
mean-field potential approach in this regime. We present a theoretical
prediction of two-photon above-threshold-ionization cross sections for the
mentioned elements. Moreover, we study how the importance of above-threshold
ionization varies with intensity. We find that for carbon, at x-ray intensities
around , two-photon above-threshold ionization of the
K-shell electrons is as probable as one-photon ionization of the L-shell
electrons.Comment: 13 pages, 4 figures, 1 tabl
Above threshold ionization by few-cycle spatially inhomogeneous fields
We present theoretical studies of above threshold ionization (ATI) produced
by spatially inhomogeneous fields. This kind of field appears as a result of
the illumination of plasmonic nanostructures and metal nanoparticles with a
short laser pulse. We use the time-dependent Schr\"odinger equation (TDSE) in
reduced dimensions to understand and characterize the ATI features in these
fields. It is demonstrated that the inhomogeneity of the laser electric field
plays an important role in the ATI process and it produces appreciable
modifications to the energy-resolved photoelectron spectra. In fact, our
numerical simulations reveal that high energy electrons can be generated.
Specifically, using a linear approximation for the spatial dependence of the
enhanced plasmonic field and with a near infrared laser with intensities in the
mid- 10^{14} W/cm^{2} range, we show it is possible to drive electrons with
energies in the near-keV regime. Furthermore, we study how the carrier envelope
phase influences the emission of ATI photoelectrons for few-cycle pulses. Our
quantum mechanical calculations are supported by their classical counterparts
Emergence of Classical Orbits in Few-Cycle Above-Threshold Ionization
The time-dependent Schr\"odinger equation for atomic hydrogen in few-cycle
laser pulses is solved numerically. Introducing a positive definite quantum
distribution function in energy-position space, a straightforward comparison of
the numerical ab initio results with classical orbit theory is facilitated.
Integration over position space yields directly the photoelectron spectra so
that the various pathways contributing to a certain energy in the photoelectron
spectra can be established in an unprecedented direct and transparent way.Comment: 4 pages, 4 figures REVTeX (manuscript with higher resolution figures
available at http://www.dieterbauer.de/publist.html
Intensity-Resolved Above Threshold Ionization of Xenon with Short Laser Pulses
We present intensity-resolved above threshold ionization (ATI) spectra of
xenon using an intensity scanning and deconvolution technique. Experimental
data were obtained with laser pulses of 58 fs and central wavelength of 800 nm
from a chirped-pulse amplifier. Applying a deconvolution algorithm, we obtained
spectra that have higher contrast and are in excellent agreement with
characteristic 2 and 10 cutoff energies contrary to that found for
raw data. The retrieved electron ionization probability is consistent with the
presence of a second electron from double ionization. This recovered ionization
probability is confirmed with a calculation based on the PPT tunneling
ionization model [Perelomov, Popov, and Terent'ev, Sov. Phys. JETP 23, 924
(1966)]. Thus, the measurements of photoelectron yields and the proposed
deconvolution technique allowed retrieval of more accurate spectroscopic
information from the ATI spectra and ionization probability features that are
usually concealed by volume averaging.Comment: 21 pages, 7 figure
Intracycle and Intercycle Interferences in Above-Threshold Ionization: the Time Grating
Within a semiclassical description of above-threshold ionization (ATI) we
identify the interplay between intracycle and intercycle interferences. The
former is imprinted as a modulation envelope on the discrete multiphoton peaks
formed by the latter. This allows to unravel the complex interference pattern
observed for the full solution of the time-dependent Schr\"odinger equation
(TDSE) in terms of diffraction at a grating in the time domain. These
modulations can be clearly seen in the dependence of the ATI spectra on the
laser wavelength. Shifts in energy modulation result from the effect of the
long Coulomb tail of the atomic potential.Comment: 10 pages, 5 figures in preprint forma
Above-threshold ionization by polarization-crafted pulses
Coherent light has revolutionized scientific research, spanning biology,
chemistry, and physics. To delve into ultrafast phenomena, the development of
high-energy, high-tunable light sources is instrumental. Here, the
photo-electric effect is a pivotal tool for dissecting electron correlations
and system structures. Particularly, above-threshold ionization (ATI),
characterized by simultaneous multi-photon absorption, has been widely
explored, both theoretical and experimentally. ATI decouples laser field
effects from the structural information carried by photo-electrons,
particularly when utilizing ultra-short pulses. In this contribution we study
ATI driven by polarization-crafted (PC) pulses, which offer precise control
over the electron emission directions, through an accurate change of the
polarization state. PC pulses enable the manipulation of electron trajectories,
opening up new avenues for understanding and harnessing coherent light. Our
work explores how structured light could allow a high degree of control of the
emitted photo-electrons.Comment: 10 page
Resonant above-threshold ionization at quantized laser intensities
Journal ArticleWe argue that quantum electrodynamics dictates resonance phenomena in multiphoton processes as the laser intensity varies. A perturbation theory is developed in which the coupling between an electron and the second quantized laser mode is treated nonperturbatively. As an example, we predict that the above-threshold ionization rate can exhibit resonance at intensities with integer ponderomotive parameter. Such quantum effects may be exploited to calibrate laser intensities
Above-threshold ionization photoelectron spectrum from quantum trajectory
Many nonlinear quantum phenomena of intense laser-atom physics can be
intuitively explained with the concept of trajectory. In this paper, Bohmian
mechanics (BM) is introduced to study a multiphoton process of atoms
interacting with the intense laser field: above-threshold ionization (ATI).
Quantum trajectory of an atomic electron in intense laser field is obtained
from the Bohm-Newton equation first and then the energy of the photoelectron is
gained from its trajectory. With energies of an ensemble of photoelectrons, we
obtain the ATI spectrum which is consistent with the previous theoretical and
experimental results. Comparing BM with the classical trajectory Monte-Carlo
method, we conclude that quantum potential may play a key role to reproduce the
spectrum of ATI. Our work may present a new approach to understanding quantum
phenomena in intense laser-atom physics with the image of trajectory.Comment: 10 pages, 3 figure
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