52 research outputs found
Interfering one-photon and two-photon ionization by femtosecond VUV pulses in the region of an intermediate resonance
The electron angular distribution after atomic photoionization by the fundamental frequency and its second harmonic is analyzed for a case when the frequency of the fundamental scans the region of an intermediate atomic state. The angular distribution and its left-right asymmetry, due to the two-pathway interference between nonresonant one-photon and resonant two-photon ionization, sharply change as a function of the photon energy. The phenomenon is exemplified by both solving the time-dependent Schr\"odinger equation on a numerical space-time grid and by applying perturbation theory for ionization of the hydrogen atom in the region of the 1s\text{\ensuremath{-}}2p transition for femtosecond pulses as well as an infinitely long exposure to the radiation. Parametrizations for the asymmetry and the anisotropy coefficients, obtained within perturbation theory, reveal general characteristics of observable quantities as functions of the parameters of the radiation beam
Photoelectron angular distribution in two-pathway ionization of neon with femtosecond XUV pulses
We analyze the photoelectron angular distribution in two-pathway interference
between non\-resonant one-photon and resonant two-photon ionization of neon. We
consider a bichromatic femtosecond XUV pulse whose fundamental frequency is
tuned near the atomic states of neon. The time-dependent
Schr\"odinger equation is solved and the results are employed to compute the
angular distribution and the associated anisotropy parameters at the main
photoelectron line. We also employ a time-dependent perturbative approach,
which allows obtaining information on the process for a large range of pulse
parameters, including the steady-state case of continuous radiation, i.e., an
infinitely long pulse. The results from the two methods are in relatively good
agreement over the domain of applicability of perturbation theory
Vector parameters in atomic ionization by twisted light: polarization of electron and residual ion
The electron and ion properties observed in a photoionization inherit a
symmetry properties of both a target and a radiation. Introducing a symmetry
breaking in a photoionization process one can expect to observe a noticeable
variation of the vector correlation parameters of either outgoing photoelectron
or a residual ion. One of the ways to violate symmetry is to irradiate a matter
by the twisted radiation which involves an additional screw.
In the paper we present the extension of the approach developed in [Phys.
Rev. A 108, 023117 (2023)] for the photoelectron angular distribution to the
other vector correlation parameters, exactly photoelectron spin polarization,
orientation and alignment of the residual ion. Usually two conditions are
needed to produce polarized photoelectrons: a system possesses a helix and a
noticeable spin-orbital interaction. In the paper we investigate if a twisted
light brings an additional helicity to a system. As an illustrative example we
consider ionization of valence -shell of atomic krypton by circularly and
linearly polarized Bessel light. The photoelectron spin components are analyzed
as a function of the cone angle of the twisted radiation
Displacement effect in strong-field atomic ionization by an XUV pulse
We study strong-field atomic ionization driven by an XUV pulse with a
non\-zero displacement, the quantity defined as the integral of the pulse
vector potential taken over the pulse duration. We demonstrate that the use of
such pulses may lead to an extreme sensitivity of the ionization process to
subtle changes of the parameters of a driving XUV pulse, in particular, the
ramp-on/off profile and the carrier envelope phase. We illustrate this
sensitivity for atomic hydrogen and lithium driven by few-femto\-second XUV
pulses with intensity in the range. We argue that the
observed effect is general and should modify strong-field ionization of any
atom, provided the ionization rate is sufficiently high.Comment: 5 pages, 7 figure
Electron-Impact Excitation from the (4p⁵5s) Metastable States of Krypton
Theoretical results from multistate semirelativistic Breit-Pauli R-matrix calculations and two first-order distorted-wave calculations are presented for electron-impact excitation of krypton from the (4p55s) J = 0,2 metastable states to the (4p55s) and (4p55p) manifolds. Except for a few cases, in which the method to account for relativistic effects becomes surprisingly critical, fair overall agreement between the predictions from the various theoretical models is achieved for intermediate and high energies. However, significant discrepancies remain with the few available experimental data
Electron-Impact Excitation to the 4p⁵5s and 4p⁵5p Levels of Kr | Using Different Distorted-Wave and Close-Coupling Methods
Electron-impact excitation of the 4p55s and 4p55p levels of Kr I has been investigated in detail by calculating cross sections using distorted-wave and close-coupling approaches. The results are presented from the excitation thresholds up to 50 eV incident energy. They are contrasted among the different calculations and compared with other theoretical predictions and experimental data. Significant disagreement is found with many of the recent experimental data of Chilton et al. [Phys. Rev. A 62, 032714 (2000)]
Measurement of laser intensities approaching 10 15 W/cm 2 with an accuracy of 1%
Accurate knowledge of the intensity of focused ultrashort laser pulses is crucial to the correct interpretation of experimental results in strong-field physics. We have developed a technique to measure laser intensities approaching 1015W/cm2 with an accu
A new method for measuring angle-resolved phases in photoemission
Quantum mechanically, photoionization can be fully described by the complex
photoionization amplitudes that describe the transition between the ground
state and the continuum state. Knowledge of the value of the phase of these
amplitudes has been a central interest in photoionization studies and newly
developing attosecond science, since the phase can reveal important information
about phenomena such as electron correlation. We present a new
attosecond-precision interferometric method of angle-resolved measurement for
the phase of the photoionization amplitudes, using two phase-locked Extreme
Ultraviolet pulses of frequency and , from a Free-Electron
Laser. Phase differences between one- and two-photon
ionization channels, averaged over multiple wave packets, are extracted for
neon electrons as a function of emission angle at photoelectron energies
7.9, 10.2, and 16.6 eV. is nearly constant for emission
parallel to the electric vector but increases at 10.2 eV for emission
perpendicular to the electric vector. We model our observations with both
perturbation and \textit{ab initio} theory, and find excellent agreement. In
the existing method for attosecond measurement, Reconstruction of Attosecond
Beating By Interference of Two-photon Transitions (RABBITT), a phase difference
between two-photon pathways involving absorption and emission of an infrared
photon is extracted. Our method can be used for extraction of a phase
difference between single-photon and two-photon pathways and provides a new
tool for attosecond science, which is complementary to RABBITT
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