27 research outputs found
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
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
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
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
Complex attosecond waveform synthesis at fel fermi
Free-electron lasers (FELs) can produce radiation in the short wavelength range extending from the extreme ultraviolet (XUV) to the X-rays with a few to a few tens of femtoseconds pulse duration. These facilities have enabled significant breakthroughs in the field of atomic, molecular, and optical physics, implementing different schemes based on two-color photoionization mechanisms. In this article, we present the generation of attosecond pulse trains (APTs) at the seeded FEL FERMI using the beating of multiple phase-locked harmonics. We demonstrate the complex attosecond waveform shaping of the generated APTs, exploiting the ability to manipulate independently the amplitudes and the phases of the harmonics. The described generalized attosecond waveform synthesis technique with an arbitrary number of phase-locked harmonics will allow the generation of sub-100 as pulses with programmable electric fields
Many particle spectroscopy of atoms, molecules, clusters and surfaces: international conference MPS-2016
The conference on Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces (MPS-2016) brought together near to a hundred scientists in the field of electronic, photonic, atomic and molecular collisions, and spectroscopy from around the world. We deliver an Editorial of a topical issue presenting original research results from some of the participants on both experimental and theoretical studies involving many particle spectroscopy of atoms, molecules, clusters and surfaces
Angular distribution of photoelectrons generated in atomic ionization by twisted radiation
Until recently, theoretical and experimental studies of photoelectron angular
distributions (PADs) including non-dipole effects in atomic photo\-ionization
have been performed mainly for the conventional plane-wave radiation. One can
expect, however, that the non-dipole contributions to the angular- and
polarization-resolved photo\-ionization properties are enhanced if an atomic
target is exposed to twisted light. The purpose of the present study is to
develop a theory for PADs to the case of twisted light, especially for
many-electron atoms. The theoretical analysis is performed for the
experimentally relevant case of macroscopic atomic targets, i.e., when the
cross-sectional area of the target is larger than the characteristic
transversal size of the twisted beam. For such a scenario, we derive
expressions for the angular distribution of the emitted photoelectrons under
the influence of twisted Bessel beams. As an illustrative example, we consider
helium photo\-ionization in the region of the lowest dipole
and quadrupole autoionization resonances. A noticeable
variation of the PAD caused by changing the parameters of the twisted light is
predicted.Comment: One more reference has been added in the Introduction. English
throughout the manuscript has been improve
Two-photon sequential double ionization of argon in the region of Rydberg autoionizing states of Ar
A theoretical study of two-photon sequential double ionization of Ar is presented for the photon energies in the region of Rydberg autoionizing states 3p4 (1D) nl of the ion Ar+ overlapping with the particle-hole autoionizing states 3s3p6 np of neutral Ar. The atomic and ionic autoionizing states lead to sharp variations of the angular correlation function between the two outgoing electrons, as well as in the angular distributions of the first and the second emitted electrons. A strong influence of the second step ionization on the first ionization step is demonstrated