78 research outputs found
Resonant Auger decay of the core-excited CO molecule in intense X-ray laser fields
The dynamics of the resonant Auger (RA) process of the core-excited
CO(1s) molecule in an intense X-ray laser field is
studied theoretically. The theoretical approach includes the analogue of the
conical intersections of the complex potential energy surfaces of the ground
and `dressed' resonant states due to intense X-ray pulses, taking into account
the decay of the resonance and the direct photoionization of the ground state,
both populating the same final ionic states coherently, as well as the direct
photoionization of the resonance state itself. The light-induced non-adiabatic
effect of the analogue of the conical intersections of the resulting complex
potential energy surfaces gives rise to strong coupling between the electronic,
vibrational and rotational degrees of freedom of the diatomic CO molecule. The
interplay of the direct photoionization of the ground state and of the decay of
the resonance increases dramatically with the field intensity. The coherent
population of a final ionic state via both the direct photoionization and the
resonant Auger decay channels induces strong interference effects with distinct
patterns in the RA electron spectra. The individual impact of these physical
processes on the total electron yield and on the CO electron
spectrum are demonstrated.Comment: 13 figs, 1 tabe
High-Resolution Photoelectron Spectrometry Study of Conjugate Shakeup Processes in the Li 1s Threshold Region
Partial cross sections and angular-distribution asymmetry parameters of diagram and satellite lines associated with Li 1s photoionization were measured using synchrotron-radiation excitation. Special emphasis was given to a high-resolution study of the 1P and 3P conjugate shakeup satellite lines testing qualitative predictions of the conjugate shakeup model: increasing σ and decreasing β values towards threshold, both being verified. Comparison with recent relaxed Hartree-Fock calculations shows good agreement for the 1P satellite, but demonstrates also that the present theory does not seem to be able to describe the cross-section behavior of the 3P satellite correctly
Electric-octupole and pure-electric-quadrupole effects in soft-x-ray photoemission
Second-order [O(k^2), k=omega/c] nondipole effects in soft-x-ray
photoemission are demonstrated via an experimental and theoretical study of
angular distributions of neon valence photoelectrons in the 100--1200 eV
photon-energy range. A newly derived theoretical expression for nondipolar
angular distributions characterizes the second-order effects using four new
parameters with primary contributions from pure-quadrupole and octupole-dipole
interference terms. Independent-particle calculations of these parameters
account for a significant portion of the existing discrepancy between
experiment and theory for Ne 2p first-order nondipole parameters.Comment: 4 pages, 3 figure
Low-Energy Nondipole Effects in Molecular Nitrogen Valence-Shell Photoionization
Observations are reported for the first time of significant nondipole effects in the photoionization of the outer-valence orbitals of diatomic molecules. Measured nondipole angular-distribution parameters for the 3sigmag, 1piu, and 2sigmau shells of N2 exhibit spectral variations with incident photon energies from thresholds to ~200 eV which are attributed via concomitant calculations to particular final-state symmetry waves arising from (E1)[direct-product](M1,E2) radiation-matter interactions first-order in photon momentum. Comparisons with previously reported K-edge studies in N2 verify linear scaling with photon momentum, accounting in part for the significantly enhanced nondipole behavior observed in inner-shell ionization at correspondingly higher momentum values in this molecule
Non-dipole angular anisotropy parameters of semi-filled shell atoms
We present the results of calculations of outer shell non-dipole angular
anisotropy parameters for semi-filled shell atoms in the Hartree-Fock (HF)
one-electron approximation and with account of inter-electron correlations in
the frame of the Spin Polarized Random Phase Approximation with Exchange (SP
RPAE). We demonstrate for the first time that this characteristic of
photoionization process is essentially sensitive to the fact whether the
photoelectron has the same or opposite spin orientation to that of the
semi-filled shell.Comment: 15 pages, 8 figure
Angle-Resolved Photoelectron Spectroscopy of C60
Angle-resolved photoelectron spectra of gaseous C60 were recorded in the photon energy regions from 21 to 108 eV and from 295 to 320 eV. Partial cross sections σ and the angular distribution anisotropy parameter β vary significantly with photon energy, particularly in the near-threshold region of the valence and the core ionization regimes. Some of these effects may be attributed to scattering of the outgoing photoelectron by the atoms of the ionized C60 molecule. Our results indicate that the observed satellites of the C(1s) main line are most likely of shake-up character. Low-energy electrons emitted below the shake-off threshold indicate the occurrence of K-shell vacancy filling double Auger decay
Harmonic Generation from Relativistic Plasma Surfaces in Ultra-Steep Plasma Density Gradients
Harmonic generation in the limit of ultra-steep density gradients is studied
experimentally. Observations demonstrate that while the efficient generation of
high order harmonics from relativistic surfaces requires steep plasma density
scale-lengths () the absolute efficiency of the harmonics
declines for the steepest plasma density scale-length , thus
demonstrating that near-steplike density gradients can be achieved for
interactions using high-contrast high-intensity laser pulses. Absolute photon
yields are obtained using a calibrated detection system. The efficiency of
harmonics reflected from the laser driven plasma surface via the Relativistic
Oscillating Mirror (ROM) was estimated to be in the range of 10^{-4} - 10^{-6}
of the laser pulse energy for photon energies ranging from 20-40 eV, with the
best results being obtained for an intermediate density scale-length
Extreme ultraviolet emission from dense plasmas generated with sub-10-fs laser pulses
The extreme ultraviolet (XUV) emission from dense plasmas generated with
sub-10-fs laser pulses with varying peak intensities up to 3*10^16 W/cm^2 is
investigated for different target materials. K shell spectra are obtained from
low Z targets (carbon and boron nitride). In the spectra a series limit for the
hydrogen and helium like resonance lines is observed indicating that the plasma
is at high density and pressure ionization has removed the higher levels. In
addition, L shell spectra from titanium targets were obtained. Basic features
of the K and L shell spectra are reproduced with computer simulations. The
calculations include hydrodynamic simulation of the plasma expansion and
collisional radiative calculations of the XUV emission.Comment: 22 pages, 11 figures. The following article has been submitted to
Physics of Plasmas. After it is published, it will be found at
http://pop.aip.org
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