67 research outputs found
Keldysh-Rutherford model for attoclock
We demonstrate a clear similarity between attoclock offset angles and
Rutherford scattering angles taking the Keldysh tunnelling width as the impact
parameter and the vector potential of the driving pulse as the asymptotic
velocity. This simple model is tested against the solution of the
time-dependent Schr\"odinger equation using hydrogenic and screened (Yukawa)
potentials of equal binding energy. We observe a smooth transition from a
hydrogenic to 'hard-zero' intensity dependence of the offset angle with
variation of the Yukawa screening parameter. Additionally we make comparison
with the attoclock offset angles for various noble gases obtained with the
classical-trajectory Monte Carlo method. In all cases we find a close
correspondence between the model predictions and numerical calculations. This
suggests a largely Coulombic origin of the attoclock offset angle and casts
further doubt on its interpretation in terms of a finite tunnelling time
XUV ionization of the H molecule studied with attosecond angular streaking
We study orientation and two-center interference effects in attosecond
time-resolved photoionization of the H molecule. Time resolution of XUV
ionization of H is gained through the phase retrieval capability of
attosecond angular streaking demonstrated earlier by Kheifets {\em et al}
[arXiv:2202.06147 (2022)]. Once applied to H, this technique delivers an
anisotropic phase and time delay which both depend sensitively on the molecular
axis orientation. In addition, the photoelectron momentum distribution displays
a very clear two-center interference pattern. When the interference formula due
to Walter and Briggs [J. Phys. B {\bf 32} 2487 (1999)] is applied, an effective
photoelectron momentum appears to be greater than the asymptotic momentum at
the detector. This effect is explained by a molecular potential well
surrounding the photoemission center.Comment: 8 pages, 7 figure
Numerical attoclock on atomic and molecular hydrogen
Numerical attoclock is a theoretical model of attosecond angular streaking
driven by a very short, nearly a single oscillation, circularly polarized laser
pulse. The reading of such an attoclock is readily obtained from a numerical
solution of the time-dependent Schr\"odinger equation as well as a
semi-classical trajectory simulation. By making comparison of the two
approaches, we highlight the essential physics behind the attoclock
measurements. In addition, we analyze the predictions of the Keldysh-Rutherford
model of the attoclock [Phys. Rev. Lett. 121, 123201 (2018)]. In molecular
hydrogen, we highlight a strong dependence of the width of the attoclock
angular peak on the molecular orientation and attribute it to the two-center
electron interference. This effect is further exemplified in the weakly bound
neon dimer.Comment: 8 pages, 7 figure
Signature of two-electron interference in angular resolved double photoionization of Mg
The double photoionization of Mg has been studied experimentally and theoretically in a kinematic where the two photoelectrons equally share the excess energy. The observation of a symmetrized gerade amplitude, which strongly deviates from the Gaussian ansatz, is explained by a two-electron interference predicted theoretically, but never before observed experimentally. Similar to the Cooper minima in the single photoionization cross section, the effect finds its origin in the radial extent and oscillation of the target wave function
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
Intershell-correlation-induced time delay in atomic photoionization
We predict an observable Wigner time delay in outer atomic shell photoionization near inner shell thresholds. The near-threshold increase of time delay is caused by intershell correlation and serves as a sensitive probe of this effect. The time delay increase is present even when the inner and outer shell thresholds are hundreds of electron volts apart. We illustrate this observation by several prototypical examples in noble gas atoms from Ne to Kr. In our study, we employ the random phase approximation with exchange and its relativistic generalization. We also support our findings by a simplified, yet quite insightful, treatment within the lowest-order perturbation theory.S.T.M. acknowledges the support of the Chemical Sciences,
Geosciences, and Biosciences Division, Office of Basic Energy
Sciences, Office of Science, US Department of Energy, under
Grant No. DE-FG02-03ER15428
Relativistic effects in photoionization time delay near the Cooper minimum of noble-gas atoms
Time delay of photoemission from valence ns, np3/2, and np1/2 subshells of noble-gas atoms is theoretically scrutinized within the framework of the dipole relativistic random phase approximation. The focus is on the variation of time delay in the vicinity of the Cooper minima in photoionization of the outer subshells of neon, argon, krypton, and xenon, where the corresponding dipole matrix element changes its sign while passing through a node. It is revealed that the presence of the Cooper minimum in one photoionization channel has a strong effect on time delay in other channels. This is shown to be due to interchannel coupling
Angle-resolved Wigner time delay in atomic photoionization: The 4d subshell of free and confined Xe
The angular dependence of photoemission time delay for the inner nd3/2 and nd5/2 subshells of free and confined Xe is studied in the dipole relativistic random phase approximation. A finite spherical annular well potential is used to model the confinement due to fullerene C60 cage. Near cancellations in a variety of the dipole amplitudes, Cooper-like minima, are found. The effects of confinement on the angular dependence, primarily confinement resonances, are demonstrated and detailed.S.T.M. was supported by Division of Chemical Sciences,
Basic Energy Science, Office of Science, US Department of
Energy Grant No. DE-FG02-03ER15428. P.C.D. acknowledges support of an NSF Grant No. PHY-0852786 for travel
to Georgia State University
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