19 research outputs found
Intra- and intercycle interference of electron emission in laser assisted XUV atomic ionization
We study the ionization of atomic hydrogen in the direction of polarization
due to a linearly polarized XUV pulse in the presence a strong field IR. We
describe the photoelectron spectra as an interference problem in the time
domain. Electron trajectories steming from different optical laser cycles give
rise to intercycle interference energy peaks known as sidebands. These
sidebands are modulated by a grosser structure coming from the intracycle
interference of the two electron trajectories born during the same optical
cycle. We make use of a simple semiclassical model which offers the possibility
to establish a connection between emission times and the photoelectron kinetic
energy. We compare the semiclassical predictions with the continuum-distorted
wave strong field approximation and the ab initio solution of the time
dependent Schr\"odinger equation. We analyze such interference pattern as a
function of the time delay between the IR and XUV pulse and also as a function
of the laser intensity
Time Double-Slit Interference in Tunneling Ionization
We show that interference phenomena plays a big role for the electron yield
in ionization of atoms by an ultra-short laser pulse. Our theoretical study of
single ionization of atoms driven by few-cycles pulses extends the
photoelectron spectrum observed in the double-slit experiment by Lindner et al,
Phys. Rev. Lett. \textbf{95}, 040401 (2005) to a complete three-dimensional
momentum picture. We show that different wave packets corresponding to the same
single electron released at different times interfere, forming interference
fringes in the two-dimensional momentum distributions. These structures
reproduced by means of \textit{ab initio} calculations are understood within a
semiclassical model.Comment: 7 pages, 5 figure
Non-constant ponderomotive energy in above threshold ionization by intense short laser pulses
We analyze the contribution of the quiver kinetic energy acquired by an
electron in an oscillating electric field to the energy balance in atomic
ionization processes by a short laser pulse. Due to the time dependence of this
additional kinetic energy, a temporal average is assumed to maintain a
stationary energy conservation rule. This rule is used to predict the position
of the peaks observed in the photo electron spectra (PE). For a flat top pulse
envelope, the mean value of the quiver energy over the whole pulse leads to the
concept of ponderomotive energy . However for a short pulse with a fast
changing field intensity a stationarity approximation could not be precise. We
check these concepts by studying first the photoelectron (PE) spectrum within
the Semiclassical Model (SCM) for a multiple steps pulses. The SCM offers the
possibility to establish a connection between emission times and the PE
spectrum in the energy domain. We show that PE substructures stem from
ionization at different times mapping the pulse envelope. We also present the
analysis of the PE spectrum for a realistic sine-squared envelope within the
Coulomb-Volkov and \textit{ab initio} calculations solving the time-dependent
Schr\"odinger equation. We found that the electron emission amplitudes produced
at different times interfere with each other and produce a new additional
pattern, that overlap the above-threshold ionization (ATI) peaks.Comment: 9 pages, 5 figure
Laser-assisted photoionization: beyond the dipole approximation
We present a theoretical study of atomic laser-assisted photoionization
emission (LAPE) beyond the dipole approximation. By considering the
non-relativistic non-dipole strong-field approximation (non-dipole
Gordon-Volkov wave function), we analyze the different contributions to the
photoelectron spectrum (PES), which can be written in terms of intra- and
intercycle factors. We find that not only does our non-dipole approach exhibit
asymmetric emission in the direction of light propagation, but also allows
emission in dipole-forbidden directions. The former feature can be rooted both
in intra- and intercycle interference processes, whilst the latter stems from a
dependence of the sideband energy on the emission angle with respect to the
propagation direction. Our theoretical scheme, presented here for He atoms in
the 1s quantum state, is general enough to be applied to other atomic species
and field configurations.Comment: 10 pages, 7 figures. arXiv admin note: text overlap with
arXiv:2006.0065
Classical-quantum correspondence in atomic ionization by midinfrared pulses: Multiple peak and interference structures
Atomic ionization by strong and ultrashort laser pulses with frequencies in the midinfrared spectral region have revealed novel features such as the low-energy structures. We have performed fully three-dimensional quantum dynamical as well as classical trajectory Monte Carlo simulations for pulses with wavelengths from λ=2000 to 6000 nm. Furthermore, we apply distorted-wave quantum approximations. This allows to explore the quantum-classical correspondence as well as the (non) perturbative character of the ionization dynamics driven by long-wavelength pulses. We observe surprisingly rich structures in the differential energy and angular momentum distribution which sensitively depend on λ, the pulse duration τp, and the carrier-envelope phase ϕCEP
Retrieving intracycle interference in angle-resolved laser-assisted photoemission from argon
We report on a combined experimental and theoretical study of XUV ionization of atomic argon in the presence of a near-infrared (NIR) laser field. Using a table-top source of wavelength-selected femtosecond XUV pulses in combination with a velocity map imaging spectrometer we record angle- and energy-resolved photoelectron distributions and simulate the experimental data by solving the time-dependent Schrödinger equation ab initio. In order to compare with the experimental data we average the calculated energy-angle probability distributions over the experimental focal volume for different values of the magnetic quantum number of the photoelectron. This averaging procedure washes out the intracycle interference pattern, which would otherwise be observed in the form of angular modulations of the photoelectron spectra. We recover these modulations experimentally and in the simulations by evaluating the difference between two averaged distributions that are obtained for slightly different NIR laser field intensities.Fil: Hummert, Johan. Max Born Institute; AlemaniaFil: Kubin, Markus. Max Born Institute; AlemaniaFil: López, Sebastián David. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Fuks, Johanna Ildemar. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Morales, Felipe. Max Born Institute; AlemaniaFil: Vrakking, Marc J. J.. Max Born Institute; AlemaniaFil: Kornilov, Oleg. Max Born Institute; AlemaniaFil: Arbó, Diego G.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
Minimal irreversible quantum mechanics. The decay of unstable states
Brownian motion is modelled by a harmonic oscillator (Brownian particle)
interacting with a continuous set of uncoupled harmonic oscillators. The
interaction is linear in the coordinates and the momenta. The model has an
analytical solution that is used to study the time evolution of the reduced
density operator. It is derived in a closed form, in the one-particle sector of
the model. The irreversible behavior of the Brownian particle is described by a
reduced density matrix.Comment: 39 pages, 2 figure