1,444 research outputs found
Laser-induced nonsequential double ionization at and above the recollision-excitation-tunneling threshold
We perform a detailed analysis of the recollision-excitation-tunneling (RESI)
mechanism in laser-induced nonsequential double ionization (NSDI), in which the
first electron, upon return, promotes a second electron to an excited state,
from which it subsequently tunnels, based on the strong-field approximation. We
show that the shapes of the electron momentum distributions carry information
about the bound-state with which the first electron collides, the bound state
to which the second electron is excited, and the type of electron-electron
interaction. Furthermore, one may define a driving-field intensity threshold
for the RESI physical mechanism. At the threshold, the kinetic energy of the
first electron, upon return, is just sufficient to excite the second electron.
We compute the distributions for helium and argon in the threshold and
above-threshold intensity regime. In the latter case, we relate our findings to
existing experiments. The electron-momentum distributions encountered are
symmetric with respect to all quadrants of the plane spanned by the momentum
components parallel to the laser-field polarization, instead of concentrating
on only the second and fourth quadrants.Comment: 14 pages, 7 figure
Dynamical characteristics of Rydberg electrons released by a weak electric field
The dynamics of ultra-slow electrons in the combined potential of an ionic
core and a static electric field is discussed. With state-of-the-art detection
it is possible to create such electrons through strong intense-field
photo-absorption and to detect them via high-resolution time-of-flight
spectroscopy despite their very low kinetic energy. The characteristic feature
of their momentum spectrum, which emerges at the same position for different
laser orientations, is derived and could be revealed experimentally with an
energy resolution of the order of 1meV.Comment: 5 pages, 5 figure
Broadening of hot-spot response spectrum of superconducting NbN nanowire single-photon detector with reduced nitrogen content
The spectral detection efficiency and the dark count rate of superconducting
nanowire single-photon detectors (SNSPD) has been studied systematically on
detectors made from thin NbN films with different chemical compositions.
Reduction of the nitrogen content in the 4 nm thick NbN films results in a more
than two orders of magnitude decrease of the dark count rates and in a red
shift of the cut-off wavelength of the hot-spot SNSPD response. The observed
phenomena are explained by an improvement of uniformity of NbN films that has
been confirmed by a decrease of resistivity and an increase of the ratio of the
measured critical current to the depairing current. The latter factor is
considered as the most crucial for both the cut-off wavelength and the dark
count rates of SNSPD. Based on our results we propose a set of criteria for
material properties to optimize SNSPD in the infrared spectral region.Comment: 15 pages, 6 figure
Photon Momentum Transfer in Single-Photon Double Ionization of Helium
We theoretically and experimentally investigate the photon momentum transfer in single-photon double ionization of helium at various large photon energies. We find that the forward shifts of the momenta along the light propagation of the two photoelectrons are roughly proportional to their fraction of the excess energy. The mean value of the forward momentum is about 8/5 of the electron energy divided by the speed of light. This holds for fast and slow electrons despite the fact that the energy sharing is highly asymmetric and the slow electron is known to be ejected by secondary processes of shake off and knockout rather than directly taking its energy from the photon. The biggest deviations from this rule are found for the region of equal energy sharing where the quasifree mechanism dominates double ionization
Multiorbital tunneling ionization of the CO molecule
We coincidently measure the molecular frame photoelectron angular
distribution and the ion sum-momentum distribution of single and double
ionization of CO molecules by using circularly and elliptically polarized
femtosecond laser pulses, respectively. The orientation dependent ionization
rates for various kinetic energy releases allow us to individually identify the
ionizations of multiple orbitals, ranging from the highest occupied to the next
two lower-lying molecular orbitals for various channels observed in our
experiments. Not only the emission of a single electron, but also the
sequential tunneling dynamics of two electrons from multiple orbitals are
traced step by step. Our results confirm that the shape of the ionizing
orbitals determine the strong laser field tunneling ionization in the CO
molecule, whereas the linear Stark effect plays a minor role.Comment: This paper has been accepted for publication by Physical Review
Letter
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