829 research outputs found
High-speed and Non-volatile Memory Devices Using a Macroscopic Polarized Stack Consisting of Double Floating Gates Interconnected with Engineered Tunnel Oxide Barriers
Correlation dynamics between electrons and ions in the fragmentation of D molecules by short laser pulses
We studied the recollision dynamics between the electrons and D ions
following the tunneling ionization of D molecules in an intense short pulse
laser field. The returning electron collisionally excites the D ion to
excited electronic states from there D can dissociate or be further
ionized by the laser field, resulting in D + D or D + D,
respectively. We modeled the fragmentation dynamics and calculated the
resulting kinetic energy spectrum of D to compare with recent experiments.
Since the recollision time is locked to the tunneling ionization time which
occurs only within fraction of an optical cycle, the peaks in the D kinetic
energy spectra provides a measure of the time when the recollision occurs. This
collision dynamics forms the basis of the molecular clock where the clock can
be read with attosecond precision, as first proposed by Corkum and coworkers.
By analyzing each of the elementary processes leading to the fragmentation
quantitatively, we identified how the molecular clock is to be read from the
measured kinetic energy spectra of D and what laser parameters be used in
order to measure the clock more accurately.Comment: 13 pages with 14 figure
Entanglement and Timing-Based Mechanisms in the Coherent Control of Scattering Processes
The coherent control of scattering processes is considered, with electron
impact dissociation of H used as an example. The physical mechanism
underlying coherently controlled stationary state scattering is exposed by
analyzing a control scenario that relies on previously established entanglement
requirements between the scattering partners. Specifically, initial state
entanglement assures that all collisions in the scattering volume yield the
desirable scattering configuration. Scattering is controlled by preparing the
particular internal state wave function that leads to the favored collisional
configuration in the collision volume. This insight allows coherent control to
be extended to the case of time-dependent scattering. Specifically, we identify
reactive scattering scenarios using incident wave packets of translational
motion where coherent control is operational and initial state entanglement is
unnecessary. Both the stationary and time-dependent scenarios incorporate
extended coherence features, making them physically distinct. From a
theoretical point of view, this work represents a large step forward in the
qualitative understanding of coherently controlled reactive scattering. From an
experimental viewpoint, it offers an alternative to entanglement-based control
schemes. However, both methods present significant challenges to existing
experimental technologies
High-order harmonic generation with a strong laser field and an attosecond-pulse train: the Dirac Delta comb and monochromatic limits
In recent publications, it has been shown that high-order harmonic generation
can be manipulated by employing a time-delayed attosecond pulse train
superposed to a strong, near-infrared laser field. It is an open question,
however, which is the most adequate way to approximate the attosecond pulse
train in a semi-analytic framework. Employing the Strong-Field Approximation
and saddle-point methods, we make a detailed assessment of the spectra obtained
by modeling the attosecond pulse train by either a monochromatic wave or a
Dirac-Delta comb. These are the two extreme limits of a real train, which is
composed by a finite set of harmonics. Specifically, in the monochromatic
limit, we find the downhill and uphill sets of orbits reported in the
literature, and analyze their influence on the high-harmonic spectra. We show
that, in principle, the downhill trajectories lead to stronger harmonics, and
pronounced enhancements in the low-plateau region. These features are analyzed
in terms of quantum interference effects between pairs of quantum orbits, and
compared to those obtained in the Dirac-Delta limit.Comment: 10 pages, 7 figures (eps files). To appear in Laser Physic
β-Decay Half-Lives of 76;77Co, 79;80Ni, and 81Cu: Experimental Indication of a Doubly Magic 78Ni
published_or_final_versio
Coherent Electron Scattering Captured by an Attosecond Quantum Stroboscope
The basic properties of atoms, molecules and solids are governed by electron
dynamics which take place on extremely short time scales. To measure and
control these dynamics therefore requires ultrafast sources of radiation
combined with efficient detection techniques. The generation of extreme
ultraviolet (XUV) attosecond (1 as = 10-18 s) pulses has, for the first time,
made direct measurements of electron dynamics possible. Nevertheless, while
various applications of attosecond pulses have been demonstrated
experimentally, no one has yet captured or controlled the full three
dimensional motion of an electron on an attosecond time scale. Here we
demonstrate an attosecond quantum stroboscope capable of guiding and imaging
electron motion on a sub-femtosecond (1 fs = 10-15 s) time scale. It is based
on a sequence of identical attosecond pulses which are synchronized with a
guiding laser field. The pulse to pulse separation in the train is tailored to
exactly match an optical cycle of the laser field and the electron momentum
distributions are detected with a velocity map imaging spectrometer (VMIS).
This technique has enabled us to guide ionized electrons back to their parent
ion and image the scattering event. We envision that coherent electron
scattering from atoms, molecules and surfaces captured by the attosecond
quantum stroboscope will complement more traditional scattering techniques
since it provides high temporal as well as spatial resolution.Comment: 6 pages, 4 figure
Attosecond control of electrons emitted from a nanoscale metal tip
Attosecond science is based on steering of electrons with the electric field
of well-controlled femtosecond laser pulses. It has led to, for example, the
generation of XUV light pulses with a duration in the sub-100-attosecond
regime, to the measurement of intra-molecular dynamics by diffraction of an
electron taken from the molecule under scrutiny, and to novel ultrafast
electron holography. All these effects have been observed with atoms or
molecules in the gas phase. Although predicted to occur, a strong light-phase
sensitivity of electrons liberated by few-cycle laser pulses from solids has
hitherto been elusive. Here we show a carrier-envelope (C-E) phase-dependent
current modulation of up to 100% recorded in spectra of electrons laser-emitted
from a nanometric tungsten tip. Controlled by the C-E phase, electrons
originate from either one or two sub-500as long instances within the 6-fs laser
pulse, leading to the presence or absence of spectral interference. We also
show that coherent elastic re-scattering of liberated electrons takes place at
the metal surface. Due to field enhancement at the tip, a simple laser
oscillator suffices to reach the required peak electric field strengths,
allowing attosecond science experiments to be performed at the 100-Megahertz
repetition rate level and rendering complex amplified laser systems
dispensable. Practically, this work represents a simple, exquisitely sensitive
C-E phase sensor device, which can be shrunk in volume down to ~ 1cm3. The
results indicate that the above-mentioned novel attosecond science techniques
developed with and for atoms and molecules can also be employed with solids. In
particular, we foresee sub-femtosecond (sub-) nanometre probing of (collective)
electron dynamics, such as plasmon polaritons, in solid-state systems ranging
in size from mesoscopic solids via clusters to single protruding atoms.Comment: Final manuscript version submitted to Natur
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