Search results for "Generation"
showing 10 items of 3050 documents
Observation of two-XUV-photon ionization using harmonic generation from a short, intense laser pulse
1996
We report the observation of a two-photon ionization process in the XUV wavelength regime. In a near-resonant 1 + 1 ionization scheme, Ar atoms are ionized absorbing the 15 eV third harmonic photons produced in a gas jet by the 0.5 ps intense laser pulses of a KrF excimer laser emitting at 248.6 nm. The present demonstration of a non-linear process in the XUV regime reveals feasibility of high-intensity applications utilizing the uniquely high peak power of non-conventional short wavelength radiation sources based on harmonic generation.
Harmonic Generation and Nonlinear Propagation: When Secondary Radiations Have Primary Consequences
2014
In this Letter, it is experimentally and theoretically shown that weak odd harmonics generated during the propagation of an infrared ultrashort ultraintense pulse unexpectedly modify the nonlinear properties of the medium and lead to a strong modification of the propagation dynamics. This result is in contrast with all current state-of-the-art propagation model predictions, in which secondary radiations, such as third harmonic, are expected to have a negligible action upon the fundamental pulse propagation. By analyzing full three-dimensional ab initio quantum calculations describing the microscopic atomic optical response, we have identified a fundamental mechanism resulting from interfere…
Symmetries in harmonic generation by a two-color field: an application to a simple model atom
1999
We show that the parity of the order of the harmonics generated by a bichromatic field with commensurate frequencies may be related to the invariance properties of the time-dependent Hamiltonian with respect to some suitable transformations. To simplify the mathematical treatment, we have used a simple model atom to perform calculations that show the effects of the relative phase of the driving fields. Harmonic generation has been described as a two-step process that involves replicas of the Stark levels. In agreement with other previous treatments in which other model atoms were used, we have found that a small contamination of the fundamental harmonic can produce significant modifications…
Laser even harmonics generation by a plasma embedded in a static electric field
2004
Even order harmonics generation of the laser radiation due to electron-ion collisions in a plasma embedded in a constant electric field is investigated theoretically. Even harmonics are generated because the presence of a static electric field removes the invariance of the electron distribution function under the symmetry operation of velocity direction inversion. Efficiency generation dependencies are investigatedvsdifferent significant parameters as: harmonics number; the ratio of the electron quiver velocity to the thermal velocity; the orientation of the constant electric field with respect to the laser radiation electric field and its wavevector. It is shown that in the general case th…
The Non-Abelian Vector Gauge Particle ρ
2020
So far we have shown how pion self-interaction and pion-mass generation are tied together. This phenomenon, a result of the three-dimensional non-linear realization of the triplet isotopic pion field, is a consequence of a dimensional reduction from four-dimensional Euclidean space to a three-dimensional curved isotopic space with positive curvature, i.e., by way of chiral-symmetry breaking and subsequent pionic mass generation in a curved isotopic spin background with K = λ2, λ = 2f0∕mπ, which is taken from low-energy π − N interaction.
Polarity and bioelectrical patterning in a linear chain of non-excitable cells
2020
Abstract Polarity in multicellular systems is influenced by bioelectrical signals because electric potentials can act as spatio-temporal patterns for other biochemical processes that eventually emerge as long-lasting biological outcomes. We study the role of the electric potential in establishing head-tail polarity for the case of a chain of non-excitable cells. This biophysical model incorporates both single-cell (membrane ion channels) and multicellular (intercellular gap junctions) characteristics. The results are presented in the form of a bioelectrical phase space that complements traditional biochemical approaches and provides qualitative insights for the case of anterior/posterior po…
Polarization of the Radiation Emitted in GaAs Semiconductors Driven by Far Infrared Fields
2010
The effects due to the mixing of two far infrared electric fields on the harmonic generation process in low doped GaAs bulks are studied by a three dimensional multivalleys Monte Carlo simulation. The conversion efficiency is calculated by using the appropriate Maxwell equation for the propagation of an electro-magnetic wave along a given direction in the medium. In particular, we focus our attention on the polarization of the generated harmonics, by comparing the polarization obtained from the mixing of an oscillating field with a static electric field with that obtained in the presence of two cyclostationary fields, having an integer ratio between the two frequencies. The findings show th…
Generation of minimum energy entangled states
2020
Quantum technologies exploiting bipartite entanglement could be made more efficient by using states having the minimum amount of energy for a given entanglement degree. Here, we study how to generate these states in the case of a bipartite system of arbitrary finite dimension either by applying a unitary transformation to its ground state or through a zero-temperature thermalization protocol based on turning on and off a suitable interaction term between the subsystems. In particular, we explicitly identify three possible unitary operators and five possible interaction terms. On the one hand, two of the three unitary transformations turn out to be easily decomposable in terms of local eleme…
Landau-Majorana-Stuckelberg-Zener dynamics driven by coupling for two interacting qutrit systems
2019
A time-dependent model of two interacting spin qutrits is analyzed is analyzed and solved. The two interacting qutrits are subjected to a longitudinal field linearly varying over time as in the Landau-Majorana-St\"uckelberg- Zener (LMSZ) scenario. Although a transverse field is absent, we show the occurrence of LMSZ transitions assisted by the coupling between the two spin-qutrits. Such a physical effect permits us to estimate experimentally the coupling strength between the spins and allows the generation of entangled states of the two qutrits by appropriately setting the slope of the ramp. Furthermore, the possibility of local and nonlocal control as well as the existence of dark states o…
Dynamics of H2 molecule driven by an ultra-short laser field
2004
We describe, using a semiclassical approach, the molecular dynamics of a one-dimensional H2 molecule interacting with a laser, beyond the Born–Oppenheimer approximation. We observe and discuss different molecular behaviors, such as ionization and dissociation.