Search results for "Excitation"
showing 10 items of 1290 documents
Turing Patterns in Nonlinear Optics
2000
The phenomenon of pattern formation in nonlinear optical resonators is commonly related to an off-resonance excitation mechanism, where patterns occur due to mismatch between the excitation and resonance frequency. In this paper we show that the patterns in nonlinear optics can also occur due to the interplay between diffractions of coupled field components. The reported mechanism is analogous to that of local activation and lateral inhibition found in reaction-diffusion systems by Turing. We study concretely the degenerate optical parametric oscillators. A local activator-lateral inhibitor mechanism is responsible for generation of Turing patterns in form of hexagons.
Probing Rydberg atoms through collisions with helium in the presence of static electric and magnetic fields
2005
We report on field induced inelasticity effects in state-to-state transitions caused by collisions of helium with Rydberg atoms in the presence of parallel static electric and magnetic fields. Due to the phases accumulated by the wavefunctions of the states involved into the collision events, the transition cross sections plotted as a function of the external fields exhibit modulations. When the relative velocity of the colliding atoms is high enough, these modulations are wiped out, while sizable modifications of the cross sections may take place due to the alteration of the wavefunctions' spatial localization. The possibility of using the field-assisted collisions as a probe giving inform…
Fission dynamics: The quest of a temperature dependent nuclear viscosity
2013
This paper presents a journey within some open questions about the current use of a temperature dependent nuclear viscosity in models of nuclear fission and proposes an alternative experimental approach by using systems of intermediate fissility. This study is particularly relevant because: i) systems of intermediate fissility offer a suitable frame-work since the intervals between the compound nucleus and scission point temperatures with increasing excitation energy are much smaller than in the case of heavier systems, ii) the dependence of viscosity on the temperature may change with the fissility of the composite system; iii) the opportunity to measure also observables in the evaporation…
Excitation of phase patterns and spatial solitons via two-frequency forcing of a 1:1 resonance.
2000
We show that a self-oscillatory system, driven at two frequencies close to that of the unforced system (resonance 1:1), becomes phase locked and exhibits two equivalent stable states of opposite phases. For spatially extended systems this phase bistability results in patterns characteristic for real order parameter systems, such as phase domains, labyrinths, and phase spatial solitons. In variational cases, the phase-locking mechanism is interpreted as a result of the periodic "rocking" of the system potential. Rocking could be tested experimentally in lasers and in oscillatory chemical reactions.
Monte Carlo analysis of electronic noise in semiconductors under sub‐terahertz cyclostationary mixed fields
2006
This paper reports the results of Monte Carlo simulations of electronic noise in a GaAs bulk driven by two mixed high-frequency large-amplitude periodic electric fields. Under these conditions, the system response shows some peculiarities in the noise performance, such as a resonant-like enhancement of the spectra near the two frequencies of the applied fields. The relations among the frequency response and the velocity fluctuations as a function of intensities and frequencies of the sub-terahertz mixed excitation fields have been investigated. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of inelastic couplings on 32S + 24MG sub-barrier fusion
1988
Elastic, inelastic and mutual excitation angular distributions have been measured for 32S+ 24Mg at 65, 75, 56.3, 95 and 110 MeV of 32S incident energy. The data have been analysed by optical model and coupled channel calculations. Energy-dependent optical potentials have been obtained which have been used to describe the 32S + 24Mg fusion data of Berkowitz et al2). Barrier penetration and coupled channel models are compared. It is found that the energy-dependence of the empirical potentials is essential if a consistent simultaneous description of elastic, inelastic an fusion data is required.
Study of the 2n-evaporation channel in the 4,6He+206,208Pb reactions
2009
Abstract Excitation functions of the reaction products were measured for the reactions induced by 4,6 He projectiles on 208,206 Pb targets, leading to the same compound nucleus. This was accomplished by using the stacked-foil activation technique. The identification of the reaction products (accumulated in the Pb targets) was done by their radioactive α -decays. The excitation functions for the various products were obtained at energies including the sub-Coulomb barrier region. A large value of the fusion cross section was observed in the case of the reaction induced by the weakly bound 6 He projectile.
Rydberg Series Excitation of a Single Trapped Ca+40 Ion for Precision Measurements and Principal Quantum Number Scalings
2021
A complete set of spectroscopic data is indispensable when using Rydberg states of trapped ions for quantum information processing. We carried out Rydberg series spectroscopy for $n{S}_{1/2}$ states with $38\ensuremath{\le}n\ensuremath{\le}65$ and for $n{D}_{5/2}$ states with $37\ensuremath{\le}n\ensuremath{\le}50$ on a single trapped $^{40}{\mathrm{Ca}}^{+}$ ion. We determined the ionization energy of 2 870 575.582(15) GHz, 60 times more accurately as compared to the accepted value and contradicting it by 7.5 standard deviations. We confirm quantum defect values of ${\ensuremath{\delta}}_{{S}_{1/2}}=1.802\text{ }995(5)$ and ${\ensuremath{\delta}}_{{D}_{5/2}}=0.626\text{ }888(9)$ for $n{S}_…
Multisequential photofragmentation of size-selected gold cluster ions
2002
Time-resolved fragmentation measurements have been performed on stored, size-selected gold cluster ions ${\mathrm{Au}}_{n}^{+}$ $(n=17--21)$ that have been excited up to 15 eV by multiphoton absorption. These excitation energies are far above the clusters' dissociation thresholds and initiate multistep sequential unimolecular dissociation by evaporation of neutral monomers. The measurements allow for the determination of a combination of kinetic-energy release and radiative cooling of the excited clusters. Also, previously determined model-independent values of the cluster dissociation energies are confirmed by the present measurements. The data are consistent with thermal values of the kin…
Determination of nuclear spins of short-lived isotopes by laser induced fluorescence
1980
Abstract The spins of several nuclear ground and isomeric states have been measured for a number of mercury isotopes. The fluorescent light from the 6s6p3P1 state is observed at 2537 A after excitation with the frequency doubled output of a pulse dye laser. Four different laser induced fluorescence techniques were tested for their applicability: double resonance, Hanle effect, time delayed integral Hanle beats, and time resolved quantum beats. The sensitivity and selectivity of these models are compared with emphasis on the determination of spins of nuclei far from beta-stability, where short half lives and low production yields restrict the number of available atoms. The experiments were c…