Search results for "Stability"
showing 10 items of 3085 documents
Gap solitons and modulation instability in a dynamic Bragg grating with nonlinearity management
2008
International audience; We investigate the occurrence of modulation instability in systems in which a dynamic Bragg grating consists of alternating positive and negative Kerr coefficients. The dependence of modulation instability gain spectra over the perturbation wavenumber and system parameters is portrayed near and at the edges of the photonic band gap structure. Further, we demonstrate the generation of traveling gap solitons near the photonic band gap structure through the modulation instability
NOISE EFFECTS IN POLYMER DYNAMICS
2008
The study of the noise induced effects on the dynamics of a chain molecule crossing a potential barrier, in the presence of a metastable state, is presented. A two-dimensional stochastic version of the Rouse model for a flexible polymer has been adopted to mimic the molecular dynamics and to take into account the interactions between adjacent monomers. We obtain a nonmonotonic behavior of the mean first passage time and its standard deviation, of the polymer centre of inertia, with the noise intensity. These findings reveal a noise induced effect on the mean crossing time. The role of the polymer length is also investigated.
Shifts of the 3D - 4P transitions in different isotopes of positive calcium ions
1997
A sample of stable isotopes containing the masses 40, 42, 43 and 44 was stored under buffer-gas conditions in a Paul ion trap. After population of the metastable 3D levels by spontaneous decay of the laser-excited 4P state we observed laser-induced fluorescence when we scanned a laser across the different 3D - 4P fine-structure lines at 850, 854 and 866 nm. From the Doppler-limited lines of these transitions we deduced the isotope shifts, which are of the order of several GHz due to the large specific mass shift of the metastable 3D levels.
Experimental lifetime of the metastable 5D 3/2 state in Ba+
1992
A discrepancy exists between theoretical and experimental lifetimes of the metastable 5D3/2 state in Ba+. In order to redertermine that lifetime, we probe the population of the metastable 5D3/2 state of a Ba+ ion cloud stored in a Paul ion trap in the presence of He buffer gas as the function of time delay after pulsed laser excitation of this state. The measured decay rates at different buffer gas pressures are extrapolated to zero pressure and we obtain a radiative decay time of 48.0±5.9 s. This is not in agreement with theoretical predictions of about 80 s, but reduces the discrepancy from a previously reportet experimental value of 17.5 s. If the possibility of finestructure mixing to a…
Laser instabilities in a Gaussian cavity mode with Gaussian pump profile
1998
We analytically demonstrate that both single-mode and multimode instabilities may occur in a Gaussian-cavity-mode laser model with Gaussian pump profile. As a necessary condition, the ratio of the beam waist to the pump waist must exceed a given limiting value, which depends on the population decay rate. For an infinitely concentrated pump the plane-wave model instability thresholds are recovered, and there exists an optimum value of the waists ratio for which the second laser threshold is minimum.
Lorenz–Haken instability in a laser with arbitrary mirrors reflectivity
2000
Abstract We study the Lorenz–Haken instability in a laser with arbitrary mirrors reflectivity R . In the limit of slow population difference we demonstrate that in order to observe the instability the reflectivity must exceed the critical value R c ≃0.5379, which coincides with that found recently for the multimode (Risken–Nummedal–Graham–Haken) instability. Several other differences with respect to the uniform field limit R →1 are presented.
Precise lifetime determination of the metastable 3d 2 D 5/2 level in Ca + by "electron shelving"
1996
Ca+ ions confined as a cloud in a Paul trap were excited and cooled by radiation from two lasers, tuned to the 4s2S1/2 − 4p2P1/2 and 4p2P1/2 − 3d2D3/2 transitions. The strong fluorescence of these lines disappears when we excite the ions simultaneously by a third laser on the 3d2D3/2 − 4p2P3/2 line because of population trapping in the metastable 3d2D5/2 state, into which the 4p2P3/2 level decays. From the time dependence of the fluorescence after blocking the third laser we determined the lifetime of the 3d2D5/2 level. Our result of τ = 1064(17) ms improves earlier results and agrees with the value recently computed by Liaw using the Brueckner approximation.
Search for elements 119 and 120
2020
A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the 50Ti+249Bk and 50Ti+249Cf fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the 249Bk target partially decayed into 249Cf, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the 50Ti+249Bk and 50Ti+249Cf reactions, respectively, at a midtarget beam energy of Elab=281.5 MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical pr…
Stability and Chaotic Attractors of Memristor-Based Circuit with a Line of Equilibria
2019
This report investigates the stability problem of memristive systems with a line of equilibria on the example of SBT memristor-based Wien-bridge circuit. For the considered system, conditions of local and global partial stability are obtained, and chaotic dynamics is studied. peerReviewed
Instabilities of four-wave mixing
2005
We predict that four-wave mixing driven by a dual frequency input undergoes different instability scenarios encompassing modulational instability or multiple shock formation in the anomalous and normal dispersion regime, respectively.