1,721,063 research outputs found
A new exposure system for “in vivo” investigations of high-frequency electromagnetic fields: a preliminary study
No full text3D cavity light bullets in a nonlinear optical resonator
No full textWe consider a nonlinear ring cavity resonator filled by a saturable absorber and driven by a plane wave field. Under the slowly varying envelope and paraxial approximation, we introduce a quite general approach to the analysis of the spatio-temporal dynamics of the coherent field beyond the mean-field limit, fully taking into account propagation, diffraction and the boundary conditions imposed by the cavity. We study the stability of the stationary solutions versus spatially modulated perturbations, and identify regimes where we observe total radiation confinement and the formation of 3D localised bright structures. At difference from freely propagating light bullets, here the self-organization proceeds from the combination of difrraction, nonlinearity and resonator feedback. Such cavity light bullets (CLBs) endlessly travel the cavity roundtrip and can be independently manipulated. These characteristics makes CLBs natural candidates for optical bits and for particle-like optical probes
Three-dimensional self-organized patterns in the field profile of a ring cavity resonator
No full textWe consider the paraxial model for a nonlinear resonator filled with a saturable absorber, beyond the mean field limit. We develop a general treatment to study the modulational instabilities which give rise to pattern formation in the propagation direction z and in the transverse plane (x, y). For appropriate parametric domains we observe the first example of system self-organization in space and time proceeding from competition of linear effects with nonlinear medium properties and resonator feedback. In particular, we could observe either 3D global structures or structures which are localized in the transverse plane, showing different lengths in the longitudinal direction and endlessly travelling in the resonator
Characterization of stationary patterns and their link with cavity solitons in semiconductor microresonators
No full textWe study the periodic structures that emerge beyond the instability threshold point in a semiconductor microcavity driven by a coherent stationary holding beam; the active layer of the microresonator is bulk GaAs or multiple quantum-well GaAs-AlGaAs. We apply a numerical technique to directly establish stationary solutions of the dynamical equations governing the electric field inside the cavity and the carrier density of the active material. To overcome the heavy computational requirements in the case of two-dimensional patterns, we consider small nonorthogonal integration grids, whose geometrical properties are those of the pattern elementary cell. We investigate the mechanism of pattern formation in connection with the modulational instability threshold, and we study, both in one and two dimensions, the bifurcation structure of various branches of patterns. We show how cavity solitons are related to periodic structures and we study the behavior that cavity soliton branches may exhibit in two dimensions
THE INFREP EUROPEAN VLF/LF RADIO MONITORING NETWORK - PRESENT STATUS AND PRELIMINARY RESULTS OF THE ROMANIAN MONITORING SYSTEM
No full textThe paper presents the Romanian VLF / LF monitoring system consisting in a radio receiver - made by Elettronika S.R.L. (Italy) and provided by the Bari University - and the infrastructure that is necessary to record and transmit the collected data. This system is a part of the international initiative INFREP. Through this initiative, originated in Italy, VLF / LF radio receivers are deployed in different locations in Europe. Each one is monitoring up to ten different transmissions of radio stations across the continent. Information on electromagnetic fields' intensities created by transmitters at each receiving site and gathered from this network are indicating the quality of the propagation along the paths between the receivers and transmitters. Studying the ionosphere influences on the electromagnetic waves' propagation along a certain path is a method to put into evidence possible modifications of ionosphere lower structure and composition as earthquakes' precursor.
The VLF / LF receiver installed in Romania was put into operation in February 2009 and has proved its utility in the case of Abruzzo earthquake that occurred on 6th of April 2009 (M-w = 6.3). Since then, the receiver was relocated from Bucharest to the Black-Sea shore (Dobrogea Seismologic Observatory). Changing the receiving site produced unsatisfactory monitoring data, characterized by large fluctuations of the received signals' intensities. Trying to understand this behavior has led to the conclusion that the electric component of the electromagnetic field was possibly influenced by the local atmospheric conditions (as aerosols' concentrations could be). Starting from this observation we have run some tests which have indicated that a loop-type antenna is more appropriate than a vertical antenna, especially for highly electric-field polluted environments. Very good results were obtained with this new configuration, even in the site located at the Black-Sea shore. Future improvements of the receiver analog front-end are still possible in order to get better monitoring data by rejecting the off-band noise induced by the aerial high-voltage lines that are surrounding the site, so that for us to accomplish the best achievable surveillance in VLF / LF bands, related to seismo-electromagnetic phenomena
Pattern formation in multistacked-quantum-dot-based microcavities: modelization and role of gain asymmetries in the alpha factor - art. no. 64681B
No full textWe develop a model that describes the optical response of a semiconductor quantum dot microcavity pumped above transparency but kept slightly below threshold. The model takes into account the inhomogeneous broadening of the dot emission, the coupling mechanisms between quantum dots and the wetting layer and incorporates gain asymmetry factors in the thermo-emission and capture coefficients. The role of asymmetries with respect to alpha factor and pattern formation is investigated. We then study the conditions for the onset of bistability and modulational instability and characterize the patterns formed
EARTHQUAKE PRECURSOR RESEARCH: GROUND-SATELLITE OBSERVATIONS, LABORATORY EXPERIMENTS, AND THEORETICAL MODELS PREFACE
No full textCavity Solitons in semiconductor microresonators: Modeling aspects and role of thermal carrier-lattice dynamics
No full textWe study Optical Pattern Formation and Cavity Solitons in semiconductor microcavities. We adopt a microscopic model that describes the field, the carrier and the temperature dynamics in the quasi-equilibrium regime, within the free-carrier approximation. A detailed study of the instabilities affecting the homogeneous stationary state of the output field is performed. In this way we can address the numerical research of pattern and Cavity Solitons
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