Activitats del Grup de Recerca en Dinàmica no lineal, Òptica no lineal i Làsers (DONLL)"

Peer Reviewe

Einstein: física, tecnologia i matemàtiques

Acte inaugural del curs 2004-2005 de la Facultat de Matemàtiques i Estadística. Curs Einstein"L’any 2005 fou declarat Any Mundial de la Física. Coincideix amb el centenari de publicacions d’Albert Einstein sobre el moviment brownià, sobre els quanta de llum i sobre relativitat especial. Les idees d’Einstein publicades fa un segle van canviar per sempre la manera d’entendre la física..."Postprint (published version

All optical implementation of a stochastic logic gate using a VCSEL with external optical injection

We perform numerical simulations of the dynamics of two VCSELs optically coupled in a master-slave configuration. We show that the interplay of nonlinearity and spontaneous emission noise can yield logic behavior, and the emergent outcome of such system is a reliable logic gate. Specifically in our case represents an all-optical logic gate, with the logic input encoded in the strength of the light injected in the slave laser by the master laser, and the fast and robust response decoded from the polarization state of the light emitted by the slave laser.Peer ReviewedPostprint (author’s final draft

Controlling the likelihood of rogue waves in an optically injected semiconductor laser via direct current modulation

Extreme and rare events are nowadays the object of intensive research. Rogue waves are extreme waves that appear suddenly in many natural systems, even in apparently calm situations. Here we study numerically the rogue wave dynamics in an optically injected semiconductor laser with external periodic forcing that is implemented via direct modulation of the laser pump current. In the region of optical injection parameters where the laser intensity is chaotic and occasional ultrahigh pulses occur, our aim is to control the system by applying a weak modulation. We find that for an adequate range of frequency and amplitude parameters, the modulation can completely suppress the extreme pulses. We also show that the interplay between modulation and an external source of noise can significantly modify their probability of occurrence. These results can motivate a range of experimental and theoretical investigations in other natural systems.Peer ReviewedPostprint (published version

Enhanced efficiency of the second harmonic inhomogeneous component in an opaque cavity

In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612nm, using 3 ps pump pulses having peak intensities of the order of 10MW=cm2. We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.Peer ReviewedPostprint (published version

Comparative analysis of ferroelectric domain statistics via nonlinear diffraction in random nonlinear materials

© 2018 [Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.We present an indirect, non-destructive optical method for domain statistic characterization in disordered nonlinear crystals having homogeneous refractive index and spatially random distribution of ferroelectric domains. This method relies on the analysis of the wave-dependent spatial distribution of the second harmonic, in the plane perpendicular to the optical axis in combination with numerical simulations. We apply this technique to the characterization of two different media, Calcium Barium Niobate and Strontium Barium Niobate, with drastically different statistical distributions of ferroelectric domains.Peer ReviewedPostprint (published version

Second-harmonic generation in disordered quadratic media: role of a ferroelectric domain structure

We study theoretically the second harmonic generation in a nonlinear quadratic crystal with random distribution of ferroelectric domains. We show that the specific features of disordered domain structure greatly affect the emission pattern of the generated harmonics. This phenomenon can be used to characterize the degree of disorder in nonlinear photonic structures.Peer ReviewedPostprint (published version

Harmonic generation from metal-oxide and metal-metal boundaries

We explore the outcomes of detailed microscopic models by calculating second- and third-harmonic generation from thin-film surfaces with discontinuous free-electron densities. These circumstances can occur in structures consisting of a simple metal mirror, or arrangements composed of either different metals or a metal and a free-electron system like a conducting oxide. Using a hydrodynamic approach we highlight the case of a gold mirror and that of a two-layer system containing indium tin oxide (ITO) and gold. We assume the gold mirror surface is characterized by a free-electron cloud of varying density that spills into the vacuum, which as a result of material dispersion exhibits epsilon-near-zero conditions and local-field enhancement at the surface. For a bilayer consisting of a thin ITO and gold film, if the wave is incident from the ITO side the electromagnetic field is presented with a free-electron discontinuity at the ITO-gold interface, and wavelength-dependent epsilon-near-zero conditions that enhance local fields and conversion efficiencies and determine the surface's emission properties. We evaluate the relative significance of additional nonlinear sources that arise when a free-electron discontinuity is present, and show that harmonic generation can be sensitive to the density of the screening free-electron cloud, and not its thickness. Our findings also suggest the possibility to control surface harmonic generation through surface charge engineering.Peer ReviewedPostprint (author's final draft