Jean Toulouse

Bio: Jean Toulouse is an academic researcher from Lehigh University. The author has contributed to research in topics: Optical fiber & Brillouin scattering. The author has an hindex of 28, co-authored 203 publications receiving 3428 citations. Previous affiliations of Jean Toulouse include Alcatel-Lucent & Leiden University.

Phase diagram of the relaxor ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3

Abstract: Recently, a new orthorhombic phase has been discovered in the ferroelectric system $(1\ensuremath{-}x)\mathrm{Pb}({\mathrm{Zn}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}\ensuremath{-}x{\mathrm{PbTiO}}_{3}$ $(\mathrm{PZN}\ensuremath{-}x\mathrm{PT})$ for $x=9%,$ and for $x=8%$ after the application of an electric field. In the present work, synchrotron x-ray measurements have been extended to higher concentrations $10%l~xl~15%.$ The orthorhombic phase was observed for $x=10%,$ but, surprisingly, for $xg~11%$ only a tetragonal phase was found down to 20 K. The orthorhombic phase thus exists only in a narrow concentration range with near-vertical phase boundaries on both sides. This orthorhombic symmetry ${(M}_{C}$ type) is in contrast to the monoclinic ${M}_{A}$-type symmetry recently identified at low temperatures in the $\mathrm{Pb}({\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}){\mathrm{O}}_{3}$ (PZT) system over a triangle-shaped region of the phase diagram in the range $x=0.46--0.52.$ To further characterize this relaxor-type system, neutron inelastic scattering measurements have also been performed on a crystal of $\mathrm{PZN}\ensuremath{-}x\mathrm{PT}$ with $x=15%.$ The anomalous soft-phonon behavior (``waterfall'' effect) previously observed for $x=0%$ and 8% is clearly observed for the 15% crystal, which indicates that the presence of polar nanoregions extends to large values of x.

Spontaneous and stimulated Brillouin scattering gain spectra in optical fibers

Abstract: We study the Brillouin scattering behavior in several single-mode fibers with different waveguide characteristics in terms of their longitudinal mode structures in the gain spectrum, linewidth narrowing, and stimulated Brillouin scattering (SBS) threshold levels. Evolution from spontaneous to SBS is investigated by monitoring the Brillouin line-shape and the behavior of the longitudinal acoustooptic resonance modes that exist in the core. We compare our results with the current theory of Brillouin scattering generated from noise in the undepleted pump approximation. We also present experimentally Brillouin gain spectra in the highly depleted pump regime, where there is no analytical solution, by showing the evolution of the gain spectrum as a function of the injected laser intensity.

Polarized Raman study of the phonon dynamics in Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 crystal

Abstract: Pb(Mg 1 / 3 Nb 2 / 3 )O 3 is one of the simplest members of the class of lead relaxors and often serves as a model system for more complicated compounds. In this paper, we analyze both polarized and depolarized Raman-scattering spectra, measured in the temperature range between 1000 and 100 K, using a multiple-peak decomposition. Based on this analysis, we propose a comprehensive picture of the structural transformations in the crystal and associated dynamics. According to our model, the formation of the Fm3m symmetry in the chemically ordered regions as well as the appearance and freezing of the polar nanoregions are the consequences of the same phenomenon: the off-centered displacements of ions and their fast reorientational thermal motion. Short-lived dynamic lattice distortions are present even at the highest measured temperatures. From the Burns temperature, T d ∼620 K, their motion becomes progressively more restricted. Temperature T* ∼350 K marks the beginning of the freezing process which continues down to the temperature of the electric-field-induced phase transition, T d 0 ∼210 K. Raman scattering exists due to the presence of local lattice distortions. It is characterized by phonons with different wave vectors interacting with dynamic and static disorder.

Optical nonlinearities in fibers: review, recent examples, and systems applications

Abstract: Optical nonlinearities give rise to many ubiquitous effects in optical fibers. These effects are interesting in themselves and can be detrimental in optical communications, but they also have many useful applications, especially for the implementation of all-optical functionalities in optical networks. In the present paper, we briefly review the different kinds of optical nonlinearities encountered in fibers, pointing out the essential material and fiber parameters that determine them. We describe the effects produced by each kind of nonlinearity, emphasizing their variations for different values of essential parameters. Throughout the paper, we refer to recent systems applications in which these effects have been dealt with or exploited.

Temperature evolution of the relaxor dynamics in Pb ( Zn 1 ∕ 3 Nb 2 ∕ 3 ) O 3 : A critical Raman analysis

Abstract: At the heart of the relaxor behavior lies the development of mesoscopic or intermediate range order and the low frequency or relaxation dynamics associated with it. To investigate this development, we have measured the Raman spectra of a $\mathrm{Pb}({\mathrm{Zn}}_{1∕3}{\mathrm{Nb}}_{2∕3}){\mathrm{O}}_{3}$ (PZN) single crystal over a wide temperature range from $1000\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The spectra are analyzed using several different physical models, focusing particularly on the low frequency part. Both relaxation and coupled phonon dynamics are identified. The evolution of the relaxor dynamics is marked by three characteristic temperatures, Burns temperature, ${T}_{B}\ensuremath{\simeq}650\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and two other temperatures, ${T}_{d}\ensuremath{\simeq}470\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and ${T}_{f}\ensuremath{\simeq}340\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which together define four major ranges. Combining the fitting results from the Raman spectra and other experimental results in PZN, we describe the relaxor dynamics in these four ranges, in terms of the strength and lifetime of the correlations between off-center ions. Relating the dynamics observed in PZN to that in $\mathrm{K}{\mathrm{Ta}}_{1\ensuremath{-}x}{\mathrm{Nb}}_{x}{\mathrm{O}}_{3}$ (KTN), we develop a microscopic model based on the coexistence of a fast and a slow motion of the off-center Pb and Nb ions which accounts for both types of dynamics (coupled phonon and relaxational) between ${T}_{B}$ and ${T}_{f}$, and show evidence for a series of local phase transitions taking place below ${T}_{d}$.

Formation of glasses from liquids and biopolymers.

Abstract: Glasses can be formed by many routes. In some cases, distinct polyamorphic forms are found. The normal mode of glass formation is cooling of a viscous liquid. Liquid behavior during cooling is classified between "strong" and "fragile," and the three canonical characteristics of relaxing liquids are correlated through the fragility. Strong liquids become fragile liquids on compression. In some cases, such conversions occur during cooling by a weak first-order transition. This behavior can be related to the polymorphism in a glass state through a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The sudden loss of some liquid degrees of freedom through such first-order transitions is suggestive of the polyamorphic transition between native and denatured hydrated proteins, which can be interpreted as single-chain glass-forming polymers plasticized by water and cross-linked by hydrogen bonds. The onset of a sharp change in d dT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature. The latter may originate in strong anharmonicity in modes ("bosons"), which permits the system to access multiple minima of its configuration space. These modes, the Kauzmann temperature T(K), and the fragility of the liquid, may thus be connected.

Relaxation in glassforming liquids and amorphous solids

Abstract: The field of viscous liquid and glassy solid dynamics is reviewed by a process of posing the key questions that need to be answered, and then providing the best answers available to the authors and their advisors at this time. The subject is divided into four parts, three of them dealing with behavior in different domains of temperature with respect to the glass transition temperature, Tg , and a fourth dealing with ‘‘short time processes.’’ The first part tackles the high temperature regime T.Tg ,i n which the system is ergodic and the evolution of the viscous liquid toward the condition at Tg is in focus. The second part deals with the regime T;Tg , where the system is nonergodic except for very long annealing times, hence has time-dependent properties ~aging and annealing!. The third part discusses behavior when the system is completely frozen with respect to the primary relaxation process but in which secondary processes, particularly those responsible for ‘‘superionic’’ conductivity, and dopart mobility in amorphous silicon, remain active. In the fourth part we focus on the behavior of the system at the crossover between the low frequency vibrational components of the molecular motion and its high frequency relaxational components, paying particular attention to very recent developments in the short time dielectric response and the high Q mechanical response. © 2000 American Institute of Physics.@S0021-8979~00!02213-1#

Recent progress in relaxor ferroelectrics with perovskite structure

Abstract: Relaxor ferroelectrics were discovered almost 50 years ago among the complex oxides with perovskite structure. In recent years this field of research has experienced a revival of interest. In this paper we review the progress achieved. We consider the crystal structure including quenched compositional disorder and polar nanoregions (PNR), the phase transitions including compositional order-disorder transition, transition to nonergodic (probably spherical cluster glass) state and to ferroelectric phase. We discuss the lattice dynamics and the peculiar (especially dielectric) relaxation in relaxors. Modern theoretical models for the mechanisms of PNR formation and freezing into nonergodic glassy state are also presented.

Soil Moisture Measurement for Ecological and Hydrological Watershed-Scale Observatories: A Review

Abstract: At the watershed scale, soil moisture is the major control for rainfall–runoff response, especially where saturation excess runoff processes dominate. From the ecological point of view, the pools of soil moisture are fundamental ecosystem resources providing the transpirable water for plants. In drylands particularly, soil moisture is one of the major controls on the structure, function, and diversity in ecosystems. In terms of the global hydrological cycle, the overall quantity of soil moisture is small, ∼0.05%; however, its importance to the global energy balance and the distribution of precipitation far outweighs its physical amount. In soils it governs microbial activity that affects important biogeochemical processes such as nitrification and CO2 production via respiration. During the past 20 years, technology has advanced considerably, with the development of different electrical sensors for determining soil moisture at a point. However, modeling of watersheds requires areal averages. As a result, point measurements and modeling grid cell data requirements are generally incommensurate. We review advances in sensor technology, particularly emerging geophysical methods and distributed sensors, aimed at bridging this gap. We consider some of the data analysis methods for upscaling from a point to give an areal average. Finally, we conclude by offering a vision for future research, listing many of the current scientific and technical challenges.