The growth and saturation characteristics of stimulated Brillouin scattering (SBS) in the interaction of an intense (Ｉ≤ 10¹³ W/cm²) CO₂ laser beam with an underdense plasma are investigated experimentally. The plasma is produced by focussing a short (2 ns FWHM), CO₂ laser pulse onto a stabilized nitrogen gas jet which flows from a Laval nozzle into low pressure helium. The resulting SBS interaction is studied through observations of the intensity and spectral behavior of the backscattered light as well as through temporally resolved ruby laser Thomson scattering measurements of the spatial and spectral behavior of the SBS generated ion acoustic waves. SBS occurs primarily in the long scale length, low density plasma located in the background gas in front of the jet. Initially, the instability grows absolutely at a rate within a factor of two of the predicted temporal growth rate. The SBS reflectivity is observed to saturate at less than 10%. This low reflectivity is a result of two processes. First, the SBS interaction region and the associated ion acoustic waves are broken up into several smaller regions, hence limiting the coherence length of the waves, and second, the ion acoustic fluctuation amplitude saturates at less than 20%. The latter saturation is attributed to trapping of ions within the potential troughs of the ion acoustic waves. The observed occurrence of the first harmonic in the ion acoustic wave spectrum as well as temporal modulations in the wave amplitude and sidebands in the spectrum of the backscattered light can be explained as consequences of the ion trapping. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The goal of this dissertation has been to develop techniques in order to use Brillouin spectroscopy as a tool for studying the elastic properties of thin films on a scale of ≃100 Å. In order to develop that capability we have built a tandem multi-pass Fabry-Perot interferometer, and that interferometer was used to study the elastic properties of Langmuir-Blodgett films. These films were chosen because they can be deposited one molecular layer at a time. As a result of these investigations we have measured the density and elastic constants of the Langmuir-Blodgett film cadmium arachidate. Samples of cadmium arachidate were prepared on molybdenum and BK-7 glass substrates. Data were accumulated for a range of thicknesses and for different scattering geometries. These data will be used to argue that guided acoustic waves were observed in a highly anisotropic film. The observed guided acoustic waves will be identified as a Rayleigh wave and a tight band of Sezawa modes. No Love modes were detected in these experiments; however, evidence for reorientational modes typical of anisotropic liquids was detected. The dispersion of the Rayleigh wave as a function of thickness together with thick film scattering data were used to estimate the elastic constants in cadmium arachidate. In particular the shear elastic constant c₄₄ was found to be a small value: c₄₄ < 4.0x10⁸ N/m². The remaining elastic constants were estimated, assuming hexagonal film symmetry, to be c₆₆ < 4.5x10⁹ N/m², C₁₁ ≃ 1.1x10¹⁰ N/m², c₃₃ ≃ 2.1x10¹⁰ N/m², c₁₃ ≃ 1.0x10¹⁰ N/m², and c₁₂ > 3.x10¹⁰ N/m². It is interesting to note that the acoustical behavior of cadmium arachidate is quite similar to the smectic phase liquid crystals (c₄₄ = 0).

Thesis (Ph. D.)--Lehigh University, 2000. / Includes bibliographical references and vita.

No description available.

Copies of author's previously published articles inserted. / Includes bibliographical references. / viii, 162, [9] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A study of stimulated Brillouin scattering and its use for correcting phase aberrations in laser oscillators. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1998

Copies of author's previously published works inserted. / Bibliography: p. 119-127. / 12, 127, [8], 35 p., [3] leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis demonstrates the combined use of stimulated Brillouin scattering (SBS) for aberration correction, auto alignment and pulse compression as an ideal technology for studies of nonlinear optical processes, in particular nonlinear optical scattering (NLS). / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1998

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics and Mathematical Physics, 1998. / Copies of author's previously published works inserted. Bibliography: p. 119-127.

Chemnitz, Techn. University, Diss., 2003.

Copies of author's previously published works inserted. Bibliography: p. 119-127. This thesis demonstrates the combined use of stimulated Brillouin scattering (SBS) for aberration correction, auto alignment and pulse compression as an ideal technology for studies of nonlinear optical processes, in particular nonlinear optical scattering (NLS).

La création de nouveaux matériaux, aux propriétés souhaitées, peut être obtenue par la combinaison de deux, trois ou plusieurs composants. L'évolution des matériaux, l'amélioration de leurs performances et l´extension de leurs fonctionnalités provoquent ainsi une augmentation de la variété des matériaux disponibles: c´est désormais l´usage qui détermine les propriétés du matériau et non l´inverse. L'ajout de nanoparticules dans un polymère peut entraîner, quantitativement via la nanostructuration du polymère et qualitativement via leurs surfaces réactives, de nouvelles caractéristiques, qui ne se limitent pas à la simple addition des propriétés de chaque composant. Les interactions entre la surface des nanoparticules et les molécules du polymère peuvent être notamment à la base de la formation d´interphases, présentant des propriétés différentes de celles du polymère massif. Afin de comprendre l´influence des nanoparticules dans les propriétés mécaniques, optiques et diélectriques du composite et plus particulièrement dans la création d´interphases, ce travail s´est intéressé à des systèmes composés de particules d´Al2O3 et de SiO2 dans une résine d´époxyde. De tels matériaux, a priori simples, affichent des résultats surprenants présentés dans cette thèse. / Creation of new materials with tailor-made properties can be achieved by the combination of two, three or more components. Their development, improvement in performance and the extension of their functionalities have enlarged the diversity of these materials: The desired purpose will define the properties of the used materials and not vice-versa. The inclusion of nanoparticles in a polymer can lead quantitatively via the occurring local structure and qualitatively via the reactive surfaces of the particles to new physical properties, which are not just a simple superposition of the properties of the single components. The interactions between the nanoparticles´ surfaces and the polymer molecules are the reason for the formation of interphases, which differ in their specificities from the polymer bulk. To understand the effect of nanoparticles on the mechanical, optical and dielectric properties of composites, and moreover the formations of interphases, an, at first believed, rather simple nanocomposite produced by including Al2O3- or SiO2- nanoparticles in an industrially common epoxy resin is studied. Such materials, a priori simples show surprising results, which will be discussed in this PhD Thesis.