Mechanisms of remanent optical alignment of dyes in a gel matrix

International audienceWe present the mechanisms of a remanent alignment of polarizable molecules dispersed in a solid silica gel matrix, when submitted to powerful, femtosecond, linearly polarized, optical pulses emitted from a dye laser. This alignment can be related to third-order nonlinearities of the dopants through an orientational optical Kerr effect. Its remanence results from the strong interactions the dopants share with their host matrix, particularly through hydrogen bonds. We expose here the detailed mechanism of this phenomenon, considering that such a rotation of large chromophores may not be compatible at first sight with subpicosecond pulse durations. Through several experiments, we show that this apparent contradiction is solved once analyzed, by the structure of the excitation pulses, which cannot be simply described as ''femtosecond pulses'', but consist of two temporal components--a femtosecond one and a nanosecond one--playing different but essential roles in the proces

Temperature dependence of second-order nonlinear relaxation of a poled chromophore doped sol-gel material

International audienceSecond-order optical nonlinearity relaxations of hybrid inorganic/organic sol-gel films doped with poled Disperse Red 1 chromophores were measured by second harmonic generation at several temperatures. The decay curves were fitted to biexponentials and Ko¨hlrausch, Williams, and Watts ~KWW! stretched exponentials. It can be concluded that the KWW model well describes chromophore thermal reorientation in hybrid sol-gel materials, as is known for all-organic polymers. Using the Arrhenius law, the activation energy of the reorientation process has been determined to be about 50 or 70 kcal mol21. A stability of roughly a decade has been extrapolated at room temperature. Another experiment at room temperature gave an estimation of the stability that was found to be in qualitative agreement. It is shown that poled chromophore-doped sol-gel materials have the potential to be stable enough for applications in telecommunication device

Toward millions of laser pulses using pyrromethene and perylene doped xerogels

International audienceSignificant improvements have been obtained for solid-state dye lasers with doped xerogels. By using longitudinal pumping with a frequency-doubled Q-switched Nd: YAG laser, we obtained as much as 86% slope efficiency and 5 3 105 pulses lifetime. Furthermore, newly prepared deoxygenated samples exhibited even greater lifetime

Perylene and pyrromethene doped xerogels for solid state pulsed laser

International audienceHydrophobic photostable dye molecules such as perylenes or pyrromethenes were trapped in xerogel matrices. Using these new materials as solid-state dye lasers, we have demonstrated efficient laser operation. Slope efficiencies of up to 30% were obtained in the millijoule output-energy range. Tunabilities of up to 60 nm were observed, and more than 150,000 pulses were emitted by the same spot of a given sample when the laser was pumped at millijoule energy level

Reverse saturable absorption in solid xerogel matrices

International audienceAluminophthalocyanine (APC) and fullerene carbon 60 (C,) have been studied encaged in different silica matrices. The reverse saturable absorption properties of these doped xerogels have been compared to those of reference solutions of APC and C&,. We show that reverse saturable absorber molecules retain their properties even when they are enclosed in the pores of a solid xerogel matri

Stable photorefractive memory effect in sol-gel materials

International audienceWe report on the synthesis and the optical characterization of a photorefractive sol-gel material which contains nonlinear azo chromophore and carbazole charge transporting molecules. Both of these functional groups are covalently attached to the silica based backbone. Thin sol-gel films exhibit stable optically nonlinear properties: the electro-optic coefficient r13 measured at 633 nm is found to be 17 pm/V one day after corona poling and 15 pm/V after three weeks and over a period of several months. Photorefractivity is demonstrated by two beam coupling experiments without external applied electric field. Sol-gel films present a stable photorefractive memory effect with a net internal gain of 200 cm-

DR1 doped sol-gel planar waveguides for nonlinear devices operating at telecommunications wavelengths

International audienceWe report on linear and nonlinear optical properties of Disperse Red 1-doped solgel waveguides. The refractive-index and optical-propagation losses of the guiding layer were measured between 0.756 mm and 1.64 mm. The spectral broadening of the chromophore charge-transfer transition in the visible is modeled with a Voigt-profile function. In the telecommunications window the attenuation is dominated by the overtones of the O--H bonds vibration bands. The nonlinear optical coefficients were measured at different poling strengths with the Maker-fringe method. The nonlinear coefficient d33 was found to be 4.5 pm V21 at 1.58 mm for a poling field of 60 Vmm21

Stable doped hybrid sol-gel materials for solid-state dye laser

International audienceLaser effects have been obtained with dye-doped hybrid xerogel samples prepared several years ago and stored in different "classical" conditions. Firstly, using the same configuration of the laser cavity as was used 4-5 years ago, we have obtained almost identical laser performances, and slope conversion efficiencies were measured up to 80% and operational lifetimes, with 1-mJ initial output energy and 10-Hz repetition rate of several hundred thousand pulses obtained. Secondly, we have introduced the new pyrromethene 605 dye into a hybrid xerogel matrix and obtained good laser performances similar to the rest of the pyrromethene famil

Eyelid fat grafting: indications, operative technique and complications; a systematic review

International audienceIntroduction - Many recent studies concerning autologous fat grafting in the eyelids have been published, mostly consisting of case reports and retrospective case series. However, no study on the overall complication or satisfaction rate associated with the various grafting techniques exists. We performed a comprehensive literature review to determine the outcomes and complications of eyelid fat grafting, as well as patient satisfaction.Methods - A systematic review of the literature using the PRISMA criteria was conducted. This protocol was registered at the Prospective Register of Systematic Reviews at the National Institute for Health Research.Results - Sixteen studies, representing 1,159 patients and published between June 2004 and December 2014, were included. Satisfactory results, judged by clinical examination, were observed in all studies. Few postoperative complications were reported.Conclusions - We demonstrated that the procedures were easy to perform, and achieved satisfactory and sustainable results with few complications in both reconstructive and cosmetic surgery. However, a wide disparity exists in the various fat harvesting, fat purification, and reinjection techniques. Further studies are required to assess the long-term outcomes. Our conclusions should be accepted cautiously due to the small number of articles and the lack of evidence in published studies.<br

Magnetically textured y-Fe2O3 nanoparticles in a silica gel matrix: structural and magnetic properties

International audienceThis paper is devoted to magnetic and structural properties of anisotropic g -Fe2O3 superparamagnetic particles dispersed in a transparent xerogel matrix. The effect of frozen anisotropy axes and magnetic texture, induced by a magnetic field applied during the solidification of the matrix on the in-field magnetization process, is studied by alternating gradient force magnetometry and first and second order magneto-optical effects. The changes of magnetization curves with respect to the ferrofluid solution at the same particle concentration are interpreted on the basis of an existing statistical approach extended to systems with particle size distribution, which has to be taken into account for real samples. A very good agreement between the experiment and theory was achieved for a log-normal distribution of diameters which well resembles that deduced from electron microscopy observations in different imaging modes. This structural analysis states the parameter values used in calculations and confirms the relevance of basic assumptions of the model for the specimens studied. The experimental results and the related theoretical discussion should be of use to understand magnetic properties of other magnetically textured superparamagnetic system