B. Sahraoui

Nonlinear optics and surface relief gratings in alkynyl–ruthenium complexes

Generally, the organometallic complexes rich in carbon and containing π-conjugated chains are materials interesting for the study of electronic transfer processes. Currently, the ruthenium–acetylide organometallic complexes form part of the most studied organometallic compounds in nonlinear optics. In this work, we highlight the nonlinear optical properties and the photo-induced structure of new organometallic complexes containing a ruthenium–acetylide donor fragment able to compete with the strongest organic donors. We determine, using various experimental techniques (degenerate four-wave mixing, second and third harmonic generation), the influence of the functionalization of these molecular structures on the improvement of their second-and third-order nonlinear optical properties exploiting in particular the nature of the acceptor fragment and the π-conjugated transmitter. Also we present the dynamics of formation of photo-induced surface relief gratings using a transmission holographic technique and the atomic force microscopy on ruthenium–acetylide complexes containing an azobenzene fragment.

Second- and third-order nonlinearities of novel push-pull azobenzene polymers.

In this work, the second- and third-order nonlinear optical response of spin-deposited thin films of three different push-pull side chain azobenzene polymers is investigated by the second- and third-harmonic Maker fringes techniques using 30 ps laser pulses at a fundamental wavelength of 1064 nm. Measurements were carried out before and after aligning the chromophores by corona poling of the films, while different polarization configurations have been utilized. Strong dependence of the response upon the structure of the systems has been found, which is related to the different charge transfer within the molecules. The reported findings are compared with already published results.

Photoinduced effects in the Sb2Se3–BaCl2–PbCl2 glasses

Photoinduced optical phenomena in amorphous Sb2Se3–BaCl2–PbCl2 glasses are studied using experimental spectroscopic and theoretical quantum chemical methods. Photoinduced two-photon absorption (TPA) (for λ=10.6 μm) and second harmonic generation (SHG) (for the output wavelengths 5.3 μm) were measured. CO laser (λ=5.5 μm) was used as a source of photoinducing light. We have found that with an increasing CO-laser exposure the SHG maximum output signal increases and achieves its maximum value at CO photon fluence 18×1013 phot./cm2 per pulse after two hours of illumination. The output SHG signal was more than one order less comparing with ZnS crystals in case of its third rank nonlinear optical susceptibility tensor components χ222 (λ=10.6 μm). With decreasing temperature the SHG signal strongly increases within the 26–32 K temperature range. Time-dependent probe-pump measurements show an existence of SHG maximum at time delay about 45 ps. Good correlation between SHG and TPA was observed. Spectral positions ...

Grating inscription in picosecond regime in thin films of functionalized DNA

Polymers containing azo-benzene groups are useful holographic recording materials. In these materials the efficient mixed amplitude and phase gratings, frequently accompanied with photoinduced-surface relief gratings, can be inscribed with polarized laser light. The light-induced trans-cis-trans photoisomerization of azo-benzene groups is responsible for optical anisotropy in such systems. The aim of the present work is to study the dynamics of grating inscription in Disperse Red 1 doped deoxyrbonucleic acid- hexadecyltrimethylammonium material (DR1-DNACTMA) using 16 ps laser pulses (532 nm, 1.3 mJ). Results are compared with that obtained for other polymeric matrices loaded with DR1. The dynamics of the grating growth, due to repeated pulses from picosecond laser with 10 Hz repetition rate, was probed by measuring the intensity of the first order of diffraction of a cw He-Ne. We report results in function of the light polarization of writing beams. In this paper we present the first results of the grating inscription in functionalized DNA (in the picosecond pulse regime).

Third harmonic generation in undoped and X doped ZnO films (X: Ce, F, Er, Al, Sn) deposited by spray pyrolysis

There is a current interest in research of wide band gap semiconductor materials for the purposes of third order nonlinear optical properties in view of optoelectronics applications. Materials for nonlinear optics should present important changes of nonlinear intensity, dependence on changes of nonlinear refractive index, short response time, and weak absorption losses. We report the results of the third order nonlinear optical susceptibilities of undoped and doped (cerium, fluorine, erbium, aluminum, and tin) zinc oxide films using the third harmonic generation technique at 1064 nm wavelength region in picoseconds regime. Thin films were grown on glass substrate by the spray pyrolysis technique at different temperatures of substrates and characterized by using the x-ray diffraction, scanning electron microscope, transmission, and photoluminescence. A strong third harmonic signal was obtained from the studied films with a good crystallinity and roughness. We have found that at high conductivity, there is ...

Third-order nonlinear optical properties and two-photon absorption in branched oligothienylenevinylenes

Abstract We report measurements of the third-order susceptibilities and two-photon absorption in branched oligothienylenevinylenes derivatives C 42 H 62 S 2 , C 114 H 174 S 6 , C 252 H 366 N 3 O 6 P 3 S 12 , using degenerate four wave mixing (DFWM) technique at λ=532 nm in picosecond regime. All the studied compounds show large third-order nonlinear optical properties with comparison with known materials such as, polydiacetylene, octupolar molecules and their dipolar subunits. We show the influence of the number of branches on the benzene cycle. We demonstrate that the values of third-order susceptibilities χ 〈3〉 and two-photon absorption coefficients β increase as the number of branches increase. As consequence the studied complexes can be very interesting for optical limiting applications.

Electronic and nuclear contributions to the third-order nonlinear optical susceptibilities of new p-N, N ? -dimethylaniline tetrathiafulvalene derivatives

We report large third-order nonlinear optical susceptibilities (?3?)(ijkl) of new tetrathiafulvalene derivatives, using the degenerate four-wave mixing (DFWM) method. To understand the physical nature of the optical nonlinearities, we separate their electronic and nuclear contributions. The electronic contribution to the third-order nonlinear optical susceptibilities of the molecules turns out to be dominant. From DFWM measurements we also deduce the values of the second-order hyperpolarizabilities gamma, which are ~10(5) greater than the gamma value of CS(2).

Calculation of structural, optical and electronic properties of ZnS, ZnSe, MgS, MgSe and their quaternary alloy Mg1−xZnxSySe1−y

Abstract The structural and electronic properties of the binary semiconductor compounds ZnS, ZnSe, MgS and MgSe in the cubic structure are calculated using the self-consistent scalar-relativistic full potential linear-augmented plane wave method (FP-LAPW) within the local (spin) density approximation (LSDA). From the calculated values of the band-gap energy we have determined the electronic and optical properties of quaternary alloys Mg1−xZnxSySe1−y using the simple tight-binding sp3s* theory, which incorporates compositional disorder as an effective potential. In addition, the refractive index of MgS, MgSe, ZnS and ZnSe was computed using both real and imaginary parts of the dielectric function. The result indicates that the refractive index increases with allowing for the Mg1−xZnxSySe1−y lattice matched to GaAs.

Low temperature anomalies in polyvinyl alcohol photopolymers

Acoustooptical parameters in a mixture of polyvinyl alcohol (PVA) polymers with modified polyvinyl alcohol (MPA) were investigated as functions of the MPA content, time of exposure and temperature. The maximum value of the acoustooptical quality coefficient was achieved for values of the MPA content above 70%. It was proposed to use the polyvinyl alcohol photopolymers as acoustooptical modulators and deflectors. An essential influence of the polyvinyl alcohol modifications on the acoustooptical parameters was unambiguously shown. Also, a critical dependence of the acoustooptical coefficients on the sample thickness was revealed. The data on the acoustooptical quality coefficient correlate well with the data obtained for the sound losses coefficient.

Amplified spontaneous emission in the spiropyran-biopolymer based system

Amplified spontaneous emission (ASE) phenomenon in the 6-nitro-1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indolin] organic dye dispersed in a solid matrix has been observed. The biopolymer system deoxyribonucleic acid blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride served as a matrix. ASE appeared under sample excitation by UV light pulses (λ=355 nm) coming from nanosecond or picosecond neodymium doped yttrium aluminum garnet lasers and has been reinforced with green (λ=532 nm) light excitation followed UV light pulse. The ASE characteristics in function of different excitation pulse energies as well as signal gain were measured.