The nonlinear optical properties of gold nanoparticles dispersed in optically transparent matrices Al 2 O 3 , ZnO, and SiO 2 are investigated using the classical and off-axis techniques of the Z -scan method at a wavelength of 532 nm (radiation from a nanosecond Nd: YAG laser). The experimental data on the nonlinear refraction in composite materials are obtained. The nonlinear refractive indices and the light absorption coefficients are determined, and the real and imaginary parts of the third-order nonlinear susceptibility for the structures under investigation are calculated. It is demonstrated that, for the composite materials under consideration, the nonlinear properties of the medium under the chosen conditions of laser irradiation are predominantly determined by the Kerr effect and the contribution of this effect exceeds the contribution of the thermal lens.

Third-order nonlinear-optical properties of gold nanoparticles embedded in Al2O3, ZnO and SiO2 have been investigated by the Z-scan method at the wavelength of 532nm using nanosecond Nd3+:YAG laser radiation. The nonlinear refractive index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility are deduced. The results of the investigation of nonlinear refraction using the off-axis Z-scan configuration are presented and the mechanisms responsible for the nonlinear response are discussed. The prevailing influence of the electronic Kerr effect over the possible thermo-optical contribution is demonstrated.

Optical nonlinearities of Au nanoparticles embedded in zinc oxide (ZnO) matrix have been investigated by the Z-scan method at the wavelength of 532nm using nanosecond Nd3+:YAG laser radiation. The nonlinear refractive index has been measured and the real part of the third-order nonlinear susceptibility is deduced. The results of the investigation of nonlinear refraction using the off-axis Z-scan configuration are presented and the mechanisms responsible for the nonlinear response are discussed. The nonlinear refraction is found to be negative (self-defocusing) in the vicinity of the surface plasmon resonance. Moreover, its strength is shown to be larger for materials having higher gold concentration. Finally, the prevailing influence of the electronic Kerr effect over the possible thermo-optical contribution is demonstrated.

The efficiency of second harmonic generation for melaminium bis(trichloroacetate) was estimated relatively to KDP: deff=3.09deff (KDP). Room temperature FT IR and FT Raman spectra were recorded. Some spectral features of this new crystal are referred to corresponding one for melamine crystal as well as for other trichloroacetates. Differential scanning calorimetric measurements performed on powder sample indicate the phase transition point at approximately 276 and 239K for heating and cooling, respectively.

Copper nanoparticles were elaborated in an indium tin oxide matrix by ion implantation. The nonlinear refraction and absorption coefficients of the composite materials obtained were measured using the z-scan method with nanosecond pulses (τ=7 ns) at the wavelength of 532 nm. In addition to the conventional on-axis z-scan configuration, measurements were carried out in the off-axis scheme to get a better sensitivity. The mechanisms responsible for nonlinear refraction and absorption in these nanocomposite materials are discussed. By using the temporal trace of the signal in the off-axis configuration, we show the thermal lensing effect to be negligible as compared with pure electronic ones.

The nonlinear absorption of nanocomposite layers based on ZnO implanted with Cu+ ions with an energy of 160 keV in implantation doses of 10(16) and 10(17) ions/cm2 was investigated. The values of the nonlinear absorption coefficient were measured by the Z-scan method at a wavelength of 532 nm by use of nanosecond and picosecond laser pulses. Possible optical applications of these materials are discussed.

The first X-ray diffraction and vibrational spectroscopic analysis of a novel complex between l-lysine and l-tartaric acid is reported. The structure was solved in two temperatures (320 and 260K) showing incommensurate phase between them. Room-temperature powder infrared and Raman measurements for the l-lysine-l-tartaric acid molecular complex (1:1) were carried out. DSC measurements on powder samples indicate two phase transitions points at about 295, 300 and 293, 300K, for heating and cooling, respectively, with noticeable temperature interval between them. Second harmonic generation efficiency deff=0.35 deff (KDP).

Negative nonlinear refraction is observed in the photorefractive crystal Bi12GeO20 (BGO) using 7-ns, 532-nm pulsed radiation. The nonlinear refractive index of BGO is measured to be γ=−3.8×10−13cm2W−1 using the z-scan technique. The self-defocusing of nanosecond pulses is attributed to the appearance of free carriers generated from defects, donors, and interband transitions. The nonlinear losses caused by two-photon absorption and self-scattering from dynamic grating are discussed. The nonlinear absorption coefficient is measured to be β=3.8×10−8cmW−1. Moreover, a variation of γ and β with intensity is observed. The comparison with self-focusing and two-photon absorption previously measured using 55-ps pulses is discussed.

Single crystals of a new L-histidinium salt: L-histidinium L-tartrate hemihydrate, [(C3H4N2)+C3H6NO2]·(C4H5O6)−·0.5H2O, were obtained by slow evaporation of an aqueous solution at room temperature. The compound crystallises in a non-centrosymmetric space group of the monoclinic system. The L-histidine molecule occurs in the zwitterion form, with additional protonation of the N(3) ring atom, while the tartaric acid is singly ionised with one COO− carboxylate group. The vibrational spectra are in full agreement with the structure obtained from X-ray crystallography. The salt is a good second harmonic generator: the SHG efficiency was measured as deff=0.79deff(KDP).

X-ray single crystal diffraction and the vibrational spectroscopic analysis of a new melaminium salt, tetrakis(2,4,6-triamino-1,3,5-triazin-1-ium) bis(selenate) trihydrate, (C3H7N6+)4·(SeO42−)2·3H2O, is reported. The compound crystallizes in the non centrosymmetric space group of triclinic system. Second harmonic generation efficiency deff=0.4deff(KDP). Intense hydrogen-bonded network is present in the crystal structure of the complex with notable vibrational effects.

The crystals of a new molecular complex, i.e. p-nitroaniline with L-tartaric acid were obtained by slow evaporation of an aqueous solution at room temperature. Room temperature powder infrared measurements were carried out. Tentative assignment for most bands was done. Very strong and broad absorption in the region of 3200–1800 cm-1 of infrared spectrum is observed. This notable vibrational effect suggests the presence of intense hydrogen-bonded network in the crystal structure of the complex. Second harmonic generation (SHG) efficiency d eff = 3.85 d eff (KDP). Some spectral features of this new crystal are referred to corresponding one for two other crystals comprising p-nitroaniline molecule i.e. p-nitroanilinium perchlorate and p-nitroanilinium-p-toluene-sulphonate.

The third-order nonlinear optical response of materials composed of noble metal nanoparticles embedded in a dielectric matrix is large around the surface plasmon resonance frequency, due to local electric field enhancement in the particles. This response can be described by both nonlinear refraction and absorption, related to the complex third-order susceptibility, χ(3), of the composite material. χ(3) is linked with the intrinsic metal particle susceptibility, χ(3)m, whose value is ruled by interband and intraband transitions. Depending on the incident pulse power and duration, very high conduction electron temperatures can be reached subsequent to the pulse absorption, and can result in a modification of the nonlinear response ("hot electron" effect). The χ(3) real and imaginary parts of Au:SiO2 thin films, synthesized by radio-frequency sputtering, are measured simultaneously by the z-scan technique, with both nanosecond and femtosecond laser pulses at 560 nm. Comparing the results obtained in both regimes, we show, by using a simple thermal model, that the "hot electron" phenomenon which is significant when exciting with ultrashort pulses, not only reduces the modulus of χ(3) by three orders of magnitude, but also greatly affects its phase.

Powder Kurtz-Perry measurements were performed for the title crystals. The efficiencies of second harmonic generation were determined (0.34, 0.84, 0.80, 0.97 and 1.01) relative to potassium hydrogen phosphate. The l-lysine moiety was characterized by wavenumbers and relative intensities of the infrared and Raman bands originating from internal vibrations. The presence of hydrogen bonds in the studied crystals is noted and the potential role of this type of intermolecular interaction in the second harmonic generation phenomena is discussed.

The crystals of the new melaminium salt, i.e., 2,4,6-triamino-1,3,5-triazin-1,3-ium tartrate monohydrate C3H8N62+.C3H4O62-.H2O were obtained by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in noncentrosymmetric space group of monoclinic system. The melamine molecule occurs in di-protonated form while the tartaric acid is doubly ionized with two COO- carboxylic groups. DSC, measurements do not indicate clearly on the occurrence of phase transition in the temperature region 113-293 K. Second harmonic generation efficiency d(eff) similar to d(eff) (KDP). (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Crystals of anilinium perchlorate, C 6 H 5 NH + 3ClO - 4, were obtained by slow evaporation of an aqueous solution at room temperature. Powder Kurtz-Perry measurements were performed for the title material. The efficiency of second harmonic generation was estimated relative to KDP: d = 0.21d K D P . Room temperature powder infrared and Raman measurements for the title solid and its deuterated analogue were carried out. The vibrational spectra in the regions of the internal vibrations of the ions corroborate the X-ray data (reported by Paixao et al. [1]). Differential scanning measurements performed on the powder sample indicate a first order phase transition at about 220 K. Apossible mechanism of the phase transition is suggested in relation to disorder of the hydrogen atoms on nitrogen atoms (reported in [1]). The role of the aniline molecule in the second harmonic generation is discussed.

We report a study on the third-order nonlinear optical properties of nanocomposite thin films composed of gold particles embedded in a silica host matrix. Samples of various metal volume fractions, ranging from 8 to 35%, are synthesized by the sputtering technique. Some of them are annealed. Nonlinear optical measurements, which are performed by using the z-scan technique, reveal both a very large nonlinear absorption and a weak nonlinear refraction close to the surface plasmon resonance frequency of the particles. We especially study the effect of the metal concentration and the influence of thermal treatment on the real and imaginary components of the third-order nonlinear susceptibility. Our results reveal that, as the metal concentration reaches a few percent, the mutual electromagnetic interactions between particles greatly enlarge the nonlinear optical response of the material and can not be neglected in the theoretical analysis. Moreover, the thermal treatment leads, for a given concentration, to a significant increase of the nonlinear response, which is ascribed to a modification of the material morphology. We finally point out that the material nonlinear properties are very sensitive to the incident wavelength through the local field enhancement phenomenon.