Georges Boudebs

Experimental and theoretical study of higher-order nonlinearities in chalcogenide glasses

Abstract We investigate experimentally and theoretically the nonlinear properties of two distinct chalcogenide glasses. Nonlinearities are measured through a spatially resolved Mach–Zehnder interferometer. It is shown that the resulting nonlinear index coefficient cannot be correctly described with the usual cubic model. A more convenient theory is developed assuming a medium with two-photon nonlinear absorption and both cubic ( n 2 ) and quintic ( n 4 ) nonlinear index variations. The resulting closed-form expression for the effective nonlinear index coefficient allows to extract the cubic and quintic index coefficients.

Diode-pumped 99 fs Yb : CaF2 oscillator

We demonstrate the generation of 99 fs pulses by a mode-locked laser oscillator built around a Yb:CaF(2) crystal. An average power of 380 mW for a 13 nm bandwidth spectrum centered at 1053 nm is obtained. The short-pulse operation is achieved thanks to a saturable absorber mirror and is stabilized by the Kerr lens effect. We investigated the limits of the stabilization process and observed a regime slowly oscillating between mode locking and Q switching.

Nonlinear optical properties of chalcogenide glasses: comparison between Mach-Zehnder interferometry and Z-scan techniques

Abstract To explore the potentialities of chalcogenide glasses for ultrafast optical switching, the nonlinear refractive indices of different compositions are measured. Several binary glasses as well as ternary ones have been characterized. Nonlinear measurements has been performed through a pump/probe experiment using a Mach–Zehnder interferometer coupled to a CCD camera. Nonlinear refractive index as high as 12×10−18 m2/W have been obtained in the ternary (Ge–Se–As) system. A comparison with the nonlinear coefficients obtained with the Z-scan technique is performed. Results show that, although the order of magnitude is the same, a systematic discrepancy exists, in particular for high nonlinear absorption for which the relative error reaches up to 50%. We show that this is a consequence of the use of simplified formulas derived in the Z-scan technique. Indeed, a detailed analysis demonstrates that both techniques perfectly agree when a higher-order development is used for the determination of the nonlinear coefficient from the Z-scan technique.

Photo-stability of pulsed laser deposited Ge(x)As(y)Se(100-x-y) amorphous thin films.

Quest for photo-stable amorphous thin films in ternary Ge(x)As(y)Se(100-x-y) chalcogenide system is reported. Studied layers were fabricated using pulsed laser deposition technique. Scanning electron microscope with energy dispersive X-ray analyzer, Raman scattering spectroscopy, transmittance measurements, variable angle spectroscopic ellipsometry, and non-linear imaging technique with phase object inside the 4f imaging system were employed to characterize prepared thin films. Their photo-stability/photo-induced phenomena in as-deposited and relaxed states were also investigated, respectively. In linear regime, we found intrinsically photo-stable relaxed layers within Ge(20)As(20)Se(60) composition. This composition presents also the highest optical damage threshold under non-linear optical conditions.

Nonlinear optical properties of glasses in the system Ge/Ga-Sb-S/Se.

We report n2 measurements of selected chalcogenide glasses using a modified Z-scan technique. Measurements were made with picosecond pulses emitted by a 10 Hz Q-switched, mode-locked Nd:YAG laser at 1064 nm under conditions suitable to characterize ultrafast nonlinearities. The nonlinear index increases significantly up to 246 times the n2 for fused silica with an increase of SbS3 units and also very slightly with the replacement of Ge by Ga or S by Se. We have attributed the variation of n2 to the total number of electronic lone pairs and to the position of the absorption band gap, which are induced by the presence of GaS4 units or Se-Se bonds in the glass structure.

Comparison of Z-scan and THG derived nonlinear index of refraction in selected organic solvents

Nonlinear index of refraction of a series of organic solvents, measured by the nonlinear imaging (z-scan) technique, is compared with the same values derived from optical third-harmonic generation (THG). The systematic differences in the values obtained from the z-scan measurements and from THG are attributed to three factors: the value of the standard used in THG measurements, important rotational contribution in z-scan measurements, and the difference in dispersion for n2 derived from Kerr susceptibility and those derived from THG measurements. Using the recently proposed standard silica susceptibility value, one obtains a very good agreement for silica and significant differences for the solvents, particularly for CS2 and chlorobenzene. A correction based on a three-level model for centrosymmetric media is applied for dispersion.

Structure, nonlinear properties, and photosensitivity of (GeSe_2)_100-x(Sb_2Se_3)_x glasses

Chalcogenide glasses from (GeSe2)​100-​x(Sb2Se3)​x system were synthesized, with x varying from 5 to 70, in order to evaluate the influence of antimony selenide addn. on nonlinear optical properties and photosensitivity. Nonlinear refractive index and two photon absorption coeffs. were measured both at 1064 nm in picosecond regime using the Z-​scan technique and at 1.55 μm in femtosecond regime using an original method based on direct anal. of beam profile change while propagating in the chalcogenide glasses. The study of their photosensitivity at 1.55 μm revealed highly glass compn. dependent behavior and quasi-​photostable compns. have been identified in femtosecond regime. To better understand these characteristics, the evolution of the glass transition temp., d. and structure with the chem. compn. were detd.

Second and third order nonlinear optical properties of microrod ZnO films deposited on sapphire substrates by thermal oxidation of metallic zinc

We report the preparation of microcrystalline ZnO thin films on sapphire substrates using a simple method based on the thermal evaporation of metallic Zn in vacuum with further annealing process. The aim of annealing in the oxygen atmosphere in the range of 800–850°C was to obtain the high quality ZnO films. The surface morphology was studied by scanning electron microscopy and atomic force microscopy. The polycrystalline films with ZnO microrods at different stages of their growth were investigated. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064nm in picosecond regime. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications of the investigated materials in the optical switching devices based on refractive index changes.We report the preparation of microcrystalline ZnO thin films on sapphire substrates using a simple method based on the thermal evaporation of metallic Zn in vacuum with further annealing process. The aim of annealing in the oxygen atmosphere in the range of 800–850°C was to obtain the high quality ZnO films. The surface morphology was studied by scanning electron microscopy and atomic force microscopy. The polycrystalline films with ZnO microrods at different stages of their growth were investigated. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064nm in picosecond regime. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications of the investigated materials in the optical switching devices based on refractive index changes.

Chalcogenide glasses as solid state optical limiters at 1.064 μm

Abstract Chalcogenide glasses present high values for third-order non-linear optical properties, i.e., high non-linear refractive indices (800 times as high as the non-linearity of silica glass at 1.064 μm) and a high non-linear absorption coefficient, which can reach more than 5 cm/GW. We study here the optical limiting properties of several chalcogenide glasses at 1.064 μm with a picosecond pulsed Nd:YAG laser and we observed a real optical limiting behavior. In the case of GeAs2Se2, glass for example, the decrease of the transmitted intensity is around 75% compared to the theoretical linear transmission, for incident pulses of 5 GW/cm2. The comparison between the theoretical non-linear transmission induced by the two photon absorption effect and the experimental non-linear transmittance shows that the optical limiting properties are mainly due to non-linear absorption.

4f coherent imager system and its application to nonlinear optical measurements

We present a powerful but simple technique based on a 4f coherent imager system with top-hat beams to characterize nonlinear optical properties. We describe the theoretical model and the experimental details of the measurement for materials having nonlinear refraction with or without nonlinear absorption. We show that it is possible to characterize the nonlinearities by analyzing the intensity profile of the image after nonlinear filtering through the material placed in the Fourier plane of the setup. We will show that, as in the Z-scan technique, the use of top-hat beams instead of Gaussian beams increases the sensitivity of the measurement. Intensity-dependent nonlinearities can be studied by use of this single laser-shot technique. We validate this nonlinear imaging technique by measuring the absolute value of the n2 coefficient for CS2 and some well-known chalcogenide glasses (As2S3, As2Se3, GeSe4, and Ge10As10Se80). Our values are in good agreement with those obtained by other techniques.