Robust self-trapping of vortex beams in a saturable optical medium

We report the first observation of robust self-trapping of vortex beams propagating in a uniform condensed medium featuring local saturable self-focusing nonlinearity. Optical vortices with topological charge m=1, that remain self-trapped over ~ 5 Rayleigh lengths, are excited in carbon disulfide using a helical light beam at 532 nm and intensities from 8 to 10 GW/cm^2. At larger intensities, the vortex beams lose their stability, spontaneously breaking into two fragments. Numerical simulations based on the nonlinear Schr\"odinger equation including the three-photon absorption and nonpolynomial saturation of the refractive nonlinearity demonstrate close agreement with the experimental findings.Comment: 27 pages, 7 figures,to be published in Phys. Rev. A (2016

Picosecond cubic and quintic nonlinearity of lithium niobate at 532 nm

The nonlinear (NL) optical response of bulk lithium niobate (LiNbO$_3$) was investigated at 532 nm using the second harmonic of a Nd:YAG laser delivering pulses of 12 ps. The experiments were performed using the D4$\sigma$ method combined with the conventional Z-scan technique. Two- and three-photon absorption coefficients equal to 0.27 cm/GW and 2.5x10^(-26) m3/W2, respectively, were determined. The NL absorption processes were due to transitions from the valence to the conduction band and to free-carriers absorption. The third- and fifth-order NL refractive indices were $n_2=(2.5 \pm 0.6)\times 10^{-19}$ m$^2$/W and $n_4<5.5 \times 10^{-36}$ m$^4$/W$^2$. The present results give support for previous experiments that indicate possible fifth-order processes in bulk samples and channel waveguides fabricated with LiNbO$_3$

Diode-pumped 99 fs Yb : CaF2 oscillator

International audienceWe demonstrate the generation of 99 fs pulses by a mode-locked laser oscillator built around a Yb:CaF2 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

Near-infrared nonlinearity of a multicomponent tellurium oxide glass at 800 and 1,064 nm

Abstract We report on the nonlinear (NL) optical properties of glassy TeO 2 -GeO 2 -K 2 O-Bi 2 O 3 at k = 800 nm and k = 1,064 nm. Using the Kerr gate technique with a laser delivering 150 fs pulses at 800 nm, we demonstrated the fast NL response of the samples

Numerical Simulation of the Whole Thermal Lensing Process with Z-Scan-Based Methods Using Gaussian Beams

A general study of the diffracted far field due to thermal lens heating using Gaussian beams is presented. The numerical simulation considers the whole system, including both the optical and the thermal parameters. It is shown that the existing simplified relations found in the literature and used up to now only give the order of magnitude of the thermo-optical coefficients. More accurate, simplified formulas are derived to measure the induced thermal phase shift when working with Z-scan-based methods. Temperature estimation in absorbing media turn out to be more reliable whether using time-resolved or steady-state techniques. The extension of the calculation to the image formation in a 4f system is also addressed

Applications de l'imagerie à la mesure des coefficients non linéaires des verres infrarouges

Nous présentons une technique simple basée sur un système 4f pour caractériser des non linéarités. Nous montrons qu'il est possible de caractériser les non linéarités en analysant le profil d'intensité de l'image après un filtrage non linéaire induit dans le matériau placé dans le plan Fourier du montage. Les acquisitions expérimentales sont ajustée à l'aide d'un modèle théorique utilisant l'optique de Fourier pour obtenir les coefficients non linéaires. Parmi les avantages de cette méthode on compte un montage optique simple et une bonne sensibilité comparable aux autres techniques. D'autre part, en ajoutant un objet phase a l'entrée du système 4f, il est possible d'extraire le signe de l'indice de réfraction non linéaire. Différentes compositions des verres en chalcogénures ont été étudiées et caractérisées pour leurs propriétés linéaires et non linéaires.We present a simple technique based on a 4f coherent optical imaging system to characterize nonlinearities. We show that it is possible to characterize the nonlinearities by analyzing the intensity profile of the image after nonlinear filtering through the material under study in the Fourier plane of the set up. The experimental acquisitions are fitted by a simple theoretical model based on Fourier optics to obtain the nonlinear coefficient. The advantages of this method include simple optical setup, few-laser shots inside the material and a sensitivity comparable to other techniques. Further, by adding a phase object at the entry of the 4f system, it is possible to extract the sign and magnitude of the nonlinear optical refractive index of the material with only one intense laser shot and the sensitivity of the measurement can be increased. Several different compositions of chalcogenide glasses were studied and characterized for their linear and nonlinear properties.ANGERS-BU Lettres et Sciences (490072106) / SudocSudocFranceF

Nonlinear optical measurements using a 4 f coherent imaging system with phase objects

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Développement d'un banc de mesure de la forme d'onde de signaux dynamiques complexes par échantillonnage électro-optique

Nous proposons une méthode et nous réalisons l'expérience pour la caractérisation de la forme d'onde jusqu'à 100 GHz, par échantillonnage électro-optique. L'échantillonnage électro-optique permet de déterminer l'impulsion ultra rapide générée par une photodiode dans une ligne coplanaire. Dans notre système, l'impulsion électrique est échantillonnée par un train d'impulsions laser ultra-courtes par effet électro-optique. Le faisceau du laser est sépare en deux parties. Une partie du laser excite la photodiode qui génère les impulsions électriques se propageant sur une ligne coplanaire fabriquée sur un substrat en verre. L'autre partie du laser subit un délai optique variable et traverse un matériau électro-optique placé sur la ligne coplanaire. Le champ électrique entre les conducteurs de la ligne coplanaire, modifie la polarisation du laser par l'effet électro-optique. Le changement de polarisation peut être converti en une variation d'amplitude qui peut être mesurée. Pour un retard fixe, les impulsions d'échantillonnage interceptent de manière répétitive une petite portion de la forme d'onde de l'impulsion électrique. Le retard est varié pour enregistrer l'évolution temporelle de la forme d'onde de l'impulsion électrique. Nous utilisons un logiciel de simulation électromagnétique 3D pour optimiser la structure électro-optique constituée d'une ligne coplanaire sur laquelle est posée une lame électro-optique. Nous réalisons 144 lignes coplanaires sur un substrat de verre ainsi qu'un kit d'étalonnage pour étalonner l'analyseur de réseau vectoriel utilisé pour trouver la structure optimale en conditions réelles. Nous utilisons ensuite cette structure pour reconstruire la forme d'onde de l'impulsion électrique générée par la photodiode.We highlight a method and we set up the experiment for the characterization of waveforms up to 100 GHz, by electro-optic sampling. Electro-optical sampling allows to determine ultra fast pulses generated by a photodiode in a coplanar waveguide. In our system, high-speed electrical waveforms are sampled by a train of ultra-short laser pulses via the electro-optic effect. The laser beam is split into two parts. One part of the laser beam excites the photodiode, which generates electrical pulses propagating onto a coplanar waveguide fabricated on a glass substrate. The other part of the laser beam passes through a variable optical delay and crosses an electro-optic material placed on the coplanar waveguide. The electric field between the coplanar waveguide conductors changes the polarization of the optical beam passing through the electro-optical material via the electro-optic effect. The change of polarization can be converted to an amplitude variation which can be measured. For a fixed path delay between the two beams, the sampling pulses intercept repetitively one small portion of the electrical pulse waveform. We can adjust the delay to record the temporal evolution of the electrical pulse waveform. We use a 3D electromagnetic simulation software to optimize the electro-optic structure consisting of a coplanar waveguide on which is placed an electro-optic strip. We design 144 coplanar waveguides on a glass substrate and a calibration kit for the calibration of a vector network analyser used for determining the optimal structure into real working conditions. Then we use this structure for the waveform reconstruction of the electrical pulse generated by the photodiode.ANGERS-BU Lettres et Sciences (490072106) / SudocSudocFranceF

Sensitivity of the 4f coherent imaging system used in degenerate multiwave mixing experiments

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Characterization of light-induced modification of the nonlinear refractive index using a one-laser-shot nonlinear imaging technique

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