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We show experimentally a new type of parametric instability associated with the original phenomenon of beam self-cleaning in multimode fibers. Our experimental results are in good agreement with numerical solutions of the Gross-Pitaevskii equation.

The study presented in this article belongs within the context of a design of a new kind of short-range Ultra Wide-Band (UWB) Radar with an autonomous scanning capability. The generation of short pulses is performed with an optoelectronic device triggered by a laser flash and operating in linear switching mode. By adding as many optical systems as antennas, we create a transmitting array with increased radiated energy. Each of those elements are fed with bursts composed of UWB optogenerated pulses with a slightly different pulse repetition frequency allowing beam-scanning capability. This article presents in detail all the parts needed to implement the elementary radiation source and offers a mathematical method of calculation to trace back to the generated feeding signal.

A supercontinuum laser source was designed for multiplex-coherent anti-Stokes Raman scattering spectroscopy. This source was based on the use of a germanium-doped standard optical fiber with a zero dispersion wavelength at 1600 nm and pumped at 1064 nm. We analyzed the nonlinear spectro-temporal interrelations of a subnanosecond pulse propagating in a normal dispersion regime in the presence of a multiple Raman cascading process and strong conversion. The multiple Raman orders permitted the generation of a high-power flat spectrum with a specific nonlinear dynamics that can open the way to subnanosecond time-coded multiplex CARS systems.

The reshaping of multimode waves in optical fibers is a process where the spatial and spectral degrees of freedom are inherently coupled. Our experiments demonstrate that pumping a graded-index multimode fiber with sub-ns pulses from a microchip Nd:YAG laser leads to supercontinuum generation with a uniform bell-shaped spatial beam profile.

We study experimentally the spatial and spectral features of supercontinuum generation in a bulk quadratic crystal. We demonstrate the formation of the spatial polychromatic filament in the visible and near infrared domain.

Spatio-temporal mode coupling in highly multimode physical systems permits new routes for exploring complex instabilities and forming coherent wave structures. We present here the first experimental demonstration of multiple geometric parametric instability sidebands, generated in the frequency domain through resonant space-time coupling, owing to the natural periodic spatial self-imaging of a multimode quasi-continuous-wave beam in a standard graded-index multimode fiber. The input beam was launched in the fiber by means of an amplified microchip laser emitting sub-nanosecond pulses at 1064 nm. The experimentally observed frequency spacing among sidebands agrees well with analytical predictions and numerical simulations. The first order peaks are located at the considerably large detuning of 123.5 THz from the pump. These results open the remarkable possibility to convert a near-infrared laser directly into a broad spectral range spanning visible and infrared wavelengths, by means of a single resonant parametric nonlinear effect occurring in the normal dispersion regime. As a further evidence of our strong space-time coupling regime, we observed the striking effect that all of the different sideband peaks were carried by a well-defined and stable bell-shaped spatial profile., 5 pages, 4 figures

International audience; We describe and characterize a multiplex CARS microspectroscopic system that uses a nanosecond supercontinuum generated from a photonic crystal fiber and a sub-nanosecond pulse laser. This system has a high spectral resolution (2500 cm−1). The estimated spatial resolutions are 0.45 μm (lateral) and 4.5 μm (axial), respectively. This system enables us to obtain CARS spectra and corresponding images in the fingerprint region as well in the CH stretch region. Using this system, we have successfully obtained label-free and multi-mode vibrational images of a yeast cell.

International audience; We report our recent development to model quadratic and cubic ultra-broadband nonlinear dynamics in photonic devices, by means of a nonlinear single-envelope equation. We present the case of generation of tunable visible light from large band conversion, in a quadratic crystal, of the infrared continuum from standard photonic crystal fibers. Moreover, we show the study of a visible supercontinuum generation, initiated by second-harmonic generation, in a quadratic poled germanium-doped microstructured fiber.

Le diagnostic cellulaire est actuellement base sur les mesures electriques et optiques de multiples parametres associes aux cellules constituant le sang. L'utilisation de la technique de la cytometrie en flux permet d'obtenir rapidement les caracteristiques de chaque cellule grâce a leur defilement controle devant une ou plusieurs fenetres d'analyse: on mesure ainsi leur taux de fluorescence, leur diffraction ou leur impedance. Pour cela la combinaison de plusieurs sources laser emettant des rayonnements continus a differentes longueurs d'onde est necessaire mais reste relativement complexe et couteuse. L'arrivee sur le marche de sources multicolores ultracompactes (de type continuum) permet une amelioration significative du systeme d'excitation optique ce qui va contribuer a obtenir un meilleur depistage des maladies sanguines. Le choix plus grand des longueurs d'onde et la maitrise parfaite de leur ecartement spectral apportent de nouvelles solutions pour la discrimination cellulaire et cela avec une precision accrue.

Protein secondary structures in human hair have been studied with ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopy. The CARS peak-shift mapping method has been developed and applied to hair samples with and without treatments by chemical reduction and mechanical extension. It clearly visualizes the treatment induced changes in protein secondary structures and their spatial distributions. Using the new imaging technique, we found a multilayered structure in the human hair cortex.

International audience; We demonstrate that monochromatic infrared laser pulses can generate polychromatic light in noncentrosymmetric crystals simultaneously covering the ultraviolet, visible, and infrared domains. The spatial shape of the beam and its energy can influence this multicolor frequency conversion, unveiling complex and interesting dynamics. We performed our experiments in a bulk crystal of periodically poled lithium niobate, working close to the optimal condition for second-harmonic generation. We used an input laser beam wide enough that, at very low intensities, the diffraction leaves its diameter unchanged along the propagation in the crystal. At high intensities instead, as we show in this work, such a spatially wide laser beam can be reshaped into a beam of much smaller diameter and guiding multispectral components. We also show how this outcome may permit exploitation of other parameters, like the crystal temperature, for tuning the spectrum of the generated multicolor light.

In this work, a comparative study of reactive sintering and optical properties of three laser composite transparent ceramics doped with neodymium: Nd:YAG/Nd:YS1AG, Nd:YAG/Nd:LuAG and Nd:YS1AG/Nd:LuAG has been achieved. Samples were manufactured thanks to pressureless co-sintering under vacuum of bilayer powder compacts. The reaction sequence from primary oxides to final garnet phases has been investigated. Similar dilatometric behavior was observed during reactive-sintering for each composition. Differential shrinkage can be thus accommodated to some extent. Second, this work has shown that the intermediate zone at composites interface is composed of single-phased garnet solid-solution with continuous evolution from one side to the other. The thickness of the interdiffusion zone was found to be limited to about 100 μm in all cases and appeared to be well described by classical diffusion laws of Fick and Whipple-Le Claire. The analyses of spectroscopic properties of transparent ceramics composites have finally shown that composite ceramics should be suitable to produce dual wavelength emission for terahertz generation.

International audience; Supercontinuum generation in a multicore fiber in which several uncoupled cores were doped with dissimilar concentrations of germanium was studied experimentally. Germanium doping provided control over the separation between the zero-dispersion wavelength and the 1064-nm wavelength of a Q-switched Nd:YAG pump laser. Supercontinua generated independently in each core of the same piece of fiber displayed clear and repeatable differences due to the influence of germanium doping on refractive index and four-wave mixing. The spectral evolution of the subnanosecond pump pulses injected into the different cores was accurately reproduced by numerical simulations.

We report, to the best of our knowledge, the first turn-key and compact dual-output sub-nanosecond supercontinuum source applicable to ultrabroadband multiplex coherent anti-Stokes Raman scattering microspectroscopy of biological samples. The light source design and the microspectroscopy setup are described in details. Easy multicolour imaging of Caenorhabditis elegans nematode is operated successfully and discussed. Copyright © 2011 John Wiley & Sons, Ltd.

We have developed an ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopic system using a supercontinuum (SC) seeded by sub-100-ps (85 ps) laser pulses with a sub-MHz (0.82 MHz) repetition rate. Because of the high peak power and ultrabroadband spectral profile of the SC, we can efficiently generate multiplex CARS signals in the spectral range of 600–3600 cm−1, which covers the entire molecular fingerprint region, as well as the C—H and O—H stretching regions. Due to the high peak power of the new laser source, the exposure time (pixel dwell time) for CARS imaging of polymer beads was reduced to less than 1 ms (0.8 ms), which was limited by the readout time of a CCD camera. Owing to the improvement in CARS spectral quality, clear molecular fingerprinting was achieved for living HeLa cells at different phases in the cell cycle.

New tellurite glasses with a large glass forming domain were elaborated within the TeO 2 –Tl 2 O–ZnO ternary system. The evolution of the glass transition ( T g ) and onset crystallization ( T 0 ) temperatures for such tellurite glasses was studied, in particular, as a function of the Tl 2 O addition. A decrease of both T g and T 0 temperatures was observed; the former being more affected. Structural modifications induced by the addition of the modifiers were studied by Raman spectroscopy. For a fixed ZnO concentration, the increase in the Tl 2 O content leads to a destruction of the glass framework, characterized by the transformation of TeO 4 disphenoids into isolated TeO 3 2− trigonal pyramid-like ortho-groups. For a fixed Tl 2 O concentration, the ZnO addition induces similar effects on the glass structure. The optical transmission of the ((80 − x )TeO 2 – x Tl 2 O–20ZnO) ( x = 10, 20 and 30 mol%) glasses was measured in the 300–2000 nm range. Their good transparency was evidenced and a clear reduction of the optical band-gap was noticed with the increase in the Tl 2 O content. Finally, Second Harmonic Generation was unambiguously detected for each glass composition. The second order non-linearity amplitude is found to be increasing as a function of the Tl 2 O concentration, in the tested range.

International audience; We report a series of experimental results showing that the acceptance bandwidth of second harmonic generation in quadratic crystals may substantially broaden when using pumps at high intensities. We highlight the co-existence of second harmonic generation and strong unconventional spatial beam reshaping. Our experimental results are in good agreement with our numerical simulations.

International audience; The second harmonic signal at the output of an optically poled fiber was studied as a function of the input fundamental frequency power and polarization state. For an injected average power of 3 mW at 1064 nm, the measured output power at 532 nm was 10 μW. The second harmonic intensity profile was a bright green ring even if the pump was injected in the fundamental HE11 mode: we believe that the second harmonic was carried by a combination of the EH11 and HE31 modes.

National audience; Nous présentons une source de continuum infrarouge optimisée pour la micro-spectroscopie Raman cohérente (CARS) de cellules biologiques. Elle est conçue de façon à émettre une forte densité spectrale de puissance dans la bande correspondant à la zone d'empreinte digitale des liaisons chimiques d' intérêt (1080-1600 nm pour un pompage à 1064 nm) tout en maintenant une très bonne synchronisation temporelle de l'ensemble de ses composantes spectrales. Cette source est basée sur un élargissement spectral induit dans une fibre microstructurée amplificatrice à large cœur dont la longueur d'onde de dispersion nulle est positionnée au centre de la bande spectrale d' intérêt.

National audience; Nous avons montré qu'un refroidissement moléculaire pouvait être induit par un champ électrique statique appliqué à des molécules non polaires d'huile de paraffine. Cet effet a été mis en évidence grâce à une mesure de spectroscopie CARS (Coherent Anti-Stokes Raman Scattering). De manière complémentaire, l'exposition de molécules à un champ électrique permet de contrôler leur orientation et ainsi améliorer ou diminuer l'amplitude de leur signature vibrationnelle.

International audience; This paper demonstrates for the first time continuous wave (cw) and pulsed lasing effects in 1 mol. % Nd3+-doped 74.25TeO2-19.8NbO2.5-4.95WO3 glasses. It is divided into two parts:- the first part treats all the aspects related to the elaboration and the characterization of the materials. Hence, glasses elaborated within such system show a rather high glass transition temperature Tg ~ 375°C, with an excellent thermal stability of ~ 160°C. Compared to glasses synthesized in either TeO2-Nb2O5 or TeO2-WO3 binary systems, glasses fabricated within the TeO2-Nb2O5-WO3 ternary system show improved mechanical performances, with larger Young’s modulus values. The structural characteristics of the samples, studied by Raman spectroscopy, are also presented. Linear optical properties (such as refractive index and extinction coefficient) are accessed by spectroscopic ellipsometry. As well, the optical transmission of the various bulk glasses is measured, in the case of both uncoated and coated glasses. In particular, specific anti-reflective coatings at 808 nm (diode laser pump wavelength) and 1064 nm (laser emission wavelength) are respectively deposited on the two surfaces of the sample in order to minimize the losses due to Fresnel reflections at the two glass/air interfaces. In addition, another specific surface treatment (Rmax at 1064 nm) was employed to serve as the back mirror of the laser cavity. The optical transmission data testified to the real efficiency of all these coatings. Finally, the photoluminescence properties (emission and excitation spectra, and luminescence decay curve) of the Nd3+-doped glasses, measured at room temperature for bulk samples, and as a function of temperature up to Tg for powder glasses, are presented and discussed.- the second part is focused on evidencing (cw) and pulsed lasing effects in such coated bulk lasers. Cylindric samples of only a few millimeters in height and in diameter were tested and led to a laser emission around 1064 nm, characterized by a very low pump power threshold of ~ 5 mW, but with a limited slope efficiency (~ 4.6 %). The spectral characteristics were also measured and some anisotropic enlargement of the laser emission band towards longer wavelengths was noticed with increasing the pump power density. Finally, monomodal or multimodal laser emission was evidenced, depending again on the pump power density.

International audience; We consider experimentally the frequency doubling of a near infrared supercontinuum light in a periodically poled lithium niobate crystal. The supercontinuum light was generated by a photonic crystal fiber and then filtered by an infrared passband filter, in order to obtain a spectrum from 1100 nm to 1500 nm. Once that spectrum was injected in the crystal, we observed a broadband frequency conversion towards the visible domain between 560 nm and 700 nm. Our goal is to demonstrate the capability of the spatio-temporal quadratic unidirectional pulse propagation model, providing insight into the complex experimental observations. We enlighten the role of Cerenkov second-harmonic emission, nonlinear Raman-Nath and nonlinear Bragg scattering processes in the broadband frequency conversion from infrared to visible light.

We report on the experimental demonstration of a supercontinuum generation in a highly birefringent nonlinear microstructured optical fiber by use of a sub-nanosecond passively Q-switched Yb-doped double-clad fiber laser. The powerful, low-cost sub-nanosecond pulses produced by the fiber laser source permit one to generate a flat supercontinuum between 1064 and 1600 nm and a more structured spectral broadening down to 400 nm is also initiated.

Les fibres microstructurees air-silice (FMAS), apparues dans le milieu des annees 90 a l’Universite de Southampton [1] (Royaume-Uni), ont demontre un potentiel d’applications extremement vaste dans des domaines tres varies allant des telecommunications a la biophotonique, en passant par les capteurs ou les sources laser UV. Le laboratoire XLIM (ex-IRCOM, Institut de Recherche en Communications Optiques et Microondes) s’est engage, depuis 1998, dans la conception, la fabrication et la caracterisation de tels guides de lumiere. Nous presentons dans cet article les defis technologiques a relever dans la fabrication des FMAS ainsi qu’une des applications marquantes de ces fibres qu’est la generation de supercontinuum, dans les domaines infrarouge, visible et ultraviolet.

Generation of unipolar and bipolar pulses by using high- and medium-voltage silicon rectifier diodes is achieved. These components are provided by the French Atomic Energy Commission (CEA). Furthermore, these devices work in the linear mode of photoconducting switches. Generation of electrical unipolar pulses with an amplitude of 10.7 kV and a full-width at half-maximum of 300 ps by using only 1.2 mJ of optical power is demonstrated. This energy value is 10-100 times less than usually published during the past decades. Furthermore, the linear mode running of these devices permits to synchronize several generators with a precision as low as 2 ps. This low timing jitter is useful for bipolar generators in order to control their spectrum with high precision, i.e., bipolar pulses of 3 kV peak-to-peak have been generated with a cycle duration of 400 ps and an optical energy of 1 mJ

Experimental and numerical investigations of an ultra-fast reconfigurable spatial switch based on the nonlinear interaction between a weak wave (the signal) and a solitary wave (the control) at 1548 nm are reported. The non-collinear interaction in a quadratic nonlinear film waveguide gives birth to a third switched optical beam (the idler). This beam could be steered according to the transverse spatial position of the control beam.

Soliton-soliton collisions have a crucial role in enhancing the spectrum of dispersive waves in optical fibers and collisions among in-phase solitons lead to a dramatic enhancement of the dispersive wave power, as well as to its significant spectral reshaping. We obtained a simple analytical model to estimate the spectral position, width and amplitude of the dispersive waves induced by a collision of two in-phase solitons. We tested our theory in the case of a dual concentric core microstructured fiber., submitted to Photonics Tech. Lett. 5 figures

By using photoconductive semiconductor switches in the linear mode, we achieve generation of electrical pulses of duration between 43 and 300 ps with a peak voltage between 150 and 10700 V. Moreover, these generators can be synchronised with a precision lower than 5 ps and they need only 1.2 mJ of optical energy. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 121–125, 2006; Published online in Wiley InterScience www.interscience.wiley.com). DOI 10.1002/mop.21282

We report a numerical and experimental investigation on the generation of spatial self-narrowed beams with short temporal pulsed excitation in quadratic film waveguides. The impact of temporal group-velocity mismatch between the quadratic multiple interacting signals is shown. We accurately studied the spatial, temporal and spectral signals dynamics versus pulse power and phase mismatch. We show that spatial self-trapping can be induced even if the pump pulse duration is significantly shorter than the group delay mismatch between interacting waves for large enough positive phase mismatches.

Numerical and experimental investigations on ultra-fast all-optical saturable absorber on picosecond optical pulses at 1547 nm using spatial self-trapped propagation in a quadratic nonlinear film waveguide combined with spatial filtering are reported. The influences of phase-mismatch, pulse intensity and spatial filtering on the temporal reshaping mechanism are discussed to derive the optimum parameters.

We present the performances of a low repetition rate (4.5 MHz) mode locked Nd:YAG laser using a nonlinear polarization rotation effect in a type II crystal cut for second harmonic generation. We compared their performances in term of peak power, pulse duration and cavity losses with a standard resonator operating at high repetition rate (125 MHz). A gain of 10.8 and 7.3 was obtained on the energy per pulse and on the output peak power between the two lasers.

We report the design of low-cost and compact short-pulse source based on a fiber-coupled Q-switched microchip laser. The combination of stimulated Raman scattering and nonlinear polarization rotation effects in the fiber associated with appropriate filtering makes it possible to tune pulse duration down to 32 ps with peak power above 3 kW. Pulse to pulse peak power fluctuation is below 4%.

Whole families of stable optical solitons are known to exist in media with quadratic nonlinearity, and evidence of such existence has been demonstrated experimentally during the last years in several materials. However, soliton existence does not always guarantee soliton excitation. On the contrary, suitable conditions must be employed in each particular setting for solitons to be efficiently, or even actually, generated. We overview the recent developments along this line, and illustrate their paramount practical importance by discussing in detail the differences encountered with identical soliton families when they are to be excited in up-conversion or down-conversion processes. Limitations of both, the ideal theoretical predictions and the accessible experimental data are highlighted.

International audience; We demonstrate far-detuned parametric frequency conversion processes in a few mode graded-index optical fibers pumped by a Q-switched picosecond laser at 1064 nm. Through a detailed analytical and numerical analysis, we show that the multiple sidebands are generated through a complex cascaded process involving inter-modal four-wave mixing. The resulting parametric wavelength detuning spans in the visible down to 405 nm and in the nearinfrared up to 1355 nm.

We study experimentally and numerically the spectral and spatial dynamics of second harmonic generation in an all-optically poled multimode graded-index fiber. In contrast with poled single-mode fibers, in a multimode graded-index fiber a pump can generate a series of sharp sidebands around its second harmonic (SH) that originate from the sub-millimetric periodic evolution of the intensity at the fundamental frequency. The mutual interaction between the fundamental and its SH may also strongly affect the spatial distribution of guided light for both colors: when increasing the pump power, both fundamental and SH output beams evolve from disordered multimode speckles into two bell-shaped beams.

International audience; The originality of the radiation source presented here is localized in its ultrafast speed and its autonomy of scanning a large spatial area. That behavior is obtained by means of a trigger mode of radiation perfectly controlled by a single optical source. The transmitter consists of a powerful picoseconds laser, an optical power divider and n optoelectronic ultra-wideband radiation sources which produce several electric pulse trains with a repetition rate slightly different one with each other. Each train is then addressed toward a single antenna. When transmitted the electromagnetic waves interact to produce an ultrafast orientation of the array emission lobe allowing scanning of large spatial field in less than 1μs.

International audience

Broadband frequency doubling of an infrared supercontinuum is demonstrated. This unconventional Second Harmonic Generation process is obtained in a PPLN crystal excited along its Z axis, thanks to nonlinear Cerenkov and Raman-Nath interactions.

We developed an analytical approach to estimate the influence of soliton-soliton collision on the growth rate of dispersive waves in optical fibers. Our theoretical model shows an excellent agreement with numerical results.

International audience; We study spatio-temporal nonlinear dynamics in periodically-poled lithium niobate crystal. We discuss broadband conversion via cascading second harmonic generation in self-defocusing and self-focusing regime. Measurements well agree with simulations.

Experimental measurements on microwave assisted Multiplex Coherent Anti-Stokes Raman Spectroscopy (M-CARS) in liquids are presented. Nanosecond electric field applied on samples allows M-CARS signal enhancement and offers potentialities to remove non resonant background.

International audience; We investigate nonlinear focusing behavior of light beams propagating in beta-barium-borate (BBO) crystals under mismatched second-harmonic generation. We clearly identify experimentally multiple self-focusing and defocusing regions against the orientation angle, and the condition where competing quadratic and cubic nonlinearities perfectly compensate each other (zero-focusing point).

Stimulated Raman scattering was investigated in potassium titanyl phosphate. A broadband Raman cascade was generated between 1086 nm and 1250 nm. A detailed discussion is given about spatial and temporal distortions of Raman-scattered light.

We study supercontinuum generation in a multimode microstructured optical fiber by dual-wavelength pumping. We demonstrate significant blue extension of the spectrum in relatively short fiber length by exploiting cross-phase modulation between high order modes.

International audience; Highly transparent tellurite glasses and glass-ceramics based on the 85TeO2-15WO3 composition (mol%) were produced by spark plasma sintering (SPS) from powders previously prepared by the conventional melt-quenching technique and then grinded. We report a study based on the understanding of carbon contamination that is commonly observed by this nonconventional sintering technique and which constitutes a drawback for optical applications. First, the influence of the particle size of the initial amorphous powders as well as an additional pressureless sintering step prior to SPS experiments and the use of a physical carbon diffusion barrier have been investigated to reduce the carbon contamination in glass bulks. Second, once reducing the carbon contamination, glass-ceramics were obtained by varying the SPS conditions. The noncentrosymmetric γ-TeO2 phase crystallized within the bulk volume while maintaining good optical transparency and led to the generation of second harmonic. This approach paves the way to further applications in the domain of linear and nonlinear optics.

International audience; Through carrying out Raman spectroscopy under a microscope, we can observe the molecular distribution and dynamics of living cells in situ without staining or labeling. In general, Raman microscopy/microspectroscopy is classified into spontaneous Raman microscopy/microspectroscopy and nonlinear Raman microscopy/microspectroscopy. This review will first summarize the historical development of Raman microscopes, and will discuss in detail their instrumentation and applications.

Chalcogenide glasses in the [Ge–Se–As] vitreous system have been studied with respect to their third order non linear optical properties. Z-scan measurements of the non linear refractive index (n2) and non linear absorption (β) have been performed both at 1.064 and 1.43 μm and the results of the measurements have been correlated to the structures of the glasses. The figure of merit has been calculated with the purpose of a potential utilization of these glasses in the realization of ultra-fast all-optical switches. Non linearities as high as 800 times the non linearity of silica glass have been obtained and some glasses exhibit at 1.43 μm non linear optical characteristics suitable for telecommunication applications.

International audience; We introduce an experiment using electro-CARS, an electro-optical method based on the combination of ultrabroadband multiplex coherent anti-Stokes Raman scattering (M-CARS) spectroscopy and electric field stimulation. We demonstrate that this method can effectively discriminate the resonant CARS signal from the nonresonant background owing to a phenomenon of molecular orientation in the sample medium. Such molecular orientation is intrinsically related to the induction of an electric dipole moment by the applied static electric field. Evidence of the electro-CARS effect is obtained with a solution of n-alkanes (CnH2n+2, 15≤n≤40), for which an enhancement of the CARS signal-to-noise ratio is achieved in the case of CH2 and CH3 symmetric/asymmetric stretching vibrations. Additionally, an electric-field-induced second-harmonic generation experiment is performed in order to corroborate the orientational organization of molecules due to the electric field excitation. Finally, we use a simple mathematical approach to compare the vibrational information extracted from electro-CARS measurements with spontaneous Raman data and to highlight the impact of electric stimulation on the vibrational signal.

International audience; A three-mirror laser, with very di€erent spacings between the mirrors is studied numerically and experimentally. Two laser lines are emitted with a beat frequency in the tenths of GHz and a very ®ne tunability. Ó 2001 Published by Elsevier Science B.V.