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LIDAR (Light Detection and Ranging) is the only remote sensing technique that is capable to provide 3-dimensional range resolved measurements of atmospheric constituents like pollutants, humidity or the aerosol, and of atmospheric parameters like temperature or wind. Further perspectives arise from the advent of ultra-fast high-power laser sources which are capable to generate extended plasma channels in the air, so called filaments. Their extraordinary properties, like backwards-enhanced white light emission, plasma generation along their trajectories, and their electrical conductivity provide further fascinating perspectives for applications in atmospheric research and beyond. Examples are remote multi-component analyses of the air and the aerosol, bio-aerosol detection, hard target analysis and even lightning control.

We present the first broadly tunable KNbO 3 OPO in No-Tracking Configuration (NTC), pumped by a flashlamp-pumped Ti:sapphire laser. Tuning the pump laser from 733 to 841 nm yielded a tuning range from 908 nm to 1402 nm (for the signal), and 2103 to 3803 nm (for the idler). This range was limited by the mirror coatings, and continuous tuning should be achievable up to and beyond 4000 nm. Threshold was as low as 15 NW/cm 2 and efficiencies up to 10% have been observed without AR-coatings on the crystal.

Summary form only given. We present our results on the characterization and the optimization of the infrared component of the continuum efficiency is studied as a function of several laser parameters, such as pulse energy, duration, emission frequency chirp. For LIDAR application purposes, different beam transmission emitted from light filaments. Infrared configurations are studied. The fundamental beam can be sent in the atmosphere either collimated in a parallel beam or slightly focused. White light can be also re-collimated. Infrared intensities at remote distances are optimized.

Summary form only given. Ballistic motion of wavepackets within resonators, that are larger than the wavepacket length has been debated for the last quater of the 20 th century. We present here the first ever time-resolved measurement of the ballistic motion of optical femtosecond wavepackets in the equatorial portion of a pendant ethylene glycol microdroplet (670 /spl mu/m radius containing 1 g/l Coumarin 510 dye). Two femtosecond laser pulses with /spl lambda//sub 1/=1200 nm and /spl lambda//sub 2/=600 nm, respectively, are used in a pump-probe arrangement. Simultaneous absorption of both wavelengths excites the 400 nm absorption band of the Coumarin dye. The fluorescence is used as a correlation signal. Competitive processes are 3 photon-excited fluorescence of the strong /spl lambda//sub 1/ pump beam and 2 photon-excited fluorescence of the weak /spl lambda//sub 2/ probe beam. When varying the time delay between the /spl lambda//sub 1/, and /spl lambda//sub 2/ pulses, temporal coincidences within the microdroplets are observed.

International audience; The propagation of femtosecond terawatt laser pulses at reduced pressure (0.7 atm) is investigated experimentally. In such conditions, the non-linear refractive index n 2 is reduced by 30%, resulting in a slightly farther filamentation onset and a reduction of the filament number. However, the filamentation process, especially the filament length, is not qualitatively affected. We also show that drizzle does not prevent the filaments from forming and propagating.

The influence of atmospheric aerosols on the filamentation patterns created by TW laser beams over $10\phantom{\rule{0.3em}{0ex}}\mathrm{m}$ propagation scales is investigated, both experimentally and numerically. From the experimental point of view, it is shown that dense fogs dissipate quasi-linearly the energy in the beam envelope and diminish the number of filaments in proportion. This number is strongly dependent on the power content of the beam. The power per filament is evaluated to about 5 critical powers for self-focusing in air. From the theoretical point of view, numerical computations confirm that a dense fog composed of micrometric droplets acts like a linear dissipator of the wave envelope. Beams subject to linear damping or to collisions with randomly-distributed opaque droplets are compared.

We report experimental and numerical results on supercontinuum generation at ultraviolet/visible wavelengths produced by the long-range propagation of infrared femtosecond laser pulses in air.

We report the performance of a type-II KTP optical parametric oscillator-amplifier tandem pumped in a non-critical phase-matching configuration by a flashlamp-pumped Ti:Sapphire laser, scanned from 730 to 900 nm. Tunable signal and idler wavelengths are generated from 1.065 to 1.290 µm and from 2.320 to 2.970 µm, respectively, without crystal tracking. Slope efficiency is as high as 32% for the signal conversion only. A KNbO3 crystal has also been tested as a parametric amplifier in a no-tracking configuration and yields comparable gain.

Using Teramobile laser, a mobile integrated system providing 5 TW peak power in 100 fs pulses, near to a 2 m astronomical telescope, we could for the first time image the femtosecond beam from the side up to altitudes of 25 km. Spectroscopic measurements of the lidar return were performed, in the infrared as well as in the visible.

International audience; We demonstrate remote elemental analysis at distances up to 90 m, using a laser-induced breakdown spectroscopy scheme based on filamentation induced by the nonlinear propagation of unfocused ultrashort laser pulses. A detailed signal analysis suggests that this technique, remote filament-induced breakdown spectroscopy, can be extended up to the kilometer range.

The long-range propagation of two-colored femtosecond filaments produced by an infrared (IR) ultrashort pulse exciting third harmonics (TH) in the atmosphere is investigated, both theoretically and experimentally. First, it is shown that the coupling between the pump and TH components is responsible for a wide spectral broadening, extending from ultraviolet (UV) wavelengths (220 nm) to the mid-IR (4.5 microm). Supercontinuum generation takes place continuously as the laser beam propagates, while TH emission occurs with a conversion efficiency as high as 0.5%. Second, the TH pulse is proven to stabilize the IR filament like a saturable quintic nonlinearity through four-wave mixing and cross-phase modulation. Third, the filamentation is accompanied by a conical emission of the beam, which becomes enlarged at UV wavelengths. These properties are revealed by numerical simulations and direct experimental observations performed from the Teramobile laser facility.

International audience; The filamentation of femtosecond light pulses in air is numerically and experimentally investigated for beam powers reaching several TW. Beam propagation is shown to be driven by the interplay between intense, robust spikes created by the defects of the input beam and random nucleation of light cells. Evolution of the filament patterns can be qualitatively reproduced by an averaged-in-time (2D+1)-dimensional model derived from the propagation equations for ultrashort pulses.

International audience; Ultrashort, high-power laser pulses propagating vertically in the atmosphere have been observed over more than 20 km using an imaging 2-m astronomical telescope. This direct observation in several wavelength bands shows indications for filament formation at distances as far as 2 km in the atmosphere. Moreover, the beam divergence at 5 km altitude is smaller than expected, bearing evidence for whole-beam parallelization about the nonlinear focus. We discuss implications for white-light Lidar applications.

International audience; We demonstrate experimentally the first range-resolved detection and identification of biological aerosols in the air by non-linear lidar. Ultra-short terawatt laser pulses are used to induce two-photon-excited fluorescence (2PEF) in riboflavin-containing particles at a remote location. We show that, in the case of amino acid detection, 2PEF-lidar should be more efficient than linear 1PEF-lidar beyond a typical distance of 2 km, because it takes advantage of the higher atmospheric transmission at the excitation wavelengths. 2PEF-lidar moreover allows size measurement by pump-probe schemes, and pulse shaping may improve the detection selectivity.

The acoustic wave emitted from the plasma channel associated with a filament induced by a femtosecond laser pulse in air was detected with a microphone. This sonographic detection provides a new method to determine the length and the spatial profile of the free-electron density of a filament. The acoustic wave is emitted owing to the expansion of the gas in the filament, which is heated through collisions with high-energy photoelectrons generated by multiphoton ionization. Compared with other methods, the acoustic detection is simpler, more sensitive, and with higher spatial resolution, making it suitable for field measurements over kilometer-range distances or laboratory-scale studies on the fine structure of a filament.

International audience

The propagation of ultrashort, ultra-intense laser pulses gives rise to strongly nonlinear processes. In particular, filamentation is observed, yielding an ionized, conducting plasma channel where white-light supercontinuum due to self-phase modulation occurs. This supercontinuum, extending from the UV to the IR, is a suitable "white laser" source for atmospheric remote sensing, and especially Lidar (Light Detection and Ranging). Recent significant results in this regard are presented, as well as lightning control using ultrashort laser pulses. The application of ultrashort-pulse lidar to aerosol monitoring is also discussed.

High-power femtosecond laser pulses can lead to strong nonlinear interactions during the propagation through a medium. In air the well known self-guiding effect produces long intense and moderately ionized filaments, in which a broad white-light continuum from the near UV to the mid IR is generated. The forward directed white-light can be used to do range resolved broadband absorption measurements, which opens the way to a real multi-component lidar for the simultaneous detection of several trace gases. On the other hand, enhanced nonlinear scattering and characteristic emission from the filament region, as well as from the interaction of intense pulses with aerosols, can be observed. This opens perspectives towards a novel kind of analysis of atmospheric constituents, based upon nonlinear optics. Additionally, the conductivity of the filaments can be used for lightning control. Here we present the basic concepts of the femtosecond lidar, laboratory experiments and recent results of atmospheric measurements.

In this paper, we present a new methodology for urban aerosol survey, coupling Lidar measurements and numerical models. The aim of this study is build a continuous survey of aerosol impact on the local and regional scale.

Lidar signals were obtained for the first time in the near-infrared using the supercontinuum generated by the terawatt femtosecond laser of the Teramobile system. A signal up to 4 km in altitude, in the band 1–1.7 μm, was collected using a 2 m astronomical telescope. We observed a 10-fold enhancement of the infrared signal backscattered from the atmosphere compared with that expected using a previously measured laboratory spectrum. This suggests a more efficient frequency conversion into the infrared (typically 7% into the 1–1.5 μm band) under long-distance propagation conditions.

Long ionized channels appear as a result of nonlinear propagation of femtosecond terawatt pulses. We demonstrate the ability of such filament bundles to trigger and guide megavolt discharges across a gap up to 3.8 m.

Femtosecond laser pulses can cause water droplets to emit a backward white light continuum attributed to microscopic plasma inclusions. Pump experiments have been undertaken to enlighten the laser induced plasma formation via forward elastic scattering.

Summary form only given. The sound emitted from a filament was measured using a microphone. A model describes the sound emission mechanism, which allows to retrieve the light intensity as well as the free electron density in the filament.

International audience; We describe the Teramobile system, a new mobile femtosecond multi-terawatt laser and detection system based on a state-of-the art CPA laser system embedded in a standard freight container, as well as a mobile detection unit allowing a characterization of the nonlinear propagation of high power laser pulses over long horizontal distances. The unique mobility feature of the whole system opens the way to previously unreachable applications for high-power laser pulses in the field of atmospheric research (lidar, laser-triggered lightning), which are also briefly reviewed.

Summary form only given. Soot particles from combustion processes are one of the major component of urban aerosols. These particles are highly polymorphous. The smaller, almost spherical particles, (typically 20 to 60 nm in radius) undertake aggregation processes occurring during combustion and possibly during transport in the atmosphere: numerous particles with a fractal structure are produced. The impact on health of these particles, especially the smaller, is important since these particles deposited in lungs are highly toxic: carcinogenic molecules (like polycyclic aromatics) are adsorbed on the soot surface. Unfortunately, because of their size, monomers are rarely taken into account in aerosol analysis and especially in gravimetric studies. Therefore, the development of optical methods to deduce the size distribution and composition of urban aerosols (especially soot particles) over the whole size range is an important challenge. This needs to develop new experimental schemes and models to deduce the scattering properties of fractal soot particles. For that purpose, we have undertaken multiwavelength and multi-angle scattering experiments on a distribution of soot particles.

International audience; This paper reports on a model investigation of a particular episode of tropospheric ozone formation in the city of Lyon, France. A large-scale measurement campaign involving ground-based analyzers, sampling, Sodars and Lidars has been used to validate the model results. Based on validated meteorological data and primary pollutant concentrations, the numerical model has been run to obtain 3D ozone concentration profiles during the whole campaign (22-25 June 1999). The results are compared to the ozone Lidar vertical profiles. Good agreement between Lidar data and model predictions is first obtained on 22 June (but not on the following days). On 23 and 24 June, ozone concentrations are significantly underestimated by the model. The ozone Lidar measurements allowed identifying large import processes from high altitudes that explain the difference. In a second model simulation, these imports are taken into account as new boundary conditions. This yielded good agreement between the experimental data and the predicted ozone concentrations over the whole period. The evidence of high altitude ozone intrusion is confirmed by back-trajectories calculations.

This paper is devoted to two photons excited fluorescence in a spherical micro-cavity. We describe the internal fields created when two ultra-short pulses of light illuminate a spherical micro-cavity, with the time delay between the two pulses as a parameter.

In 2010, we reported [1] on a demonstration of a mobile source of high-energy near-single-cycle THz pulses based on a tilted pulse front optical rectification set-up, pumped by a mobile terawatt laser (Teramobile). The absolute value of the THz pulse energy was measured with a pyroelectric detector (Coherent Molectron J4-05). The company does not provide a spectral sensitivity dependence for this detector below 3.3 THz. In the reported experiments, generated THz pulses had broad spectra centred at 0.2 THz [1]. Previously, this detector was used for measuring the energy of near-single-cycle THz pulses with an average frequency of 0.9 THz generated by an accelerator-based source [2]. Afterwards, it was reported that the sensitivity of the Coherent pyroelectric detector at 1 THz was approximately 1.8 times less than the specified sensitivity at 1.06 lm [3], and this difference has been take into account in a following publication [7]. Recently, we compared the sensitivity of the Coherent Molectron J4-05 detector with that of another widely used pyroelectric THz detector (Microtech Instruments) [3–6]. The latter detector is provided with a calibration curve of the spectral dependence of the sensitivity in the frequency range of 0.12–3 THz. As a result, we found that at frequencies of 0.2–0.5 THz, the Coherent Molectron J4-05 detector underestimates the THz pulse energy by a factor of about 3.5 with regard to the Microtech Instruments detector. This finding evidences an additional drop of the Coherent Molectron J4-05 detector sensitivity for THz wave frequencies below 1 THz. By this comparison, we conclude that the THz pulse energy in Ref. [1] should significantly be re-estimated, up to 175 lJ (instead of the initially published value of 50 lJ), which is to the best of our knowledge the highest energy of near-single-cycle THz pulses generated by tabletop sources.

We report the first observation of white-light emission from femtosecond laser-induced plasma in a water droplet. Such emission is not observed with water in a cell. The microdroplet acts as a lens, focusing the incident light to nanosized regions within itself and directing the emission from these regions primarily back toward the laser source. This focusing increases the intensity so that multiphoton ionization generates plasma and causes it to reach the critical density during the initial part of the pulse, enabling the rest of the pulse to heat the plasma enough to emit in the visible.

We present time-resolved measurements of the ballistic trajectory of ultrashort optical wave packets circulating near the surface of a dielectric microcavity. The wave-packet dynamics are determined by using twocolor two-photon induced fluorescence of Coumarin 510 within the microcavity as a correlator. Ballistic motion of the wave packets in whispering gallery modes and rainbow trajectories has been deduced from the time delay between collisions of the two wave packets. The cavity ringdown time is measured for each of the wave packets, which retain their integrity even after several round trips.

National audience; All solid-state laser based Lidar systems allow today a direct access to the air pollution physico-chemistry. As an example, we present the characterization of an ozone episode in Paris in summer 1999, using Lidar 3D-mappings over 33 hours.; Les systèmes Lidar actuels, basés sur des lasers solides, permettent un accès direct à la physico chimie de la pollution atmosphérique. Nous présentons, en exemple, la caractérisation d'un épisode d'ozone à Paris durant l'été 1999, en utilisant les cartographies 3D obtenues sur 33 heures.

We demonstrate theoretically and experimentally that one-, two-, and three-photon excited fluorescence from dye molecules in spherical microcavities has an asymmetrical angular distribution and is enhanced in the backward direction. The enhancement ratios (of intensities at 180 degrees and 90 degrees ) are 9, 5, and 1.8 for three-, two-, and one-photon excitation, respectively. Even larger ratios are expected for microspheres with an index of refraction larger than that used in the experiments. Because of the reciprocity principle and concentration of the incident wave inside particles, the backward enhancement is expected to occur even with nonspherical particles.

TW-fs-laser pulses are used for a novel height-resolved LIDAR detection technique. This remote sensing technique should allow a multi-component analysis of atmospheric compounds in the visible and near-infrared. Results of the spectral content and conductivity of light-filaments generated by high-intensity lasers and height-resolved LIDAR-measurements in the visible are presented.

Complex energy flows within laser beams can cause them to curve as they travel.

Les caracteristiques metrologiques des appareils de surveillance de la pollution atmospherique font l'objet d'une evaluation selon la norme NF X20-300. L'application de cette norme aux appareils de type Lidar pose des problemes methodologiques particuliers pour lesquels une solution adaptee a pu etre trouvee. L'evaluation du Lidar Elight 510 M a ainsi pu etre realisee avec SO2 comme polluant. Les resultats ont ete satisfaisants.

Very efficient and stable laser operation of Ce3+ doped LiLuF4 (Ce:LLF) single crystals longitudinally pumped with a CerLiSAF pulsed laser is demonstrated for the first time.

La fluorescence du Tryptophane excite par une impulsion ultra-breve a 270 nm peut etre diminuee d'un facteur deux par une seconde impulsion a 800 nm, a l'aide d'un dispositif pompe-sonde. Cette decroissance est aussi observee pour les bacteries vivantes, dont le Tryptophane est l'un des fluorophores, tandis qu'aucune decroissance n'est observee pour d'autres molecules organiques comme le naphtalene ou le gazole, malgre des spectres d'absorption et de fluorescence similaires. Cette difference remarquable est tres prometteuse pour la distinction d'aerosols biologiques et organiques.

We present the results of a detailed Lidar study on urban aerosols performed in summer 1996 in Lyon. Mie calculations havebeen performed to determine the optical backscattering and extinction coefficients of the real size distribution obtained bysampling, and then used for Lidar measurements. The solid particles have been sampled using cut-off filters. Size distributionand composition, determined by scanning electronic microscopy (SEM) and X-Ray microanalysis, reveal two main modes at0. 1 and 0.9 .tm, the composition of which is soot for the first one and 60 % soot - 40 % silica for the second. The combinedSEM and lidar techniques allowed to obtain the first quantitative Lidar profiles of urban aerosols. Potential and limitations ofthe method are critically discussed.Keywords : lidar, aerosols, microscopy, urban 1. INTRODUCTION Atmospheric aerosols are today a key issue in air pollution. Their impact on public health and activity in heterogeneouschemistry are well recognised although few comprehensive quantitative studies have been reported so far. This is especiallytrue for urban aerosols, which variety in size and composition make a complete characterisation difficult. For instance, due tothe lack of analysing techniques, today's legislation is limited to specify a certain mass of particles per cubic centimetre',whatever the size and the composition. This is particularly unsatisfactory since obviously particles smaller than 1 im aremuch more relevant for public health than bigger ones .

Narrow bandwidth operation within 250 MHz of a flashlamp-pumped Ti: Al2O3 laser is successfully demonstrated with injection seeding from a CW laser diode. Typically, 70% energy of a 100 mJ and 50 ns pulse is injection-locked into the narrow bandwidth.

Lidar measurements at 4 wavelengths and two polarizations were performed during the SESAME campaign in Sodankyla, Finland (67.37N, 26.65E). Using the wavelength dependence of the particle scattering the aerosol size distribution and the refractive index of the PSC particles were retrieved. A liquid PSC with a refractive index of 1.36 could be observed. We assume that this PSC consists of ternary solution particles in contradiction to the NAT-hypothesis.

We introduce a new, mobile Lidar system which is based on a flashlamp-pumped Titanium:Sapphire Laser. It is constructed on industrial standard. It allows for quasisimultaneous, spatially resolved measurements of ozone as well as VOC’s and NO2 which are known as important precursors in the formation of tropospheric ozone.

An all-solid-state infrared lidar system has been developped mainly to detect hydrocarbons in the 3300nm stetching band. As an infrared laser source, an optical parametric oscillator (OPO) has been built. It is pumped by a tunable flashlamps pumped Ti:Sapphire which allows the very convenient “no-tracking” configuraion for the OPO. It has been implemented in a mobile, very compact lidar system.

Ground based LIDAR systems have been operated in Florence (Italy) and in Lauder (New Zealand) during the Lidar In space Technological Experiment (LITE). A very good agreement was found for all the cases of stratospheric aerosol measurements. Only a few correlative cloud measurements are available. For these cases no correlation was found between LITE and ground based lidar data. Our observations seem to indicate that a space borne lidar system could be a powerful tool for a global scale stratospheric aerosol survey. Time and spatial variability of tropospheric clouds make far more critical the use of a space-borne lidar for tropospheric cloud monitoring.

We compare laser-induced condensation by UV laser pulses of femtosecond, sub-picosecond, and nanosecond duration between each other, as well as with respect to near-infrared (NIR) (800 nm) ultrashort laser pulses. Particle nucleation by UV pulses is so efficient that their growth beyond several hundreds of nm is limited by the local concentration of water vapour molecules. Furthermore, we evidence a dual mechanism: While condensation induced by ultrashort UV pulses rely on nitrogen photo-oxidative chemistry like in the NIR, nanosecond laser-induced condensation occurs without NO2 production, evidencing the domination of a mechanism distinct from that previously identified in the femtosecond regime.

At relative humidities above 70%, femtosecond laser filaments generate aerosol particles and water droplets in the atmosphere. The water vapour condensation and droplet stabilization are assured by soluble species produced in the laser plasma.

We developed a new concept for lidar measurements: multispectral differential absorption. Instead of comparing the backscattered light at one absorbed and one reference wavelengths (DIAL), a broadband laser is sent into the atmosphere and the returned signal is spectrally resolved on the receiver side (MULTIDIAL). Potential advantages are thoroughly reviewed. First, experiments combining lidar with a Fourier transform spectrometer are presented. Broadband nontracking OPOs are being built for this application in the infrared to detect VOCs. This idea was also applied to the UV range. A tunable (280-300 nm) broadband Ce:LiSAF laser has been developed for this purpose. The detection is performed by a gated amplified CCD-OMA.