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International audience; SiC nanoparticles by carbothermal reduction show promising properties in terms of second harmonic and multiphoton excited luminescence. In particular, we estimate a nonlinear efficiency < d > = 17 pm/V, as obtained by Hyper Rayleigh Scattering. We also present results of cell labelling to demonstrate the potential use of SiC nanoparticles for nonlinear bioimaging by simultaneous detection of second harmonic and luminescence.

Bismuth Ferrite nanoparticles have been recently used to selectively interact with malignant cell DNA via in situ generated second harmonic in a novel theranostics protocol [Nanoscale 6(5), pp. 2929, 2014]. In this report, we extend the screening of biocompatibility of BFO uncoated uncoated nanoparticles and assess the nanoparticle- mediated production of reactive oxygen species as a function of excitation wavelength.

Proc. SPIE 8611; International audience; In this contribution we present the motivations underlying the introduction of harmonic nanoparticles, i.e. Second harmonic contrast agents for nonlinear microscopy. Their properties will be discussed in the light of various biological applications including imaging of stem cells and rare event detection in physiological media.

Shaping light with microtechnology components has been possible for many years. The Texas Instruments digital micromirror device (DMD) and all types of adaptive optics systems are very sophisticated tools, well established and widely used. Here we present, however, two very dedicated systems, where one is an extremely simple MEMS-based tunable diffuser, while the second device is complex micromirror array with new capabilities for femtosecond laser pulse shaping. Showing the two systems right next to each other demonstrates the vast options and versatility of MOEMS for shaping light in the space and time domain.

We are developing a linear array of micromirrors designed for optical, femtosecond laser pulse shaping. It is a bulkmicromachined device, capable of retarding or diminishing certain laser frequencies in order to perform phase and amplitude modulation within a frequency band spanning the UV to the near-infrared. The design consists of a linear array of mirrors fixed on either side by springs. They feature two degrees of freedom: Out-of-plane motion for phase shifting and rotational motion for binary amplitude modulation, both realized using vertical comb drives. The first applications will include femtosecond discrimination experiments on biomolecules.

There are many potential applications for MEMS micromirror devices for femtosecond pulse shaping applications. Their broadband reflectivity gives them an advantage in comparison to devices such as liquid crystal- and acousto-optical modulators because of the possibility to directly shape UV pulses in the range 250 - 400 nm, and thus address UV-absorbing molecules. The identification and discrimination of biomolecules which exhibit almost the same spectra has sparked some interest in the last years as it allows real-time, environmental and optical monitoring. Here, we present the last developments using the Fraunhofer IPMS MEMS phase former capable of accomplishing such goals.

Filamentation, which arises in the propagation of ultrashort laser pulses when the defocusing on the generated plasma dynamically balances the Kerr self-focusing, is now well described on both the laboratory scale (millijoules to tens of millijoules, meters to tens of meters) and the atmospheric scale (hundreds of millijoules, hundreds of meters to kilometers). The scalability of this propagation regime to higher energies and powers is not a priori assured, as high-order nonlinear effects may prevent long distance propagation leading, for instance, to full beam collapse. We thus investigated the atmospheric propagation of the 26 J, 32 TW laser pulses delivered by the Alise beamline, which exceed respectively by one and two orders of magnitude the characteristic power and energy of ultrashort pulses studied so far. We show that filamentation still occurs at these extreme levels. More than 400 filaments simultaneously generate a supercontinuum propagating up to the stratosphere, beyond 20 km. This constitutes the highest power "white-light laser" to date. We also discuss the results of another experiment realized with the Teramobile laser facility: we demonstrated optimal control on the propagation of ultrashort 5 TW laser pulses in air over distances up to 36 m in a closed-loop scheme. We optimized three spectral ranges within the white-light continuum, as well as the ionization efficiency. Optimization results in signal enhancements by typical factors of 2 and 1.4 for the target parameters. In the case of white-light continuum generation, the feedback-driven procedure leads to shorter pulses by reducing their chirp, while, as far as air ionization is concerned, the optimization consists in correcting the pulse from its defects and setting the filamentation onset near the detector.

The initiation and propagation of a filament generated by ultrashort laser pulses in both fog and turbulent air is investigated experimentally. Filaments can propagate through dense fog, supported by the surrounding photon bath, which is transmitted and re-feeds the filament after he diffracts on a water droplet. Filaments can can also be generated and propagated even after the beam has propagated through strongly turbulent regions, with structure parameters C n 2 up to 5 orders of magnitude larger than encountered in usual atmospheric conditions. Moreover, the filament position within the beam is not affected by the interaction with a turbulent region. This remarkable stability is allowed by the strong Kerr refractive index gradients generated within the filament, which exceed the turbulence-induced refractive index gradients by 2 orders of magnitude.

We investigated femtosecond pump-repump depletion excitation in biological fluorescent molecules (tryptophan and flavins) in solutions and in organic fluorescent interferents such as polycyclic hydrocarbons (naphthalene, diesel fuel). If the repump pulse induces in both flavins and Trp a depletion of the excited state, populated by the pump pulse, which leads to a drastic decrease of the fluorescence, such mechanism is ineffective in organic fluorescent interferents. The repump induced depletion is still observed for bacteria containing solutions. This opens interesting perspectives to discriminate biological from non-biological fluorescent particles in air.

Due to potential of applications, self-trapping of a peak-power laser pulse in a so called filament became an intensively investigated phenomenon. In this paper we demonstrate experimentally advantages of using filaments for the remote laser induced plasma spectroscopy (LIBS). This novel approach can increase effective range of conventional LIBS system up to single kilometers. We also show that Fourier-limited pulse does not optimize LIBS signal, opening the perspective for the pulse shaping techniques in a break-down spectroscopy.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.

We present the first broadly tunable KNbO3 OPO in tracking-free configuration (TFC), pumped by a flashlamp- pumped Ti:Sapphire laser. Tuning the pump laser from 733 to 841 nm yielded to an OPO 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 400 nm. Threshold was as low as 15 MW/cm2 and efficiencies up to 10% have been observed without AR-coatings on the crystal.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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 .

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.

We present the first lidar/DIAL system based on a UV-vibronic laser. A self-developed Ce:LiSAF laser was pumped by a quadrupled Nd:YAG and provided high pulse energy (5 mJ at 10 Hz), very high slope efficiency (33%), and a tuning range from 284 nm to 299 nm. The first test results of this frequency-agile Ce:LiSAF based Lidar system are presented here in the form of simultaneous measurements of SO2 and O3 concentration profiles. Potentials of other Cerium-doped materials for Lidar applications are discussed.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Recent progress in Lidar/DIAL technology has allowed to obtain 3-dimensional mappings of the concentration of air pollutants at highest sensitivity (ppbrange) and over large distances (10 km)13. This access to atmospheric dynamics allows direct correlation between emission and immission. Presently, it is possible to monitor on-line distributions of nitrogen oxides, sulfur dioxide, and ozone. Recently, also the detection of toluene and benzene in the near UV has been demonstrated4. Routine or fully automatic operation has been severely restricted, however, by the complexity and maintenance of the usually employed Nd:YAG or Excimer-pumped dye lasers. The advent of new tunable all-solid-state laser systems, such as vibronic lasers (Ti:Sapphire, LICAF, LISAF,. ..) or laser-pumped OPOs, opens a new era in the domain of userfriendly and fully automatic DIAL operation. Here, we present the first Lidar/DIAL systems which are based on a high energy flashlamp-pumped Ti:Sapphire laser. It combines wide tunability of the laser medium with reliability and ease of operation, characteristic for flashlamppumped solid state lasers. The wavelength range accessible by the laser and its extension by nonlinear optical devices makes it an ideal tool for both DIAL and meteorologic applications. This 'all solid state" laser is the heart of a new generation of stationary and mobile Lidar systems. The first of these systems, presented here, has been designed to replace the urban station in Leipzig, which routinely provides mappings of pollutants over the city since 1992. The advantages of such routine and long term Lidar measurements are presented in this paper, in comparison with former results obtained during campaigns in several large european cities. A second urban unit is being implemented in Berlin, while a mobile and very compact "all solid state" DIAL system is in construction. It will start the test phase by the end of the year, and first measurement campaigns in february.

Calibration procedures for lidar and DIAL systems are discussed. Resulting requirements for the standardization of the technique are reviewed. Possible schemes for on-line calibration, based on a standard reference cell, are presented.

Progresses in remote sensing of the atmosphere using the Udar (Light detection and ranging) technique closely follows progresses in Laser technology. We developed a mobile DIAL (differential absorption Lidar) system, based on high repetition rate Excimerpumped dye lasers, for performing 2D and 3D-mappings of concentration of NO, N02, S02, and 03. The high sensitivity of the system has been used for numerous environmental studies and measurement campaigns, providing for the first time a direct correlation between emission and immission. Attractive results have been obtained under urban conditions, because of the presence of strong concentration gradients, and fast fluctuations due to traffic. A comparative study between Lyon, Stuttgart, Geneva and Berlin will be presented. In particular, the Berlin-campaign demonstrates the possibility of detecting unknown emitters and monitoring exportation-importation processes of atmospheric pollution. A new stationary DIAL system has been recently constructed and implemented on the top of a building in the center of the city Leipzig. It will routinely perform concentration mappings of nitrogen oxides, sulfur dioxide and ozone, giving access to long term evolution of pollution distributions.

Consideration is given to a novel inversion algorithm to determine the aerosol size distribution from lidar signals obtained at several wavelengths. This algorithm is based on a nonlinear fit of the backscattered measurements using a set of predetermined functions. Size distribution profiles of tropospheric aerosols in different meteorological conditions - clear, hazy, and cloudy atmosphere - are determined on the basis of lidar measurements made in central Switzerland, which is characterized by a specific microclimate. Measurements of stratospheric clouds and aerosols created by the Pinatubo eruption were measured above Berlin and Sodankyla, Finland. These measurements are used to characterize the size distribution of these volcanic aerosols in order to estimate their influence on radiative transfer.

A high energy flashlamp-pump Ti:sapphire laser has been developed. Pulse energies up to 1200 mJ have been obtained at a repetition rate of 10 Hz. Laser tuning (700 nm to 1050 nm) is achieved by a 4-plate Lyot-filter, with a bandwidth of 0.3 nm. Q-switching has also been performed to improve the temporal (spatial) resolution, with 300 mJ output in 20 nS. These unique specifications are extremely attractive for lidar applications. A flashlamp-pumped Ti:sapphire based lidar system has been used for several multispectral investigations such as measurements of volcanic aerosols and PSCs in the polar stratosphere during the EASOE campaign. Promising applicataion of Ti:sapphire lasers, like measurements of humidity in the troposphere and the stratosphere, are presented. UV-DIAL applications for pollution monitoring using frequency-doubling-tripling or mixing are also discussed.

An algorithm for restoring stratospheric backscatter coefficients from ground-based lidar measurement is proposed. Error sources of the algorithm are analyzed including the boundary condition, the molecular backscatter coefficients, and the influence of the aerosol light extinction.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.