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The impact of nonadiabatic laser-induced molecular alignment on filamentation is numerically studied. Weak and strong field model of impulsive molecular alignment are compared in the context of nonlinear pulse propagation. It is shown that the widely used weak field model describing the refractive index modification induced by impulsive molecular alignment accurately reproduces the propagation dynamics providing that only a single pulse is involved during the experiment. On the contrary, it fails at reproducing the nonlinear propagation experienced by an intense laser pulse traveling in the wake of a second strong laser pulse. The discrepancy depends on the relative delay between the two pulses and is maximal for delays corresponding to half the rotational period of the molecule.

We present a numerical parametric study of single-cycle electromagnetic pulse generation in a DAST/SiO₂multilayer structure via collinear optical rectification of 800 nm femtosecond laser pulses. It is shown that modifications of the thicknesses of the DAST and SiO₂layers allow tuning of the average frequency of the generated THz pulses in the frequency range from 3 to 6 THz. The laser-to-THz energy conversion efficiency in the proposed structures is compared with that in a bulk DAST crystal and a quasi-phase-matching periodically poled DAST crystal and shows significant enhancement.

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.

Second Harmonic Generation (SHG) from BiFeO3 nanocrystals is investigated for the first time to determine their potential as biomarkers for multiphoton imaging. Nanocrystals are produced by an auto-combustion method with 2-amino-2-hydroxymethyl-propane-1,3-diol as a fuel. Stable colloidal suspensions with mean particle diameters in the range 100–120 nm are then obtained after wet-milling and sonication steps. SHG properties are determined using two complementary experimental techniques, Hyper Rayleigh Scattering and nonlinear polarization microscopy. BiFeO3 shows a very high second harmonic efficiency with an averaged hdi coefficient of 79612 pm/V. From the nonlinear polarization response of individual nanocrystals, relative values of the independent dij coefficients are also determined and compared with recent theoretical and experimental studies. Additionally, the particles show a moderate magnetic response, which is attributed to gamma-Fe2O3 impurities. A combination of high nonlinear optical efficiency and magnetic response within the same particle is of great interest for future bio-imaging and diagnostic applications.

Rotation profiles along the C(O)–P(O) bond of model system 1 were calculated for the S0 ,S 1 and T1 state on the B3LYP/6-31G∗ and RCIS/6-31+G∗ level of theory. Moreover, the cleavage of the bond was followed in the T1 state. The computations reveal that the efficiency of the cleavage reaction may depend on the different rotation barriers of the molecule in the electronic states attained during the photochemical pathway. It can be anticipated that specific solvation which may influence the conformational mobility and the lifetimes in the S1 and T1 states is likely to play a important role for solvent effects. © 2001 Published by Elsevier Science B.V.

An unexpected blue-fluorescence band (around 420 nm) from both micrometer-sized dried particles and aqueous droplets of riboflavin [7,8-dimethyl-10-(D-1′-ribityl)-isoalloxazine] is observed when the microparticles are irradiated with a pulsed UV (355- or 351-nm) laser. The intensity of the band increases quadratically with input laser energy density (fluence) and is attributable to a one-photon-excited fluorescence of lumichrome (7,8-dimethyl-alloxazine) that is produced by photo-degradation of riboflavin. The well-known greenish-yellow fluorescence band (at 560 nm for dried particles and 535 nm for aqueous droplets) from riboflavin increases sublinearly with UV-laser fluence. With a laser input fluence above 5 J/cm2 the riboflavin fluorescence decays earlier and the lumichrome fluorescence reaches a maximum later than the peak of the input laser pulse. The temporal dynamics of the 420- and 535-nm fluorescence peaks are consistent with a rate-equation simulation of photon-induced conversion of riboflavin to lumichrome and the subsequent fluorescence of lumichrome.

We have observed the second harmonic generation from a single crystal LiNbO3 fiber with a diameter of 63 μm. Femtosecond laser pulses form a modelocked oscillator was focused perpendicularly onto the fiber. Scattered second harmonic was analyzed in polarization and the conversion efficiency was estimated. Comparing to a bulk nonlinear crystal, the striking feature of the SHG from the microcylinder is that the nonlinear conversion takes place out off phase-matching condition. For the fundamental at 850 nm the phase-mismatching is negative, even so, a relative important conversion efficiency of 3.7 × 10 -4 was obtained for incident 1.1-nJ and 150-fs pulses (peak intensity of 1.0 x 10 9 W/cm 2 ) This conversion efficiency, independent to the phase matching, should not exhibit the sharp variation as for a bulk crystal when the incident fundamental is tuned across the phase-matched wavelength. The fiber provides then a wide bandwidth doubler. We applied this microdoubler in a second order autocorrelator.

Nous avons utilise des cristaux de KTP et de KNbO 3 comme oscillateurs parametriques optique (OPO) pompes par un laser Titane:Saphir accordable. Pour l'OPO base sur un KTP «monolithique» en configuration d'accord de phase non critique de type II (θ=90° et Φ=0°), on obtient un seuil de 0,2 MW/cm 2 et une efficacite de conversion totale de 37%. L'OPO base sur le KNbO3 permet d'obtenir un signal et une complementaire variant de 0,95 a 3,8 μm lorsque l'on balaie la pompe entre 740 et 860 nm. Implemente dans notre systeme Lidar, ce cristal nous a permis de mesurer a 3,5 μm la taille et la concentration des gouttelettes d'eau lors d'un episode de brouillard, sur une distance de 1500 m. Le rayon moyen des gouttelettes d'eau est de 8,7 μm et la concentration est de 10 mg/m 3 .

La detection optique a distance de type Lidar (Light Detection and Ranging) pourrait etre appliquee pertinemment pour diagnostiquer la presence dans l'atmosphere d'agents biologiques. R. Chang et al [1] ont recemment demontre qu'il est possible de detecter des bacteries par fluorescence induite par laser (LIF). Toutefois, en milieu reel, il faut eviter toute interference avec d'autres sources d'emission: les hydrocarbures et leurs residus de combustion. Nous presentons ici les spectres LIF comparatifs de plusieurs aerosols candidats a la detection.

Indexes of heart rate variability (HRV) and the slope of cardiac baroreflex are extensively used for non invasive assessment of circulatory autonomic control in pathophysiology. We performed this study (1) to assess the sensitivity of these indexes towards small graded postural stimulations and (2) to delineate the informations provided about the settings of both vascular tone and cardiac activity. Twenty healthy subjects were randomly tilted for eight minutes at each of the six angles: -10 degrees, 0 degrees (supine), 10 degrees, 30 degrees, 45 degrees, and 60 degrees. Instant RR-interval and finger blood pressure (BP) were continuously recorded, and venous blood was collected at the end of each 8 min position for catecholamines determination. Group average heart rate, noradrenaline and diastolic BP (DBP) increased linearly with head-up tilt angle from 10 degrees. Systolic BP (SBB) ranked only two distinct series -10 degrees, 0 degrees, 10 degrees versus 30 degrees, 45 degrees, 60 degrees, as did the number of spontaneous baroreflex (SBR) sequences. The spectral power of the low-frequency (LF) and high-frequency (HF) of RR variability and the ratio LF/HF changed rather abruptly from either 30 degrees or 45 degrees, depending on each individual. Both HF/tot i.e. the ratio of HF to total spectral RR variability and the slope of SBR decreased markedly from 10 degrees to 30 degrees and less but more gradually from 30 degrees to 60 degrees. Thus, our observations argue for gradual adjustments of vascular tone as reflected by highly consistent changes in plasma noradrenaline and diastolic arterial pressure, contrasting with a main discontinuous autonomic setting of cardiac activity as reflected by changes in the harmonic components of spectral RR variability and in the slope of cardiac baroreflex. The pattern of changes in systolic arterial pressure attested the discontinuous cardiac autonomic control rather than the gradual setting of arterial tone. We submit that these different patterns of autonomic adjustments should be considered when assessing pathophysiological states.

Analysis of the ESR line width in time-resolved (TR-ESR) experiments is shown to be a suitable tool for the measurement of addition constants of phosphinoyl and substituted benzoyl radicals. Compar...

Lidar data, collected from stations located in both the Northern and Southern hemispheres using 532nm wavelength, were employed for monitoring the evolution of stratospheric aerosol loading from January 1994 up to December 1997. Lidar data covering the pre-Pinatubo situation are available also for the 1989–1993 period only for the Antarctica station. These data are reported for comparison with the present situation. The analysis provided stratospheric aerosol loading measurements which show the return to a clean stratosphere as observed before the eruption of Mt. Pinatubo. During 1997, integrated backscattering values ranging between 8.2±3 10−5 sr−1 for Lauder and Florence/ Brasimone and 6.0±1.5 10−5 sr−1 for the polar stations of Sodankyla and Dumont d'Urville were measured. These values are smaller then the ones registered before the Pinatubo eruption: for example, at Dumont d'Urville in 1989 an integrated backscattering of 0.75± 0.12 10−4 sr−1 was measured. An evaluation of the decay time, i.e. the half time, for aerosols allowed a rough estimate of aerosol particle size. A comparison between the decay time for integrated backscattering in the 13 to 25-km region obtained for the four sites did not show any strong variability between the northern and southern hemispheres: only small differences are observed between the Arctic and Antarctic regions. A time constant of about 3 years and half was retrieved for the 1994–1997 period.

Polar stratospheric clouds (PSC) were observed with the multi-wavelength lidar of the MOANA project (Modelling and Observations of Aerosols in the Northern Atmosphere) during SESAME (Second European Stratospheric Arctic and Mid-latitude Experiment). The physical state, liquid or solid, of the cloud particles can be inferred from the lidar data. Using isentropic back-trajectories to obtain the thermal history of the sampled air masses, it is possible to reconcile most of the observations with current ideas on PSC formation and evolution. When the cloud particles were identified as liquid, changes in the size distribution of the droplets along the trajectory were calculated using a micro-physical box model. Backscatter ratios calculated from the size distributions are in broad agreement with the lidar data, giving confidence in current understanding of the evolution of ternary solution (H2SO4, HNO3 and H2O) droplets. Results from two soundings are shown which bear on the problem of the formation of solid particles. In the first, solid particles were detected. The air mass had cooled to the frost point 12 hours earlier. In the second no solid particles were detected although the air temperature was below the nitric acid trihydrate existence point, and had decreased by 12K in the previous 14 hours.

We present the results of an extensive study on urban aerosols performed in the summer of 1996 in Lyon. Non-volatile urban particles have been sampled using filters. Size distribution and composition, determined by scanning electronic microscopy (SEM) and X-Ray microanalysis, reveal two main modes at 0.1 and 0.9 μm, the composition of which is soot for the first and 60% in number soot — 40% silica for the second. Mie calculations have been performed using the actual size distribution and composition to determine the optical backscattering and extinction coefficients. The optical characteristics were then used for Lidar measurements. The combined SEM and Lidar techniques allowed to obtain the first quantitative 3D-profiles of urban aerosols concentrations. Potential and limitations of the method are critically discussed.

We present simulations of transient stimulated Raman scattering processes (SRS) for aerosol distributions with particles larger than the spatial extent of the ultrashort pump laser pulse. It is shown that this can constitute a new analysis method for transparent spherical aerosol particles, yielding simultaneously size and composition. For the first time, nonlinear treatment of the lidar equation is derived in the general case as well. Our calculations show that application of transient SRS lidar could yield simultaneous remote size and composition measurements of cloud or haze droplets without a priori hypothesis about the microdroplets.

Very efficient and stable laser operation of Ce 3+ -doped LiLuF 4 (Ce:LLF) single crystals longitudinally pumped with a Ce:LiSAF pulsed laser is demonstrated for the first time. At the peak operating wavelength of 308 nm, laser thresholds as low as 250 mJ cm −2 and laser slope efficiencies and output energies as high as 55% and 2 mJ, respectively, have been obtained at a pulse repetition rate of 20 Hz.

In this visualized experiment, protocol details are provided for in vitro labeling of human embryonic stem cells (hESC) with second harmonic generation nanoparticles (HNPs). The latter are a new family of probes recently introduced for labeling biological samples for multi-photon imaging. HNPs are capable of doubling the frequency of excitation light by the nonlinear optical process of second harmonic generation with no restriction on the excitation wavelength. Multi-photon based methodologies for hESC differentiation into cardiac clusters (maintained as long term air-liquid cultures) are presented in detail. In particular, evidence on how to maximize the intense second harmonic (SH) emission of isolated HNPs during 3D monitoring of beating cardiac tissue in 3D is shown. The analysis of the resulting images to retrieve 3D displacement patterns is also detailed.

Using terahertz and transient absorption spectroscopy, carrier dynamics in organo halide perovskite solar cell is probed. Charge generation is

We investigate the reversibility of laser filamentation, a self-sustained, non-linear propagation regime including dissipation and time-retarded effects. We show that even losses related to ionization marginally affect the possibility of reverse propagating ultrashort pulses back to the initial conditions, although they make it prone to finite-distance blow-up susceptible to prevent backward propagation., Comment: 12 pages, 3 figures

A novel bio-photonics approach based on the nonlinear optical process of second harmonic generation by non-centrosymmetric nanoparticles is presented and demonstrated on malignant human cell lines. The proposed method allows to directly interact with DNA in absence of photosensitizing molecules, to enable independent imaging and therapeutic modalities switching between the two modes of operation by simply tuning the excitation laser wavelength, and to avoid any risk of spontaneous activation by any natural or artificial light source.

We demonstrate the cooperative effect of near infrared (NIR) and ultraviolet (UV) beams on laser-induced condensation. Launching a UV laser after a NIR pulse yields up to a 5-fold increase in the production of nanoparticles (25–300 nm) as compared to a single NIR beam. This cooperative effect exceeds the sum of those from the individual beams and occurs for delays up to 1 μs. We attribute it to the UV photolysis of ozone created by the NIR pulses. The resulting OH radicals oxidize NO2 and volatile organic compounds, producing condensable species.

The mammalian circadian timing system consists of a master pacemaker in the suprachiasmatic nucleus (SCN) in the hypothalamus, which is thought to set the phase of slave oscillators in virtually all body cells. However, due to the lack of appropriate in vivo recording technologies, it has been difficult to study how the SCN synchronizes oscillators in peripheral tissues. Here we describe the real-time recording of bioluminescence emitted by hepatocytes expressing circadian luciferase reporter genes in freely moving mice. The technology employs a device dubbed RT-Biolumicorder, which consists of a cylindrical cage with reflecting conical walls that channel photons toward a photomultiplier tube. The monitoring of circadian liver gene expression revealed that hepatocyte oscillators of SCN-lesioned mice synchronized more rapidly to feeding cycles than hepatocyte clocks of intact mice. Hence, the SCN uses signaling pathways that counteract those of feeding rhythms when their phase is in conflict with its own phase.

Potential impacts of lightning-induced plasma on cloud ice formation and precipitation have been a subject of debate for decades. Here, we report on the interaction of laser-generated plasma channels with water and ice clouds observed in a large cloud simulation chamber. Under the conditions of a typical storm cloud, in which ice and supercooled water coexist, no direct influence of the plasma channels on ice formation or precipitation processes could be detected. Under conditions typical for thin cirrus ice clouds, however, the plasma channels induced a surprisingly strong effect of ice multiplication. Within a few minutes, the laser action led to a strong enhancement of the total ice particle number density in the chamber by up to a factor of 100, even though only a 10 −9 fraction of the chamber volume was exposed to the plasma channels. The newly formed ice particles quickly reduced the water vapor pressure to ice saturation, thereby increasing the cloud optical thickness by up to three orders of magnitude. A model relying on the complete vaporization of ice particles in the laser filament and the condensation of the resulting water vapor on plasma ions reproduces our experimental findings. This surprising effect might open new perspectives for remote sensing of water vapor and ice in the upper troposphere.

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.

The consideration of the higher-order Kerr effect (HOKE) drastically improves the quantitative agreement between measured and simulated harmonic yield as well as intensity and electron density in laser filaments generated by pulses below a few hundreds of fs. In longer pulses, the plasma defocusing plays a much more important role.

Optimal Dynamic Discrimination based on the phase-shaping of deep ultraviolet femtosecond pulses was applied to selectively modulate the time-resolved fluorescence depletion of pairs of tryptophan-containing dipeptides. Our results indicate that phase-sensitive excitation allows their differential identification, beyond the limits of linear and time-resolved spectroscopy.

Narrow bandwidth operation within 250 MHz of a flashlamp-pumped Ti:Al 2 O 3 laser is successfully demonstrated with injection seeding from a CW laser diode. Seeding is shown sensitive even to very small injected power. Typically, 70% energy of a 100 mJ and 50 ns pulse is locked into the narrow bandwidth. This seeding efficiency is essentially limited in our experiments by the spatial hole burning in a laser rod with linearly polarized laser beam. It is also limited by mode mismatching between slave laser and seeding laser due to thermal effect on the laser rod induced by short and intense pumping flash.

We demonstrate laser control of high-voltage discharges over a gap of 1.2 m filled with a dense water cloud. Self-guided filaments generated by ultrashort laser pulses are transmitted through the cloud and ionize a continuous plasma channel. The cloud typically reduces the discharge probability in given experimental conditions by 30%, but has almost no influence on the threshold required to trigger single discharge events, both in electrical field and laser energy. This result is favorable for real-scale lightning control applications.

We observed the filamentation of mid-infrared ultrashort laser pulses (3.9 μm, 80 fs) in molecular gases. It efficiently generates a broadband supercontinuum over two octaves in the 2.5–6 μm spectral range, with a red-shift up to 500 nm due to the Raman effect, which dominates over the blue shift induced by self-steepening and the gas ionization. As a result, the conversion efficiency into the Stokes region (4.3–6 μm) 65% is demonstrated.

We present a novel optical aerosol particle detector based on Xe flash lamp excitation and spectrally resolved fluorescence acquisition. We demonstrate its performances on three natural pollens acquiring in real-time scattering intensity at two wavelengths, sub-microsecond time-resolved scattering traces of the particles’ passage in the focus, and UV-excited fluorescence spectra. We show that the device gives access to a rather specific detection of the bioaerosol particles.

Ultra-intense lasers generate filaments that can be used not only for the analysis of the atmosphere (multi-pollutant Lidar) but also for its control, e.g. laser induced lightning triggering and water cloud condensation. 150-word Biography: After having lead research projects at the ETH-Lausanne and the University Berlin and being a Professor at the University Lyon and visiting Professor at Yale University, Prof. J.P. Wolf joined the University of Geneva in 2005. Since then he set up a new team at the Group of Applied Physics (GAP), dedicated to the biomedical and atmospheric applications of ultrashort lasers (www.gap.unige.ch/biophotonics). He now concentrates his research activities on coherent control of biological systems, advanced non-linear microscopy and imaging of living cells and applications of laser filamentation to atmospheric diagnostics and control. He was awarded an ERC Advanced Grant in 2011, the Prix La Recherche 2005, the Grand Prix de Physique de l’Academie des Sciences 2002, and the Technology Award of the Land Berlin-Brandenburg in 1993. He is member of the Institut Universitaire de France since 1996 and NATO Senior Fellow. Article not available.

We experimentally demonstrate that the transmission of a 1030~nm, 1.3~ps laser beam of 100 mJ energy through fog increases when its repetition rate increases to the kHz range. Due to the efficient energy deposition by the laser filaments in the air, a shockwave ejects the fog droplets from a substantial volume of the beam, at a moderate energy cost. This process opens prospects for applications requiring the transmission of laser beams through fogs and clouds., 11 pages, 5 figures

We present the first lidar/DIAL system based on an Ultra Violet (UV) vibronic laser. A Nd:YAG-pumped Ce:LiSAF laser has been developed for this purpose, providing high pulse energy (5 mJ at 10 Hz), very high slope efficiency (33%), and a tuning range from 284 to 299 nm. Simultaneous measurements of SO2 and O3 concentration profiles are presented using this frequency-agile Ce:LiSAF-based lidar system.

We show that spectral phase shaping of fs-laser pulses can be used to optimize laser-cell membrane interactions in water environment. The energy and peak intensity thresholds required for cell poration with single pulse in the nJ range can be significantly reduced (25% reduction in energy and 88% reduction in peak intensity) by using temporal Airy pulses, controlled by positive third order dispersion, as compared to bandwidth limited pulses. Temporal Airy pulses are also effective to control the morphology of the induced pores, with prospective applications from cellular to tissue opto-surgery and transfection.

We have measured the single and double photoionization efficiency of Hgn mass selected clusters as a function of photon energy between 30 and 110 eV for masses ranging from n=1 to 36 for the singly ionized and from n=5 to 70 for the doubly ionized clusters, using the light beam issued from a wiggler at the BESSY synchrotron. The results show in all cases a spectrum similar to the 5d→ef shape resonance previously observed in the isolated atom. In contrast, the expected 5p→6p transition allowed by hybridization of the 6s and 6p orbitals is not observed. We also compared the mass spectra of singly and doubly charged mercury clusters ionized by electron impact (30–90 eV) to those of clusters ionized by synchrotron radiation (30–70 eV). We found that the ratio Hg2+n/Hg+n was higher for photoionization at low energy and for electron impact ionization at high energy. Finally, we estimated the critical stability size of the triply charged clusters.

We demonstrate that ultrashort and ultraintense light filaments survive their interaction with water droplets as large as 95 μm and that they are transmitted through water clouds having an optical thickness as high as 3.2 (transmission 5%). In contrast with linear optics, this remarkable transmission through optically dense media results from a dynamic energy balance between the quasisolitonic structure and the surrounding laser photon bath, which acts as an energy reservoir. Implications for free-space laser communications, remote sensing, and telemetry are discussed.

Optics Express, 20 (23), ISSN:1094-4087

Label-free selective discrimination of spectrally similar biomolecules, such as peptides and proteins using Optimal Control strategies is a challenge in a variety of practical applications such as label-free fluorescence imaging and protein identification. The principle of Optimal Control is based on the fact that a suitably shaped laser field can differently drive the dynamics of almost identical quantum systems [1, 2].

In the quest for the next generation of imaging bio-markers, successful probes have to prove to be non toxic, bright, stable against long term excitation, and able to generate a sharp contrast against background fluorescence. In all these respects, Harmonic Nanoparticles (HNPs, “nanodoublers”) are receiving an increasing attention as they also open a series of alternative detection possibilities simply not accessible with the present generation of fluorescent dyes and quantum dots. In the first part of the chapter, we report on this novel labelling method with unprecedented wavelength flexibility, enabled by the non-resonant nature of the second harmonic process. The possibility of employing infrared excitation and the consequent deeper tissue penetration is especially promising for their in vivo applications [1]. The phase-coherent optical response of HNPs can also be exploited to fully characterize the excitation laser pulse in the focal spot of a high-NA objective with nanometric resolution. This proof-of-principle “nano-FROG” experiment [2] sets the ground for further phase-sensitive self-referenced applications, after the recent demonstration of harmonic holography and heterodyne detection with external references.

We propose a new technique for efficient generation of 6 THz near-single-cycle transients though optical rectification of 800 nm fs laser pulses in a DAST/SiO 2 multilayer structure. The use of such a composite material allows to obtain phase-matching and control cascaded nonlinear processes.

The exact quantum time-dependent optical response of hydrogen under strong field near infrared excitation is investigated and compared to the perturbative model widely used for describing the effective atomic polarization induced by intense laser fields. By solving the full 3D time-dependent Schr\"{o}dinger equation, we exhibit a supplementary, quasi-instantaneous defocusing contribution missing in the weak-field model of polarization. We show that this effect is far from being negligible in particular when closures of ionization channels occur and stems from the interaction of electrons with their parent ions. It provides an interpretation to higher-order Kerr effect recently observed in various gases., Comment: 5 pages, 4 figures

We present a novel concept for optical spectroscopy called nonlinear correlation spectroscopy (NLCS). NLCS analyses coherent field fluctuations of the second and third harmonic light generated by diffusing nanoparticles. Particles based on noncentrosymmetric nonlinear materials such as KNbO(3) show a strong second as well as third harmonic response. The method and the theory are introduced and experimental NLCS results in fetal calf serum are presented showing the promising selectivity of this technique for measurement in complex biological environments.

International audience; Potassium niobate nonlinear nanoparticles are used for the fi rst time to monitor the evolution of embryonic stem cells (ESC) by second harmonic microscopy. These particles feature the complete absence of photo-bleaching and unlimited excitation wavelength fl exibility. The potential of this approach is made evident for tissueregeneration studies and applications, by capturing a high-speed movie of ESCderived cardiomyocytes autonomously beating within a cluster. Time-resolved data are analyzed to retrieve 3D information of the contraction pattern at the cellular level.

We report the first (to our knowledge) experimental results and numerical simulations on mid-IR femtosecond pulse filamentation in argon using 0.1 TW peak-power, 80 fs, 3.9 μm pulses. A broadband supercontinuum spanning the spectral range from 350 nm to 5 μm is generated, whereby about 4% of the mid-IR pulse energy is converted into the 350-1700 nm spectral region. These mid-IR-visible coherent continua offer a new, unique tool for time-resolved spectroscopy based on a mid-IR filamentation laser source.

International audience; Nonlinear optical nanocrystals have been recently introduced as a promising alternative to fluorescent probes for multiphoton microscopy. We present for the first time a complete survey of the properties of five nanomaterials (KNbO3, LiNbO3, BaTiO3, KTP, and ZnO), describing their preparation and stabilization and providing quantitative estimations of their nonlinear optical response. In the light of their prospective use as biological and clinical markers, we assess their biocompatibility on human healthy and cancerous cell lines. Finally, we demonstrate the great potential for cell imaging of these inherently nonlinear probes in terms of optical contrast, wavelength flexibility, and signal photostability.

We propose a DAST/SiO(2) multilayer structure for efficient generation of near-single-cycle THz transients with average frequency around 6 THz via collinear optical rectification of 800 nm femtosecond laser pulses. The use of such a composite material allows compensation for the phase mismatch that accompanies THz generation in bulk DAST crystals. The presented calculations indicate a strong increase in the THz generation efficiency in the DAST/SiO(2) structure in comparison to the case of bulk DAST crystal.

We review the recent results about laser-induced condensation based on self-guided filaments generated by ultrashort laser pulses. After recalling the physico-chemistry of cloud particle formation in the atmosphere and the physics of laser filamentation, we discuss experimental results on laser-induced condensation and its relevance for modulating precipitation.

The effects that could give rise to an isotopic shift in the spectrum of a triatomic Jahn—Teller distorted molecule are discussed. Comparison between calculations and experimental observations in the A–X band systems of 21Li3, 20Li3 and 19Li3 confirms the dominant influence of variations in the kinetic energy whereas any change in the electronic motion can be neglected. The isotopic shift mass dependence is drastically different for pseudo-rotational or vibronic series and allows an efficient probing of Jahn—Teller potential surfaces.