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Accurate dynamic three-dimensional (4D) imaging of the heart of small rodents is required for the preclinical study of cardiac biomechanics and their modification under pathological conditions, but technological challenges are met in laboratory practice due to the very small size and high pulse rate of the heart of mice and rats as compared to humans. In 4D X-ray microtomography (4D μCT), the achievable spatio-temporal resolution is hampered by limitations in conventional X-ray sources and detectors. Here, we propose a proof-of-principle 4D μCT platform, exploiting the unique spatial and temporal features of novel concept, all-optical X-ray sources based on Thomson scattering (TS). The main spatial and spectral properties of the photon source are investigated using a TS simulation code. The entire data acquisition workflow has been also simulated, using a novel 4D numerical phantom of a mouse chest with realistic intra- and inter-cycle motion. The image quality of a typical single 3D time frame has been studied using Monte Carlo simulations, taking into account the effects of the typical structure of the TS X-ray beam. Finally, we discuss the perspectives and shortcomings of the proposed platform.

We introduce a method for detection of chiral molecules using sequences of three pulses driving a closed-loop three-state quantum system. The left- and right-handed enantiomers have identical optical properties (transition frequencies and transition dipole moments) with the only difference being the sign of one of the couplings. We identify twelve different sequences of resonant pulses for which chiral resolution with perfect contrast occurs. In all of them the first and third pulses are $\pi/2$-pulses and the middle pulse is a $\pi$-pulse. In addition, one of the three pulses must have a phase shift of $\pi/2$ with respect to the other two. The simplicity of the proposed chiral resolution technique allows for straightforward extensions to more efficient and more robust implementations by replacing the single $\pi/2$ and $\pi$-pulses by composite pulses. We present specific examples of chiral resolution by composite pulses which compensate errors in the pulse areas and the detuning of the driving fields., Comment: 7 pages, 5 figures

The partial reflection of an electromagnetic (EM) wave from a medium leads to absorption of momentum in the direction perpendicular to the surface (the standard radiation pressure) {and, for oblique incidence on a partially reflecting medium}, also in the parallel direction. This latter component drives a transverse current and a slowly growing, quasi-static magnetic field in the evanescence ``skin'' layer. Through a simple model we illustrate how EM momentum is transfered to ions and estimate the value of the magnetic field which may be of the order of the driving EM wave field, i.e. up to several hundreds of megagauss for high intensity laser-solid interactions., Comment: 7 pages, 2 figures

We demonstrate the use of a femtosecond frequency comb to coherently drive stimulated Raman transitions between terahertz-spaced atomic energy levels. More specifically, we address the $3d~^2D_{3/2}$ and $3d~^2D_{5/2}$ fine structure levels of a single trapped $^{40}$Ca$^+$ ion and spectroscopically resolve the transition frequency to be $\nu_D = 1{,}819{,}599{,}021{,}534 \pm 8$ Hz. The achieved accuracy is nearly a factor of five better than the previous best Raman spectroscopy, and is currently limited by the stability of our atomic clock reference. Furthermore, the population dynamics of frequency-comb-driven Raman transitions can be fully predicted from the spectral properties of the frequency comb, and Rabi oscillations with a contrast of 99.3(6)\% and millisecond coherence time has been achieved. Importantly, the technique can be easily generalized to transitions in the sub-kHz to tens of THz range and should be applicable for driving, e.g., spin-resolved rovibrational transitions in molecules and hyperfine transitions in highly charged ions., Comment: 9 pages, 8 figures

Optics Express, 26 (9), ISSN:1094-4087

We apply attosecond transient absorption spectroscopy (ATAS) to explore the effects of a nonzero permanent dipole on electron dynamics at the subfemtosecond scale, exemplified in the polar LiF molecule. In contrast with nonpolar systems, a familiar feature of the ATA spectra--the light-induced structures--are observed adjacent to a bright state. Moreover, a previously unobserved ladder structure is identified. The new observations are analyzed in the context of a model based on fixed-nuclei adiabatic states, supported by full numerical simulations. Analytic calculations originating in the adiabatic model shed light on the nature and origins of the new findings., Comment: 13 pages, 6 figures

7 pags., 4 figs. -- Open Access funded by Creative Commons Atribution Licence 4.0, The combination of single particle detection and ultrafast laser pulses is an instrumental method to track dynamics at the femtosecond time scale in single molecules, quantum dots and plasmonic nanoparticles. Optimal control of the extremely short-lived coherences of these individual systems has so far remained elusive, yet its successful implementation would enable arbitrary external manipulation of otherwise inaccessible nanoscale dynamics. In ensemble measurements, such control is often achieved by resorting to a closed-loop optimization strategy, where the spectral phase of a broadband laser field is iteratively optimized. This scheme needs long measurement times and strong signals to converge to the optimal solution. This requirement is in conflict with the nature of single emitters whose signals are weak and unstable. Here we demonstrate an effective closed-loop optimization strategy capable of addressing single quantum dots at room temperature, using as feedback observable the two-photon photoluminescence induced by a phase-controlled broadband femtosecond laser. Crucial to the optimization loop is the use of a deterministic and robust-against-noise search algorithm converging to the theoretically predicted solution in a reduced amount of steps, even when operating at the few-photon level. Full optimization of the single dot luminescence is obtained within ∼100 trials, with a typical integration time of 100 ms per trial. These times are faster than the typical photobleaching times in single molecules at room temperature. Our results show the suitability of the novel approach to perform closed-loop optimizations on single molecules, thus extending the available experimental toolbox to the active control of nanoscale coherences., This research was funded by the European Commission (ERC Adv. Grant 247330-NanoAntennas and ERC Adv. Grant 670949-LightNet), Spanish Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0522), Plan Nacional Project FIS2012-35527, co-funded by FEDER, the Catalan AGAUR (2014 SGR01540) and Fundació CELLEX (Barcelona). PMdR acknowledges financial support from Spanish Government MINECO-FPI grant and European Science Foundation under the PLASMON-BIONANOSENSE Exchange Grant program. MGS acknowledges financial support from grants MICINN TEC2011-22422 and MINECO TEC2014-52642-C2-1-R.

This document was prepared as part of the briefing material for the Workshop of the CERN Council Strategy Group, held in DESY Zeuthen from 2nd to 6th May 2006. It gives an overview of the physics issues and of the technological challenges that will shape the future of the field, and incorporates material presented and discussed during the Symposium on the European Strategy for Particle Physics, held in Orsay from 30th January to 2nd February 2006, reflecting the various opinions of the European community as recorded in written submissions to the Strategy Group and in the discussions at the Symposium., Comment: 199 pages, PDF file

International audience; We report for the first time on the anticorrelated emission of high-order harmonics and energetic electron beams from a solid-density plasma with a sharp vacuum interface-plasma mirror-driven by an intense ultrashort laser pulse. We highlight the key role played by the nanoscale structure of the plasma surface during the interaction by measuring the spatial and spectral properties of harmonics and electron beams emitted by a plasma mirror. We show that the nanoscale behavior of the plasma mirror can be controlled by tuning the scale length of the electron density gradient, which is measured in situ using spatial-domain interferometry.

Pre-selected patterns on an n-type Si surface are fabricated by electrochemical etching in the presence of a weak optical signal. The constructive role of noise, namely, stochastic resonance (SR), is exploited for these purposes. SR is a nonlinear phenomenon wherein at an optimal amplitude of noise, the information transfer from weak input sub-threshold signals to the system output is maximal. In the present work, the amplitude of internal noise was systematically regulated by varying the molar concentration of hydrofluoric acid (HF) in the electrolyte. Pattern formation on the substrate for two different amplitudes (25 ± 2 and 11 ± 1 mW) of the optical template (sub-threshold signal) was considered. To quantify the fidelity/quality of pattern formation, the spatial cross-correlation coefficient (CCC) between the constructed pattern and the template of the applied signal was calculated. The maximum CCC is obtained for the pattern formed at an optimal HF concentration, indicating SR. Simulations, albeit using external noise, on a spatial array of coupled FitzHugh-Nagumo oscillators revealed similar results.Pre-selected patterns on an n-type Si surface are fabricated by electrochemical etching in the presence of a weak optical signal. The constructive role of noise, namely, stochastic resonance (SR), is exploited for these purposes. SR is a nonlinear phenomenon wherein at an optimal amplitude of noise, the information transfer from weak input sub-threshold signals to the system output is maximal. In the present work, the amplitude of internal noise was systematically regulated by varying the molar concentration of hydrofluoric acid (HF) in the electrolyte. Pattern formation on the substrate for two different amplitudes (25 ± 2 and 11 ± 1 mW) of the optical template (sub-threshold signal) was considered. To quantify the fidelity/quality of pattern formation, the spatial cross-correlation coefficient (CCC) between the constructed pattern and the template of the applied signal was calculated. The maximum CCC is obtained for the pattern formed at an optimal HF concentration, indicating SR. Simulations, albeit us...

Using ab initio non-Born-Oppenheimer simulations, we demonstrate the amplification of XUV radiation in a high-harmonic-generation-type process using the example of the hydrogen molecular ion. A small fraction of the molecules is pumped to a dissociative excited state from which IR-assisted XUV amplification is observed. We show that starting at sufficiently high IR driving field intensities, the ground-state molecules become quasitransparent for XUV radiation, while due to stabilization, gain from excited states is maintained. While the basic physics should also be observable in atomic media, the main advantage of the investigated molecular laser is, first, efficient lasing from field-free excited states with a high mean angular momentum and, second, the possibility to tune the amplified XUV frequency windows via control of the internuclear distance.

The existence of localized electromagnetic structures is discussed in the framework of the 1-dimensional relativistic Maxwell-fluid model for a cold plasma with immobile ions. New partially localized solutions are found with a finite-difference algorithm designed to locate numerically exact solutions of the Maxwell-fluid system. These solutions are called quasi-solitons and consist of a localized electromagnetic wave trapped in a spatially extended electron plasma wave. They are organized in families characterized by the number of nodes $p$ of the vector potential and exist in a continuous range of parameters in the $\omega-V$ plane, where $V$ is the velocity of propagation and $\omega$ is the vector potential angular frequency. A parametric study shows that the familiar fully localized relativistic solitons are special members of the families of partially localized quasi-solitons. Soliton solution branches with $p>1$ are therefore parametrically embedded in the continuum of quasi-solitons. On the other hand, geometric arguments and numerical simulations indicate that $p=0$ solitons exist only in the limit of either small amplitude or vanishing velocity. Direct numerical simulations of the Maxwell-fluid model indicate that the $p>0$ quasi-solitons (and embedded solitons) are unstable and lead to wake excitation, while $p=0$ quasi-solitons appear stable. This helps explain the ubiquitous observation of structures that resemble $p=0$ solitons in numerical simulations of laser-plasma interaction., Comment: 11 pages, 12 figures, corrected a reference

We investigate the nonlinear transmission of a ~280-layer turbostratic graphene sheet for near-infrared amplifier laser pulses (775 nm, Ti:sapphire laser) with a duration of 150-fs and 20-fs. Saturable absorption is observed in both cases, however it is not very strong, amounting to ~13% transmittance change for the 20-fs (150-fs) pulses at a peak intensity of 30 GW/cm2 (4 GW/cm2). The dependence on incident peak intensity is reproduced well using a theoretical model for the time-dependent saturable absorption, where the excited carriers vacate the photo-excited energy range within 3-5 fs, which we attribute to energy redistribution due to carrier-carrier scattering. This is also supported by spectrally resolved measurements for the 20-fs pulses, which show a marked dependence of the degree of saturation on the photon energy. A key result is that the shorter pulses do not yield a lower saturation fluence, due to the combined effects of the broader excitation bandwidth, and the rapid and broad energy redistribution. We also predict the potential performance of multilayer graphene samples for removing pedestal and pre-pulse structure from ultrafast high-energy pulses.

When an excited atom is embedded into an environment, novel relaxation pathways can emerge that are absent for isolated atoms. A well-known example is interatomic Coulombic decay, where an excited atom relaxes by transferring its excess energy to another atom in the environment, leading to its ionization. Such processes have been observed in clusters ionized by extreme-ultraviolet and X-ray lasers. Here, we report on a correlated electronic decay process that occurs following nanoplasma formation and Rydberg atom generation in the ionization of clusters by intense, non-resonant infrared laser fields. Relaxation of the Rydberg states and transfer of the available electronic energy to adjacent electrons in Rydberg states or quasifree electrons in the expanding nanoplasma leaves a distinct signature in the electron kinetic energy spectrum. These so far unobserved electron-correlation-driven energy transfer processes may play a significant role in the response of any nano-scale system to intense laser light., In clusters, relaxation of excited atoms can lead to ionization of nearby atoms, a process known as interatomic Coulomb decay. Here, the authors report on a so far unobserved correlated electronic decay process following Rydberg atom generation in clusters ionized by intense near-infrared fields.

International audience; Increasing the electron density of collisionally pumped plasma-based soft-x-ray lasers offers promising opportunities to deliver ultrashort pulses. However, strong nonlinear effects, such as overionization-induced refraction and self-focusing, hinder the propagation of the laser beam and thus the generation of elongated volume of lasing ions to be pumped. Using a particle-in-cell code and a ray-tracing model we demonstrate that optically preformed waveguides allow for addressing those issues through a self-regulation regime between self-focusing and overionization processes. As a result, guiding intense pulses over several millimeters leads to the implementation of saturated plasma amplifiers.

A high-order harmonic generation process using carrier-envelope phase stabilized few-optical-cycle light pulses is investigated. A time-frequency analysis of generated spectra is used to retrieve direct information about the temporal structure of the generated extreme ultraviolet radiation.

We regard the rovibrational wave packet dynamics of NaI in a static electric field after femtosecond excitation to its first electronically excited state. The following quasibound nuclear wave packet motion is accompanied by a bonding situation changing from covalent to ionic. At times when the charge separation is present, i.e., when the bond-length is large, a strong dipole moment exists and rotational excitation takes place. Upon bond contraction, the then covalently bound molecule does not experience the external field. This scenario repeats itself periodically. Thus, the vibrational dynamics causes a situation which is comparable to the interaction of the molecule with a train of pulses where the pulse separation is determined by the vibrational period. (C) 2004 American Institute of Physics.

Combining photon-echo and frequency-resolved pump-probe techniques with extremely short laser pulses that consist of only few optical cycles, we investigate the dynamics of the equilibrated hydrated electron. The pure dephasing time of the hydrated electron deduced from the photon-echo measurements is approximately 1.7 fs. The shape of the absorption spectrum is excellently described by an extended Lorentzian contour which spectral width is fully determined by the pure dephasing time. The experimental data is successfully described with a model in which the excited state lifetime is approximately 50 fs in water and approximately 70 fs in heavy water. The deuteration effect on the lifetime strongly suggests that OH(OD)-vibrational modes in the first solvation shell act as accepting modes for the energy relaxation.

Different metal homogeneous nanoparticles have been extensively studied in recent years due to their wide range of potential applications. It is very interesting to investigate core-shell nanoparticles with oxide shell from core metal. The formation of oxide shell on metallic nanoparticles can be achieved by different chemical and physical methods including also natural oxidation of pure metallic nanoparticles in gaseous or liquid media, containing oxygen components (air, water, etc.). We numerically calculated efficiency factors of absorptionKabs, scatteringKsca, and extinctionKextof radiation with wavelengthλin the spectral interval 150–1000 nm by spherical homogeneous metallic and two-layered (metal core – oxide metal shell) nanoparticles: Al, Al-Al2O3and Zn, Zn-ZnO with core radii in the range 5–50 nm and shell thickness 5 nm. Analysis of presented results has been carried out.

We propose a new criterion for the assessment of ultrashort pulse reconstruction quality. Our idea is based on the use of a two-dimensional Wigner representation of the electric field. This allows introducing a single measure to represent the quality of both phase and amplitude retrieval. The new criterion is employed to examine two contemporary pulse characterization techniques: FROG (Frequency Resolved Optical Gating) and SPIDER (Spectral Interferometry for Direct Electric-field Reconstruction). For SPIDER, the influence of reference pulse stretching on the quality of phase extraction is investigated.Next, we ascertain the limitations in the use of a Fabri-Perrot etalon in the SPIDER apparatus for producing delayed pulse replicas. For the FROG technique we examine the impact of the doubling crystal orientation on the quality of the amplitude-phase retrieval of sub-5-fs pulses. The introduced criterion is also applied to study the respective sensitivity of FROG and SPIDER to the limited phase-matching bandwidth of the non-linear medium and detector noise.

The problem of measuring broad-band femtosecond pulses by the technique of second-harmonic generation frequency-resolved optical gating (SHG FROG) is addressed. We derive the full equation for the FROG signal, which is valid even for single-optical-cycle pulses. The effect of the phase mismatch in the second-harmonic crystal, the implications of the beam geometry, and the frequency-dependent variation of the nonlinearity are discussed in detail. Our numerical simulations show that, under carefully chosen experimental conditions and with a proper spectral correction of the data, the traditional FROG inversion routines work well even in the single-cycle regime. The developed description of the SHG FROG signal was applied to measure the white-light continuum pulses in the spectral region of 500–1100 nm. The obtained spectral phase of these pulses served as a target function for the pulse compressor design. The pulses produced by compression around 800 nm were also characterized by SHG FROG. The resulting pulse duration measures 4.5 fs which corresponds to ~2.5 optical cycles.

Employing photon echo techniques, we investigate the early relaxation dynamics of the equilibrated hydrated electron within the first 200 fs upon photoexcitation. The use of 5-fs laser pulses provided unprecedented temporal resolution of our measurements. We show that even for extremely short pulse durations the signals obtained in photon echo spectroscopy, can be described in the conventional way, provided care is taken of the spectral filtering effect and experimental beam arrangement. We next conclude that the absorption spectrum of the hydrated electrons is primarily homogeneously broadened. The comparison of two pulse photon echo experiments on pure water and on hydrated electrons allows us to measure the pure dephasing time of ∼1.6 fs. The line shape of the absorption spectrum is described excellently by an extended Lorentzian contour with a spectral width fully determined by the pure dephasing time. From the polarization-dependent transient grating experiments we establish that the polarization ani...

We present a sub-5-fs 1-MHz-repetition-rate all-solid-state laser system based on the fibre-compression of the output of a cavity-dumped Ti:sapphire oscillator. Frequency-resolved optical gating is applied to measure precisely the phase correction needed for the compression, and to characterise the 4.5-fs pulses. The applications of the developed laser in nonlinear experiments on liquid-phase dynamics are discussed.

We have synthesized, characterized and studied the third-order nonlinear optical properties of polydiacetylene (PDA) nanovesicles decorated by silver nanoparticles. The second molecular hyperpolarizability gamma(-omega;omega, -omega,omega) of the sample was investigated by the antiresonant ring interferometric nonlinear spectroscopic (ARMS) technique using lemtosecond modelocked Ti:sapphire laser in the spectral range of 720-820 nm. The observed dispersion of gamma has been explained in the framework of three-essential states model involving the ground state, a one-photon excited state and a two-photon excited state. The energy of two-photon state, transition dipole moments and line width of the transitions have been estimated. Our investigation reveals that the spectral dispersion characteristic of y for coated PDA nanovesicles is qualitatively similar to that observed for uncoated PDA nanovesicles but bears no resemblance to that observed in silver nanoparticles. The presence of silver nanoparticles increases the 7 values of coated nanovesicles slightly as compared to that of uncoated nanovesicles, suggesting a definite but weak coupling between free electrons of metal nanoparticles and IT -electrons of polymer in the composite system. (c) 2013 Elsevier B.V. All rights reserved.

A tightly-focused ultrashort pulsed laser beam incident upon a cell membrane has previously been shown to transiently increase cell membrane permeability while maintaining the viability of the cell, a technique known as photoporation. This permeability can be used to aid the passage of membrane-impermeable biologically-relevant substances such as dyes, proteins and nucleic acids into the cell. Ultrashort-pulsed lasers have proven to be indispensable for photoporating mammalian cells but they have rarely been applied to plant cells due to their larger sizes and rigid and thick cell walls, which significantly hinders the intracellular delivery of exogenous substances. Here we demonstrate and quantify femtosecond optical injection of membrane impermeable dyes into intact BY-2 tobacco plant cells growing in culture, investigating both optical and biological parameters. Specifically, we show that the long axial extent of a propagation invariant (“diffraction-free”) Bessel beam, which relaxes the requirements for tight focusing on the cell membrane, outperforms a standard Gaussian photoporation beam, achieving up to 70% optoinjection efficiency. Studies on the osmotic effects of culture media show that a hypertonic extracellular medium was found to be necessary to reduce turgor pressure and facilitate molecular entry into the cells. Publisher PDF

In this paper, we demonstrate novel properties in the phenomenology of supercontinuum generation in sapphire with diffractive lenses and provide a complete spatial, spectral, and temporal characterization of the so-generated pulses. Filament formation inside the sample is analyzed and related to the measured spectra, finding that clipping of the filament results in blueshifted spectra. For comparison, filament formation with refractive lenses is also examined, and the roles of diffraction and extension of the focusing region are inspected. The tunability achieved in the anti-Stokes side of the spectrum is also extended to the ultraviolet by frequency mixing with infrared femtosecond pulses., European Commision (EC). Funding FP7/SP4/INFRA. Project Code: 228334

We report enhanced supercontinuum generation in water doped with gold nanoparticles of different shapes under modest ultrafast (35 fs) laser excitation. Reasonably, flat supercontinuum spectra covering similar to 1.45-2 eV (855-620 nm) are observed with as much as similar to 161 meV (63 nm) increase in the visible extent compared to pure water for dopants whose surface plasmon resonance (SPR) overlaps the excitation laser spectrum. We use a phenomenological self-phase modulation model to rationalize our results, taking cognizance of plasma contributions to the third-order susceptibility of water along with SPR-induced field enhancement. Such large spectral broadening may be useful for several applications involving imaging or microscopy with modest incident intensities. (C) 2013 AIP Publishing LLC.

Broadband (1.6-18 THz) terahertz time-domain spectroscopy (THz-TDS) and time-resolved terahertz spectroscopy (TRTS) were performed on a 54 mu m thick chalcogenide glass (As30Se30Te40) sample with a two-color laser-induced air plasma THz system in transmission and reflection modes, respectively. Two absorption bands at 2-3 and 5-8 THz were observed. TRTS reveals an ultrafast relaxation process of the photoinduced carrier response, well described by a rate equation model with a finite concentration of mid-bandgap trap states for self-trapped excitons. The photoinduced conductivity can be well described by the Drude-Smith conductivity model with a carrier scattering time of 12-17 fs, and we observe significant carrier localization effects. A fast refractive index change was observed 100 fs before the conductivity reached its maximum, with 2 orders of magnitude larger amplitude than expected for the optically induced THz Kerr effect, indicating that free carriers are responsible for the transient index change. (C) 2016 Chinese Laser Press

International audience; A Calvet-type differential scanning calorimeter has been implemented on a synchrotron beamline devoted to X-ray absorption spectroscopy. As a case study, the complex crystallization process in amorphous Ge(15)Sb(85) phase-change material is followed by simultaneous calorimetric and quick-EXAFS measurements. A first crystallization at 514(1) K is related to the crystallization of an Sb-rich phase accompanied by segregation of Ge atoms. Upon further heating, the as-formed amorphous Ge regions crystallize at 604(1) K. A quantitative analysis of the latent heat allows a Ge(11)Sb(89) stoichiometry to be proposed for the first crystallized phase.

A novel method for ultrashort IR pulse characterization is presented. The technique utilizes a frequency-resolved pump-probe geometry that is common in applications of ultrafast spectroscopy, without any modifications of the setup. The experimental demonstration of the method was carried out to characterize 70-fs IR pulses centered at 3 mum. (C) 2002 Optical Society of America.

International audience; The possibility of inducing a magnetic field via surface plasma-wave excitation is investigated with a simple nonrelativistic hydrodynamic model. A static magnetic field is predicted at the plasma surface, scaling with the square of the surface-wave field amplitude, and the influence of the electron plasma density is studied. In the case of resonant surface-wave excitation by laser this result can be applied to low intensities such that the electron quiver velocity in the field of the surface wave is less than its thermal velocity.

Ramsey-like schemes have been recently introduced in combination with high-order laser harmonic sources for high-resolution spectroscopic studies in the extreme ultraviolet (XUV). Here we demonstrate a novel method, combining measurements only in a limited subset of randomly chosen time-sampling intervals, which lead us to perform the first high-resolution XUV spectroscopy of atomic argon with a simple split-pulse setup. Providing an experimentally simple and convenient solution to the problem of performing high-resolution absolute frequency measurements in the XUV, our approach will help paving new roads into this challenging spectral territory.

We demonstrate the capabilities of a new optical microelectromechanical systems device that we specifically developed for broadband femtosecond pulse shaping. It consists of a one-dimensional array of 100 independently addressable, high-aspect-ratio micromirrors with up to 3 mu m stroke. We apply linear and quadratic phase modulations demonstrating the temporal compression of 800 and 400 nm pulses. Because of the device's surface flatness, stroke, and stroke resolution, phase shaping over an unprecedented bandwidth is attainable. (C) 2010 Optical Society of America

Direct quantum dynamics simulations were performed to model the radiationless decay of the first excited state S(1) of fulvene. The full space of thirty normal mode nuclear coordinates was explicitly considered. By default, ultrafast internal conversion takes place centred on the higher-energy planar region of the S(1)/S(0) conical intersection seam, giving the stepwise population transfer characteristic of a sloped surface crossing, and leading back to the ground state reactant. Two possible schemes for controlling whether stepwise population transfer occurs or not-either altering the initial geometry distribution or the initial momentum composition of the photo-excited wavepacket-were explored. In both cases, decay was successfully induced to occur in the lower-energy twisted/peaked region of the crossing seam, switching off the stepwise population transfer. This absence of re-crossing is a direct consequence of the change in the position on the intersection at which decay occurs (our target for control), and its consequences should provide an experimentally observable fingerprint of this system.

International audience; Ultrafast dynamics of excited molecules is studied through time-resolved two-vacuum-ultraviolet (vuv)- photon ionization using a nonlinear volume autocorrelator unit. The two-vuv-photon process is induced by the intense fifth harmonic radiation of a femtosecond Ti:sapphire laser. In a proof-of-principle experiment, ultrafast dynamics of excited ethylene and oxygen molecules are investigated. Molecular decay times are deduced by comparing the experimental data with the results of a numerical model that accounts for the spatial and temporal characteristics of the harmonic field. The present experiments pave a convenient way for time domain investigations in the vuv-xuv spectral region in all states of matter at few femtosecond to subfemtosecond temporal scales.

We generate ultrabroadband pulses, spanning the 1200-2100 nm wavelength range, from an 800 nm pumped optical parametric amplifier (OPA) working at degeneracy. We compress the microjoule-level energy pulses to nearly transform-limited 8.5 fs duration by an adaptive system employing a deformable mirror. To our knowledge, these are the shortest light pulses generated at 1.6 mu m. (C) 2008 Optical Society of America.

After introducing the importance of non-linear processes in the extreme-ultra-violet (XUV) spectral regime to the attosecond (asec) pulse metrology and time domain applications, we present two successfully implemented techniques with excellent prospects in generating intense asec pulse trains and isolated asec pulses, respectively. For the generation of pulse trains two-color harmonic generation is exploited. The interferometric polarization gating technique appropriate for the generation of intense isolated asec pulses is discussed and compared to other relevant approaches. New Journal of Physics

The rotovibrational dynamics excited by optical filamentation in molecular gases is studied in the temporal domain. Two time-delayed replicas of the same laser pulse have been used to generate a first filament, for the rotovibrational excitation of the sample, and a second collinear filament probing the Raman dynamics. The Fermi doublet structure in CO2 as well as the very fast stretching mode of H-2 were clearly resolved. (C) 2008 Optical Society of America

We propose a smart nanoparticle, a ``regulatron,'' that exploits a cycle of dynamic plasmonic feedback to self-regulate its temperature to a fixed range. One kind of regulatron can be conceived from $\mathrm{V}{\mathrm{O}}_{2}$ and Au; the temperature of this particle when illuminated by laser irradiation of suitable intensities and wavelengths is $\ensuremath{\sim}340\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We expect that regulatrons of this and other compositions will be useful in applications such as photothermal medical therapeutics.

Nitrogen lasers have been used for many years to make dye solutions lase. A nitrogen laser, which transverse electrical discharge in gas at atmospheric pressure has been built in our laboratory. It has been characterized and applied to pump different dyes: Rhodamine 6G, Coumarin 440, DOTCI, and pyranine in simple “on axis” geometric configuration. It has been shown that pyranine can lase in the absence of any optical external mirror cavity, this happens at very low threshold, and in different solvents. Dyes under consideration can be grouped into two major classes according to their lasing behavior independently on their concentration in the solvent: Rhodamine 6G and DOTCI can lase both axially or transversally and Coumarin 440 and pyranine can lase only axially. Other intriguing features have been observed that span from simultaneous multiple beam generation, to super fluorescence and to distribute axial pumping of dye solutions. A preliminary basis for understanding and controlling such processes is the spatial energy distribution and the energy density of the beam.

We generate self-phase-stabilized pulses by difference-frequency generation of a hollow-fibre broadened supercontinuum followed by two-stage optical parametric amplification. This system allows the production of broadband pulses widely tuneable in the near-IR wavelength region. Energies up to 0.2 mJ with 15 fs pulse width are demonstrated. These characteristics make this source suitable as a driver for attosecond pulse generation.

The authors report on a scheme for the generation of few-optical-cycle pulses broadly tunable in the visible with passively stabilized carrier-envelope phase (CEP). The system starts with an infrared optical parametric amplifier in which both pump and seed are derived from an amplified, non-CEP-stabilized Ti:sapphire laser. The passively stabilized idler beam is then spectrally broadened through white-light generation and seeds a blue-pumped noncollinear optical parametric amplifier. The system produces few-optical-cycle pulses tunable from 500 to 800 nm, with energy up to 5 mu J and 0.23 rad rms CEP fluctuations. (c) 2007 American Institute of Physics.

We report on a novel correlated electronic decay process following extensive Rydberg atom formation in clusters ionized by intense near-infrared fields. A peak close to the atomic ionization potential is found in the electron kinetic energy spectrum. This new contribution is attributed to an energy transfer between two electrons, where one electron decays from a Rydberg state to the ground state and transfers its excess energy to a weakly bound cluster electron in the environment that can escape from the cluster. The process is a result of nanoplasma formation and is therefore expected to be important, whenever intense laser pulses interact with nanometer-sized particles.