Two-Photon Ionization and Three-Photon Above-Threshold Ionization of Argon

Studies of nonlinear laser-matter interaction have been so far limited to wavelengths from the near ultraviolet to infrared, because of the low brightness of currently available sources outside this range. However nonlinear processes in the VUV/Soft X-ray domain would initiate multiphoton innershell spectroscopy, XUV nonlinear optics and applications of such processes to metrology. The probability of multiphoton transitions decreases rapidly with the number of photons involved. A typical two-photon bound-free transition has a rate of the order of .1 ps{sup {minus}1} at 10{sup 12} W.cm{sup {minus}2} and scales as the square of the intensity. Such an intensity is therefore required to saturate a two-photon transition with a 100 fs pulse. This is difficult to achieve with the present state-of-the-art techniques for producing intense XUV pulses. To the authors knowledge, only two cases of such transitions have been reported so far. The first one is a two-photon ionization of argon by the third harmonic of a KrF laser. Since the photon energy (15 eV) is just below the ionization energy (15.75 eV) for argon, the transition is quasi-resonant. The second case is a two-photon ionization of helium by the 9th harmonic of a Ti:S laser. In the latter case an autocorrelation measurement of the harmonic pulse has been reported. In the present work, the authors report on two-photon ionization of argon at 133 nm (9.3 eV) from the third harmonic of a frequency doubled Ti:S laser, and a three-photon above-threshold ionization involving two 9.3 eV photons and one 3.1 eV photon

Demonstrator of Time Services based on European GNSS signals: the H2020 DEMETRA Project

During 2015-2016, a European Consortium of 15 partners from 8 different countries, developed the DEMETRA (DEMonstrator of EGNSS services based on Time Reference Architecture), a project funded by the European Union in the frame of the Horizon 2020 program. This project aims at developing and experimenting time dissemination services dedicated to specific users like traffic control, energy distribution, finance, telecommunication, and scientific institutions. Nine services have been developed. These services provide time dissemination with accuracy levels from millisecond to the sub-ns, and also additional services like certification, calibration, or integrity. Five of these services are based on the European GNSS. After a development phase (see PTTI 2016 presentation) the full DEMETRA system has been working during six months for demonstration. The paper will report about the experimentation results, showing performances and limits of the proposed time dissemination services, aiming to foster the exploitation of the European GNSS for timing applications

Molecular dynamics of liquid benzene via femtosecond pulses laser excitation

We analyse the complex response of liquid benzene to the applied 45 fs FHWM optical pulses by using a polarization sensitive transient grating technique. An electronic contribution to the nonlinear polarization is distinguished from three other processes which, we demonstrate, originate in polarizability modifications associated to molecular motions. Additionally, we present evidence that orientation of C6H6 molecules towards the applied optical field is not instantaneous. The time it takes for the molecules to orient along the incident field is measured

Temporal and Angular Resolution of the Ionization-Induced Refraction of a Short Laser Pulse in Helium Gas

International audienceThe refraction of a short and intense laser pulse focused in helium gas has been studied both experimentally and numerically. Using the time-frequency correspondence of a 120 fs laser pulse linearly chirped to 1.8 ps, the ionization-induced refraction is resolved both temporally and angularly. Two-dimensional numerical simulations are performed to calculate the laser propagation, from the focusing lens to the detector. With such a simulation, we get a quantitative agreement with the experiment, both for the refraction of the chirped pulse and for the ionization-induced blueshifted spectrum of the compressed pulse

Extending plasma accelerators: Guiding with capillary tubes

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Temporal dependence of high-order harmonics in the presence of strong ionization

International audienceThe temporal behavior of the 19th harmonic of a Ti:sapphire laser generated in argon was investigated by a cross-correlation technique at intensities close to saturation. Pulses about half as long as predicted on the basis of the scaling law of the atomic dipole strength on intensity were found. Analysis shows that this is a consequence of both the intensity-dependent dipole phase and the depletion of the medium by ionization

Demonstrator of Time Services based on European GNSS signals: the H2020 DEMETRA Project

During 2015-2016, a European Consortium of 15 partners from 8 different countries, developed the DEMETRA (DEMonstrator of EGNSS services based on Time Reference Architecture), a project funded by the European Union in the frame of the Horizon 2020 program. This project aims at developing and experimenting time dissemination services dedicated to specific users like traffic control, energy distribution, finance, telecommunication, and scientific institutions. Nine services have been developed. These services provide time dissemination with accuracy levels from millisecond to the sub-ns, and also additional services like certification, calibration, or integrity. Five of these services are based on the European GNSS. After a development phase (see PTTI 2016 presentation) the full DEMETRA system has been working during six months for demonstration. The paper will report about the experimentation results, showing performances and limits of the proposed time dissemination services, aiming to foster the exploitation of the European GNSS for timing applications

Monomode guiding of 10(16) W/cm(2) laser pulses over 100 Rayleigh lengths in hollow capillary dielectric tubes

International audienceno abstrac

The Horizon 2020 DEMETRA project: DEMonstrator of EGNSS services based on Time Reference Architecture

DEMETRA (DEMonstrator of EGNSS services based on Time Reference Architecture) is a project co-funded by the EU through the research and innovation programme 'Horizon 2020'. The DEMETRA project started in January 2015 and lasts 24 months. Based on the current practice of national metrological laboratories, identifying the additional necessities of the timing users, DEMETRA will define and develop a prototype of a European time disseminator, based on EGNSS. Nine different time services are proposed for demonstration by consortium partners. The DEMETRA partnership, including Scientific Institutions, GNSS Industries, and a Service Provider cover the different faces of the project, including an analysis of commercial potential in terms of market and business development