We present a new operating mode, using a charged coupled device as dispersionless spectrometer dedicated to repetitive x-ray sources in the multi-keV domain. This enables to get spectra with high statistics in a short acquisition time and a way compatible with the operation of other diagnostics requiring accumulation. Several reconstruction algorithms for the spreading events are discussed, and a near Fano-limited resolution is demonstrated by using single pixel events. In this case, a method to take into account partial canceling of the events is presented. Experimental characterization and detailed modeling of the detector are performed, which allow to determine absolute number of photon with +/-35% accuracy. Characterization of the 5-25 keV x rays emitted by a short pulse laser-produced plasma is reported, as well as their dependency with the atomic number, the laser duration, and energy.

We present the first experimental evidence of the subpicosecond duration of x-ray pulses emitted from laser-irradiated clusters, demonstrating the suitability of such a debris free target for ultrafast x-ray science applications. The K-shell emission (approximately 3 keV) from large Ar clusters (6 x 10(5) to 4 x 10(6) atoms) is time resolved, when irradiated by ultrashort (40 fs to 5 ps) and intense laser pulses (10(15-17) W/cm2). The observations are supported by hydrodynamical and collisional-radiative calculations, that reproduce the extremely short x-ray pulse duration.

The full characterization of a time resolved x-ray spectrometer is presented. It is based on the coupling of a conical crystal with a subpicosecond x-ray streak camera. The detector is designed to operate in accumulation mode at high repetition rate (up to 1 kHz) allowing signal to noise ratio as high as 104:1. Optical switches have been used to limit the jitter induced in the subpicosecond range, demonstrating the very long term stability (a few hours) of the entire device. The data analysis have been developed to get the spectral and temporal resolution of an ultrashort laser-plasma-based x-ray source.

We report on a joint experimental–theoretical effort to shed light on the dynamics of rare gas (Ar) nanoclusters irradiated by short and intense laser pulses. The experiments employ a streak camera coupled to a conical crystal to yield energy- and time-resolved X-ray spectra, in the keV range on picosecond scale. These spectra display ultrafast subpicosecond ionization dynamics, leading to highly charged states such as Ar16+, and indicate that the duration of the energetic X-rays is less than the experimental 1.3ps temporal resolution. The theoretical calculations rely on the well-known nanoplasma model, which has been improved to represent the collisional ionization processes that are of importance in nanoplasma dynamics. Allowance is made for high-order ionization transitions involving intermediate excited states. The simulations indicate significant populations of excited states of highly charged ions, in agreement with the experimental findings. Further, detailed collisional-radiative calculations indicate that the duration of the X-ray bursts is less than 100fs.

Interaction of femtosecond (30 fs - 5 ps) and intense (up to 10 17 W/cm 2 ) laser pulses with Ar clusters (180 to 350 A radius) has been studied. The laser absorption and the cluster heating have been measured using different diagnostics, demonstrating the production of very hot and dense plasmas, in the keV range. A special attention has been devoted to the K-shell x-ray emission spectra (2.9-3.3 keV). X-ray emission has been observed from ions in very high charge states (Ar 16+ ). Time-resolved measurements have been performed, giving evidence, for the first time, of extremely short x-ray pulses (<3 ps). Simulations based on both an hydrodynamic model and collisional-radiative atomic physics reveal an extremely brief x-ray emission burst (down to the sub-picosecond) consistent with measurements.

Les agrégats de gaz rares constituent un état de la matière intermédiaire entre les cibles solides massives et les atomes en phase gazeuse.Il a été démontré que les agrégats irradiés sont sources d'ions, d'électrons, de neutrons ainsi que de rayonnement allant du visible aux X durs.Cette source peut-être produite avec un taux de répétition élevé et a l'avantage de ne pas produire de débris, dommageables pour les optiques notamment, et de présenter une très forte conversion de l'énergie laser incidente.Nous nous intéressons au rayonnement X particulièrement, en le caractérisant en intensité, spectre et durée, comme préalable à toute application de cette source X et comme moyen privilégié d'étude de la physique des plasmas nanométriques chauds et denses.En collaboration avec l'INRS-Énergie (Varenne, Qc, Canada), nous avons mis en oeuvre une caméra à balayage de fente dont la résolution temporelle est de 800 fs rms.En focalisant des impulsions laser courtes (30 fs -5 ps) et intenses (jusqu'à 10 17 W/cm 2 ) sur des agrégats d'argon dont le rayon varie de 15 à 30 nm, nous avons démontré que l'émission X dont l'énergie est supérieure à 2 keV est plus courte que 2 ps, limité par la résolution temporelle.En couplant la caméra à un cristal tronconique, dont la conception a été réalisée au LULI (Palaiseau, France), nous nous sommes intéressés au rayonnement de couche K dans la gamme 2,9 -3,2 keV.Nous avons démontré que ce rayonnement a une durée inférieure à 3 ps (limite de la résolution temporelle), et que les raies étaient émises avec un écart relatif inférieur à 1 ps.Une simulation basée sur le modèle nano-plasma proposé par T. Ditmire et sur le code collisionnel-radiatif Transpec a été développée au CELIA.Les spectres X résolus en temps calculés reproduisent à la fois la brièveté d'émission du rayonnement X et les états de charge élevés observés.

Solid target experiments carried out on copper targets with both p- and s-polarized 130 fs Ti:Sapphire laser pulses at intensities of 3 x 10 16 W/cm 2 indicate the presence of hot electron jets with electron energies of 80 to over 250 keV and cone angles of the order of 10 degrees at the higher energies with directions dependent on the incident polarization. For comparison, studies on an Argon cluster jet targets with 50 fs duration Ti:Sapphire laser pulses at vacuum intensity of 10 17 W/cm 2 indicated no detectable hot electron jet emission with electron energies above 50 keV. A 2D PIC simulation of the p-polarized solid target interaction predicts features similar to those observed experimentally.

The propagation of an intense (up to 10(17) W/cm(2)) and short laser pulse (down to 40 fs) is studied through a well characterized high density Ar cluster jet obtained at the output of a supersonic nozzle. The x-ray emission from the irradiated clusters is measured as a function of the focusing depth inside the jet, with a spatial resolution of the emitting plasma. A strong refraction of the laser pulse is observed, limiting the interaction at the entrance of the jet and decreasing the effective laser intensity on clusters. Calculations indicate that it is due to the ionization of the residual gaseous phase present in the cluster jet. As the focal volume is modified, this effect should be considered for any quantitative analysis of the laser-cluster interaction.

Interaction of femtosecond (30 fs - 5 ps) and intense (up to 10(17) W/cm(2)) laser pulses with Ar clusters (180 to 350 angstrom radius) has been studied. The laser absorption and the cluster heating have been measured using different diagnostics, demonstrating the production of very hot and dense plasmas, in the keV range. A special attention has been devoted to the K-shell x-ray emission spectra (2.9 - 3.3 keV). X-ray emission has been observed from ions in very high charge states (Ar16+). Time-resolved measurements have been performed, giving evidence, for the first time, of extremely short x-ray pulses down to the sub-picosecond. Simulations based on both an hydrodynamic model and collisional-radiative atomic physics reveal an extremely brief x-ray emission burst consistent with measurements.

Intense (up to a few 10(17) W/ cm2) femtosecond (down to 40 fs) laser pulses are focused onto a partially clusterized argon gas jet. The target was previously characterized and optimized in order to get a homogeneous and dense jet of clusters with a well controlled size. The interaction leads to x-ray emission that is absolutely calibrated and spectrally resolved using a high resolution time-integrated spectrometer in the K-shell range (from 2.9 to 4.3 keV). X-ray spectra are investigated as a function of different laser temporal parameters such as the nanosecond prepulse contrast, the laser pulse duration, and the femtosecond delay between two different laser pulses. The cluster size ranges from 180 to 350 angstroms and irradiation by laser pulses with both linear and circular polarization is investigated. The experimental results are discussed in terms of the laser-cluster interaction dynamics. They are compared with the predictions of collision-dominated nanoplasma models. However, further interaction processes are required in order to explain the observed characteristic lines demonstrating highly charged ions up to Ar16+.

Rare gas cluster jets are an intermediate medium between solid and gas targets. Laser-cluster jets interaction may generate a great number of energetic particles such as X-rays, UV, high harmonics, ions, electrons and neutrons. To understand all the mechanisms involved in this interaction we need to make a complete study of individual cluster response to an ultra-short laser pulse. We studied the laser interaction with our Argon cluster gas jet, which is well characterized in cluster size and density, to enlarge the knowledge of this interaction. We measured absorption, heating and X-ray emission spectra versus laser parameters and clusters size (~15-30 nm). We show that there is a strong refraction effect on laser propagation due to the residual gas density. This effect was confirmed by laser propagation simulation with a cylindrical 2D particle code WAKE. The role played by refraction was to limit maximum laser intensity on the focal spot and to increase interaction volume. By this way, X-ray emission was observed with laser intensity not so far from the ionization threshold (few 1014 W.cm-2). We also studied plasma expansion both at cluster scale and focal volume scale and deduced the deposited energy distribution as a function of time. Thanks to a simple hydrodynamic model, we used these results to study cluster expansion. X-ray emission is then simulated by TRANSPEC code in order to reproduce X-ray spectra and duration. Those results revealed an extremely brief X-ray emission consistent with a preliminary measure by streak camera (~ps).

The interaction of high-power, ultra-short, femtosecond laser pulses with matter, particularly solids and atomic gas clusters has been an area of extensive research in recent years. In particular, gas cluster targets, with their high densities and resistance to heat conduction, combine the advantages of both gas and solid targets. High temperature and high-density plasmas with satellite lines from multiply charged ions have been observed: 2p-1s emissions in Li-like through F-like ions appear in the experimental spectrum. The experimental satellite spectra show sensitivity to pulse duration, laser contrast, and cluster size. Since the laser energy is deposited in such a short timescale, a time-dependent model is being developed to study the plasma formation in such systems. In the present work, preliminary time-integrated spectra simulated from this model are presented assuming different initial conditions for the pre-plasma. The computational model also includes a provision for non-thermal electrons at energies substantially above the mean plasma temperature.

Multi-keV X-ray source from intense laser-cluster interaction was experimentally studied. A special effort was first made in order to characterize the cluster target. K-shell emission of Argon clusters (around 3 keV) was then studied when irradiated by kHz, 30 fs, 10(17) W.cm(-2) laser pulses. High-resolution spectra are presented, in this spectral range, as a function of laser duration and average cluster size. Signature of very highly charged ions (Ar16+) was observed with relatively low intensity laser pulses (few 10(15) W.cm(-2)). This feature is not yet clearly understood nor reproduced by simulations. Optimal laser pulse duration was observed for X-ray production, depending on the cluster size. For the first time to our knowledge, the duration of K-shell X-ray bursts was measured with a home-made streak camera to be on the picosecond scale.

The heating of clusters by femtosecond laser pulses is studied theoretically and experimentally. Both the formation of a cluster target and the results of experimental studies of the cluster plasma by the methods of X-ray emission spectroscopy are considered. A numerical model of cluster formation in a supersonic gas jet is proposed. It is shown that detailed studies of two-phase gas-dynamic processes in a nozzle forming the jet give the spatial distributions of all parameters required for the correct calculation of the cluster heating by short laser pulses. Calculations of nozzles of different configurations show that in a number of cases an almost homogeneous cluster target can be formed, whereas in other cases the distributions of parameters prove to be not only inhomogeneous but also even nonmonotonic. A simple physical model of the plasma production by a femtosecond laser pulse and a picosecond prepulse is proposed. It is shown that a comparison of X-ray spectra with detailed calculations of the ion kinetics makes it possible to determine the main parameters of the plasma being produced.

Plasmas have been created by irradiating atomic clusters of argon with high-contrast, ultrashort (<100 fs) laser pulses and recording the corresponding K-shell emission spectra. The high-resolution Ar K-shell spectra were analyzed using a theoretical two-temperature collisional-radiative model of irradiated atomic clusters incorporating the effects of highly energetic electrons (similar to5 keV). Comparison of the measured spectrum with the calculations indicates that a supercritical density near N-e=2x10(22) cm(-3) was attained in the shortest-pulse and highest-contrast shots. Results from additional experiments using pulses on the order of 300-400 fs are also consistent with a hydrodynamic model of laser-cluster interactions.

The satellite structure of 1 s 2 p 1,3 P 1 -1 s 21 S 0 lines of the He-like argon ion in plasma produced by a 45-fs laser pulse in a gas-jet cluster target is measured with a high spectral resolution. Radiation transitions 2 p → 1 s from autoionizing states (AISs) are detected for ions ranging from Li-like to F-like. The spectrum observed is theoretically simulated with the use of the spectroscopic data for the AISs of multicharged ions obtained within the multiconfiguration relativistic Hartree-Fock method. Good agreement with experimental data is obtained when the main population channels of these states are taken into account for typical values of cluster-target plasma parameters.

The parameters of a plasma produced upon the interaction of ultrashort laser pulses with cluster targets are measured by the methods of X-ray spectroscopy. The dependence of the plasma parameters on the initial properties of a cluster target (the design of a supersonic nozzle, the average size of clusters, the spatial inhomogeneity) and the laser pulse properties (its duration and contrast) is studied. The plasma diagnostics is performed using the model of formation of emission spectra, which was proposed earlier and includes a number of fitting parameters, which provide good agreement with experimental spectra. The systematic experimental studies performed by us showed that our model of cluster heating by ultrashort pulses is indeed a physical model, and the fitting parameters represent the average values of plasma parameters in the corresponding space-time regions.

Line emission spectrum of a laser plasma produced in an argon cluster jet target was measured on the n 1 P 1−1 1 S 0 ( n =5–9) transitions of the helium-like Ar XVII ion for a pulse duration varying from 45 fs to 1.1 ps and a constant fluence of ∼10 5 J/cm 2 . The independent modeling of the relative intensities of the transitions from the n =5,..., 10 levels, as well as of the 2 1 P 1 − 1 2 S 0 and 2 3 P 1 −1 2 S 0 lines and dielectronic satellites indicates that the electron temperature is anomalously low and that the electron density in emitting plasma increases with shortening the laser pulse. The excitation from the ground state by a small fraction of hot electrons is expected to be the main channel of populating the Ar XVII levels.

A field study of fluoride pollution and of its consequences was made over a period of five years in the vicinity of an alumina reduction plant. This study, based upon the use of a static soda impregnated paper sampler, shows that the results obtained are in good agreement with the atmospheric fluoride concentrations obtained with dynamic samplers, especially when fluoride is present in gaseous form (HF). The results suggest that vertically mounted paper samplers are less sensitive to the collection of particulate fluorides. Collection rate is strongly influenced and increases with speed. If this parameter is known, an accurate estimation of the absolute atmospheric concentration is possible; the values shown by this technique are in good correlation with the value (annual mean) of pasture fluoride content. As a correlation exists between pasture fluoride content and the symptoms shown by cattle, the static filter samplers can predict disease in the case of slow chronic fluorosis. The field study agrees with earlier laboratory experiments and shows the validity of these simple and inexpensive types of exposure methods.