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When studying the interaction between a fast heavy ion projectile and a solid target, we can be interested either by the target itself (for instance, the formation of tracks in insulating materials) or by what happens to the ion. These different studies are obviously strongly connected. In our group, we mainly concentrate on the transport of electrons in ion excited states. Two extreme representations may be used to evaluate, especially, the electronic ion stopping in matter. These two aspects are linked to the response of the target electrons:In the first picture, the solid is seen as an assembly of atoms and the HCIs undergo a series of binary ion‐ atom collisions with the target electrons. This pure collisional approach has been used in the Bethe theory to calculate the ion stopping power. The ensemble of ion‐atom cross sections forms the database of any theoretical treatment.In the other picture, closer in spirit to the dielectric theory first proposed by Bohr, the target electrons are considered to respond collectively to the passage of the projectile. The HCIs induce a polarization of the medium described as a wake of electronic density fluctuation trailing the ion, the so‐called wake field. The gradient of the wake potential leads to the establishment of an electric field, and its local value at the projectile can be used to calculate the stopping power. Its value can be as high as that of the electric field experienced by an electron on the first Bohr orbit, i.e., 5.4 109 V/cm.Both types of calculations appear to achieve good agreement with stopping power measurements, despite a rather different physical picture for the behavior of the target electrons. It is clear that the response of the target electrons to the passage of the ion has direct consequences on the projectile ion: it is slowed down, but not only, the populations in its excited states are also altered by the presence of the environment (the solid). Notably, the presence of the wake field may mix the ion excited states by Stark effect in a coherent manner while a pure collisional response of target electrons destroys any coherence. Hence, the group tackled the study of the production and transport of projectile excited states. The analysis of the de‐excitation of these excited states allow us to probe the solid response.High values of electric field are also reachable with intense laser pulses inducing also a strong perturbation in the matter. Laser excitation/ionization of nanometer‐sized atomic clusters offers opportunity to explore ultrafast many particle dynamics. Indeed, submitted to strong optical fields, the response of free clusters is often very different from that of single atoms/molecules. Large clusters, similarly to solids, couple very efficiently to intense sub‐picosecond laser pulses. Near 100 % of the laser radiation can be absorbed giving rise to the observation of highly charged ions with energies reaching MeV and warm electrons with a fraction having keV energies. Another fascinating feature of this interaction is its efficiency for converting photons in the eV range to X‐rays with keV energies. This emission is due to the de‐excitation of HCIs having inner shell vacancies. The lifetime of these excited states being very short (down to some fs), their observation gives access to the dynamical evolution of the irradiated cluster on a time scale comparable to that of the laser pulse duration. Our group has performed several experiments to measure the evolution of absolute photon yields and charge state distributions of the emitting ions with different physical parameters governing the interaction; namely intensity, polarization, pulse duration and wavelength of the laser as well as the size of the clusters. These various studies have allowed us to determine the ionization mechanisms in inner shells and their time competition. In this manuscript, I only present the influence of the laser intensity.

The full permanent magnet "supernanogan" type ECR (electron cyclotron resonance) ion source, SIMPA (Source d'Ions Multicharges de Paris) has been jointly operated by LKB (Laboratoire Kastler Brossel) and INSP (Institut des NanoSciences de Paris) since 2004. Since this time numerous projects have been started to use the extracted beam in atomic physics and surface physics experiments and the x-ray radiation of the ECR plasma for plasma and atomic physics investigations. In this paper recent achievements will be reported that include the first use of an electrostatic ion trap * for trapping highly charged ions on the beam line of an ECR ion source and electron temperature and density measurements with the help of the observation of the bremsstrahlung spectrum of the electrons in the ECR plasma of the source.** Also a new vacuum double crystal spectrometer *** is under construction in our lab that will allow us to measure the very narrow inner shell transitions of highly charged ions produced in the ECR plasma and provide new x-ray standards with this method for the atomic physics community.

International audience; An increasing number of experiments in the field of low energy ion physics (< 25 keV/charge) requires pulsed beams of highly charged ions. Whereas for high-intensity beams (> µA) a pulsed beam chopper, installed downstream to the analyzing dipole, is used. For low-intensity beams (< 100 nA) the ion intensity delivered during the pulse may be increased by operating the ECR discharge in the afterglow mode [1]. This method gives satisfactory results (ie average current during the beam pulse is higher than the current in the CW mode) for high charge state ions. In this paper, we report on results of the afterglow mode for beams of 22Neq+, 36Arq+ and 84Krq+ ions. Furthermore, a new promising “Micro Pulsed Beam” mode will be described with encouraging preliminary results for 84Kr27+ and 36Ar17+ ions.

In ion-solid collisions, more excited states of projectile ions with high angular momenta l are populated than in ion-atom collisions. The use of 13.6 MeV/u Ar18+ projectile ions and solid carbon targets allowed us to study Ar17+ excited states initially populated by electron capture. Using various targets with increasing thickness from 3.5 to 200 µg/cm², the evolution of excited states from the single collision condition to the population equilibrium was investigated. We observed the evolution of the Lyman line intensities as a function of the ion transit time inside the target (sensitive to core state population) and as a function of the ion time of flight behind the target (sensitive to Rydberg state population). To explain the experimental results, a complete theorical analysis of the transport of excited states inside the medium was performed. We used two different collisional models. The first one is a rate equation model based on a statistical description of binary collisions of the projectile with target atoms. The second one is a classical transport theory based on an equation describing the motion of the projectile electron on a classical orbit perturbed by a stochastic force. A comparison with experiment shows that a such collisional approach allows to interpret the excited l-state population, but fails in describing the core state population. The observed l mixing in these states is much larger than predicted by the models. The polarization of the medium induced by the projectile ion, with both models do not take into account, could be responsible for this mixing by means of the Stark effect., Dans les collisions ion-solide, les états de l'ion projectile de grand moment angulaire l sont en moyenne beaucoup plus peuplés que lors des collisions ion-atome. L'utilisation d'ions projectiles Ar18+ d'énergie 13,6 MeV/u et de cibles solides de carbone nous a permis d'étudier les états excités de l'ion Ar17+ peuplés par capture. La gamme d'épaisseur de cibles choisie a permis d'effectuer cette étude de la condition de collision unique (3,5 µg/cm²) jusqu'à l'équilibre des populations (200 µg/cm²). Nous avons observé l'évolution des intensités des transitions Lyman en fonction du temps de transit de l'ion dans la cible (évolution sensible à la population des états de coeur) ainsi qu'en fonction du temps de vol de l'ion derrière la cible (évolution sensible à la population des états de Rydberg). Pour expliquer les résultats expérimentaux, une analyse complète du transport des états excités dans la cible a été réalisée. Nous avons utilisé deux modèles de type collisionnel. Le premier est un modèle d'équations d'évolution basé sur une description statistique des collisions binaires du projectile avec les atomes cibles. Le second est un modèle de transport classique basé sur l'équation décrivant le mouvement de l'électron projectile sur une orbite classique perturbé par une force stochastique. Une comparaison avec l'expérience montre que ces approches collisionnelles permettent de refléter assez bien la population en moment angulaire des états très excités mais nettement moins bien celle des états de coeur. Le mélange l observé pour ces états est beaucoup plus important que prévu par ces modèles. La polarisation du milieu induite par l'ion projectile (non prise en compte par les modèles) pourrait être responsable d'un tel mélange par l'intermédiaire de l'effet Stark.

Interaction of high intensity ultrashort laser pulses with matter has received considerable attention in the last few years. With clusters in intense optical fields (F > 109 V/cm), the energy coupling between radiation and matter is extremely efficient, providing specific features that are not observed when atoms, small molecules or even solid are used as targets : multicharged ions reaching the MeV, hot electrons up to few keV and keV x-ray photons are produced in the laser heated cluster plasma. Here, we focus on the x-ray generation related to the production of highly stripped and excited ions. We study deexcitation of species from Ar12+ to Ar16+ with K vacancy for Ar clusters and from Xe24+ to Xe34+ with L vacancies for Xe clusters. The goal is to understand how electrons initially produced by Optical Field Ionisation (OFI) can reach enough energy to generate a strong production of ions with inner shell vacancies. We have performed quantitative studies(*) on the evolution of absolute photon emission yields and complete charge state distributions with different physical parameters governing the interaction ; namely intensity, polarization, pulse duration and wavelength of the laser, size and atomic number of the clusters. KeV x-rays are studied from rare-gas clusters irradiated with intense (I ~ 1014–1018 W cm-2) infrared and blue laser pulses of 50 – 2000 fs duration. Our measurements give rise to fundamental results like an optimum heating time in the x-ray production and an intensity threshold unexpectedly low (~ 1015 W/cm2 at 50 fs and ~ 2 1014 W/cm2 at 575 fs). The set of data and the behavior of x-ray yields with the physical parameters explored will be presented and discussed. (*) Experiments are performed on the LUCA (Laser Ultra Court Accordable) in Saclay, France.

Absolute Ar XK (3 keV) and Xe XL (4 keV) photon yields are measured as a function of laser peak intensity, for large (104 - 105 atoms) argon and xenon clusters submitted to intense laser pulses. A clear threshold behavior is observed. The intensity threshold is found as low as 2 1014 Wcm-2, a value matching the production of singly-charged argon or doubly-charged xenon by optical field ionization. Possible mechanisms involved in the inner-shell ionization are discussed. The outcome on the optimization of keV X-ray production is underlined., Comment: 1 table, 4 figures. submitted to Physical Review Letters

Interaction of high intensity ultrashort laser pulses with matter has received considerable attention in the last few years. With clusters in intense optical fields (F > 109 V/cm), the energy coupling between radiation and matter is extremely efficient, providing specific features that are not observed when atoms, small molecules or even solid are used as targets : multicharged ions reaching the MeV, hot electrons up to few keV and keV x-ray photons are produced in the laser heated cluster plasma. Here, we focus on the x-ray generation related to the production of highly stripped and excited ions. We study deexcitation of species from Ar12+ to Ar16+ with K vacancy for Ar clusters and from Xe24+ to Xe34+ with L vacancies for Xe clusters. The goal is to understand how electrons initially produced by Optical Field Ionization (OFI) can reach enough energy to generate a strong production of ions with inner shell vacancies. We have performed quantitative studies(*) on the evolution of absolute photon emission yields and complete charge state distributions with different physical parameters governing the interaction ; namely intensity, polarization, pulse duration and wavelength of the laser, size and density of the clusters. KeV x-rays are studied from rare-gas clusters irradiated with intense (I ~ 1014–1018 W cm-2) infrared and blue laser pulses of 50 – 2000 fs duration. Our measurements give rise to fundamental results like an optimum heating time in the x-ray production and an intensity threshold unexpectedly low (~ 1015 W/cm2 at 50 fs and ~ 2 1014 W/cm2 at 575 fs). The set of data and the behavior of x-ray yields with physical parameters will be presented and discussed. (*) Experiments are performed on the LUCA (Laser Ultra Court Accordable) in Saclay.

Tout comme l'interaction d'ions multichargés avec la matière, des impulsions laser (d'une durée comprise entre 50 fs et 1ps) de très haute intensité ( Ilaser > 1017 W/cm2 soit un champ électrique > 109 V/cm) induisent une excitation électronique extrêmement intense de la cible. En particulier, il a été observé expérimentalement que l'interaction d'un faisceau laser femtoseconde de grande puissance avec un jet d'agrégats de gaz rare ([Ar]n, [Kr]n ou [Xe]n avec n compris entre 104 et 106) conduit à la production d'ions fortement multichargés (Xe30+ par exemple), à l'éjection d'électrons très énergétiques (jusqu'à Ecin ~ 3 keV) ou bien encore à la génération de rayons X durs (EhΝ > keV). L'ensemble de ces résultats expérimentaux tend finalement à prouver l'existence d'un très fort couplage énergétique entre le rayonnement électromagnétique incident et ces nano objets, beaucoup plus important que ce qui est observé pour une cible atomique (jet gazeux) voire une cible solide. Alors que de nombreuses équipes à travers le monde se sont principalement intéressées à l'étude de la production ionique, nous avons, en ce qui nous concerne, étudié précisément et quantitativement le rayonnement X issu de cette interaction tout en contrôlant au mieux l'ensemble des paramètres physiques gouvernant l'interaction (intensité laser, durée d'impulsion, longueur d'onde ou polarisation du laser, taille et densité des agrégats ...). Il sera donc présenté et discuté lors de ce séminaire les principaux résultats expérimentaux que nous avons obtenus lors de diverses campagnes d'expériences réalisées auprès du Laser Ultra Court Accordable du SPAM au CEA / Saclay.

International audience; The interaction between short laser pulses (electric field > 109 V/m) and Van Der Waals clusters induces an intense electronic excitation of the matter. In particular, the energy coupling between the radiation and the matter is much more efficient than for atomic or solid targets. Experimentally, highly charged ions (like Xe40+), energetic electrons (with Ekin > 3keV) and keV x-rays have been observed. Whereas many studies concentrated on ion emission yields [1], we are interested on the x-ray production (E > 1 keV) when large rare gas cluster ((Ar)n, (Kr)n and (Xe)n with n>104 atoms/cluster) are submitted to intense (up to 5 1017 W/cm2) ultra - short (50 fs to 1 ps) laser pulses (IR-800 nm or UV-400 nm). The x-rays observed are emitted by highly charged ions: for example, from Ar11+ to Ar16+ with K vacancies in the case of Ar clusters [2] and from Xeq+ with q " 24 with L vacancies in the case of xenon. Our goal is to understand how electrons initially produced by optical field ionisation can reach enough energy to generate a strong production of ions with inner shell vacancies. Because the heating mechanisms involved remain controversial, we perform studies, under well-controlled conditions, on the evolution of the absolute photon emission yields and the complete charge state distribution with different physical parameters governing the interaction (like intensity, polarization, and wavelength of the laser, size and density of the clusters). A set of experimental data will be presented and discussed. References [1] Ditmire et al., Phys. Rev. A 53 (1996) 3379. [2] Lamour et al., Proc. of SPIE 4504 (2001) 97 and Rozet et al Physica Scripta T92 (2001) 113. [3] Adoui et al NIM B 205 (2003) 341.

The population dynamics of the internal state of 60 MeV/u Kr35+ ions traversing amorphous carbon foils is studied theoretically and experimentally. This system is of particular interest as the times scales for collisional distribution, mixing due to the wake field, and radiative processes are comparable to each other. A transport theory based on a quantum-trajectory Monte Carlo method is developed, which treats the collisional and radiative redistribution of states on the same footing. The simulations exhibit clear signatures for the interplay between radiative decay and collisional mixing. Good agreement with experimental data is found.

International audience

International audience; We have performed studies of keV X-ray production from (Ar)n , (Kr)n and (Xe)n rare gas clusters (with n between 104 and 106 atoms/cluster) submitted to intense (~10^18 W/cm2) infrared (800 nm) laser pulses. Up to 10^6 3 keV photons per pulse at a moderate (~10^15/cm3) atomic density have been observed. High resolution spectroscopy studies in the case of (Ar)n clusters have also been performed, giving unambiguous evidence of highly charged (up to heliumlike) ions with K vacancies production. We have determined the photon energies and the absolute photon emission yields as a function of several physical parameters governing the interaction : size and atomic number of the clusters, peak intensity of the laser. Unexpectedly low laser intensity thresholds (~10^15Wcm-2) have been measured. The results obtained indicate nevertheless that X-rays may be emitted before cluster explosion on a subpicosecond time scale, and that several mechanisms must be involved in the first stage of the production of the hot nanoplasma induced from each cluster.

Performed studies of keV X-ray production from (Ar)n, (Kr)n and (Xe)n rare gas clusters (with n between 104 and 106 atoms/cluster) submitted to intense (18 W/cm2) infrared (800 nm) laser pulses. Up to 106 3 keV photons per pulse at a moderate (1015/cm3) atomic density have been observed. High resolution spectroscopy studies in the case of (Ar)n clusters have also been performed, giving unambiguous evidence of highly charge (up to heliumlike) ions with K vacancies production. We have determined the photon energies and the absolute photon emission yields as a function of several physical parameters governing the interaction: size and atomic number of the clusters, peak intensity of the laser. Unexpectedly low laser intensity thresholds ( approximately=1015 Wcm-2) have been measured. The result obtained indicate nevertheless that X-rays may be emitted before cluster explosion on a subpicosecond time scale, and that several mechanisms must be involved in the first stage of the production of the hot nanoplasma induced from each cluster

International audience; We have performed studies of keV x-ray production from (Ar)n , (Kr)n and (Xe)n rare gas clusters (with n between 104 and 106 atoms/cluster) submitted to intense (~10^18 W/cm2) infrared (790 nm) laser pulses. We have determined the photon energies and the absolute photon emission yields as a function of several physical parameters governing the interaction : size and atomic number of the clusters, peak intensity of the laser. Up to 10^6 3 keV photons per pulse at a moderate (10^15/cm3) atomic density have been observed. High resolution spectroscopy studies in the case of (Ar)n clusters have also been performed, giving unambiguous evidence of highly charged (up to heliumlike) ions with K vacancies production. The results obtained indicate that X-rays are emitted before cluster explosion on a subpicosecond time scale, and shed some light on the mechanisms involved in the first stage of the production of the nanoplasma induced from each cluster.

International audience; Experimental studies of the production and transport of projectile excited states in solid carbon targets have been performed for Ar17+ and Kr35+ at high velocity (respectively vp=23 and 35.6 a.u.). A range of target thicknesses from single collision condition to equilibrium has been investigated. Charge state distributions, nΛ populations of core and Rydberg projectile states, as well as the population of fine structure substates (nΛj) are determined. Theoretical predictions have been developed both in a collisional and a dynamical screening picture, using quantum as well as classical descriptions for the transport of projectile excited states. Discussions based on a comparison between experimental results and the different types of calculations are presented.

Two different types of descriptions can be used to calculate the slowing down of a projectile through materials. For both approaches, improvements towards fully ab initio calculations are attempted by several groups while, in the past, the prediction of stopping power of heavy ions had to rely on the use of "free parameters" like the effective nuclear charge of the projectile. The first description assumes that ion-solid interaction is the result of a series of binary collisions with the target electrons. In this collisional picture, the evolution of charge state distributions of the projectile at the exit of solid targets, involving core state populations, can be successfully predicted in many cases (like for the ETACHA code). In the other one (the dielectric theory), the target electrons are considered to respond collectively to the passage of the projectile. The polarization of the medium can be described as a wake of electronic density fluctuation trailing the ion. The gradient of the wake potential defines an electric field responsible for the stopping power. This electric field also acts directly on the excited levels of the projectile and will induce, among other effects, binding energy shifts as well as Stark mixing of substates. Until recently, only "quasi-free" target electrons were considered in this approach. Up to now, it exists in fact very few experimental results that can be used to decide which of these pictures is the most appropriate and to define eventually their validity limits. In particular, tests on the predictions of the wake model concerning the spatial extension of the electronic density fluctuations are needed. Atomic physics experiments can be used to shed some light on ion-matter interaction. Looking at one partner of the collision, namely the excited state populations of the projectile, the response of the material may be probed.