Saturation effects in laser-induced breakdown spectroscopy in water for elemental analysis have been investigated. Existing theoretical model of laser-induced plasma in solids has been applied to liquid phase under some simplifying assumptions to take account of the laser pulse energy dependence of atomic emissions from Na and Cu in aqueous solution. The theory was found to explain the emission process for laser energies up to but below the saturation level. The saturation limit of the emission with laser pulse energy corresponds well with that of the plasma temperature deduced from blackbody emission considerations. The saturation energies for atomic emissions were found to be lower for bulk excitations compared to water jet excitations. The dependence of signal strength on sample concentration indicated that the concentration values at saturation are lower at higher laser energies, as is expected from the theoretical model.

We present two contrasting cases of the interaction of a high intensity laser beam with overdense plasma, namely the case of a circular polarization, and the case of a linear polarization of the laser beam. An Eulerian-Vlasov code is used for the numerical solution of the one-dimensional relativistic Vlasov-Maxwell set of equations, for both electrons and ions. The laser beam is incident normally on the plasma surface. We consider the case when the laser wave free space wavelength λ0 is greater than the scale length of the jump in the plasma density at the plasma edge Ledge (λ0 ≫ Ledge) and the ratio of the plasma density to the critical density is such that n/ncr ≫ 1. The incident high intensity laser radiation is pushing the electrons at the plasma surface through the ponderomotive pressure, producing a sharp density gradient at the plasma surface. There is a build-up of the electron density at this sharp edge that creates a space-charge, giving rise to a longitudinal electric field. The results obtained differ substantially in several aspects when circular or linear polarization for the incident laser wave is considered. In the case of a circular polarization, the radiation pressure is pushing the sharp edge in the forward direction, and the ions are accelerated and reach a free streaming expansion phase where they are neutralized by the electrons. For the case of a linear polarization, there is a standing structure with a sharp edge that forms at the wave front, and in this case, the electrons at the plasma edge oscillate nonlinearly in the field of the wave, which periodically goes to zero. This results in an important distorsion in the reflected electromagnetic wave that includes the generation of harmonics. We present two simulations to illustrate the differences between these two cases. The generation and propagation of collisionless shock waves in these systems are investigated. The results underline the importance of including the ion dynamics in the interaction of high intensity laser waves with overdense plasmas.

In this work, a laser-produced plasma source was used to create xenon (Xe) photoionized plasmas. An extreme ultraviolet (EUV) radiation beam was focused onto a gas stream, injected into a vacuum chamber synchronously with the EUV pulse. Energies of photons exceeding 100 eV allowed for inner-shell ionization of Xe atoms. Creation of N-shell vacancies resulted in N-shell fluorescence and was followed by multiple ionization. Time-integrated EUV spectra, corresponding to excited states in Xe II–V ions, were recorded. Several emission lines detected in the 39–65 nm wavelength range were not reported earlier. They were not identified due to lack of a corresponding information in published databases. Except spectral measurements in the EUV range, time resolved ultraviolet and visible spectra, originating from Xe II and III ions, were recorded. For spectral lines, corresponding to radiative transitions in Xe II ions, electron temperature was calculated based on a Boltzmann plot method. Based on this method the temperature was measured for different time delays according to the driving EUV pulses.

Advancement of ion acceleration by intense laser pulses is studied with ultra-thin nanometer-thick diamond like carbon and micrometer-thick Titanium target foils. Both investigations aim at optimizing the electron density distribution which is the key for efficient laser driven ion acceleration. While recently found maximum ion energies achieved with ultra-thin foils mark record values micrometer thick foils are flexible in terms of atomic constituents. Electron recirculation is one prerequisite for the validity of a very simple model that can approximate the dependence of ion energies of nanometer-thick targets when all electrons of the irradiated target area interact coherently with the laser pulse and Coherent Acceleration of Ions by Laser pulses (CAIL) becomes dominant. Complementary experiments, an analytical model and particle in cell computer simulations show, that with regard to ultra-short laser pulses (duration ~45 fs at intensities up to 5 × 1019 W/cm2) and a micrometer-thick target foil with higher atomic number a close to linear increase of ion energies manifests in a certain range of laser intensities.

An analytical formalism of self focusing and self-phase modulation of an intense short pulse laser in a plasma due to relativistic and ponderomotive nonlinearities is developed. In the paraxial ray approximation, the pulse retains its Gaussian radial profile, however, its spot size varies with the distance of propagation in a periodic manner. It is influenced by self focusing. The frequency of the laser undergoes red shift. For a tanhyperbolic temporal profile of pulse, the red-shift is maximum at the foot of the pulse and decreases slowly as one goes to higher and higher intensity portions. The effect of ponderomotive nonlinearity is very significant in this respect. The maximum downshift occurs at a distance at which the laser acquires a minimum spot size. With retarded time normalized axial intensity increases more at z ~ Rd and the radial intensity is also more narrowly peaked at z ~ Rd, where Rd = 2π r02/λ is the Rayleigh length, r0 and λ are the spot size and wavelength of the laser pulse respectively.

We use a two-dimensional particle-in-cell simulation to investigate the dynamic polarization and stopping power for an ion beam propagating through a two-component plasma, which is simultaneously irradiated by a strong laser pulse. Compared to the laser-free case, we observe a reduction in the instantaneous stopping power that initially follows the shape of the laser pulse and becomes particularly large as the laser frequency approaches the plasma electron frequency. We attribute this large reduction in the ion stopping power to an increase in plasma temperature due to the energy absorbed in the plasma from the laser pulse through the process of wave heating. In addition, dynamic polarization of the plasma by the ion is found to be strongly modulated by the laser field.

The article presents the results of the experimental research on precision measurement of total stopping range and energy deposition function of intermediate and heavy ion beams in cold solid matter. The “thick target” method proves to be appropriate for this purpose. Two types of detectors were developed which provide an error of the total stopping range measurement of less than 3% and of the beam energy deposition function of about 7%. The experiments with 58Ni+26, 197Au+65, and 238U+72 ion beams in the energy range 100–300 MeV/u were performed on SIS-18 (Gesellschaft für Schwerionenforschung, Darmstadt) in 1999–2001. The measured data on the total stopping ranges for the above ion species in bulk and foiled Al and Cu targets are presented. The investigation showed that there is a noticeable discrepancy between the measured stopping ranges and the theoretically predicted ones. Also, it was shown that realistic ion energy deposition depends on the type of target (bulk or foiled). Further investigation is necessary to clarify the latter.

This paper reports the measurement of the energy loss of protons at the energy of 100 keV penetrating a partially ionized hydrogen plasma. The plasma of ne ≈ 1015–16 cm−3; Te ≈ 1–2 eV and lifetime of about 8 µs is created by the hydrogen gas discharge. The experimental results show an increase of a factor of 2.8 in the energy loss, which are in good agreement with the Bethe, Standard Stopping Model, Li–Petrasso and Vlasov models’ predictions within the error limit. The Bethe–Bloch Coulomb logarithm term is found to increase by a factor of 4.0 for free electrons as compared with the situation where bound electrons prevail. The potential application of protons energy loss for diagnosing the electron density in plasma is proposed too.

The fast ignitor concept for inertial confinement fusion relies on the generation of hot electrons, produced by a short-pulse ultrahigh intensity laser, which propagate through high-density plasma to deposit their energy in the compressed fuel core and heat it to ignition. In preliminary experiments designed to investigate deep heating of high-density matter, we used a 20 joule, 0.5–30 ps laser to heat solid targets, and used emission spectroscopy to measure plasma temperatures and densities achieved at large depths (2–20 microns) away from the initial target surface. The targets consisted of an Al tracer layer buried within a massive CH slab; H-like and He-like line emission was then used to diagnose plasma conditions. We observe spectra from tracer layers buried up to 20 microns deep, measure emission durations of up to 200 ps, measure plasma temperatures up to Te=650 eV, and measure electron densities above 1023 cm−3. Analysis is in progress, but the data are in reasonable agreement with heating simulations when space-charge induced inhibition is included in hot-electron transport, and this supports the conclusion that the deep heating is initiated by hot electrons.

The optimum convolution of dual short pulse for producing the maximum wakefield and the highest dissociation probability of CH4 has been investigated. By using three fundamental shapes of pulses though four different arrangements, the generated wake are considered in plasma. It is found that when the first and second pulses were rectangular–triangular and sinusoidal pulse shapes, respectively, the resultant wakefield amplitude is the highest. This effect opens up a new novel way by pulse shaping mechanism in the photo dissociation dynamics of molecules and controlling of chemical reactions in the desired channels by short pulse intense lasers for reducing the computation time of genetic algorithm model. Using field assisted dissociation model, the dissociation probability for a CH4+ molecule exposed to a 100 femtosecond 8 Jcm−2 Ti:Sapphire laser pulse is calculated. Here, the highest possible dissociation probability of the methane ion is calculated by the gradient optimization method in which the gradient of a function should be in the direction of the local extremes. The C-H molecular bond of CH4+ ion is assumed to be in the same direction as the electric field component of the laser pulse. These results show that there is an excellent match with experimental data. The remarkable feature of this work is that the sensitivity of the dissociation probability of the initial bond length q, is studied and the desired product channel is controlled by variation of the laser intensity and it's time evolution by introducing a characteristic vectored space for intensity and duration of two tailored rectangular femtosecond laser pulses.

A theoretical model of resonance absorption initiated by self-focusing filamentation is proposed on the bases of experiments on the 2ω0 time resolved spectrum, slow ion emission and filamentation of 3ω0/2 emission. A number of aspects of the experimental results can be well explained by this model.

The Low Temperatures Laboratory of CEA/Grenoble (France) is involved in the development of cryogenic systems for inertial fusion since a ten of years. A conceptual design for the cryogenic infrastructure of the Laser MegaJoule (LMJ) facility has been proposed. Several prototypes have been designed, built and tested like for example the 1500 bars cryo compressor for the targets filling, the target positioner and the thermal shroud remover.

The HIPER project will necessitate the development of such equipments. The main difference is that this time, the cryogenic targets are direct drive targets. The first phase of HIPER experiments is a single shot period. Based on the experience gained the last years, not only by our laboratory but also by Omega and G.A teams, we could design the new HIPER equipments for this phase.

Some experimental results obtained with the prototypes of the LMJ cryogenic system are given and a first conceptual design for the HIPER single shot cryogenic system is shown.

The energy spectra of heavy ions emitted from laser-produced plasmas were determined by the use of a technique relying on the implantation of plasma ions into a substrate located close to the plasma. Ion energy spectra were reconstructed from depth profiles of the implanted ions measured by the standard Rutherford back-scattering (RBS) technique employing 2 MeV alpha particles scattered at 170° laboratory angle. The energy spectra of Ag, Au, Sn, and Pb ions, implanted into aluminum or steel foils, are presented. A review of other techniques for ion energy spectrum measurement is presented and their limitations are discussed.

We describe two approaches to the design of a direct-drive high-gain pellet for inertial confinement fusion reactors that has enhanced stability due to the reduction in the Rayleigh-Taylor growth rate and enhanced thermal smoothing of laser imprint. The first design incorporates an overcoat containing a high-Z element that radiatively heats the ablator during the foot of the laser pulse. The second incorporates a very low density foam ablator that is compressed by a series of transmitted and reflected shocks. Both designs enhance thermal smoothing by developing a very long density scale length and high electron densities in the ablator blowoff.

Low-fluence laser interaction with metallic target is investigated in a wide range of irradiance, from 5 × 106 to 1011 W/cm2, with 4- and 30-ns laser-pulse durations and 1.06-μm wavelength. Edge effects are avoided by means of large surfaces of irradiation (5 cm2). Specific diagnostics such as a ballistic pendulum and a piezoelectric quartz gauge are developed to measure the total momentum imparted to the target, as well as the temporal evolution of the stress at the rear side of the target. Specular reflection and sidescattering of the laser light from the target are also measured. The behavior of 2024 aluminum alloy is particularly studied. The results are interpreted in terms of liquid-vapor transition and change in laser absorption.

In light of experimental data, the theoretical analysis of surface absorption is reviewed, showing the dependence on metal temperature and laser wavelength. The thermal and mechanical coupling is also calculated.

Numerical simulations are performed with a 1–D Lagrangian hydrodynamic code including modifications for low-pressure regimes. The multiphase equation of state is extended to take into account negative pressures. An elastoplastic module is introduced into the code. A quite good agreement is obtained with the measurements of the stress and of the mechanical coupling coefficient.

Kinetic collisionless expansion of a spherical cluster composed of light and heavy cold ions and hot electrons is studied for arbitrary electron temperature. A wide set of regimes of plasma expansion, from nearly quasi-neutral to Coulomb explosion, is described from a unified description. The time evolution of the velocity, density, and energy spectra for accelerated ions is studied. The study demonstrates that an optimum light ion concentration from few percent to few tens percent, depending on the electron temperature, leads to a quasi-monoenergetic spectra with numbers as high as 70–80% of the total number of light ions.

The radiation characteristics of a high-current hydrogen thyratron plasma have been modeled in order to study this aspect of the physics of the conductive phase of thyratron operation. The intensities and radiative energy efficiencies of the atomic and molecular systems have been calculated in detail. A model is developed that is useful for studies of photoemission. For discharge parameters Te ≈ 1 eV, ionization fraction of ∼10−2 and background density of 1016 cm−3, the total power of the emitted radiation is estimated to be of the order of 5% of the total input power during the conductive phase.

In the present paper, we have investigated the growth of a Gaussian perturbation superimposed on a Gaussian laser beam. The nonlinearity we have considered is of relativistic type. We have setup the nonlinear differential equations for beam width parameter of the main beam, growth and width of the laser spike by using the WKB and paraxial ray approximation. These are coupled ordinary differential equations and therefore these are simultaneously solved numerically using the Runge Kutta method. It has been observed from the analysis that self-focusing/defocusing of the main beam and the spike determine the growth dynamic of the spike.

This work is devoted to improving relativistic self-focusing of intense laser beam in underdense unmagnetized plasma. New density profiles are introduced to achieve beam width parameter up to the wavelength of the propagating laser. By investigating variations of the beam width parameter in presence of different density profiles it is found that the beam width parameter is considerably decreased for the introduced density ramp comparing with uniform density and earlier introduced density ramp profiles. By using this new density profile high intensity laser pulses are guided over several Rayleigh lengths with extremely small beam width parameter.