Littérature scientifique sur le sujet « Laser-matter interaction, laser-plasma physics, laser-based ion acceleration, TNSA »

Basic properties of generation of high-current ion beams using the skin-layer ponderomotive acceleration (S-LPA) mechanism, induced by a short laser pulse interacting with a solid target are studied. Simplified scaling laws for the ion energies, the ion current densities, the ion beam intensities, and the efficiency of ions' production are derived for the cases of subrelativistic and relativistic laser-plasma interactions. The results of the time-of-flight measurements performed for both backward-accelerated ion beams from a massive target and forward-accelerated beams from a thin foil target irradiated by 1-ps laser pulse of intensity up to ∼ 1017 W/cm2 are presented. The ion current densities and the ion beam intensities at the source obtained from these measurements are compared to the ones achieved in recent short-pulse experiments using the target normal sheath acceleration (TNSA) mechanism at relativistic (>1019 W/cm2) laser intensities. The possibility of application of high-current ion beams produced by S-LPA at relativistic intensities for fast ignition of fusion target is considered. Using the derived scaling laws for the ion beam parameters, the achievement conditions for ignition of compressed DT fuel with ion beams driven by ps laser pulses of total energy ≤ 100 kJ is shown.

Abstract The laser-matter interaction using nominal laser intensity above 1015 W/cm2 generates in vacuum non-equilibrium plasmas accelerating ions at energies from tens keV up to hundreds MeV. From thin targets, using the TNSA regime, plasma is generated in the forward direction accelerating ions above 1 MeV per charge state and inducing high-ionization states. Generally, the ion energies follow a Boltzmann-like distribution characterized by a cutoff at high energy and by a Coulomb-shift towards high energy increasing the ion charge state. The accelerated ions are emitted with the high directivity, depending on the ion charge state and ion mass, along the normal to the target surface. The ion fluencies depend on the ablated mass by laser, indeed it is low for thin targets. Ions accelerated from plasma can be implanted on different substrates such as Si crystals, glassy-carbon and polymers at different fluences. The ion dose increment of implanted substrates is obtainable with repetitive laser shots and with repetitive plasma emissions. Ion beam analytical methods (IBA), such as Rutherford backscattering spectroscopy (RBS), elastic recoil detection analysis (ERDA) and proton-induced X-ray emission (PIXE) can be employed to analyse the implanted species in the substrates. Such analyses represent ‘off-line’ methods to extrapolate and to character the plasma ion stream emission as well as to investigate the chemical and physical modifications of the implanted surface. The multi-energy and species ion implantation from plasma, at high fluency, changes the physical and chemical properties of the implanted substrates, in fact, many parameters, such as morphology, hardness, optical and mechanical properties, wetting ability and nanostructure generation may be modified through the thermal-assisted implantation by multi-energy ions from laser-generated plasma.

In several experiments, faster ions were produced from the backside of solid targets irradiated by powerful laser pulses. The ion acceleration was considered due to the negative electrostatic sheath formed on the backside of the target (TNSA), or to the expansion wave starting at the backside surface, or to the expansion wave and to its embedded electrostatic rarefaction shock. In this experiment, ions have been generated by transferring energy to a controlled amount of mass before the target become transparent by gas dynamic expansion (controlled amount of mass mode (CAM)). The targets used were thin transparent disks causally isolated from the holder to trim down, during the interaction process, unwanted effects due to the surrounding parts. Two kinds of target corresponding to a different set of parameters were designed (LARGE and SMALL). Both targets were conceived to survive, in the actual contrast conditions, to the low power pulse forerunning the giant laser pulse, bigger margin but lower performances being assigned to LARGE. For comparison standard square foils under the same focusing conditions, were also studied (LARGE-LIKE and SMALL-LIKE irradiation).

AbstractNanostructured targets, based on hydrogenated polymers with embedded nanostructures, were prepared as thin micrometric foils for high-intensity laser irradiation in TNSA regime to produce high-ion acceleration. Experiments were performed at the PALS facility, in Prague, by using 1315 nm wavelength, 300 ps pulse duration and an intensity of 1016W/cm2and at the IPPLM, in Warsaw, by using 800 nm wavelength, 40 fs pulse duration, and an intensity of 1019W/cm2. Forward plasma diagnostic mainly uses SiC detectors and ion collectors in time of flight (TOF) configuration. At these intensities, ions can be accelerated at energies above 1 MeV per nucleon. In presence of Au nanoparticles, and/or under particular irradiation conditions, effects of resonant absorption can induce ion acceleration enhancement up to values of the order of 4 MeV per nucleon.

AbstractWe report on the experimental observation of Smith–Purcell (SP) radiation generation by charged particle beam from laser–matter interactions. High-power laser pulses were focused onto a thin metal foil target to generate proton beams with energies up to 1.7 MeV via the target normal sheath acceleration (TNSA) process. The particle beam from the TNSA process was sent close to a periodic structure to generate SP radiation. Sub-μJ terahertz pulses were recorded using a pyroelectric detector. Simultaneous measurement of the ion spectra allowed us to estimate the power of the emitted radiation and compare it with the experimental results. The distance between the grating and the particle beam was varied and its effect on the emitted radiation was studied.

Ion acceleration from high intensity short pulse laser interactions is of great interest due to a number of applications, and there has been significant work carried out with laser energies up to a few 100 J with 10's of femtosecond to 1 ps pulse durations. Here, we report results from an experiment at the OMEGA EP laser, where laser energy and pulse length were varied from 100 to 1250 J and 0.7–30 ps, respectively, in the moderate ([Formula: see text]) laser intensity regime. Ions and electrons were simultaneously measured from disk targets made of CH and CD by a Thomson parabola and a magnetic spectrometer, respectively. Measurements showed that the electron temperature, [Formula: see text] (MeV), has a dependence on the laser energy, [Formula: see text] (J), and pulse duration, [Formula: see text] (ps), and its empirical scaling was found to be [Formula: see text]. The maximum proton and deuteron energies are linearly dependent on the electron temperature, [Formula: see text] and [Formula: see text], respectively. A significant increase in proton numbers with the laser energy was also observed. The increase in the maximum proton energy and proton count with higher energy longer duration pulses presented in this article shows that such laser conditions have a great advantage for applications, such as the proton radiograph, in the moderate laser intensity regime.

Abstract Proton radiography using short-pulse laser drivers is an important tool in high-energy density (HED) science for dynamically diagnosing key characteristics in plasma interactions. Here we detail the first demonstration of target-normal sheath acceleration (TNSA)-based proton radiography the NIF-ARC laser system aided by the use of compound parabolic concentrators (CPCs). The multi-kJ energies available at the NIF-ARC laser allows for a high-brightness proton source for radiography and thus enabling a wide range of applications in HED science. In this demonstration, proton radiography of a physics package was performed and this work details the spectral properties of the TNSA proton probe as well as description of the resulting radiography quality.

In the present work, we propose the production of a hybrid graphene based material suitable to be laser irradiated with the aim to produce quasi-monoenergetic proton beams using a femtosecond laser system. The unique lattice structure of the irradiated solid thin target can affect the inside electron propagation, their outgoing from the rear side of a thin foil, and subsequently the plasma ion acceleration. The produced targets, have been characterized in composition, roughness and structure and for completeness irradiated. The yield and energy of the ions emitted from the laser-generated plasma have been monitored and the emission of proton stream profile exhibited an acceleration of the order of several MeVs/charge state.

We report on progress in the understanding of the effects of kilotesla-level applied magnetic fields on relativistic laser–plasma interactions. Ongoing advances in magnetic-field–generation techniques enable new and highly desirable phenomena, including magnetic-field–amplification platforms with reversible sign, focusing ion acceleration, and bulk-relativistic plasma heating. Building on recent advancements in laser–plasma interactions with applied magnetic fields, we introduce simple models for evaluating the effects of applied magnetic fields in magnetic-field amplification, sheath-based ion acceleration, and direct laser acceleration. These models indicate the feasibility of observing beneficial magnetic-field effects under experimentally relevant conditions and offer a starting point for future experimental design.

The Laser Plasma Division at the Centre for Advanced Technology is engaged in a variety of research and development activities on laser-plasma interaction with special emphasis on laser-matter interaction at ultra-high intensities. An important aspect of our future work is studies in laser-plasma based acceleration using an elaborate infrastructural set-up of ultra-fast laser and plasma diagnostic systems and recently acquired 10TW, 50fs Ti :Sapphire laser system. This paper presents outline of the planned studies in this field.

Recently, ultra-intense laser-driven ion acceleration has turned out to be an extremely interesting phenomenon, capable to produce ion beams which could potentially be suitable for applications as hadron therapy or dense matter diagnostics. The present PhD thesis is addressed to the study of Target Normal Sheath Acceleration (TNSA), namely the laser-based ion acceleration mechanism which dominates the presently accessible experimental conditions. The work is focused in particular on the theoretical modeling of TNSA, motivated by the need for an effective description which, by adopting proper approximations that can limit the required computational efforts, is capable to provide reliable predictions on the resulting ion beam features, given an initial laser-target configuration. Indeed, the development of a robust TNSA theoretical model would mean a deeper comprehension of the key physical factors governing the process, allowing at the same time to draw guidelines for potential experiments in the next future. In this dissertation, in order to achieve a significant advancement in the TNSA modeling field, the results of two original works are reported, the first is focused on a critical, quantitative analysis of existing descriptions, and the second, starting from the conclusions of such an analysis, is dedicated to the extension of a specific model, aiming at the inclusion of further, crucial, TNSA aspects. The quantitative analysis consists in the comparison of six well-known published descriptions, relying on their capability in estimating the maximum ion energy, which is tested over an extensive database of published TNSA experimental results, covering a wide range of laser-target conditions. Such a comparative study, despite the technical issues to be faced in order to reduce the arbitrariness of the results, allows to draw some interesting conclusions about the effectiveness of the six models considered and about TNSA effective modeling in general. According to the results, the quasi-static model proposed by M. Passoni and M. Lontano turns out to be the most reliable in predicting the ion cut-off energy, at the same time achieving such estimates through a self-consistent treatment of the accelerating potential. This work highlights also the limits of such a TNSA model, and of the main approximations usually adopted to obtain the different maximum ion energy estimates. Thus, starting from such considerations, an extension of this Passoni-Lontano model is proposed, including new crucial elements of TNSA physics within the description. In particular, further insights of the hot electron population dynamics are implemented, leading to a refined maximum energy prediction, which exhibits more solid theoretical bases, and which broadens the predicting capability of the original model to a larger range of system parameters. The resulting estimates are validated by means of literature experimental data and numerical simulations, demonstrating a remarkable agreement in most of the cases. The achieved model turns out to be particularly suitable in reproducing the maximum ion energy dependence on the target thickness, while some promising insights are obtained in the Mass Limited Targets (MLT) case. Nonetheless, further theoretical work is still required to attain a quantitative agreement with recently published experimental results on MLTs.