Anna Levy

Double plasma mirror for ultrahigh temporal contrast ultraintense laser pulses

We present and characterize a very efficient optical device that employs the plasma mirror technique to increase the contrast of high-power laser systems. Contrast improvements higher than 10(4) with 50% transmission are shown to be routinely achieved on a typical 10 TW laser system when the pulse is reflected on two consecutive plasma mirrors. Used at the end of the laser system, this double plasma mirror preserves the spatial profile of the initial beam, is unaffected by shot-to-shot fluctuations, and is suitable for most high peak power laser systems. We use the generation of high-order harmonics as an effective test for the contrast improvement produced by the double plasma mirrors.

Field ionization model implemented in Particle In Cell code and applied to laser-accelerated carbon ions

A novel numerical modeling of field ionization in PIC (Particle In Cell) codes is presented. Based on the quasistatic approximation of the ADK (Ammosov Delone Krainov) theory and implemented through a Monte Carlo scheme, this model allows for multiple ionization processes. Two-dimensional PIC simulations are performed to analyze the cut-off energies of the laser-accelerated carbon ions measured on the UHI 10 Saclay facility. The influence of the target and the hydrocarbon pollutant composition on laser-accelerated carbon ion energies is demonstrated.

Investigation of laser-driven proton acceleration using ultra-short, ultra-intense laser pulses

We report optimization of laser-driven proton acceleration, for a range of experimental parameters available from a single ultrafast Ti:sapphire laser system. We have characterized laser-generated protons produced at the rear and front target surfaces of thin solid targets (15 nm to 90 μm thicknesses) irradiated with an ultra-intense laser pulse (up to 1020 W⋅cm−2, pulse duration 30 to 500 fs, and pulse energy 0.1 to 1.8 J). We find an almost symmetric behaviour for protons accelerated from rear and front sides, and a linear scaling of proton energy cut-off with increasing pulse energy. At constant laser intensity, we observe that the proton cut-off energy increases with increasing laser pulse duration, then roughly constant for pulses longer than 300 fs. Finally, we demonstrate that there is an optimum target thickness and pulse duration.

Investigation of longitudinal proton acceleration in exploded targets irradiated by intense short-pulse laser

It was recently shown that a promising way to accelerate protons in the forward direction to high energies is to use under-dense or near-critical density targets instead of solids. Simulations have revealed that the acceleration process depends on the density gradients of the plasma target. Indeed, under certain conditions, the most energetic protons are predicted to be accelerated by a collisionless shock mechanism that significantly increases their energy. We report here the results of a recent experiment dedicated to the study of longitudinal ion acceleration in partially exploded foils using a high intensity (∼5 × 1018 W/cm2) picosecond laser pulse. We show that protons accelerated using targets having moderate front and rear plasma gradients (up to ∼8 μm gradient length) exhibit similar maximum proton energy and number compared to proton beams that are produced, in similar laser conditions, from solid targets, in the well-known target normal sheath acceleration regime. Particle-In-Cell simulations, p...

Proton acceleration by moderately relativistic laser pulses interacting with solid density targets

We use two-dimensional (2D) particle-in-cell simulations to study the interaction of short-duration, moderately relativistic laser pulses with sub-micrometric dense hydrogen plasma slabs. Particular attention is devoted to proton acceleration by the target normal sheath mechanism. We observed that improved acceleration due to relativistic transparency of the target is unlikely for the shortest pulses, even for ultra-thin (~10 nm) targets. This mechanism would require either longer pulses or higher laser intensities. As the target density and thickness, pulse length, duration and polarization are varied, we see clear relationships between laser irradiance, hot electron temperature and peak proton energy. All these explain why, at a given incident laser energy level, the highest proton energy is not always obtained for the shortest-duration, highest-intensity pulse.

Proton Acceleration With High-Intensity Laser Pulses in Ultrahigh Contrast Regime

We investigate the interaction of a high-intensity (~5.1018 W/cm2) and short (~65 fs) laser pulse with thin foils (from 0.08 to 105 mum) in a regime of ultrahigh contrast (> 1010). This paper shows that for thicknesses less than about 10 mum, proton acceleration from both sides of the target presents quite symmetric features. Proton bunches emitted from each side show similar maximum energies and spatial characteristics. Moreover, we show that for ultrahigh-contrast pulses, the efficient acceleration mechanism is related to the Brunei effect and not to the ponderomotive force. Simulations performed with a 2-D particle-in-cell code are in close agreement with all experimental data.

Laser-Driven Ion Generation with Short, Intense, and High Contrast Pulses

About 10 years ago, first experimental works on high intensity( > 1018 W cm − 2) laser-driven proton acceleration showed the great potential of these ions bunches for different application domains (as, for instance, high resolution radiography, isochore heating, and fast ignition). Moreover, the prospect of a future exploitation of such high energy ions in hadron-therapy certainly further incited the scientific research in this domain. One of the goal of the present research lies in increasing the peak proton energy as this is a critical point for a number of applications. Reducing the target thickness is one of the suggested ways to get higher peak proton energies. Nevertheless, that can be realized using only very high contrast laser pulses.