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The 2D projection phase-contrast imaging performance of the ultrafast laser-based x-ray (ULX) source has been investigated. The potential of such a novel x-ray source has been assessed by imaging a reference object (Contrast Detail Evaluation phantom) in the in-line holography geometry and by applying a simple 1D numerical model to the data analysis. The results indicate that the ULX is a promising technique for 2D projection phase-contrast imaging and for implementation of phase-contrast micro-Computed Tomography (μ-CT). This is because by using high contrast laser pulse ULX simultaneously provides a very small x-ray source size along with a high average x-ray flux. In addition, due to the ultrashort x-ray burst duration, ULX might allow practical implementation of ultrafast phase-contrast stroboscopy and time-of-flight based electronic scatter rejection. This technique is also of interest for time resolved radiography to follow shock waves and radiative fronts propagating in an opaque matter. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, we report on bi-dimensional Particle-In-Cell simulations performed in order to reproduce the laser-driven proton acceleration obtained when a commercial 200 TW Ti:Sa Laser hits a solid target. The laser-to prepulse contrast was enhanced using plasma mirrors yielding to a main-to-prepulse contrast of ~1012. We varied the pulse duration from 30 fs to 500 fs and the target thickness from 30 nm to several tens of μm. The on-target laser energy was up to 1.8J leading to an intensity in excess of 1020W cm-2. A comparison between numerical and existing experimental data [S. Fourmaux et al., Phys. Plasmas 20, 013110 (2013)] is performed, showing a good agreement between experimental results and simulations which confirms that for ultra-thin targets there is an optimum expansion regime. This regime depends on the target thickness and on the laser intensity: if the target is too expanded, the laser travels through the target without being able to deposit its energy within the target. If the target is not sufficiently expanded, the laser energy is reflected by the target. It is important to note that maximum proton energies are reached at longer pulse durations (in the 100 fs regime) than what is currently the best compression pulse length for this type of lasers (typically 20-30 fs). This duration, around 50-100 fs, can be considered a minimum energy transfer time between hot electrons to ions during the considered acceleration process. [ABSTRACT FROM AUTHOR]

Interaction of intense Ti:sapphire laser with solid targets has been studied experimentally by measuring hard x-ray and hot electron generation. Hard x-ray (8–100 keV) emission spectrum and Kα x-ray conversion efficiency (ηK) from plasma have been studied as a function of laser intensity (1017–1019 W/cm2), pulse duration (70–400)fs, and laser pulse fluence. For intensity I>1×1017 W/cm2, the Ag ηK increases to reach a maximum value of 2×10-5 at an intensity I=4×1018 W/cm2. Hot electron temperature (KTh) and ηK scaling laws have been studied as a function of the laser parameters. A stronger dependence of KTh and ηK as a function of the laser fluence than on pulse duration or laser intensity has been observed. The contribution of another nonlinear mechanism, besides resonance absorption, to hard x-ray enhancement has been demonstrated via hot electron angular distribution and particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

We show through experiments that a transition from laser wakefield acceleration (LWFA) regime to a plasma wakefield acceleration (PWFA) regime can drive electrons up to energies close to the GeV level. Initially, the acceleration mechanism is dominated by the bubble created by the laser in the nonlinear regime of LWFA, leading to an injection of a large number of electrons. After propagation beyond the depletion length, leading to a depletion of the laser pulse, whose transverse ponderomotive force is not able to sustain the bubble anymore, the high energy dense bunch of electrons propagating inside bubble will drive its own wakefield by a PWFA regime. This wakefield will be able to trap and accelerate a population of electrons up to the GeV level during this second stage. Three dimensional particle-in-cell simulations support this analysis and confirm the scenario. [ABSTRACT FROM AUTHOR]