95 research outputs found
Coloration quenching of radiochromic films irradiated with proton energies close to maximum energy loss
Optimization of plasma mirror reflectivity and optical quality using double laser pulses
We measure a record 962.5 % specularly reflected energy fraction from an interaction with a plasma mirror surface preionised by a controlled prepulse and find that the optical quality is dependent on the inter pulse time delay. Simulations show that the main pulse reflected energy is a strong function of plasma density scale length, which increases with the time delay and reaches a peak reflectivity for a scale length of 0.3 m, which is achieved here for a pulse separation time of 3 ps. It is found that the incident laser quasi near field intensity distribution leads to nonuniformities in this plasma expansion and consequent critical surface position distribution. The plasma mirror optical quality is found to be governed by the resultant perturbations in the critical surface position, which become larger with inter pulse time delay
Quantitative phase contrast imaging of a shock-wave with a laser-plasma based X-ray source
X-ray phase contrast imaging (XPCI) is more sensitive to density variations than X-ray absorption radiography, which is a crucial advantage when imaging weakly-absorbing, low-Z materials, or steep density gradients in matter under extreme conditions. Here, we describe the application of a polychromatic X-ray laser-plasma source (duration ~0.5 ps, photon energy >1 keV) to the study of a laser-driven shock travelling in plastic material. The XPCI technique allows for a clear identification of the shock front as well as of small-scale features present during the interaction. Quantitative analysis of the compressed object is achieved using a density map reconstructed from the experimental data
Guided Electromagnetic Discharge Pulses Driven by Short Intense Laser Pulses: Characterisation and Modelling
Strong electromagnetic pulses (EMP) are generated from intense laser
interactions with solid-density targets, and can be guided by the target
geometry, specifically through conductive connections to the ground. We present
an experimental characterization, by time- and spatial-resolved proton
deflectometry, of guided electromagnetic discharge pulses along wires including
a coil, driven by 0.5 ps, 50 J, 1e19 W/cm2 laser pulses. Proton-deflectometry
data allows to time-resolve first the EMP due to the laser-driven target
charging and then the return EMP from the ground through the conductive target
stalk. Both EMPs have a typical duration of tens of ps and correspond to
currents in the kA-range with electric-field amplitudes of multiple GV/m. The
sub-mm coil in the target rod creates lensing effects on probing protons, due
to both magnetic- and electric-field contributions. This way, protons of 10
MeV-energy range are focused over cm-scale distances. Experimental results are
supported by analytical modelling and high-resolution numerical
particle-in-cell simulations, unraveling the likely presence of a surface
plasma, which parameters define the discharge pulse dispersion in the
non-linear propagation regime
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