E. Martinolli

Proton radiography as an electromagnetic field and density perturbation diagnostic (invited)

Laser driven proton beams have been used to diagnose transient fields and density perturbations in laser produced plasmas. Grid deflectometry techniques have been applied to proton radiography to obtain precise measurements of proton beam angles caused by electromagnetic fields in laser produced plasmas. Application of proton radiography to laser driven implosions has demonstrated that density conditions in compressed media can be diagnosed with million electron volt protons. This data has shown that proton radiography can provide unique insight into transient electromagnetic fields in super critical density plasmas and provide a density perturbation diagnostics in compressed matter.

Subfemtosecond, coherent, relativistic, and ballistic electron bunches generated at ω0 and 2ω0 in high intensity laser-matter interaction

Harmonics of the laser light have been observed from the rear side of solid targets irradiated by a laser beam at relativistic intensities. This emission evidences the acceleration of subfemtosecond electron bunches by the laser pulse in front of the target. These bunches emit coherent transition radiation (CTR) when passing through the back surface of the target. The spectral features of the signal recorded for targets of thicknesses up to several hundred microns are consistent with the electrons being accelerated by both the laser electric field—via vacuum heating and/or resonance absorption,—and the v×B component of the Lorentz force. The spatial study of the radiation shows that the relativistic electrons causing the CTR radiation are coherent and propagate ballistically through the target, originating from a source with a size of the order of the laser focal spot.

Conical crystal spectrograph for high brightness x-ray Kα spectroscopy in subpicosecond laser–solid interaction

A high brightness crystal spectrograph was designed and successfully used to study the x-ray Kα spectrum of aluminum as a diagnostic for target heating due to suprathermal electrons in subpicosecond laser–solid interaction experiments. Conical geometry was chosen in order to enhance spatial focusing, since an extremely low signal-to-noise ratio was expected for the photon flux, and to have a reasonable spectral range while occupying only a small solid angle within the target chamber. Very high image brightness is obtained through strong spatial focusing, as well as good spectral resolution. A simple analytical model and three-dimensional numerical simulation are presented to describe the crystal characteristics. The performance of the spectrograph was tested both on an optical bench and with a ray-tracing code. The experimental spectra allowed us to estimate the target temperature and characterize the fast electron transport. The spectrograph is considered to be particularly useful, in the configuration d...

Propagation In Matter Of Currents Of Relativistic Electrons Beyond The Alfven Limit, Produced In Ultra‐High‐Intensity Short‐Pulse Laser‐Matter Interactions

This paper reports the results of several experiments performed at the LULI laboratory (Palaiseau, France) concerning the propagation of large relativistic currents in matter from ultra‐high‐intensity laser pulse interaction with target. We present our results according to the type of diagnostics used in the experiments: 1) Kα emission and Kα imaging, 2) study of target rear side emission in the visible region, 3) time resolved optical shadowgraphy.

Generation and Transport of Fast Electrons in Laser Irradiated Targets at Relativistic Intensities

The transport of relativistic electrons in solid targets irradiated by a short laser pulse at relativistic intensities has been studied both experimentally and numerically. A Monte‐Carlo collision code takes into account individual collisions with the ions and electrons in the target. A 3D‐hybrid code takes into account these collisions as well as the generation of electric and magnetic fields and the self‐consistent motion of the electrons in these fields. It predicts a magnetic guiding of a fraction of the fast electron current over long distances and a localized heating of the material along the propagation axis. In experiments performed at LULI on the 100 TW laser facility, several diagnostics have been implemented to diagnose the geometry of the fast electron transport and the target heating. The typical conditions were: E1 ⩽ 20 J, λ = 1 μm, τ ≈ 300 fs, I ≈ 1018−5.1019W/cm2. The results indicate a modest heating of the target (typically 20–40 eV over 20 μm to 50 μm), consistent with an acceleration o...

Study of Fast Electron Propagation in Ultra-Intense Laser Pulse Interaction with Solid Targets Using Rear Side Optical Self-Radiation and Reflectivity-Based Diagnostics

Experimental results are reported on transport through a solid target of fast-electrons created by an ultra-intense laser pulse interaction. In particular, the goal was to determine the heating induced in the material by the fast electrons. Such a study is of great interest within the context of the Fast Igniter [1] approach to Inertial Confinement Fusion, where the heating needed to ignite nuclear reactions is supposed to be achieved by a sub-ps fast electron bunch. Experimentally, the main point is therefore to observe the propagation geometry of the fast electron beam and to estimate the amount of energy which can be carried and deposed in dense matter by a given electron source. So far, theory and simulations have not yet provided a complete picture of the prop-agation phenomena. Therefore, experimental work is requried in order to understand and dis crimed the basic processes involved.

Effects of self-generated electric and magnetic fields in laser-generated fast electron propagation in solid materials: Electric inhibition and beam pinching

We present some experimental results which demonstrate the presence of electric inhibition in the propagation of relativistic electrons generated by intense laser pulses, depending on target conductivity. The use of transparent targets and shadowgraphic techniques has made it possible to evidence electron jets moving at the speed of light, an indication of the presence of self-generated strong magnetic fields.