Fast ions and hot electrons in the laser–plasma interaction

Abstract

Data on the emission of energetic ions produced in laser–matter interactions have been analyzed for a wide variety of laser wavelengths, energies, and pulse lengths. Strong correlation has been found between the bulk energy per AMU for fast ions measured by charge cups and the x-ray-determined hot electron temperature. Five theoretical models have been used to explain this correlation. The models include (1) a steady-state spherically symmetric fluid model with classical electron heat conduction, (2) a steady-state spherically symmetric fluid model with flux limited electron heat conduction, (3) a simple analytic model of an isothermal rarefaction followed by a free expansion, (4) the lasnex hydrodynamics code [Comments Plasma Phys. Controlled Fusion 2, 85 (1975)], calculations employing a spherical expansion and simple initial conditions, and (5) the lasnex code with its full array of absorption, transport, and emission physics. The results obtained with these models are in good agreement with the experiments and indicate that the detailed shape of the correlation curve between mean fast ion energy and hot electron temperature is due to target surface impurities at the higher temperatures (higher laser intensities) and to the expansion of bulk target material at the lower temperatures (lower laser intensities).

Energetic proton generation in ultra-intense laser–solid interactions

“…It is based on a picture that arose 20 years ago during the Los Alamos Helios laser program, modified somewhat because of differences in target geometry and laser pulse length. Details can be found in Gitomer, et al 7 The first point to discuss is that they quickly realized that the majority of the ions detected with their spectrometer were protons, independent of target material. The cause for this was traced to a thin (~ 50 Angstroms) layer of contaminant, which is always present in the experiments, a large fraction of which are hydrogen atoms.…”

High-intensity laser-driven proton acceleration: influence of pulse contrast

“…Gitomer et al (1986) provides a review of early ion measurements with long pulse (nanosecond) CO 2 lasers. In these experiments, at focused intensities of approximately 10 16 W cm K2 , protons and carbon ions were accelerated to energies of the order of tens of keV.…”

Investigations of Field Dynamics in Laser Plasmas with Proton Imaging

“…l is the effective extension of the electric and magnetic field 47 protons. The contamination layer consists of hydrocarbon and water mainly [76,88]. The shown spectra were generated by irradiating a 5 µm thick Titanium foil with the Ti:Sa laser at an intensity of about 10 19 W/cm 2 .…”