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).

A time-of-flight ion collector was used to measure the energy of ions from the plasma produced by a high-power CO2 laser pulse focused on a flat polyethylene target. At laser irradiances exceeding 5×1012 W/cm2 at the target, high-energy ion current spikes appeared in addition to the ion current from an expanding thermalized plasma. The measured arrival time of these spikes was consistent with the assumption that ions of different charge and mass were accelerated by a high potential during the laser pulse which was produced by a steep pressure gradient at the plasma surface. The accelerating potential (equal to the measured energy of a singly charged ion) was proportional to the laser irradiance at the target to the 2/3 power. At an irradiance of 2×1014 W/cm2, the H+ ion energy was 140 keV. About 90% of the total ion energy appeared as high-energy ions.

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can make an order-of-magnitude estimate of r using a classical hard-sphere model for the collisions where the rotons are assumed to be stationary, and the He^ quasiparticles move with a mean speed {v) = {^kT/m^''Y''^, Thenwhere r'Ms the mean collision frequency, n is the number density of atoms, and m^'^-^2,Zm^ is the effective mass of the He^ quasiparticle. Using a value ofa = 1.6xl0"^^ cm^ measured by Herzlinger and King,^ this expression becomes r(°K) = 5.7X, in satisfactory agreement with our results.

Generation of vacuum ultraviolet radiation by plasma nonlinearities AIP Conf. Proc. 90, 224 (1982); 10.1063/1.33764Photoionization quantometer for absolute intensity measurements of vacuum ultraviolet and soft xray radiation from laser plasma Rev. Sci. Instrum. 52, 16 (1981);