Two-dimensional ion emission from laser-produced plasmas

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Abstract
The expansion of laser-produced plasmas in two-dimensions is examined analytically using an asymptotic (time→∞) isothermal self-similar model. The ion emission velocity and energy spectra are calculated and expressions given for the number and energy of expanding ions as a function of angle to the target. By relating the total ion kinetic energy of expansion to the temperature of the initial plasma, it is shown that ion probe signals give a measure of the initial plasma temperature. The model is extended to a plasma with two initial temperatures (a ‘hot’ component and a ‘cold’ component) and it is shown that the ion energy spectra here can be used to deduce the initial temperatures of the ‘hot’ and ‘cold’ ions and the relative number of the ‘hot’ ions to the ‘cold’ ions. The results are used to interpret data from an array of ion probes (at different angles to the target) for a plasma produced by irradiating a 25 μm thick nickel foil with a ∼20 ρs neodymium laser pulse.