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Residual energy in plasmas produced by intense subpicosecond lasers.

This paper presents parameter studies to find the optimum conditions for the production of a cold highly ionized plasma suitable for the generation of recombination x-ray lasers. The effect of space-charge fields on the residual electron energy of optical-field-ionized plasmas is studied using a classical theory of above-threshold ionization and particle-in-cell simulations. The dependence of the residual energy on the pump-laser wavelength and peak intensity is strongly influenced by the dependence of the quiver energy on these parameters. The effect of space-charge fields indicates that the residual energy can be minimized by a suitable matching of the laser pulse length to the plasma density. The effect of collisional heating on the residual energy is also discussed.