Plasma ion spectra from laser produced plasmas at λ = 1·06 μm and λ =0·53 μm

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Abstract
Wavelength dependent absorption in laser-plasma interactions was investigated by measuring the energy spectra of freely expanding plasmas in their asymptotic stage of expansion. The experiments were performed with both 1·06- and 0·53-μm-wavelength light incident on flat tantalum targets. The experimental conditions were chosen adequately to ensure that inverse bremsstrahlung was the dominating absorption mechanism. As a result it is found that the absorption is enhanced at the shorter wavelength by a factor of 1·3. Primarily this leads to a higher ionisation state of the plasma and higher kinetic ion energies and temperatures, respectively, while the amount of ablated mass is approximately the same.