Plasmas were generated by 400 fs KrF laser pulses at intensities of ∼${10}^{17}$ W ${\mathrm{cm}}^{\mathrm{-}2}$ on aluminum targets. Reflectivity and x-ray emission were measured as a function of laser polarization, angle of incidence, and intensity. For the same absorbed intensity, p-polarized laser light is up to a factor of 5 more efficient in generating x rays (>0.5 keV) than s-polarized light. These results show the importance of an additional absorption process, besides collisional absorption, for short scale length plasmas that is effective for p-polarized light only and has the characteristics of resonance absorption.

• Received 20 August 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.794