Onset of diffuse reflectivity and fast electron flux inhibition in 528-nm-laser - solid interactions at ultrahigh intensity

Using a high-power femtosecond frequency-doubled Nd:glass laser system with a contrast ratio of 1012, the interaction between light and matter up to intensities of 1019 Wcm-2has been investigated. The absorption of the laser light in solid aluminum is almost independent of the polarization, peaks at about 25 degree, and reaches values of almost 45%. Assuming an exponential electron distribution, a temperature of 420 keV at 4x1018 Wcm-2was measured. These experiments and the detection of the hard-x-ray radiation (60 keV - 1 MeV) implied a conversion efficiency of 10-4 - 10-3 into suprathermal electrons. A second low-energy electron distribution either with trajectories mainly parallel to the target surface or with a reduced penetration depth due to flux inhibition was also inferred from Kα line radiation measurements. copyright 1997 The American Physical Society