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Abstract

In laser-matter-interaction studies there is a continued interest in the emission and transport of x-rays in laser-irradiated solids. We have irradiated metal foil targets with 0.532 μm laser light with pulse lengths of 2.4 to 2.6 us at absorbed irradiances of 10¹² to 10¹³ W/cm . Calorimetric measurements of the energy of x-ray emission by the laser-produced plasma on the target frontside indicate that copper is a better emitter than aluminum or molybdenum in an x-ray band ≥ 800 eV. Measurements comparing x-ray transmission through irradiated foil targets with that through identical, unperturbed filters indicate enhanced transmission of x-ray energy through the targets. Temporally-resolved measurements on aluminum targets show that x-ray transmission through the target is strongly time-dependent, with x-ray power transmission through the targets, with the greatest contribution being that resulting from 2D rarefaction of the target after shock breakout. This corroborates earlier observations of delayed x-ray heating of the target rear surface. Enhanced transmission of x-rays through the targets at the moment of shock breakout was also observed, consistent with a shift of the K-shell x-ray absorption edge in the shocked aluminum plasma allowing increased transmission of the aluminum He[sub α] and IC x-ray lines. Other models which may yield similar enhanced x-ray transmission are investigated and rejected on the basis of experimental measurements on layered targets composed of an aluminum substrate and a copper layer as an x-ray source. Similar enhanced x-ray transmission has also been observed in laser-irradiated magnesium targets. The results provide the first experimental evidence of substantial increase in x-ray transport due to a shift of the K-shell photoabsorption edge induced by shock-compression of a dense plasma.