Efficient coupling of high-intensity subpicosecond laser pulses into solids

Abstract
We demonstrate a new technique for enhancing the absorption of high-intensity, ultrashort-duration laser pulses by solids. Targets consisting of gold gratings and gold clusters were found to absorb greater than 90% of the incident high-intensity laser light. This is in contrast to less than 10% absorption by flat surfaces. As a result of this strong coupling of the laser to a high-density plasma, conversion efficiency of laser energy to x rays of greater than 1% was observed for x rays above 1 keV. Efficiency of nearly 25% was observed for emissions greater than 30 eV. These conversion efficiencies are more than an order of magnitude greater than those measured from flat targets.