Low-threshold generation of harmonics and hard x radiation in a laser plasma. 2. Multipeak generation

The conditions for the generation of hard x radiation with a multipeak structure in a plasma pumped by a long pulse from a free-running CO$_2$ laser at a low intensity ($q\lesssim$10 GW/cm$^2$) have been studied. This x-ray generation had been observed in a previous study by the present authors. It is shown that this generation of hard x radiation with a multipeak structure leads to a more than tenfold increase in the yield of hard x radiation per laser pulse, under optimum conditions. This increase results from the additional peaks in the x-ray signal. An explanation of this effect is proposed.