Dependence of soft x-ray conversion on atomic composition in laser produced plasma of gold–copper mix-Z targets

Abstract

A comparative experimental study of soft x-ray emission from laser-irradiated Au–Cu mix-Z targets of different atomic compositions has been performed. Plasma was produced from planar targets using second-harmonic laser pulses from an Nd:glass laser at a focused intensity of ∼1013 W cm−2. Radiation intensity in the spectral region ∼15–150 Å and integrated x-ray yield for mix-Z target were observed to be higher than those for individual elements. The maximum conversion occurred for an atomic composition of Au 0.43–Cu 0.57. These observations are consistent with the variation of Rosseland mean opacity with atomic composition calculated using a screened hydrogenic average atom model.

Enhanced x-ray emissions from Au-Gd mixture targets ablated by a high-power nanosecond laser

“…In 1992, Nishimura observed that the mixtures of Au-Tb and Au-Sm showed higher laser to x-ray conversion efficiencies at the photon energy of 0.1-2 keV comparing with their individual materials. 20 Afterwards, higher x-ray emissions from laser-irradiated Au/Cu mixture targets than those for individual elements in the spectral region 1.5-15 nm, and in a narrow spectral region of 0.15-0.39 nm, were obtained successively by Chakera in 2003, 21 and by Chaurasia in 2008. 22 However, in these experiments, x-ray emissions have been measured only at a certain direction and the angular distribution of the x-ray emissions, which is necessary for the overall x-ray conversion efficiency, have not been measured.…”

Ion emission from laser ablation of Cu and Cu98/Be2 alloy targets

“…It was experimentally proved that by increasing the fraction of an admixture in metallic alloy targets, the yields of ion emission and of X-ray radiation are enhanced up to a maximum. If the admixture fraction exceeds this optimal value, the yields decrease up to a value corresponding to the pure admixture (7,8). In contrast to the high Z-admixtures or to the high content admixture metallic alloys, a very low content of an admixture in a target material can significantly enhance the ion emission, as was presented in (9) for 2 mass% of silicon admixture in a laser-produced iron plasma generated with the use of a KrF laser.…”

Ion dynamics in laser-produced plasmas from mixed high-Z targets

“…Langmuir ion probes have been used extensively to investigate the parameters of plasma plumes from metal targets, using nanoseconds (6-8) as well as ultra-short laser pulses (9,10). Recently, results on enhanced X-ray yield (soft and characteristic lines) from metallic alloys of gold and copper have been reported (11). This has been explained on the basis of the fact that if two high-Z elements are mixed in the right proportion, the high-opacity region of one element overlaps with the low-opacity region of the other (12), thus, resulting in an overall increased Rosseland mean opacity as compared to either of the two individual elements.…”