Efficient soft x-ray sources from laser-irradiated gold foam targets with well-controlled impurities

As an important x-ray source, enhancement of x-ray emissions from laser-produced plasmas is significant for various applications. Due to less expanding kinetic loss, gold foam with low initial density can have an enhanced x-ray conversion efficiency compared with solid-density gold. However, low-Z impurities within gold foam targets will diminish the enhancement remarkably, and should be tightly controlled. This paper presents an experimental study of a high brightness laser plasma soft x-ray source, based on a 0.36 g cm(-3) gold foam target with negligible impurities irradiated by nanosecond laser pulses with power density around 3 x 10(14) W cm(-2) at the Shenguang II laser facility. A conversion efficiency, from multi-eV to multi-keV, of 51.2% is achieved in the x-ray emissions-about 21% relative enhancement compared with a solid-density gold target, and the highest conversion efficiency for Au foam planar targets yet. Good agreement has been achieved between the semi-analytical model prediction and the experimental results.