News Picks : Plasma from "hairy" target releases high-energy x rays
20 November 2013
Ars Technica: Lasers are used to ionize atoms, which emit x rays when they recombine with the electrons. When a laser is focused on a solid block of material, it creates a layer of plasma composed of positively charged ions and negatively charged electrons. At a certain point, that plasma layer prevents the laser from ionizing more of the material. To allow the laser to penetrate more deeply, an international team of researchers has altered the target’s structure. They created 55-nm-wide, 5-µm-long “hairs” of nickel spaced 130 nm apart. The laser could then ionize atoms along the entire length of the hairs. A measurement of the released radiation showed that up to 26 of each nickel atom’s 28 electrons were released into the plasma. The resulting plasma reached densities, pressures, and temperatures close to what is seen in fusion experiments, which is a significant improvement over previous nonfusion laser–plasma experiments. More importantly, the plasma generated 50 times more x rays and the resulting radiation had shorter wavelengths than in traditional experiments, which makes the technique potentially very useful for imaging. And it may be possible to use lasers that are more readily available, such as those developed for research and commercial purposes.