ACS Photon. (2016)

Optically excited gold nanoparticles can act as an efficient source of hard X-rays. That's the conclusion of a study performed by an international collaboration of scientists from Taiwan, Japan, Australia and Lithuania. The team excited an aqueous suspension of gold nanoparticles (diameter 10–100 nm) with near-infrared, femtosecond laser pulses (800 nm, 40 fs) and observed that the resulting nanoplasma emitted hard X-rays with an energy of 15 keV (wavelength 1 Å). The X-ray generation is driven by bulk plasmon excitation in gold at 138 nm following a 6-photon absorption of the infrared laser pulses. The most efficient X-ray generation was for gold nanoparticles of 40 nm diameter and when the laser pulses were pre-chirped to a duration of 370 fs. According to the researchers, future studies will need to discover a means for controlling the directionality of the emission in order for the approach to find use in practical applications.