In the new study, the physicists shot xenon atoms with FLASH, an X-ray laser that USES intense photons in the extreme ultraviolet energy range, about forty times the energy of visible light.

Single isolated attosecond (as) extreme ultraviolet (XUV) pulses can be generated via the nonlinear optical interaction between intense few-cycle laser fields and noble gas atoms.

Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy.