Multiphoton-induced X-ray emission at 4–5 keV from Xe atoms with multiple core vacancies

Abstract

SEVERAL recent experimental findings1–3 have pointed to a possible route for making an X-ray laser, which could in principle provide an imaging system capable of molecular resolution4. The method involves the multiphoton excitation of atoms in van der Waals clusters or in molecules to yield ions with core-electron vacancies1,2, which can then decay by emission of X-rays, in conjunction with a self-chanelling propagation mode of electromagnetic radiation3. The multiphoton excitation may be stimulated by ultrahigh-brightness, subpicosecond pulses of laser light5. We have previously observed2 emission of X-rays from L-shell transitions in core-excited krypton atoms using this approach. Here we report the multiphoton production of X-rays of wavelength 2–3 A from highly ionized xenon atoms which possess a large number of innershell vacancies while retaining several electrons in relatively weakly bound outer orbitals. Atoms with this ‘inverted’ electronic configuration are designated ‘hollow atoms’6,7. We find that generation of hollow atoms can become the dominant excitation mode for such systems, making their exploitation in an X-ray laser a real possibility.