population inversion   arises for typically 100 femtoseconds during the interaction of a slow highly charged ion (HCI) with a solid surface. Despite this limited lifetime, the formation and decay of a hollow atom can be conveniently studied from ejected electrons and soft X-rays, and the trajectories, energy loss and final charge state distribution of surface-scattered projectiles.
A population inversion occurs briefly, usually within 100 femtoseconds, when a slow, highly charged ion (HCI) collides with a solid surface. This phenomenon allows researchers to investigate the creation and destruction of hollow atoms using emitted electrons and soft X-rays, as well as analyzing the trajectories, energy loss, and final charge states of scattered projectiles.