Abstract

Collisionally excited X-ray lasing in [Ne]-like Ti with a gain value of 19 cm^-1 at a drastic reduced pump level of only a few Joules was demonstrated recently [1]. This achievement is based on a novel two step excitation scheme, which was proposed some years ago [2]. The scheme comprises at first a long (ns) heating pulse to establish a [Ne]-like ionic stage of desired target atoms in a plasma and second a short (ps) excitation pulse to produce efficiently a transient population inversion in the [Ne]-like ions. Due to the short pulse produced fast heating of the preformed plasma, a transient inversion [2] occurs, which is related to the different population rates of the levels via collision and not determined by the slower relaxation rates of the excited levels relevant in the quasi-steady state (QSS) regime. The transient inversion yields favourably much higher gain values (several tens of cm^-1) as well shorter X-pulse output as obtained in the QSS regime (several cm^-1) with long pulse pumping.

© 1997 Optical Society of America