Investigation of X-ray amplification in neon clusters

We have experimentally investigated the feasibility of X-ray lasing in Li-like Ne ions produced by the interaction of intense, 28-fs laser pulses with gaseous clusters of neon. The idea of the proposed recombination (n=3-4) X-ray laser is based on adiabatic cooling of fast expanding small-sized Ne clusters. The driving laser beam was focused into a cryogenically cooled gas jet of Ne, and time-integrated spectra were simultaneously measured in transverse and longitudinal direction with respect to the laser axis. The transverse spectrum from Ne at the temperature of about -137 degree sign C showed dominant emission from highly placed levels (n=4) in Ne7- ions whilst the resonance lines (n=2-3) at 8.8, 9.8, and 10.3 nm remained very weak suggesting enhanced recombination from Ne8-. In the longitudinal spectrum, the lasing line candidate corresponding to the 3d-4f transition of Ne7+ at 29.24 nm has been observed as a distinct, but not dominant