Collective XUV emission from a dense gas: a route towards novel coherent light sources

We propose to measure pressure dependent prompt and delayed emission from a well- defined gas target while tuning the pressure continuously from zero to 0.5 bars. At room temperature, this is enough to change the target condition from the one described by a collection of individual atoms to the weakly coupled atomic ensemble with a few nm average interatomic distance. A suitable probe for the proposed project is a fully coherent and tunable free electron laser beam at Fermi facility in Trieste, Italy that can deliver tens of fs long EUV light pulses with up to 1015 W/cm² maximum intensity in the 10-60 nm wavelength range.