Generation of high flux, highly coherent extreme ultraviolet radiation in a gas cell

We report the generation of extreme ultraviolet radiation with high photon flux (1010-1012 photon/cm2 s), high spatial coherence (up to 0.95), and good spatial beam profile by high-order harmonic generation in various noble gases (argon, neon, and helium) in a gas cell. The photon flux was determined using an extreme ultraviolet spectrometer equipped with a charge-coupled device camera and the spatial coherence was determined from Young double-slit interference fringes. The high-order harmonic emission is confined to just a few orders because of the small phase mismatch in the cut-off region that allows macroscopic phase matching to be satisfied for just a few harmonics in this region. The efficiency and spatial beam profile are studied as a function of gas pressure and geometrical configuration.