The generation of intense high harmonic (HHG) source

Although the HHG beam possesses laser-like properties, the low conversion efficiency from the fundamental to the high harmonics limits the number of applications to a small fraction of what we can dream of. One of the major limiting factors for a better conversion is phase matching, as it is crucial to have a coherent build up from all the atoms to focus all the radiated energy into a well collimated beam. Other factors that limit the photon yield of the harmonics are low recombination cross sections and high rate of ionization throughout the harmonic generation, which takes energy from the laser and defocuses it. Our approach to generating intense HHG source is to attack the problem on all fronts: a) we improve the harmonic yield at the single atom response by using resonant atoms. b) we start with higher photon flux in the driving laser beam, to end up with higher photon flux in the HHG beam. c) we reduce relative absorption effects and improve phase matching conditions in the loose focusing geometry.