High harmonic generation in an active grating

We study theoretically and experimentally High Harmonic Generation (HHG) using two non collinear driving fields focused in gases. We show that these two fields form a non stationary blazed active grating in the generation medium. The intensity and phase structure of this grating rule the far field properties of the emission, such as the relative amplitude of the diffraction orders. Full macroscopic calculations and experiments support this general analysis. This insight into the HHG process allows us to envision new structuration schemes to convert femtosecond lasers to attosecond pulses with increased efficiency.