Phase-matched high-order-harmonic generation by self-guided intense femtosecond laser pulses

We describe the phase-matched high-order-harmonic generation of femtosecond Ti:sapphire laser pulses in a self-guiding channel. Generation efficiency of the high-order harmonic was improved by phase-matched propagation in the guiding channel. The harmonics around the 49th harmonic (16 nm) were enhanced by two orders of magnitude compared to those in the plateau with a 7-mm-long, self-guided pulse in Ne. High-harmonic conversion efficiency of 1 0(-6) was obtained, producing > nJ harmonics in the cutoff region around the 49th harmonic. The results are well explained by considering both the intrinsic phase based on the single-atom response and the macroscopic phase matching in the high-intensity interaction region.