Phase-matched high-order harmonic generation by guided intensefemtosecond pulses

摘要

We describe the phase-matched high-order harmonic generation ofnfemtosecond Ti:sapphire laser pulses a with two different guidingnmethods. Generation efficiency of the high-order harmonic was improvednby phase-matched propagation in the guiding channel. More than 100-foldnenhancement around the 25th harmonic (32 nm) was obtained with an3-cm-long Ar-filled hollow fiber. The harmonics around the 49th harmonicn(16 nm) were also enhanced by two orders of magnitude compared to thosenin the plateau with a 7-mm-long, self-guided pulse in Ne. High-harmonicnconversion efficiency of 10-6 was obtained by phase-matchednpropagation in Ne, producing >nJ harmonics in the cutoff regionnaround the 49th harmonic. In both experiments, the harmonics near thencutoff region were preferentially enhanced. The results are wellnexplained by considering both the intrinsic phase based on thensingle-atom response and the macroscopic phase matching in thenhigh-intensity interaction region. The flat intensity profile achievednin the guided structure is considered to clearly manifest the intrinsicnphase behavior of the harmonics