Selection of high-order harmonics from a single quantum path for the generation of an attosecond pulse train

Abstract

By applying an intense 28-fs laser pulse to a helium gas jet, spectrally resolved high-order harmonics originating from different quantum paths were obtained. The selection of high-order harmonics from a single quantum path could be achieved by controlling the phase-matching condition. Comparison of the observed harmonic spectrum with a calculation indicated that an attosecond pulse train with a single attosecond pulse per half-optical cycle was produced.