Probing attosecond pulse trains using “phase-control” techniques

We propose a method for the measurement of attosecond beating structures that result from the superposition of harmonics of laser radiation. It utilizes the phase control of the excitation probability of atoms through different interfering channels. The channels consist of multiphoton excitation by the fundamental frequency and single-photon excitation by the superposition of the harmonic fields, or alternatively, by each harmonic or frequency interval within the bandwidth of each harmonic. The method is sensitive to the relative phase of the harmonics, including phases introduced by chirp, and thus allows evaluation of the temporal structure of the superimposed harmonic fields. An experimental setup for the implementation of the method based on freestanding transmission grating is suggested as well.