Plasmon signatures in high harmonic generation

Abstract. High harmonic generation in complex multi-electron systems is investigated theoretically. The harmonic spectra exhibit two cutoffs. The first cutoff is in good agreement with the well established, single active electron cutoff law. The second cutoff presents a signature of multi-electron dynamics. The strong laser field excites nonlinear plasmon oscillations. Electrons that are ionized from one of the multi-plasmon states and recombine to the ground state gain additional energy, thereby creating the second plateau. This finding gives experimental access to a so far hardly explored regime of quantum physics- the non-perturbative, nonlinear dynamics of multi-electron systems.

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