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Resonantly enhanced harmonic generation via dressed states with large Autler–Townes splittings

We investigate harmonic generation of ultrashort, picosecond pump laser pulses toward the vacuum-ultraviolet spectral regime, enhanced by preparation of dressed states in media of rare gas atoms. A control laser, with appropriately matched frequency and/or peak intensity serves to generate dressed states with large, tunable Autler–Townes splittings in the THz range. The energetic position of the dressed states is laser-controlled to match multiple pump laser photons. This enables resonance enhancement of harmonic generation also for typically fixed-frequency and off-resonant pump laser pulses. Moreover, the tunable Autler–Townes splittings also serve to compensate and even exploit inevitable Stark shifts of atomic resonances, which otherwise reduce the nonlinear response of the medium. We provide convincing experimental data to demonstrate the concept in argon and xenon, yielding enhancements of harmonic generation by 1–2 orders of magnitude.