Coherent Light-Matter Interactions Driven by Intense XUV Pulses from Seeded FELs

In coherent light-matter interactions the coherent state produced by the light pulse remains coherent during the entire period of observation. One of the well-known examples of such interactions is the Rabi oscillation—a periodic transfer of population in a two-level system induced by an external electromagnetic field. While these oscillations have been studied in light-matter interactions since the discovery of laser itself, most of the studies are limited to long wavelengths, typically ranging from microwave to visible radiation. Here, we discuss how such oscillations can be generated at shorter wavelengths, for example in the extreme ultraviolet domain, using intense femtosecond pulses from seeded free-electron lasers. When a two-level system is undergoing Rabi oscillations, it can be described via an ‘atom + photon’ dressed-state, the properties of which can be further manipulated to study quantum entanglement between massive particles. Our results offer opportunities to employ these intense laser pulses for generating and controlling coherent light-matter interactions across ultrashort timescales.