Intense x-ray and extreme ultraviolet (XUV) light sources have been available for decades, however, due to weak nonlinear interaction in the XUV photon energy range, observation of Rabi oscillation induced by XUV pulse remains a very challenging experimental task. Here we suggest a scheme where photoionization of a He medium by an intense XUV pump pulse is followed by a strong population inversion and Rabi oscillation at the ${\mathrm{He}}^{+}(1s-3p)$ transition and is accompanied by superfluorescence (SF) of the 7.56 eV pulse at the ${\mathrm{He}}^{+}(3p-2s)$ transition. Our numerical simulations show that the Rabi oscillation at the ${\mathrm{He}}^{+}(1s-3p)$ transition induced by an XUV pulse with photon energy 48.36 eV results in significant signatures in the SF spectra, allowing us to identify and characterize the XUV induced Rabi-oscillatory regime. The proposed scheme provides a sensitive tool to monitor and control ultrafast nonlinear dynamics in atoms and molecules triggered by intense XUV.

• Received 28 February 2023
• Accepted 2 June 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.043201