  Non-perturbative resonant multiphoton ionization $(1+1)$ is studied using the
resolvent operator technique. Scaling parameters for effective two-level
Hamiltonians are computed for hydrogen and helium atoms to provide a
quantitative description of Rabi oscillations at XUV wavelengths, which were
recently observed using a seeded Free-Electron Laser [S. Nandi et al., Nature
608, 488-493 (2022)]. The resulting photoelectron spectra exhibit a range of
Autler-Townes doublets, which are studied for different intensities, detunings
and interaction times. We identify a photoelectron signature that originates
from stabilization against ionization of helium atoms interacting with intense
circularly polarized XUV light. Thus, our work shows how it is possible to test
the prediction of dressed-atom stabilization by Beers and Armstrong [B. L.
Beers and L. Armstrong, Phys. Rev. A 12, 2447 (1975)], without the demanding
requirement of atomic saturation in the time domain.
