Title: Strong light shifts from near-resonant and polychromatic fields: comparison of Floquet theory and experiment,
Abstract: We present a non-perturbative numerical technique for calculating strong
light shifts in atoms under the influence of multiple optical fields with
arbitrary polarization. We confirm our technique experimentally by performing
spectroscopy of a cloud of cold $^{87}$Rb atoms subjected to $\sim$ kW/cm$^2$
intensities of light at 1560.492 nm simultaneous with 1529.269 nm or 1529.282
nm. In these conditions the excited state resonances at 1529.26 nm and 1529.36
nm induce strong level mixing and the shifts are highly nonlinear. By
absorption spectroscopy, we observe that the induced shifts of the 5P3/2
hyperfine Zeeman sublevels agree well with our theoretical predictions.. We
propose the application of our theory and experiment to accurate measurements
of excited-state electric-dipole matrix elements.