Microwave transitions in atomic sodium: Radiometry and polarimetry using the sodium layer

We calculate, via variational techniques, single- and two-photon Rydberg microwave transitions, as well as scalar and tensor polarizabilities of the sodium atom using the parametric one-electron valence potential, including the spin-orbit coupling. The trial function is expanded in a basis set of optimized Slater-type orbitals, resulting in highly accurate and converged eigenenergies up to n = 60. We focus our studies on the microwave band 90-150 GHz due to its relevance to laser excitation in the Earth's upper-atmospheric sodium layer for wavelength-dependent radiometry and polarimetry, as precise microwave polarimetry in this band is an important source of systematic uncertainty in searches for signatures of primordial gravitational waves within the anisotropic polarization pattern of photons from the cosmic microwave background. We present the most efficient transition coefficients in this range, as well as the scalar and tensor polarizabilities compared with available experimental and theoretical data.