We calculate the two-color ionization profile of atomic hydrogen in the presence of both a weak tunable high-frequency laser field and a low-frequency laser field of moderate intensity. The high-frequency spectroscopic light is used to probe the structure of Rydberg states dressed by the low-frequency field. We construct the photoionization spectrum from the sum of the resonance contributions by calculating the transition dipole moments between the initial state and the dressed Rydberg states, analogous to the study of photoionization in the presence of a dc field carried out by Alvarez and Silverstone [Phys. Rev. Lett. 63, 1364 (1989)].
We present a study of higher-order Raman ($\mathrm{\ensuremath{\Lambda}}, V$, and
S) transitions between Rydberg states involving the absorption and emission of at least three photons in the interaction of two-color corotating circularly polarized laser pulses with the hydrogen atom. Our analysis is based on results of numerical solutions of the corresponding time-dependent Schr\"odinger equation. The results for the interaction with ($\ensuremath{\omega},2\ensuremath{\omega}$) fields show that the simultaneous interaction with both fields results in an excited state distribution over a broad range of magnetic quantum numbers. Indications of the impact of the $\mathrm{\ensuremath{\Lambda}}, V$, and
S transitions are found via the analysis of final distributions resulting from the preparation of the atom in specific Rydberg states. Furthermore, we show that similar mechanisms for the redistribution of population between Rydberg states are present in two-color fields with larger differences in the central frequencies, i.e., ($\ensuremath{\omega},3\ensuremath{\omega}$) and ($\ensuremath{\omega},4\ensuremath{\omega}$) fields.
We discuss three proposed schemes of initializing circular-state Rydberg atoms via optical couplings provided by the ponderomotive effect in contrast to the current circularization methods that utilize electric-dipole interactions. In our first proposed method, a radial optical trap consisting of two Laguerre-Gaussian beams of opposite winding numbers transfers orbital angular momentum to the Rydberg atom, providing a first-order coherent coupling between an F state and a circular state. Additionally, we propose a one-dimensional ponderomotive optical lattice modulated at rf frequencies, providing quadrupolelike couplings in the hydrogenic manifold for rapid adiabatic passage through a series of intermediate Rydberg states into the circular state. For the third proposed scheme, a two-dimensional ponderomotive optical lattice with a time-orbiting trap center induces effectively the same coupling as a ${\ensuremath{\sigma}}^{+}$- or ${\ensuremath{\sigma}}^{\ensuremath{-}}$-polarized rf field of tunable purity for all-optical rapid adiabatic passage into the circular state.