Control of the Rabi sideband patterns from transient excitation gratings in filament wake channels in a dense gas*

In a dense gas, the filamentation at a crossing of two femtosecond laser beams results in transient gratings of ionic and excited-atom densities. The laser intensity grating produced by the interference affects the electron impact processes in a dense gas, which result in these excitation and ionization gratings. The excitation gratings are specific of the dense-gas setting; they are controlled by the crossing angle as well as by the phase delay between the beams. The presence of these gratings in the wake of the laser pulse can be verified by their effect on the Rabi sideband emission. When a picosecond probe laser pulse is incident normally on the grating, the oscillating electric field of the pulse couples with the transitions in the excited state manifold of the gas atoms, causing the emission of frequencies red-shifted and blue-shifted about the carrier frequency. This Rabi sideband radiation emitted by the grating lines interferes constructively to form a characteristic spatial-spectral pattern on a remotely placed screen. These patterns are modified by the crossing angle, inter-beam phase delay, the pump and the probe pulse characteristics, and the distance between the screen and grating. We demonstrate how the characteristics of the Rabi sideband patterns are quantitatively associated with the grating features. We also investigate how the Rabi sideband patterns are robustly controlled by the modification in probe pulse shape.