Yoked superfluorescence transients

A dense sample of atomic rubidium vapor excited by a short (4 ps) transform-limited laser pulse two-photon resonant with the 5S − 5D transition in a large Fresnel number geometry emits a delayed omnidirectional IR superfluorescence pulse (coherent flash) on the 5D → 6P transition. This involves a coherent population transfer to the 6P level and results in a prompt directional yoked [1] UV emission along 6P → 5S. This is a manifestation of a parametric four-wave mixing which occures in the absence (after) the pump pulses. The omnidirectional character of the 5D → 6P superfluorescence is confirmed by the observation of a conical pattern of the UV emission for a composite noncollinear, |Ik1| = |Ik2| excitation [2]. If the two excitation pulses are delayed with respect to each other, this conical pattern is not formed but a transient grating is induced in the 5S state. When this grating is interrogated by a third pulse, it responds by producing conical superfluorescence photon echo emission on the 6P → 5S transition. [1] J. H. Brownell, X. Lu, and S. R. Hartmann, Phys. Rev. Lett. 75, 3265 (1995) [2] A. I. Lvovsky, S. R. Hartmann, and F. Moshary, Phys. Rev. Lett. 82, 4420 (1999)