Coherent ultraviolet generated by wavepackets interacting with χ⁽³⁾ In Rb and K atoms

Wavepackets formed from the ns and (n-2)d states of Rb and K (n = 8 for K, 11 and 12 for Rb) have been observed by four wave mixing in pump-probe experiments. The temporal behavior of the wavepacket is observed by monitoring the coherent ultraviolet radiation generated near the alkali mp ²P → ²S_1/2 resonance transitions (7 ≤ m ≤ 12 for Rb) when a ∼100 fs, red probe pulse (λ ∼620 nm) is scattered by the wavepacket established by an earlier (identical) pump pulse. The spatial and spectral characteristics of the ultraviolet emission are well-described by axially phase-matched, four wave mixing and all of the prominent frequency components of the wavepackets are associated with energy differences between pairs of excited states for which Δl = 0 or 2. These results demonstrate that the wavepacket modulates χ⁽³⁾ of the medium, thus rendering the wavepacket detectable.