INTERACTION OF ATOMIC WAVE-PACKETS WITH 4-WAVE-MIXING - DETECTION OF RUBIDIUM AND POTASSIUM WAVE-PACKETS BY COHERENT ULTRAVIOLET EMISSION

The observation of an atomic wave packet by use of a coherent, nonline ar-optical process is reported. Wave packets formed in K or Rb vapor b y two-photon excitation of ns and (n - 2)d states (n = 8 for K; n = 11 , 12 for Rb) with red (similar to 620-nm), 80-100-fs pulses were detec ted by four-wave mixing in pump-probe experiments. The temporal behavi or of the wave packet is observed by monitoring the coherent UV radiat ion generated near the alkali mp(2)P --> S-2(1/2) (7 less than or equa l to m less than or equal to 12 for Rb; 5 less than or equal to m less than or equal to 7 for K) resonance transitions when a probe pulse is scattered by the wave packet established by the earlier (identical) p ump pulse. The spatial and spectral characteristics of the UV emission are well described by axially phase-matched four-wave mixing, and all the prominent frequency components of the wave packets are associated with energy differences between pairs of excited states for which Del ta iota I = 0 or Delta iota = 2. These results demonstrate that the wa ve packet modulates chi((3)) of the medium, thus rendering the wave pa cket detectable. (C) 1998 Optical Society of America.