Spiking dynamics of frequency upconverted field generated in continuous-wave excited rubidium vapors

We report on spiking dynamics of frequency upconverted emission at 420 nm generated on the 6 P 3 / 2 − 5 S 1 / 2 transition in Rb vapor two-photon excited to the 5 D 5 / 2 level with laser light at 780 and 776 nm. The spike duration is shorter than the natural lifetime of any excited level involved in the interaction with both continuous and pulsed pump radiation. The spikes at 420 nm are attributed to temporal properties of the directional emission at 5.23 µm generated on the population-inverted 5 D 5 / 2 − 6 P 3 / 2 transition. A link between the spiking regime and cooperative effects is discussed. We suggest that the observed stochastic behavior is due to the quantum-mechanical nature of the cooperative effects rather than random fluctuation of the applied laser fields.