Observations of Ultrafast Superfluorescent Beatings in a Cesium Atomic Vapor Excited by Femtosecond Laser Pulses

Picosecond and femtosecond superfluorescent beatings are observed from a dense atomic vapor. Cesium atoms are excited by femtosecond laser pulses via two-photon processes into their coherent superpositions of the ground 6S and excited 8S states. The yoked superfluorescent blue light at lower transitions of 6S - 7P is recorded and studied. Delayed buildup time of this blue light is measured as a function of the input laser beam power using a high-resolution 2 ps streak camera. At low power and density, a beating with a period of 100 picoseconds representing the ground state splitting is observed. The autocorrelation measurements of the generated blue light exhibit a beating with a quasi-period of 230 fs corresponding to the splitting of the 7P level. Understanding and, eventually, controlling the intriguing nature of superfluorescent beatings may permit a rapid quantum operation free from the rather slow spontaneous emission processes from atoms and molecules.