Evolution dynamics of a dense frozen Rydberg gas to plasma

• Published in: Physical review. A, Atomic, molecular, and optical physics Atomic, molecular, and optical physics, 2004-10, Vol.70 (4), Article 042713
• Main Authors: Li, Wenhui, Noel, Michael W., Robinson, Michael P., Tanner, Paul J., Gallagher, Thomas F., Comparat, Daniel, Laburthe Tolra, Bruno, Vanhaecke, Nicolas, Vogt, Thibault, Zahzam, Nassim, Pillet, Pierre, Tate, Duncan A.
• Format: Article
• Language: English
• Subjects: ATOM-ATOM COLLISIONS; ATOMIC AND MOLECULAR PHYSICS; ATOMS; COLD PLASMA; ELECTRON-ATOM COLLISIONS; ELECTRONS; EVOLUTION; PHOTOIONIZATION; PHOTON-ATOM COLLISIONS; RYDBERG STATES; TRAPPING; TRAPS
• ISSN: 1050-2947; 1094-1622
• DOI: 10.1103/PhysRevA.70.042713

Dense samples of cold Rydberg atoms have previously been observed to spontaneously evolve to a plasma, despite the fact that each atom may be bound by as much as 100 cm{sup -1}. Initially, ionization is caused by blackbody photoionization and Rydberg-Rydberg collisions. After the first electrons leave the interaction region, the net positive charge traps subsequent electrons. As a result, rapid ionization starts to occur after 1 {mu}s caused by electron-Rydberg collisions. The resulting cold plasma expands slowly and persists for tens of microseconds. While the initial report on this process identified the key issues described above, it failed to resolve one key aspect of the evolution process. Specifically, redistribution of population to Rydberg states other than the one initially populated was not observed, a necessary mechanism to maintain the energy balance in the system. Here we report new and expanded observations showing such redistribution and confirming theoretical predictions concerning the evolution to a plasma. These measurements also indicate that, for high n states of purely cold Rydberg samples, the initial ionization process which leads to electron trapping is one involving the interactions between Rydberg atoms.