Selfsynchronization and dissipation-induced threshold in collective   atomic recoil lasing
  Networks of globally coupled oscillators exhibit phase transitions from incoherent to coherent states. Atoms interacting with the counterpropagating modes of a unidirectionally pumped high-finesse ring cavity form such a globally coupled network. The coupling mechanism is provided by collective atomic recoil lasing (CARL), i.e. cooperative Bragg scattering of laser light at an atomic density grating, which is self-induced by the laser light. Under the rule of an additional friction force, the atomic ensemble is expected to undergo a phase transition to a state of synchronized atomic motion. We present the experimental investigation of this phase transition by studying the threshold behavior of the CARL process. 
C. von Cube, S. Slama, D. Kruse, C. Zimmermann, Ph.W. Courteille,   G.R.M. Robb, N. Piovella, and R. Bonifacio