Coherent instabilities in a semiconductor laser with fast gain recovery
  We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general. 
C. Y. Wang, L. Diehl, A. Gordon, C. Jirauschek, F. X. Kaertner, A.   Belyanin, D. Bour, S. Corzine, G. Hoefler, M. Troccoli,...