Wang, Christine Y.Diehl, L.Gordon, A.Jirauschek, C.Kärtner, F. X.Belyanin, A.Bour, D.Corzine, S.Höfler, G.Troccoli, M.Faist, J.Capasso, Federico2019-09-172007Wang, Christine Y., L. Diehl, A. Gordon, C. Jirauschek, F. X. Kärtner, A. Belyanin, D. Bour, et al. 2007. “Coherent Instabilities in a Semiconductor Laser with Fast Gain Recovery.” Physical Review A 75 (3). https://doi.org/10.1103/physreva.75.031802.1050-29471094-1622http://nrs.harvard.edu/urn-3:HUL.InstRepos:41371459We 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.en-USJournal Article2019-09-1710.1103/PhysRevA.75.031802