Observing the Intrinsic Linewidth of a Quantum-Cascade Laser: Beyond the Schawlow-Townes Limit

S. Bartalini, S. Borri, P. Cancio, A. Castrillo, I. Galli, G. Giusfredi, D. Mazzotti, L. Gianfrani, P. De Natale
2010 Physical Review Letters  
A comprehensive investigation of the frequency-noise spectral density of a free-running mid-infrared quantum-cascade laser is presented for the first time. It provides direct evidence of the leveling of this noise down to a white noise plateau, corresponding to an intrinsic linewidth of a few hundred Hz. The experiment is in agreement with the most recent theory on the fundamental mechanism of line broadening in quantum-cascade lasers, which provides a new insight into the Schawlow-Townes
more » ... a and predicts a narrowing beyond the limit set by the radiative lifetime of the upper level.
doi:10.1103/physrevlett.104.083904 pmid:20366933 fatcat:tf7okcy3kzfslliieru4il6pye