Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow-Townes limit

Year: 2010

Authors: Bartalini S., Borri S., Cancio P., Castrillo A., Galli I., Giusfredi G., Mazzotti D., Gianfrani L., De Natale P.

Autors Affiliation: Istituto Nazionale di Ottica (INO)–CNR, Largo Fermi 6, 50125 Firenze FI, Italy; European Laboratory for Non-linear Spectroscopy (LENS), Via Carrara 1, 50019 Sesto Fiorentino FI, Italy; Dipartimento di Scienze Ambientali–Seconda Universita` di Napoli, Via Vivaldi 43, 81100 Caserta CE, Italy

Abstract: A comprehensive investigation of the frequency-noise spectral density of a free-running midinfrared 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 hertz. 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 formula and predicts a narrowing beyond the limit set by the radiative lifetime of the upper level.


Volume: 104 (8)      Pages from: 083904  to: 083904

More Information: We gratefully acknowledge M. Yamanishi, Hamamatsu Photonics, for his invaluable support on the theory, F. Marin, University of Firenze, for fruitful discussions, and M. Giuntini and A. Montori, LENS, for their help on driving electronics. We thank Alpes Laser for providing additional information on the laser. This work was partially supported by Ente Cassa di Risparmio di Firenze, Centro Regionale di Competenza INNOVA, and CNR and the other European research funding Agencies participating in the European Science Foundation EUROCORES Program EUROQUAM-CIGMA.
KeyWords: Limit sets; Line broadening; Midinfrared; Noise spectral density; Radiative lifetime, Laser theory; Spectral density, Quantum cascade lasers
DOI: 10.1103/PhysRevLett.104.083904

Citations: 97
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