We demonstrate heterodyne mixing of two free-running, multimode, 3.3-THz quantum cascade lasers by use of a point-contact Schottky diode. By temperature tuning the emission wavelength of one laser, a difference frequency signal spanning the 2–4-GHz range is obtained, with a signal-to-noise ratio of 30 dB. The frequency of the heterodyne signal is subject to random fluctuations of a few megahertz, principally from instabilities in the temperatures of the devices. From single-shot measurements we derive an instantaneous linewidth for a single Fabry–Perot mode of 20 kHz, corresponding to an integration time of 3.6 ms.
© 2004 Optical Society of America
(040.2840) Detectors : Heterodyne
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.5960) Lasers and laser optics : Semiconductor lasers
(260.3090) Physical optics : Infrared, far
(300.3700) Spectroscopy : Linewidth
S. Barbieri, J. Alton, H. E. Beere, E. H. Linfield, D. A. Ritchie, S. Withington, G. Scalari, L. Ajili, and J. Faist, "Heterodyne mixing of two far-infrared quantum cascade lasers by use of a point-contact Schottky diode," Opt. Lett. 29, 1632-1634 (2004)