Oscillators based on Raman gain, known in the literature as Raman lasers, have until now necessitated an external optical pump. A powerful multi-watt fundamental laser radiation is usually required to offset a small value of the Raman gain coefficient, typically several 10 -9cm/W in most Raman-active media. For example, these limitations in solid-state Raman lasers which employ scattering off a vibrational (phonon) resonance in a crystal or fiber have led to high thresholds and small conversion efficiencies. 3 If these could be overcome such lasers would find important applications as compact light sources due to their spectral agility and could extend the range of semiconductor lasers. An important step in this direction was the recent demonstration of near infrared Raman lasers, in which ultralow threshold was achieved thanks to the use of high quality-factor dielectric microsphere resonators. 8 Here we demonstrate a compact injection Raman laser operating in the mid-infrared, in which low threshold and high conversion efficiency are achieved by integrating within the active region of a quantum cascade region a Raman section designed to resonantly enhance the Raman gain by many orders of magnitude.
