Coherent sources of mid-infrared (mid-IR) radiation are of great interest for a wide range of scienti?c and technological applications from spectroscopy and frequency metrology to information technology, industrial process control, pho- chemistry, photobiology and photomedicine. The mid-IR spectrum, which may be de?ned as wavelengths beyond ?2um, covers important atmospheric windows, and numerous molecular gases, toxic agents, air, water, and soil pollutants, c- ponents of human breath, and several explosive agents have strong absorption ?ngerprints in this region. The development of...