High-brightness LWIR quantum cascade lasers.

Long-wave infrared (LWIR, ≈8-12µ) quantum cascade lasers (QCLs) are drawing increasing interest, as they provide the possibility of long-distance transmission of light through the atmosphere owing to the reduced water absorption. However, their development has been lagging behind the shorter wavelength QCLs due to much bigger technological challenges. In this Letter, through band structure engineering based on a highly localized diagonal laser transition strategy and out-coupler design using an electrically isolated taper structure, we demonstrate high beam-quality single-mode LWIR QCLs with high-brightness (2.0 for ≈10µ, 2.2 for ≈9µ, 5.0 for ≈8µ) light extraction from a single facet in continuous-wave operation at 15°C. These results mark an important milestone in exploring the lighting capability of inter-sub-band semiconductor lasers in the LWIR spectral range.