External Cavity Stabilized LWIR QCL

Lasers based on quantum cascade (QC) gain media represent a powerful new tool for optical detection in the infrared spectral region, needed to help detect the proliferation of weapons of mass destruction. They have been demonstrated to be reliable, compact, efficient, bright sources of spectrally narrow radiation in midwave-, longwave-, and far-infrared. The ultimate utility of QC lasers, however, will be greatly enhanced if their tuning range can be increased. In this project, the quantum cascade gain medium will be incorporated into an external optical cavity, in order to increase the tuning range by over an order of magnitude. In addition to designing the external optical cavity, the quantum cascade medium will be modified to suppress the intrinsic optical cavity formed by its front and back facets. Phase I demonstrated that continuous-mode/hop-free tuning, with both cryogenic and room temperature quantum cascade lasers operating near 8 microns, could be achieved when the lasers were built into an external optical cavity. In order to reduce the facet reflectance, a number of approaches ¿ including horizontal angling, vertical angling, and anti-reflection (AR) coating ¿ were evaluated. The room temperature, anti-reflection coated laser performed best, tuning stably and consistently in a single external cavity longitudinal mode for more than 78 nanometers. In Phase II, a commercial, prototype, external-cavity quantum cascade laser system, emitting in the 8 to 14 micron spectral region, will be developed. This external cavity system will have a tuning range over 350 nm, which would be more that an order of magnitude greater than its inherent tuning range. Commercial Applications and other Benefits as described by the awardee: The broadly-tunable, longwave-infrared, external-cavity quantum cascade laser should meet an unfilled need for narrow linewidth spectroscopic systems in the 8 to 14 micron spectral region. Such systems should find use in the high-precision spectroscopy of gas molecules related to national defense, homeland security, treaty verification, and industrial safety. Customers would include researchers ¿ in DOE laboratories, university-based research teams, and industrial companies ¿ developing advanced sensors for hazardous gas leak detection and process monitoring.