Micro-integrated terahertz quantum-cascade laser for high-resolution spectroscopy (Micro-QCL)

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Quantum-cascade lasers (QCLs) are promising radiation sources for high-resolution spectroscopy with sub-MHz or even kHz spectral resolution for the terahertz (THz) spectral region. The most significant advantages for the application of a QCL in a heterodyne or laser absorption spectrometer are the very small intrinsic linewidths, high output powers, continuous-wave (cw) emission, and a certain frequency tunability. The key objective of this proposal is the development of micro-integrated THz QCLs for high-resolution spectroscopy and future space applications for two frequencies, namely 3.5 THz and 4.7 THz. These frequencies are very important for the detection of the hydroxyl radical (OH) and neutral atomic oxygen (O) in atmospheric research as well as in astronomy. This will be achieved by high-level integration of the QCL chip with the all important optical components in a small micro-optical assembly, not larger than a matchbox. This micro-integrated QCL includes the components for optical isolation, outcoupling and beam shaping, as well as fiber and optical components for laser-induced frequency tuning. In addition, the active medium and the resonator will be optimized with the goal of achieving a cw output power of 1 mW at 80 K with a Gaussian-shaped output beam. The micro-integrated QCL will be operated in a compact mechanical cryocooler and its performance will be evaluated by high-resolution (Lamb-dip) molecular spectroscopy. Heterodyne spectrometers with QCLs have been proposed for NASA as well as for ESA space missions, but so far the low technology readiness level of THz QCLs prevents them from realization. The micro-integrated THz QCL, which will be developed in this project, will be a major step forward for space applications.