  We describe the properties of a continuous-wave room-temperature quantum
cascade laser operating at the long wavelength of 17 $\mu$m. Long wavelength
mid-infrared quantum cascade lasers offer new opportunities for chemical
detection, vibrational spectroscopy and metrological measurements using
molecular species. In particular, probing low energy vibrational transitions
would be beneficial to the spectroscopy of large and complex molecules,
reducing intramolecular vibrational energy redistribution which acts as a
decoherence channel. By performing linear absorption spectroscopy of the v2
fundamental vibrational mode of N2O molecules, we have demonstrated the
spectral range and spectroscopic potential of this laser, and characterized its
free-running frequency noise properties. Finally, we also discuss the potential
application of this specific laser in an experiment to test fundamental physics
with ultra-cold molecules.
