Demonstration and Frequency Noise Characterization of a 17 µm Quantum Cascade Laser

The spectral performance of a novel continuous‐wave room‐temperature distributed feedback quantum cascade laser operating is evaluated at the long wavelength of 17 µm. By demonstrating broadband laser absorption spectroscopy of the fundamental vibrational mode of molecules, the spectral range is determined and the spectroscopic potential of this laser is established. The frequency noise is characterized and the line width of this new device is measured, uncovering a discrepancy with the current consensus on the theoretical modeling of quantum cascade lasers. The results confirm the potential of such novel narrow‐line‐width sources for vibrational spectroscopy. Extending laser spectroscopy to longer wavelength is a fascinating prospect that paves the way for a wide range of opportunities from chemical detection, to frequency metrology as well as for exploring light‐matter interaction with an extended variety of molecules, from ultra‐cold diatomic species to increasingly complex molecular systems.