High performance quantum cascade lasers for the λ=4 to 17 μm region and their chemical sensing applications

Recent advances in quantum cascade (QC) lasers are presented. These include widely tunable single-mode distributed feedback (DFB) lasers with dynamic single-mode emission up to high current levels in the range of the CO₂ laser, at λ≈9.5-10.5 μm, and at λ≈4.6-4.7 μm, and single-mode DFB lasers at λ≈16 μm based on new surface plasmon waveguides with dual-metal gratings. Single-mode and tunable QC-DFB lasers have successfully been used in various trace-gas sensing applications including collaborations with Jet Propulsion Laboratory, Stanford University and Informed Diagnostics, and Rice University. Examples are the detection of stratospheric methane and nitrous oxide by wavelength modulation spectroscopy, the sub-part per billion in volume (ppb-v) detection of ammonia by cavity ring down spectroscopy, methane concentration and isotopic composition measurements, and the detection of complex molecules (e.g. ethanol) in open air by multipass direct absorption spectroscopy. A QC-DFB laser has been frequency-stabilized to ~10 kHz of continuous wave linewidth, as recently measured by collaborators at Pacific Northwest National Laboratory and JILA, University of Colorado. Finally, high-speed operated, gain switched QC lasers showed a pulse duration as short as 45 ps