Quantum cascade lasers (QCLs) are powerful mid-infrared (MIR) light sources for gas sensing, but factors such as manufacturing complexity, efficiency, system integration, and portability have limited their adoption for gas sensing systems so far. Optical gas sensing is widely used by industrial, environmental, and medical sectors where noncontact measurement, real-time response, and reliable operation are required. Applications such as process monitoring, emissions measurement, and respiratory gas analysis often involve complex gas mixtures and rapidly changing conditions, which demand sensors capable of both selectivity and sensitivity.
Many established optical sensing systems operate within the near-infrared (NIR) range (~0.83 to 1.55 µm), where efficient light sources and highly sensitive detectors are available.
Decades of development driven by the telecommunications industry led to reliable components—including indium gallium arsenide (InGaAs) detectors—that enable low-power operation and fast response times. But gas absorption features within the NIR spectrum are generally weaker and often lie close together spectrally, which can limit the ability to distinguish multiple gases within complex mixtures.
MIR (~3 to 11 µm) sensing addresses these limitations by targeting stronger and more distinct absorption bands. Although MIR technologies are less mature overall, the improved spectral separation available within this region supports more specific gas identification. QCLs provide a flexible and spectrally precise MIR light source, which enables direct access to narrow absorption features within a wide wavelength range and extends the applicability of MIR-based optical sensing to environments in which high measurement specificity is required.
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