Near-Infrared Broadband Cavity-Enhanced Spectroscopic Multigas Sensor Using a 1650 nm Light Emitting Diode

A near-infrared broadband cavity-enhanced sensor system was demonstrated for the first time using an energy-efficient light emitting diode (LED) with a central emission wavelength at 1650 nm and a light power of ∼16 mW. A portable absorption gas cell was designed for realizing a compact and stable optical system for easy alignment. An ultrashort 8-cm-long cavity was fabricated consisting of two mirrors with a ∼99.35% reflectivity. Methane (CH₄) measurement was performed employing two detection schemes, i.e., NIRQuest InGaAs spectrometer and scanning monochromator combined with phase-sensitive detection. Retrieval of CH₄ concentration was performed using a least-squares fitting algorithm. Sensitivities (i.e., minimum detectable absorption coefficient) were achieved of 1.25 × 10^-6 cm^-1 for an averaging time of 45 s using the NIRQuest InGaAs spectrometer and 1.85 × 10^-6 cm^-1 for an averaging time of 8 min using the scanning spectrometer in combination with lock-in detection. Field monitoring of CH₄ gas leakage was performed using the NIRQuest spectrometer. Multigas sensing of CH₄ and acetylene (C₂H₂) was carried out simultaneously using the high-resolution scanning spectrometer. A linear response of the retrieved concentration level versus nominal value was observed with a large dynamic range, demonstrating the reliability of the compact LED-based near-infrared broadband cavity-enhanced absorption spectroscopy (NIR-IBBCEAS) for multigas sensing applications.