Mid-infrared telemetry sensor based calibration gas cell for CO detection using a laser wavelength locking technique

Abstract

A CO telemetry sensor was designed based on the quantum cascade laser-tunable diode laser absorption spectroscopy (QCL-TDLAS) technology using the fundamental frequency absorption band of CO gas molecules at 4.58 μm. A Fresnel lens with a diameter of 250 mm is utilized to achieve a large area of light collection. The application of light beam tracking method realizes the visualization of telemetry optical path and improves the target tracking capability of telemetry system. Laser wavelength locking technique are investigated to lock the sensor wavelength, thus solving the wavelength drift caused by environmental temperature changes. The second harmonic/laser power signal technique based on wavelength modulated spectroscopy(2f/LPS-WMS) is used to reduce the interference of background noise and laser power intensity by normalizing the second harmonic (2f) with the laser power signal (LPS). Several gas telemetry experiments were performed to verify the sensor performance and the positive linear response of the sensor for CO telemetry was demonstrated. The sensor was tested for stability for approximately 1 h and the Allan -Werle deviation was analyzed. The minimum limit of detection (LOD) of the sensor was 23.07 ppb·m with an averaging time of 62 s. The sensor was reportedly deployed outdoors for the measurement of CO concentration in atmospheric environments.