High sensitivity open‐path gas sensor based on a triangular multi‐pass cell

Abstract In this article, a gas sensing technique utilizing a compact multi‐pass absorption cell in a triangular configuration was proposed for open‐path trace gases detection. To demonstrate this technique, an open‐path gas sensor system was developed by combing the innovated triangular multi‐pass cell with a near infrared distributed feedback diode laser (at 1.65 μm) for simultaneous detection of atmospheric CH 4 and H 2 O. A Gaussian‐noise‐limited limit of detection of approximate 52 ppb and 445 ppm were achieved for CH 4 and H 2 O, respectively, with 1 Hz sampling rate and at normal atmospheric pressure. Allan variance analysis indicates that a sensitivity of 5.5 ppb (for CH 4 ) and 75 ppm (for H 2 O) could be obtained at the optimal averaging time of 300 s, which is comparative with the mid‐infrared laser based gas sensors. This technique will be a critical tool for developing low‐cost open‐path trace gas monitoring networks for environmental, industrial, and public security applications.