A near-infrared carbon dioxide sensor system using a compact folded optical alignment structure

Abstract

A compact optical alignment structure and a novel beam-tracing method were proposed for tunable laser absorption spectroscopy (TLAS) based gas measurements, in order to minimize sensor size and ease beam alignment procedure. A near-infrared carbon dioxide (CO2) sensor system was developed based on the alignment structure. A distributed feedback (DFB) laser centered at 6361.3 cm-1 and a multi-pass gas cell (MPGC) with an effective optical path length of 29.8 m were employed. The sensor system was integrated as standalone equipment by customizing an aluminum baseplate for a stable field operation. A series of experiments were carried out to assess the performance of the sensor system. A limit of detection (LoD) of ~ 7.1 parts-per-million in volume (ppmv) at a 0.4 s averaging time was obtained, and the LoD was reduced to ~ 277 parts-per-billion in volume (ppbv) at an optimum averaging time of 153.6 s. Considering gas mixing times, the rise and fall time were measured to be ~ 290 s and ~ 200 s, respectively.