Ppb-level nitric oxide photoacoustic sensor based on a mid-IR quantum cascade laser operating at 52 °C

Abstract

A ppb-level nitric oxide (NO) photoacoustic sensor was reported for outdoor environmental monitoring. The sensor employed a continuous wave (CW), distributed feedback (DFB), mid-infrared (mid-IR) quantum cascade laser (QCL) operating at a high temperature of 52 °C, which allow avoiding any water-cooling systems and thereby reduces its size, weight and cost of the photoacoustic NO sensor. The QCL emits at 5.26 μm, which corresponds to a strong NO absorption doublet R(6.5). A differential photoacoustic cell was designed to operate together with the QCL, resulting in a detection sensitivity of ˜7 ppb at atmospheric pressure with a 1-s averaging time. An Allan–Werle deviation analysis indicated that a ppt-level detection sensitivity can be reached with an integration time of >100 s. The performance of this sensor system was evaluated in terms of humidity, linearity and stability. Continuous measurements covering a haze period were performed to demonstrate the stability and robustness of the reported NO sensor system.