Atmospheric N2O gas detection based on an inter-band cascade laser around 3.939 µm*

N 2 O is a significant atmospheric greenhouse gas that contributes to global warming and climate change. In this work, the high sensitivity detection of atmospheric N 2 O is achieved using wavelength modulation spectroscopy (WMS) with an inter-band cascade laser operating around 3.939 µm. A LabVIEW-based software signal generator and software lock-in amplifiers are designed to simplify the system. In order to eliminate the interference from water vapor, the detection was performed at a pressure of 0.1 atm (1 atm = 1.01325×10 5 Pa) and a drying tube was added to the system. To improve the system performance for long term detection, a novel frequency locking method and 2 f/ 1 f calibration-free method were employed to lock the laser frequency and calibrate the power fluctuations, respectively. The Allan deviation analysis of the results indicates a detection limit of ∼ 20 ppb (1 ppb = 1.81205 µg/m 3 ) for a 1 s integration time, and the optimal detection limit is ∼ 5 ppb for a 40-s integration time.