Oxygen detection based on Faraday modulation spectroscopy and wavelength modulation spectroscopy: A comparison

An oxygen sensor system was developed based on Faraday modulation spectroscopy (FAMOS). In the system, a distributed feedback laser near 760.9 nm was used as the light source and a 30-cm long gas cell was employed for gas absorption. The first harmonic was extracted by a commercial lock in amplifier for the derivation of concentration. Oxygen measurement experiments were conducted the performance of the sensor system was obtained. In addition, oxygen sensor system with wavelength modulation spectroscopy (WMS) scheme was developed with the same light source and gas cell for a direct comparison. Based on Allan deviation analysis, a detection limit of 0.186% for the WMS scheme and a detection limit of 0.108% for the FAMOS scheme were acquired at an averaging time of 1 s. The precisions can be further improved to 0.032% and 0.03% at an averaging time of 15 s, respectively.