Hybrid Faraday rotation spectrometer for sub-ppm detection of atmospheric O_2

Faraday rotation spectroscopy (FRS) of O2 is performed at atmospheric conditions using a DFB diode laser and permanent rare-earth magnets. Polarization rotation is detected with a hybrid-FRS detection method that combines the advantages of two conventional approaches: balanced optical-detection and conventional FRS with an optimized analyzer offset angle for maximum sensitivity enhancement. A measurement precision of 0.6 ppmv·Hz-1/2 for atmospheric O2 has been achieved. The theoretical model of hybrid detection is described, and the calculated detection limits are in excellent agreement with experimental values