Molecular Oxygen Detection Using Frequency Modulation Diode Laser Spectroscopy

There are a variety of industrial and research applications for molecular oxygen (O2) sensors. Most existing oxygen sensors, however, are either intrusive and have slow response (e.g. electrochemical methods and mass spectrometry) or are expensive (e.g. UV laser-induced fluorescence). An attractive method for detecting O2 that is both non-intrusive and relatively inexpensive was first demonstrated by Kroll et al1 and involves the use of wavelength modulation (at 5 KHz) spectroscopy techniques with a GaAlAs diode laser. In this paper we extend this earlier work by making spectroscopic measurements of O2 using high frequency (≈1 GHz) modulation of GaAlAs lasers. This so-called frequency modulation spectroscopy (FMS) technique has the potential for achieving near quantum noise limited sensitivity and time response on the order of microseconds.