Measurement of oxygen concentration using laser diode spectroscopy

Laser Spectroscopy provides a non-intrusive method for measuring the concentration of a species in a sample. This paper is a part of the development of employing laser spectroscopy techniques outside of a lab setting. Monitoring the presence of gaseous oxygen within a fuel tank is of great importance due to the volatility of the fuel/oxygen mixture and the threat it creates to the area surrounding the fuel tank. A technique using absorption spectroscopy to monitor the concentration of oxygen within the tank has been developed. Light from a laser diode is sent through a test cell containing an unknown concentration of oxygen. Oxygen molecules absorb some of the light and a photodiode measures the amount of light that passes through the cell. A correlation between the amount of light through the test cell and the oxygen concentration is obtained and compared with measured concentrations from an O2 analyzer. It was found that there was a measurable difference in output from the photodiode when the concentration of oxygen was changed within the test cell. The laser diode system effectively monitors the oxygen concentration in real-time in the test cell and provides a simple and low-cost alternative to standard oxygen analysers.