Quantitative diode laser absorption spectroscopy near 2 μm with high precision measurements of CO2 concentration

A diode laser sensor was developed to measure CO2 concentration using absorption spectroscopy at 2 mum. The simplicity of the optical setup and detection electronics makes this spectrometer very compact and well suited for field studies, while the use of optical fibers enables one to probe remote environments. This sensor is capable of providing absolute measurements, with the concentration being inferred from the directly measured absorption spectra, without using calibration cells. This ensures versatility as well as widespread applicability, and a linear response over a large dynamic range. Its analytical capabilities were carefully tested by a large variety of measurements, also with use of a certified CO2/air mixture. The precision of mixing ratio retrievals was about 0.2% while the accuracy was 0.9% for measurements of ambient CO2 concentration. The spectrometer is also capable of providing high precision measurements of the water vapor concentration in ambient air. Specifically, simultaneous detection of both molecular species is demonstrated. Although the performance of our spectrometer can be improved with some effort, it is already competitive with commercially available infrared gas analyzers for atmospheric monitoring applications. In addition, it is an attractive tool for continuous measurements of volcanic gas concentrations. (C) 2001 American Institute of Physics.