Phase Methods in Absorption Spectroscopy

The analysis of the air gas composition is a challenging task because the well-being and health of the people depend on its quality. Most methods to analyze the gaseous medium are not perfect, and the necessary sensitivity, selectivity, and accuracy are often lack. The article analyzes a possibility to optimize the selectivity and accuracy of interferometric (refractometric) gas analysis devices. The main idea of the work is to demonstrate the possibility of a transition from the direct measurement of the ratio between the light flux intensities to the measurement of frequency shifts and radiation frequency, which significantly increases the accuracy and sensitivity of the measurements. In order to enhance the selectivity of the analysis, measurements are proposed to be done in the area of the anomalous dispersion of the analyzed gas component. The presence of the phase component of the useful signal, which is several orders of magnitude larger than the amplitude component in the region of the anomalous dispersion of the analyte and linearly depends on the concentration, allows the measurements to be made in a wide interval of analyte concentrations. All that opens new opportunities for interferometric methods of gas analysis. (author)