Selective scheme of gas concentration measurement based on acousto-optic spectral filters with multi-frequency control signal

Abstract

A scheme for measuring the concentration of components of gas mixtures improving the selectivity of conventional optical absorption spectroscopy is proposed. The scheme is based on the use of acousto-optic spectral filter as a dispersion element which is fed simultaneously several control signals with frequencies corresponding to the maxima and minima of absorption in the optical spectrum of the measured gas. The scheme is implemented on the basis of the acousto-optic filter based on paratellurite TeO2 crystal, providing the high resolution achieved by reducing the absorption of ultrasound due to the special technology of the growth of high quality crystals and the use of absorption anisotropy of ultrasound in paratellurite. Experimental verification of this approach with measuring the concentration of nitrogen dioxide has confirmed the effectiveness of the proposed scheme.