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Abstract

An interferometric gas component measurement apparatus has a light source (27), a measurement path (30) which contains the gas components to be measured, a polarizer (11), a double refracting plate arranged with its optical axis at 45.degree. to the polarization direction, two doubly refracting plates (14, 20) arranged with their optical axes at 45.degree. to one another and an analyzer (13). The light which passes through the measurement path is concentrated into an output gap (32) and reflected via a holographic concave grid (33) onto a diode row (22). The thickness of the individual plates is so selected that specific linear combinations of the thicknesses result in phase displacements between the beams polarized perpendicular to one another in the plates, with these phase displacements corresponding to the reciprocal of the quasi-periodic line splitting of selected vibration and/or rotation bands of the gas molecules of the gas components to be measured. The output signal of the diode row (22) and the output signal of a rotary position transducer (34) are applied to an electronic evaluation circuit which, at different rotational positions of the rotating plates (14, 20) determines the concentrations (C1, C2, C3) of gases present on the measurement path (30) from the signals received from the diode row (22) (FIG. 1).

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