Interferometric device for detecting gas

Claim 1

Interferometric device for the detection and/or analysis of gas, of the type comprising an optical assembly forming the image of a luminous source (S) on the sensitive element of the detector, this image being formed through a cell (C) containing the gaseous mixture to be analyzed which is followed by an interferometry assembly (I) comprising a birefringent plate (L) and a modulating means located between an analyser and a polarizer followed by an interferential filter wherein, the analyser and the polarizer consist of two polarizing prisms (W 1 and W 2 ) the optical axes of which are perpendicular to that of the device and each give two photometrically identical images which are rectilinearly and perpendicularly polarized and the modulating means consist of a photoelastic modulator (M) comprising a silica or fluorine plate excited by a piezoelectric ceramic caused to vibrate in order to give said plate a birefringency variable through compression, having an axis parallel to that of the birefringent plate (L), the interferential filter being constituted by a grating multiplexer device (H, H').