Abstract: An interferometric unit consisting of a birefringent plate combined with an isotropic plate.This unit makes it possible to work with materials whose birefringence is slight and/or to reduce the necessary thickness of the birefringent plate. The unit is suited for integration into an interferometric device whose particular application is the detection of gases with quasi-periodic absorption structure absorbing in the infra-red.

Abstract: Process and interferometric device for detecting and measuring the concentration, in a single operation, of all gases, having almost periodic absorption structures, contained in a gaseous mixture, each of the gases being associated with a characteristic path difference. Luminous flux is analyzed after passage through a cell containing the mixture, using to a multiple-wave interferometer, for example, a Fabry-Perrot interferometer, in which the inside faces of plates therein are highly reflective, and one of which plates is displaceable at a constant speed, it thus being possible to sweep a very wide range of path difference. Analysis of the output signal is performed frequency band by frequency band, by seeking the maximum.

Abstract: The present invention concerns a process and a device for determining the cloud point of a diesel oil, comprising a light source and, aligned on a single axis, a diaphragm comprising a central hole on the said axis, an objective forming the image of the hole on a light trap, and behind the screen, a wide-diameter photoelectric detector intended to deliver an electric current when it receives a light flux, and, disposed between the objective and the screen, a cell containing a diesel oil sample to be analyzed, means for controlling the temperature of this sample being associated to the said cell.

Abstract: Interferometric device for the detection and/or analysis of gas, of the type comprising an optical assembly forming the image of a light source on the sensitive element of the detector, comprising a photoelastic modulator comprising a silica or fluorine plate associated to a piezoelectric ceramic to vibrate in order to give the plate a birefringency variable by compression, having an axis parallel to that of a birefringent plate and an interferential filter constituted by a grating multiplexer device; and having application to the interferometric detection of gas through high-sensitivity.

Abstract: Selective modulation interferometric detector, intended for specifically detecting and/or identifying at least one gas in a gaseous mixture, especially with the aim of carrying out analysis and/or proportioning operations, the assembly E consists of a first strip L.sub.1 of interferometric quality having plane and parallel faces, of thickness e and index n introducing a displacement .DELTA.=2ne adapted to the gas to be analyzed, this strip L.sub.1 supplying on the detector a brilliant fringe, and a second strip L.sub.2 made of the same material as the first strip L.sub.1 which is slightly prismatic and supplying on the detector average illumination.

Abstract: A highly luminous device for interferential spectrometry, comprises a birefringent beam-splitting interferometer combined with an optical system supplying localized fringes. As the beam-splitter element, it has at least one birefringent prism mounted along the optical axis of the device and producing an angular splitting, such as a Wollaston prism, of materials suitable for the construction of such prisms and selected as a function of birefringence and transparent over a wide range of wave lengths. The beam-splitter is placed between a polarizer and an analyzer of variable orientation to obtain flux modulation.