Patent ID: 6219144
Filing Date: 2001-04-17
Classification: G01B,G01N

Abstract:
Interferometric apparatus for measuring the effects of the refractive index of a gas in a measurement path, said interferometric apparatus comprising:interferometer means comprising first and second measurement legs, said first and second measurement legs having optical paths structured and arranged such that at least one of them has a variable physical length and at least one of them is at least in part occupied by the gas and one of them is at least in part be occupied by a predetermined medium, the optical path length difference between said first and second measurement legs varying in accordance with the difference between the respective physical lengths of their optical paths and the properties of said gas and said predetermined medium;means for generating at least two light beams having different wavelengths;means for introducing first and second predetermined portions of each of said light beams into said first and second measurement legs, respectively, of said interferometer means so that beams at one of said wavelengths of said first and second predetermined portions of said light beams travel through at least one of said first and second measurement legs along predetermined optical paths a different number of passes than beams at the other of said wavelengths to compensate for the relative rates at which the physical path lengths of said first and second measurement legs are changing, said predetermined first and second portions of said light beams emerging from said interferometer means as exit beams containing information about the respective optical path lengths through said first and second measurement legs at said wavelengths;means for combining said exit beams to produce mixed optical signals containing information corresponding to the phase differences between each of said exit beams from corresponding ones of said predetermined paths of said first and second measurement legs at said wavelengths;means for detecting said mixed optical signals and generating electrical interference signals containing information corresponding to the effects of the indices of refraction of the gas and said predetermined medium at said different beam wavelengths and the relative physical path lengths between said first and second measurement legs and their rates of change; andelectronic means for analyzing said interference electrical signals to determine the effects of said gas in said measurement legs.