Method and arrangement for measuring the optical absorptions of gaseous mixtures

An arrangement for measuring a gas of interest by its optical absorption characteristics, said measuring arrangement comprising:

• a source of electromagnetic radiation;
• means for directing such electromagnetic radiation through such gas of interest;
• a first light signal, emerging from passage through such gas of interest, has associated therewith, periodic transmission spectra representative of the absorption lines of such gas of interest;
• an interferometric device receptive of said first light signal and having associated therewith, a periodic spacing equal to the periodicity of the absorption lines of such gas of interest;
• means for varying an applied electric field of first and second predetermined strengths to said interferometric device so as to modulate such periodic spacing of said interferometric device between transmission spectra which substantially coincide with such absorption lines and transmission spectra which fall between such absorption lines;
• and,
• means for detecting at least an amount of such gas of interest as a function of the intensity of such periodic transmission spectra following passage through such gas of interest.

A method for measuring a gas of interest by its optical absorption characteristics, said measuring method comprising the steps of:

• directing a light beam through a quantity of such gas of interest such that a light signal representative of the absorption lines of the gas of interest is generated thereby;
• passing said light signal through a birefringent etalon device which has associated therewith, a periodic spacing substantially equivalent to such absorption lines associated with such gas of interest;
• applying an electrical field at two distinct field strengths to the birefringent etalon to modulate its transmission spectra from wavelengths which substantially coincide with the absorption lines of the gas of interest and wavelengths which fall between such absorption liens;
• and
• determining at least an amount of such gas of interest as a function of the relationship such spectra which coincide with such absorption lines and such spectra which fall between such absorption lines.

An arrangement for measuring a gas of interest by its optical absorption characteristics, said measuring arrangement comprising:

• a source of electromagnetic radiation;
• means for directing such electromagnetic radiation through such gas of interest;
• a first light signal, emerging from passage through such gas of interest, has associated therewith, periodic transmission spectra representative of the absorption lines of such gas of interest;
• means for modulating said first light signal between transmission spectra which substantially coincide with such absorption lines and transmission spectra which fall between such absorption lines;
• an interferometric device receptive of said first light signal and having associated therewith a periodic spacing equal to the periodicity of the absorption liens of such gas of interest, said interferometric device further having associated therewith, a second periodic spacing substantially equivalent to such transmission spectra which fall between such absorption lines;
• said interferometric device being shifted from said periodic spacing to said second periodic spacing by application of an electrical field thereto;
• and
• means for detecting at least an amount of such gas of interest as a function of the intensity of such periodic transmission spectra following passage through such gas of interest.