Method and apparatus for remotely and portably measuring a gas of interest

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

• directing a light beam to an area backed by a reflective surface, where such gas of interest may be such that a light signal representative of such absorption line characteristics can be back reflected toward a light signal receiving device;
• collecting such back reflected light signal by such receiving device;
• passing said light signal through a light modulating arrangement such that such light signal is modulated at a first frequency;
• directing said light signal modulated at said first frequency 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 electric field to a modulating arrangement associated with such birefringent etalon to modulate such once modulated light signal between spectra which substantially coincide with such absorption lines and spectra which fall between such absorption lines, said electric field having associated therewith a second frequency distinct from such first frequency and related thereto by a whole integer factor other than one;
• and
• distinguishing between such light signal at such first frequency and such light signal at such second frequency an determining therefrom at least a quantity of such gas of interest.

An apparatus for remotely measuring a gas of interest by is optical absorption line characteristics, said remote measuring apparatus comprising:

• a source of electromagnetic radiation;
• means for directing such electromagnetic radiation through such as of interest to a remote, reflective surface;
• mans for receiving a reflected light signal produced as a result of such electromagnetic radiation passing through such gas of interest and having at least a portion thereof reflected in a direction toward said receiving means;
• light modulator means optically coupled to said receiving mean for once modulating said light signal at a first frequency;
• means for modulating said once modulated light signal at a second frequency related to said first frequency by a whole integer factor other than one, said modulating means including an interferometric device receptive of said light signal and having associated therewith, a periodic spacing equal to the periodicity of the absorption lines of such gas of interest, said interferometric device further having associated therewith, a second periodic spacing substantially equivalent to transmission spectra which fall between such absorption lines, to produce a twice modulated light signal;
• wherein said interferometric device is modulated between said first and said second frequency be application of an electric 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.

An apparatus for rapid scanning of the concentration of a remote gas using optical absorption line characteristics of the gas, the apparatus comprising:

• a source of electromagnetic radiation;
• means for directing the electromagnetic radiation toward a remote, reflective surface;
• means for receiving reflected electromagnetic radiation from the remote surface;
• a light switch optically coupled to said receiving means for producing polarized pulses of light at a first frequency from the reflected electromagnetic radiation;
• a birefringent etalon optically coupled to the light switch, the etalon having periodic transmission spectra shiftable between first spectra which coincide with such absorption lien characteristics and second spectra which fall between such absorption line characteristics, to produce pulses containing the first spectra and pulses containing the second spectra;
• means for distinguishing the pulses containing the first spectra and the pulses containing the second spectra;
• means for correlating pulses of the first spectra and pulses of the second spectra in time;
• means for determining gas concentration from correlated pulses of the first spectra and the second spectra.