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

  • US 5,076,699 A
  • Filed: 05/01/1989
  • Issued: 12/31/1991
  • Est. Priority Date: 05/01/1989
  • Status: Expired due to Fees
First Claim
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1. An apparatus for rapid scanning of the concentration of a remote gas of interest using optical absorption line characteristics of such gas, said measuring apparatus comprising:

  • a broadband source of infrared radiation;

    means for direction the broadband infrared radiation to a remote, reflection surface;

    means for receiving a reflected portion of the infrared radiation, wherein the intensity of the reflected portion is subject to unpredictable change due to shifts in infrared radiation transmission direction crossing areas of varying concentration of the gas of interest and hitting reflective surfaces of differing albedo;

    light modulator means optically coupled to said receiving means for modulating said reflected portion at a first frequency and outputting a modulated reflected portion;

    means for modulating said modulated reflected portion at a second frequency related to the first frequency by an integral factor, said modulating means including a birefringent etalon device having a periodic spacing equal to the periodicity of the absorption lines of the gas of interest, said modulating mean further effective such that, with an electric filed applied thereto, the periodic transmission spectra of said birefringent etalon device is shifted between spectra which coincide with such absorption line characteristics and spectra which fall between such absorption line characteristics, and outputting a twice modulated reflected portion; and

    means for distinguishing between said twice modulated reflected portion at such first frequency and at such second frequency and determining therefrom, at least a quantity of such gas of interest.

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