Patent ID: 6015969
Filing Date: 2000-01-18
Classification: G01N

Abstract:
A multiple-frequency spectroscopic quantitation method for measuring light-absorbing species in turbid inhomogeneous mediums, the method comprising:generating a light beam having two different wavelengths of light;the generating of said two different wavelengths of light being such that one wavelength is selected not to be absorbed by a particular one of the individual targeted species and the other wavelength is selected to be strongly absorbed by the particular one of the individual targeted species,optically splitting said light beam into a sample beam and a reference beam;passing said sample beam through a sample comprised of a turbid inhomogeneous medium that is host to a plurality of individual targeted species;optically collecting said sample beam affected by said turbid inhomogeneous medium into a reflected sample beam;reflecting said reference beam on a variable distance mirror with a highly reflective surface;optically collecting reflections of said reference beam from said mirror into a reflected reference beam;optically mixing said affected sample beam and said reflected reference beam, wherein those photons in the affected sample beam that are within a coherence length of having traveled the same distance in their respective pathlengths as those photons in the reflected reference beam provide for interference fringes for each of said two different wavelengths of light that have an amplitude proportional to the square root of the number of selected photons in the reflected sample beam;detecting and demodulating the amplitudes of said interference fringes for each of said two different wavelengths of light and providing an electric signal proportional to each of said interference fringe amplitudes; andratioing said proportional electrical signals and relating a ratio derived therefrom to a concentration of said individual targeted species in said turbid inhomogeneous medium.