Optics: measuring and testing – For light transmission or absorption – Of fluent material
Patent
1992-12-23
1995-06-13
McGraw, Vincent P.
Optics: measuring and testing
For light transmission or absorption
Of fluent material
356342, G01N 2149, G01N 2159
Patent
active
054248434
ABSTRACT:
Optical measurements of turbid media, that is media characterized by multiple light scattering, is provided through an apparatus and method for exposing a sample to a modulated laser beam. The light beam is modulated at a fundamental frequency and at a plurality of integer harmonics thereof. Modulated light is returned from the sample and preferentially detected at cross frequencies at frequencies slightly higher than the fundamental frequency and at integer harmonics of the same. The received radiance at the beat or cross frequencies is compared against a reference signal to provide a measure of the phase lag of the radiance and modulation ratio relative to a reference beam. The phase and modulation amplitude are then provided as a frequency spectrum by an array processor to which a computer applies a complete curve fit in the case of highly scattering samples or a linear curve fit below a predetermined frequency in the case of highly absorptive samples. The curve fit in any case is determined by the absorption and scattering coefficients together with a concentration of the active substance in the sample. Therefore, the curve fitting to the frequency spectrum can be used both for qualitative and quantitative analysis of substances in the sample even though the sample is highly turbid.
REFERENCES:
patent: 4929847 (1990-05-01), Yamazoe et al.
Berns Michael W.
Haskell Richard C.
Svaasand Lara O.
Tromberg Bruce J.
Tsay Tsong T.
Dawes Daniel L.
McGraw Vincent P.
The Regents of the University of California
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