Optics: measuring and testing – For light transmission or absorption
Patent
1999-05-14
2000-09-26
Kim, Robert H.
Optics: measuring and testing
For light transmission or absorption
356319, G01N 2100, G01J 342, G01J 3427
Patent
active
061249378
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to optical spectroscopy, and more particularly, to a method and device for combined absorption and reflectance spectroscopy.
BACKGROUND OF THE INVENTION
Spectroscopy is used for analytics, environmental control, quality control, and process control. Radiant energy is directed towards a substance and the absorption, diffuse reflection, dispersion, fluorescence, or refraction of the substance can be measured in order to determine the substance and its properties.
The prior art includes two major types of spectroscopy: (1) Absorption spectroscopy; and (2) Reflectance spectroscopy.
Conventional absorption methods are used for the detection of absorbing substances in measurement volumes, such as liquids, gases, or solids.
Radiation of a defined wavelength is coupled into the measurement volume. On its way through the measurement volume, the coupling radiation is attenuated by absorbing substances within the measurement volume. After a defined distance, the coupled radiation is again decoupled and directed to an optoelectronic receiver, which records the attenuated intensity I. The quotient of the attenuated and unattenuated intensity I.sub.o is the transmission T:
This law from Bouger-Beer-Lambert describes the relationship between transmission and the total absorption coefficient .alpha..sub.T (for the sake of simplicity dispersion has been ignored here). The term .chi. is the distance which the coupling radiation travels in the measurement volume. (BERGMANN and SCHAEFER: Textbook of Experimental Physics. Optics. Berlin-New York, Walter de Gruyter, 1993 and SCHMIDT, W.: Optical Spectroscopy. Weinheim-New York-Basel-Cambridge-Tokyo, VCH Verlagsgesellschaft, 1994.)
A special absorption method is based on the principle of evanescent wave fields or attenuated total reflection (ATR). Here, radiation is coupled into a light conducting solid, e.g., ATR crystal or an optical waveguide and after passing through a defined distance decoupled again. The optical waveguide is in contact with the measurement volume to be investigated. In the optical waveguide, the coupling radiation is totally reflected at the boundary surface with a measurement volume, whereby a small portion of the radiation penetrates into the measurement volume (evanescent wave) and interacts therewith. Thus, the coupling radiation is attenuated. This attenuation is measured. The classical relationship in Formula (1) applies. (BERGMANN and SCHAEFER: Textbook of Experimental Physics. Optics. Berlin-New York, Walter de Gruyter, 1993)
In the case of measurement volumes with very low optical densities (e.g., gases), the distance traveled by the coupled radiation in the measurement volume is increased in order to obtain evaluable signals. Long paths may be realized, for example, with the help of reflecting elements. (BAUMBACH, G.: Air Cleaning. Berlin-Heidelberg-New York, Springer Verlag, 1992) In DE 4104316A1, an internally reflecting spherical cell is introduced, in which the coupled radiation is reflected back and forth multiple times and then decoupled again and directed to a receiver. In DE 4124545A1, a gas absorption cell is described.
Recently, a method for the determination of total absorption has been proposed. Rather than measuring the coupling radiation attenuated after traveling a defined distance, the interaction radiation (fluorescence and dispersion) generated by the coupling radiation is measured. The special characteristic of this method is that the coupled radiation is almost completely absorbed by the measurement volume after a long path. (DD 301 863 A7. DE 43 37 227 A1, and MITTENZWEY, K.-H., J. RAUCHFUSS, G. SINN, H.-D. KRONFELDT: A new fluorescence technique to measure the total absorption coefficient in fluids. Fres. J. Anal. Chem., 354 (1996) 159-162 as well as MITTENZWEY, K.-H. & G. SINN: MPSS: A new scattering technique for measuring the total absorption in fluids. Appl. Spectr. 51 (1997) 2, 82-85)
Reflectance spectroscopy combines diffuse reflection and specular refl
REFERENCES:
patent: 3910701 (1975-10-01), Henderson et al.
patent: 5125742 (1992-06-01), Wilks, Jr.
patent: 5317378 (1994-05-01), Mould et al.
patent: 5345306 (1994-09-01), Ichimura et al.
patent: 5381237 (1995-01-01), Sela
patent: 5459566 (1995-10-01), Pearson et al.
Bergmann et al., "Experimentalphysik", Polarisation und Doppelbrechung des Lichtes, pp. 468-471 (1993) (English summary of relevant parts).
Bergmann et al. "Experimentalphysik", Absorption der Strahlung, pp. 237-241 (1994) (English summary of relevant parts).
Schmidt, "Optische Spektroskopic" pp. (first page no number) 316-317 (1994) English summary of relevant parts).
Baumbach, "Luftreinhaltung", 5 Messtechniken zur Erfassung von Lufverunreinigungen, p. 178 (1992) German (English summary of relevant parts).
Kortum, "Reflexionsspektroskopie", pp. 106-109 (1969) (English summary of relevant parts).
Gerber, "Portable Cell For Simultaneously Measuring the Coefficients of Light Scaterring and Extinction for Ambient Aerosols" Item No. XP-002059096, Applied Optics, pp. 1009-1014, vol. 18, No. 17 (Apr. 1, 1979), U.S.
Mittenzwey et al., "MPSS: A New Scattering Technique for Sensitive Measuring of the Total Absorption of Fluids", Applied Spectroscopy, vol. 51, No. 2 (1997) U.S.
Colwell, "Manual of Remote Sensing" Remote Sensing Applications in Agriculture, p. 2141 (1983) U.S.
Mittenzwey et al. "A new Flourescence Technique to Measure the Total Absorption Coefficient in Fluids", Fresinius J. Anal Chem (1996) 354:159-162.
Mittenzwey Klaus-Henrik
Sinn Gert
Kim Robert H.
Natividad Philip
Optosens Optische Spektroskopie und Sensortechnik GmbH
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