Dispersive near-IR Raman spectrometer

Details Dispersive near-IR Raman spectrometer Dispersive near-IR Raman spectrometer

1999-12-17

2002-04-16

Evans, F. L. (Department: 2877)

Optics: measuring and testing

By dispersed light spectroscopy

With raman type light scattering

Reexamination Certificate

active

06373567

ABSTRACT:

CROSS REFERENCES TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDS SPONSORED R & D
Not Applicable.
REFERENCE TO MICROFICHE APPENDIX
Not Applicable.
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to the field of instrumentation used for Raman spectroscopy. The instrument can be used to analyze solids, liquids, and gasses.
II. Description of Prior Art
Raman spectroscopy was discovered by Chandrasekhara Venkata Raman in the early 1900's. See C. V. Raman,
The molecular scattering of light: Nobel lecture
, Calcutta University Press, Calcutta, 1930. In its original form, filtered solar energy was used to generate Raman scattering of molecular samples. The resulting Raman spectra contained vibrational information about the molecular species, thus allowing them to be identified with a spectral “fingerprint”. Since its inception, the technique has undergone radical change. In particular, the widespread use of lasers as excitation sources in the 1970's resulted in a renaissance of this method of chemical analysis. Indeed, many investigators reported the use of Raman not only to qualitatively identify molecular species, but also to conduct quantitative analysis of these species. Since the generated Raman spectral intensity is linearly dependent on the excitation power, lasers quickly became the excitation method of choice. However, the large size of lasers in general at that time, the difficulty in aligning optics, and the overall fragility of the systems relegated Raman spectroscopy as a laboratory method. In addition, due to limitations of the utilized spectrometers and detectors, visible and ultra-violet wavelength lasers were used exclusively. This often gave rise to intense and interfering fluorescence which obscured the weak Raman scattering. Also, the acquisition of a single Raman spectrum was very time consuming since a moving dispersive grating was used to scan the dispersed Raman wavelengths across a single element detector. The acquisition of a single spectrum often required more than 1 hour. The subsequent invention and commercialization of the FT-Raman spectrometer (Fourier Transform Raman Spectrometer) resulted in a second renaissance of Raman spectroscopy in the 1980's. In this instrument, a Nd:YAG laser (flash lamp pumped solid state laser emitting at 1064 nm) was used to excite the sample and the resulting Raman signal was detected using an interferometer with a single element detector. This resulted in a much superior Raman signal in a shorter acquisition time due to the multiplex effect. In addition, the use of a near-IR laser resulted in complete elimination of fluorescence in most samples and a severe reduction of fluorescence in all samples. (Chase, D. Bruce., “Fourier transform Raman spectroscopy”, Journal of the American Chemical Society, Volume 108, 1986, pages 7485-8). These instruments were rapidly adopted by both academia and industry (Cooper, John B.; Wise, Kent L.; Groves, J., “Determination of octane numbers and Reid vapor pressure of commercial petroleum fuels using FT-Raman spectroscopy and partial least-squares regression analysis”, Analytical Chemistry, Volume 67, 1995, pages 4096-100; Cooper; John B, Bledsoe, Jr.; Roy R, Wise; Kent L., Sumner; Michael B, Welch; William T, Wilt; Brian K, U.S. Pat. No. 5,892,228: Process and apparatus for octane numbers and reid vapor pressure by Raman spectroscopy, Apr. 6, 1999; Cooper; John B., Flecher, Jr.; Philip E., Welch; William T. , U.S. Pat. No. 5,684,580: Hydrocarbon analysis and control by Raman spectroscopy, Nov. 4, 1997; Cooper; John B., Wise; Kent L., Welch; William T., Sumner; Michael B., U.S. Pat. No. 5,596,196: Oxygenate analysis and control by Raman spectroscopy, Jan. 21, 1997; Cooper, John B, Wise, Kent L., Bledsoe, Roger R., “Comparison of Near-IR, Raman, and Mid-IR Spectroscopies for the Determination of BTEX in Petroleum Fuels”, Applied Spectroscopy, Volume 51, 1997, pages 1613-16). To date there have been numerous improvements on the original design including improvements in detectors, interferometers, and lasers (Chase, Bruce., “Fourier transform Raman spectroscopy”, Analytical Chemistry, Volume 59, 1987, pages 881A-2A; Asselin, Kelly J, Chase, B., “FT-Raman Spectroscopy at 1.339 Micrometers”, Applied Spectroscopy, Volume 8, 1994, pages 699-704; Burch; Robert V., U.S. Pat. No. 5,247,343: Raman spectrometer having optical subtraction filters, Sep. 21, 1993).
Unfortunately, these instruments have remained costly and also very sensitive to vibrations; thus making them unlikely candidates for industrial applications other than research labs. In the late 1980's, the development of four key technologies led to the third renaissance of Raman spectroscopy in the 1990's. These were the development of silicon based CCD (charge coupled device) array detectors; the development of small low cost near-IR diode lasers; the development of fast image corrected dispersive spectrographs (see for example Battey; David E., Owen; Harry, Tedesco; James M., U.S. Pat. No. 5,442,439: Spectrograph with multiplexing of different wavelength regions onto a single opto-electric detector array, Sep. 24, 1996); and the emergence of high-quality fiber optics. In combination, these components allowed a new generation of Raman spectrometers to emerge based on the older dispersive Raman technique used originally by Raman himself (Lombardi, Daniel R., Mann, Charles K., Vickers, Thomas J., “Determination of Water in Slurries by Fiber-Optic Raman Spectroscopy”, Applied Spectroscopy, Volume 49, 1995, pages 220-25). The use of a CCD silicon array detector allowed the entire spectrum to be acquired simultaneously, hence giving rise to the multiplex advantage which was previously only attainable through the use of the FT-Raman method (Frank, Christopher J.; Redd, Douglas C. B.; Gansler, Ted S.; McCreery, Richard L., “Characterization of Human Breast Biopsy Specimens with Near-IR Raman Spectroscopy”, Analytical Chemistry, Volume 66, Number 3, 1994; Wang, Yan.; McCreery, Richard L. “Evaluation of a diode laser/charge coupled device spectrometer for near-infrared Raman spectroscopy”, Analytical Chemistry, Volume 61, 1989, pages 2647-51; Angel, Stanley M.; Myrick, Michael L., “Near-infrared surface-enhanced Raman spectroscopy using a diode laser”, Analytical Chemistry, Volume 61, 1989, pages 1648-52; Tedesco; James M., Owen; Harry, Chang; Byung J., U.S. Pat. No. 5,011,284: Detection system for Raman scattering employing holographic diffraction, Apr. 30, 1991; and Vickers, Thomas J, Rosen, Christopher A, Mann, Charles K, “Compact Raman Spectrometers: Data Handling Methods, Applied Spectroscopy, Volume 50, 1996, pages 1074-80).
The use of fiber optics and remote probes allowed for easy sampling (Schwab, Scott D.; McCreery, Richard L., “Versatile, efficient Raman sampling with fiber optics”, Analytical Chemistry, Volume. 56, 1984, pages 2199-204; Myrick, M. L.; Angel, Stanley M.; Desiderio, R., “Comparison of some fiber optic configurations for measurement of luminescence and Raman scattering”, Applied Optics, Volume 29, 1990, pages 1333-44; Owen; Harry, Tedesco; James M., Slater; Joseph B., U.S. Pat. No. 5,377,004: Remote optical measurement probe, Dec. 27, 1994; Pelletier; Michael J. , U.S. Pat. No. 5,862,273: Fiber optic probe with integral optical filtering, Jan. 19, 1999; Carrabba; Michael M., Rauh; R. David, U.S. Pat. No. 5,112,127: Apparatus for measuring Raman spectra over optical fibers, May 12, 1992; Schrader; Bernhard, U.S. Pat. No. 5,534,997: Raman spectrometer using a remote probe with enhanced efficiency, Jul. 9, 1996).
The use of diode lasers allowed for some reduction of fluorescence (Smith; Brian J. E., U.S. Pat. No. 5,657,120: Laser diode system for Raman spectroscopy, Aug. 12, 1997; Angel, S. Michael.; Myrick, Michael L., “Wavelength selection for fiber optic Raman spectroscopy”, Applied Optics, Volume 29, 1990, pages 1350-2; Vickers, Thomas J., Mann, Charles K., Tseng, Ching-Hui, “Changes in Raman Spectra Due to Near-IR Excitation”, Applied Spectrosc

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