Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
1998-03-12
2001-01-30
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
C356S305000
Reexamination Certificate
active
06181418
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to optical spectrometers or spectrophotometers and, more particularly, to a concentric spectrometer.
BACKGROUND OF THE INVENTION
A spectrometer is a device which receives a light signal as an input and produces as an output a light signal which is spread out, or dispersed, in space according the different wavelength components, or colors, of the input light signal. A detector attached to the spectrometer can analyze the output signal, called the spectrum, in order to quantify the amount of each wavelength component present in the input signal.
Spectrometers are used in myriad scientific and industrial applications. For example, they are used for the precise determination of color; such an application known as colorimetry. There are many commercial applications in which the precise knowledge of the color content of a sample material is vital to the successful outcome of a project. For example, in the automotive industry, exact color matching is essential when a portion of a vehicle is being painted so that the repainted portion matches the original color of the rest of the vehicle; the ability to repaint only the repaired portion of the vehicle rather than repainting the entire vehicle leads to considerable savings of money, materials, and time. Another example is in the aerospace industry; if an engineering determination is made for an optimum color scheme for an aircraft which minimizes its ability to be detected by the enemy, it is vital that the exact color specified can be provided by the paint supplier. These are only two of many possible examples of the importance of proper color matching in industrial applications.
Regardless of their specific application, it is important for spectrometers to be capable of preventing noise from interfering with the desired sample measurement. Two noise sources which represent a significant problem in state-of-the-art spectrometers are stray light and re-entrant spectra: stray light refers to any light arriving at the spectrometer output which results from anything other than the spectral dispersion of the input signal; re-entrant spectra refers to spectra resulting from multiple reflections off of the grating between the detector and entrance slit, thus giving rise to unwanted secondary spectra. It is appreciated that stray light and re-entrant spectra represent obstacles to achieving an improved signal-to-noise ratio, thus limiting measurement accuracy or sensitivity, dynamic range, and/or acquisition speed, while also generally requiring that applications using any excitation optical signal (e.g., colorimetry) must generally operate at higher power for a given acquisition or sampling time.
There is a need, therefore, for further improvements in spectrometers, and particularly, for a spectrometer which eliminates or substantially reduces noise, such as stray light and re-entrant spectra, in order to provide an improved signal-to-noise ratio.
SUMMARY OF THE INVENTION
The present invention overcomes the above, and other, limitations of prior and background art spectrometers by providing a concentric spectrometer having reduced stray light and re-entrant spectra within the spectrometer. In accordance with an aspect of the present invention, a spectrometer includes an entrance aperture through which an optical radiation signal is received, an exit aperture, an optical system, and a detector. The optical system includes a diffraction element, and directs the optical radiation signal along a non-direct optical path from the entrance aperture to the exit aperture via the diffraction element which spatially disperses the optical radiation signal according to wavelength. The detector is optically coupled to the exit aperture and detects at least a portion of the optical radiation signal directed by the optical system to the exit aperture. The optical radiation signal preferably includes a plurality of input optical radiation signals each guided into the entrance aperture by a respective optical fiber, with the optical fibers linearly oriented and spaced such that regions of zero input radiation are provided between the optical fiber cores.
The non-direct optical path is such that any diffracted radiation derived from energy dispersion by the diffraction element of the optical radiation incident thereon as it is directed by the optical system from the entrance aperture along the non-direct optical path cannot impinge on the entrance aperture. In accordance with an aspect of the present invention, the optical system is monocentric and is symmetric about an optical axis, the diffraction element spatially disperses the radiation according to wavelength along a dispersion direction, and the entrance aperture and exit aperture are separated from and located on opposite sides of a plane which contains the optical axis and is parallel to the dispersion direction, thereby providing the non-direct optical path between the entrance and exit apertures. The optical system may be implemented with a Dyson-type optical configuration, having a spherical plano-convex lens and a spherical concave diffraction grating which have a common center of curvature and optical axis. Alternatively, the optical system may be implemented with an Offner-type optical configuration, having a concave mirror and a convex diffraction grating which also have a common center of curvature and optical axis.
In accordance with another aspect of the present invention, the spectrometer includes a light trap structure which mitigates or eliminate stray light due to reflection of light incident on the exit aperture region but which does not impinge on the active area of the detector. In the Dyson-type optical configuration, the spherical plano-convex lens may incorporate the light trap structure, and preferably includes a combination of beveling, light absorbing media, and diffuse (e.g., substantially non-specular) reflecting characteristics.
In accordance with yet another aspect of the present invention, the detector is implemented as a two-dimensional area array detector which concurrently detects spectral signals corresponding to a plurality of input optical radiation signals input to the entrance slit. Additionally, the two-dimensional area array detector may be used to detect the spectral signal corresponding to at least one optical radiation signal input at the entrance slit and a signal corresponding to a region of zero input radiation at the entrance slit. The detected signal corresponding to the zero-input radiation region may be used to correct the detected input optical radiation signal(s) for stray light effects.
REFERENCES:
patent: 3185021 (1965-05-01), Thompson
patent: 3554649 (1971-01-01), Ridgway
patent: 3922089 (1975-11-01), Danielson et al.
patent: 4012147 (1977-03-01), Walrafen
patent: 4462687 (1984-07-01), Krause
patent: 4526470 (1985-07-01), Kaye
patent: 4546256 (1985-10-01), Denisou et al.
patent: 4568187 (1986-02-01), Kita et al.
patent: 4729658 (1988-03-01), Poultney
patent: 4743112 (1988-05-01), Burke
patent: 4850706 (1989-07-01), Mikes
patent: 4895445 (1990-01-01), Granger
patent: 4984888 (1991-01-01), Tobias
patent: 4995721 (1991-02-01), Krupa et al.
patent: 4997281 (1991-03-01), Stark
patent: 5042893 (1991-08-01), Ona
patent: 5066127 (1991-11-01), Schwenker
patent: 5087123 (1992-02-01), Gerlacher et al.
patent: 5088823 (1992-02-01), Smith et al.
patent: 5139335 (1992-08-01), Lundeen et al.
patent: 5479258 (1995-12-01), Hinnrichs et al.
patent: 5488474 (1996-01-01), Fateley et al.
Dyson, J., “Unit Magnification Optical System without Seidel Aberrations”, Journal of the Optical Society of America, vol. 49, No. 7, Jul. 1959.
Offner, A., “New Concepts in Projection Mask Aligners,” Optical Engineering, vol. 14, No. 2, Mar.-Apr. 1975.
Mertz, L., “Concentric spectrographs,” Applied Optics, vol. 16, No. 12, Dec. 1977.
Kingslake, R., “Lens Design Fundamentals,” Academic Press, 1978.
McMahan Robert K.
Palumbo Perry A.
Van Aken Harold R.
Weber William L.
Evans F. L.
Gretag Macbeth LLC
Morgan & Finnegan L.L.P.
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