Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1998-06-19
2000-07-11
Kim, Robert H.
Optics: measuring and testing
By particle light scattering
With photocell detection
356346, G01B 902
Patent
active
060880996
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method for spectral analysis of objects, i.e., spectral imaging. More particularly the present invention relates to an interferometer based method aimed at spectral imaging of a moving object, to determine the spectral intensity of each pixel thereof. Spectral intensity according to the invention may be due to light emitted (naturally occurring or induced fluorescence) from, reflected or scattered by and/or transmitted through the moving object, all are further referred hereinbelow as light emitted from the object.
Spectroscopy is a well known analytical tool which has been used for decades in science and industry to characterize materials and processes based on the spectral signatures of chemical constituents. The physical basis of spectroscopy is the interaction of light with matter. Traditionally, spectroscopy is the measurement of the light intensity emitted, transmitted, scattered or reflected from an object, as a function of wavelength, at high spectral resolution, but without any spatial information. Spectral imaging, on the other hand, is a combination of high resolution spectroscopy and high resolution imaging (i.e., spatial information).
A spectrometer is an apparatus designed to accept light, to separate (disperse) it into its component wavelengths, and measure the light's spectrum, that is the intensity of the light as a function of its wavelength. An imaging spectrometer, also referred herein as a spectral imager, is one which collects incident light from a scene and measures the spectra of each pixel (i.e., picture element) thereof.
Thus, spectral imaging is a technology which enables the measurement of the spectrum of light emitted from every point (pixel) of an object. A spectral imager is an instrument that measures and stores in memory for later retrieval and analysis the spectrum of light emitted from every point of the object which is placed in its field of view. A spectral image is a collection of spectra of the object measured by a spectral imager. It is usually organized as an intensity function defined in a three dimensional space in which two dimensions are of an image (x and y), and one is of a spectral axis (.lambda.). As such, a spectral image is usually referred to as a "cube" of data or "spectral cube".
There are three basic types of spectral imaging methods. These are (i) grating based spectral imaging, (ii) filters based spectral imaging (iii) and interferometer based spectral imaging.
In grating based spectral imaging systems, also known as slit-type imaging spectrometers, such as for example the DILOR system: [see, Valisa et al. (September 1995) presentation at the SPIE Conference European Medical Optics Week, BiOS Europe '95, Barcelona, Spain], only one axis of a CCD (charge coupled device) array detector (the spatial axis) provides real imagery data, while a second (spectral) axis is used for sampling the intensity of the light which is dispersed by the grating as function of wavelength. The system also has a slit in the first focal plane, limiting the field of view at any given time to a line of pixels. Therefore, a full image can only be obtained after scanning the grating or the incoming beam in a direction parallel to the spectral axis of the CCD in a method known in the literature as line scanning. The inability to visualize the two-dimensional image before the whole measurement is completed, makes it impossible to choose, prior to making the measurement, a desired region of interest from within the field of view and/or to optimize the system focus, exposure time, etc. Grating based spectral imagers are in use for remote sensing applications, because an airplane (or satellite) flying over the surface of the Earth provides the system with a natural line scanning mechanism.
It should be further noted that slit-type imaging spectrometers have a major disadvantage since most of the pixels of one frame are not measured at any given time, even though the fore-optics of the instrument actually collec
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Delori, F.C., "Spectropgotometer for Noninvasive Measurement of Intrinsic Fluorescence and Reflectance of the Ocular Fundus" Appl. Optics, 33(31): pp 7439-7452, 1994.
Buckwald Robert A.
Cabib Dario
Applied Spectral Imaging Ltd.
Friedman Mark M.
Kim Robert H.
Lee Andrew H.
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