WO1999053298A1

WO1999053298A1 - Method and system of on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma

Info

Publication number: WO1999053298A1
Application number: PCT/IL1999/000196
Authority: WO
Inventors: Israel Schechter; Danny Moshe; Nadav Horesh
Original assignee: Greenvision Systems Ltd.
Priority date: 1998-04-10
Filing date: 1999-04-11
Publication date: 1999-10-21
Also published as: GB2352517A; AU3342799A; GB2352517B; DE19983118T1; GB0026822D0

Abstract

A method and system of real time, on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma. In the method, three-dimensional spectral images are generated from two-dimensional images of non-thermal atomic emissions of a spatially extended sample. Two-dimensional images are acquired by using multiple fields of view of an imaging spectroscopic system. For spectral images acquired using a scanning interferometer, one plasma plume is produced in each region for each position of the scanning element of the interferometer, with a different subregion of the region being excited to produce each plume. The spectral images are compared to a database of atomic emission spectra to determine elemental content in each region. In the absence of a database of atomic emission spectra, the spectral images of the various regions are compared to each other to estimate elemental content of each region. The system features a synchronized elemental analysi spectroscopic imaging system, including means (18, 20) for setting at separate fields of view within each region of the sample, a gated excitation energy source (26) for inducing atomic emissions of the sample, a gated CCD (32), an optical system (28), control/data links (38), a control system, and data processing equipment (40) featuring algorithms for performing quantitation, classification, and scanalysis of the spectral data.

Description

METHOD AND SYSTEM OF ON-LLNE ELEMENTAL ANALYSIS BY TEMPORAL GATED IMAGING OF ATOMIC EMISSIONS INDUCED BY LASER PLASMA

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to methods and systems of elemental analysis and, more particularly, to a method and system of on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma. There are many industrial processes in which it is desirable to know, in real time, elemental content of feed and/or effluent material. Elemental analysis is particularly important in pollution abatement, especially with respect to identification and control of heavy elements as part of compounds either used or formed in industrial processes. Hereinafter, the term 'heavy elements' refers, in general, to elements of the periodic table of elements whose atomic number is 22 (i.e., element titanium) or greater, and in particular, to heavy metal elements of the periodic table of elements whose atomic number is 22 or greater. Heavy element analysis is particularly important in pollution abatement. For example, in the operation of a coal-fired power plant, it is desirable to monitor the emission of metals such as mercury during coal combustion; in the operation of an oil refinery, it is desirable to monitor the emission of metals such as nickel from the combustion of crude oil; in the operation of an oil-fired power plant, it is desirable to monitor the emission of metals such as nickel from the combustion of the fuel oil; and in the operation of a fleet of diesel-powered trucks, it is desirable to monitor the emission of metals such as nickel from the combustion of diesel fuel.

Methods and systems of elemental analysis that have sensitivities in the parts-per- trillion range, for example, atomic absorption, are known. These, however, are not suitable for real-time, on-line analysis. XRF (x-ray fluorescence) has been used on line, but it requires complicated equipment, such as a vacuum chamber, and is difficult to use in real time with small sample sizes. Because even a low level of heavy metal contamination is 2 environmentally deleterious, it is important that analytical methods used to detect heavy metal pollution give rapid turnaround times even for small sample sizes. There is thus a need for, and it would be highly advantageous to have, a real-time, on-line method and system of analysis for heavy metals with a sensitivity at least in the parts-per-billion range. An example of a method and system for real-time, on-line chemical analysis of paniculate samples in which the sample is excited to emit light, for example fluorescence, is that of US Patent No. 5,880,830, issued to Schechter, and manufactured by Green Vision Systems Ltd. of Tel Aviv, Israel. Emitted light is recorded by an instrument such as a scanning interferometer that generates a set of interferogram images, which in turn are used to produce a spectral image, or image cube, of the sample. A spectral image, or image cube, is a three dimensional data set (a volume) of voxels in which two dimensions are the spatial dimensions of the sample and the third dimension is the wavelength of the imaged light, such that coordinates of a voxel in a spectral image or image cube may be represented as (x,y,l). At any particular wavelength, the sample is imaged in two dimensions, so that voxels corresponding to that wavelength constitute the pixels of a monochromatic image of the sample at that wavelength. The spectral image is analyzed to produce a two dimensional map of the chemical composition of the sample.

In a preferred embodiment of the method of US Patent No. 5,880,830, spectral images are acquired using a scanning interferometer, such as the one described by Cabib et al. in US Patent No. 5,539,517 and manufactured by Applied Spectral Imaging, Ltd. of Migdal Haemek, Israel, under the name 'ASI SD2000'. In this apparatus, the optical .path difference, hereinafter, also referred to as OPD, internal to the interferometer is varied by moving a scanning element of the interferometer. At each position of the scanning element, within a selected field of view, or region of the sample, a two-dimensional interferogram image, featuring pixels, of the sample is acquired that includes a particular linear combination of the target wavelengths. At the end of a sequence of data acquisition, data points from a set of several two-dimensional interferogram images, are used for plotting pixel intensity vs OPD for that region. Data from these plots and are then disentangled by linear inversion, involving the use of Fast Fourier Transforms, to produce plots of pixel intensity vs wavelength, corresponding to the same region. Data from these plots are used for generating a regional spectral image featuring three-dimensional voxels. Typically, scanning of upto two hundred different optical path differences, corresponding to the same number of interferogram images, may be needed in order to enable generation of an accurate spectral image of the sample. This 3 method includes analysis of multiple fields of view, or regions, whereby individual regions of a sample are excited m succession with sufficient energy, for example, using ultra-violet light, to produce a sequence of multiple emissions. The set of generated regional spectral images are statistically analyzed to give an elemental composition map representative of an entire sample

With respect to atomic emissions of a plasma sample, induced by laser light or other similar excitation light or energy source incident on the sample, the fundamental limitation of applying the method of US Patent No 5,880,830, and other currently used methods of spectral imaging, to real-time, on-lme elemental analysis is with respect to the time domain within which atomic emission data is acquired. In these methods, emission, and thus, spectral data are obtained in a continuous manner from the instant a region of the sample is exposed to the incident excitation source. Analysis of a plasma, for example, in this manner results in mixing thermal effects, due to blackbody radiation of the plasma plume, with electronic effects, due to actual chemical charactenstics of the sample It is known that immediately following formation of a laser pulse induced plasma, where a plasma initially has an exceedingly high peak temperature (e.g., > 10,000 deg C), the plasma exhibits blackbody thermal radiation, along with corresponding thermal decay, for a duration of on the order of 10 to 100 microseconds. At a finite time following most of this thermal decay, atomic components of the plasma, still containing excited levels of electronic energy, release this nonthermal electronic energy in the form of light emission. Atomic emissions of light are recorded in the form of atomic emission spectra. It is this atomic emission of nonthermal electronic energy, and not emission of the thermal black body radiation, which features relevant information regarding chemical composition of a given sample

By minimizing contπbution of thermal effects in emission spectra corresponding to electronic/chemical effects of a sample, accuracy and precision of elemental analysis are improved compared to methods of elemental analysis which don't separate out or at least minimize thermal effects of plasma decay. Thus, there is a need for, and it would be highly advantageous, to have a method and system of real time, on-line elemental analysis which minimizes thermal effects inherent in the formation of laser induced plasmas. Such an improved method and system would include a means of effecting a time delay, or temporal gating, of acquisition of atomic emissions of the sample, to follow plasma formation after a finite time, pπor to interferometry, for example, in a spectral imaging method including interferometry. Thus, there is a need for a method and system of real time, on-line elemental 4 analysis which includes temporal gating of the acquisition of atomic emission data, for laser or other high eneinduced plasmas.

Another limitation of methods and systems featuring -the use of interferometers for elemental analysis relates to the accuracy of emission or image data that are obtained from multiple use of a single field of view of a given sample. In commonly applied interferometry methods featuring the use of laser induced plasmas, for example, for a laser induced plasma plume of a selected region or subregion of a sample, there is only enough time to acquire one interferogram image per selected OPD, at a given position of the scanning element, since it takes upto about 0.1 second to re-position the scanning element for acquisition of a next interferogram image, compared to microsecond lifetimes of plasma plumes. To acquire another interferogram image, the same region or subregion must be excited again to produce another plasma plume. Unfortunately, due to laser instability and other geometric and matrix related effects, the second plasma plume would not have the same geometric characteristics as the first one, to within desired accuracy and precision. These effects introduce additional variables during acquisition of spectral data, which directly affect, and need to be separated from, image information relating exclusively to the desired chemical composition of a sample. Higher accuracy of spectral data is achieved by having an interferometer or similar method featuring the use of multiple fields of view for obtaining data in a same region of a given sample. Elemental analysis would then be based on the analysis of several separate regions of a sample, where each region represents data obtained by using multiple fields of view.

There is thus a need for, and it would be highly desirable to have a method and system of real time, on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser or other high energy source plasma, whereby thermal effects of plasma plumes are minimized. Moreover, it would be highly advantageous to have such a real-time, on-line method and system of elemental analysis with a sensitivity in the parts-per-billion range, whereby results accurately represent an entire sample, with spectral imaging being performed with a minimum of interference from laser instability and other geometric and matrix related effects, via utilizing multiple fields of view during data acquisition and analysis.

SUMMARY OF THE INVENTION

The present invention relates to methods and systems of elemental analysis and, more particularly, to a method and system of on-line elemental analysis by temporal gated imaging 5 of atomic emissions induced by laser plasma. Practical application of the present invention is for better monitoring and control of any industrial process where real time, on-line elemental

• analysis is needed. In particular, the present invention is well suited for real time, on-line monitoring and quality control of combustion gases in the petroleum industry, and for checking purity and uniformity of powders, commonly used in the pharmaceutical and bulk chemical industries.

The method and system of the present invention leads to higher quality of results of elemental analysis via a temporal gating spectral imaging technique. This translates to obtaining spectral imaging data of plasma plumes more representative of actual electronic/chemical information of analytical samples, as a result of minimizing contribution of thermal effects during decay of plasma plumes. Additionally, the same method and system of the present invention results in high accuracy of elemental analysis results, whereby multiple fields of view are used during atomic emission data acquisition, in which acquired spectral data is obtained from a multiple of targeted subregions in a given region of the sample, each subregion in a separate field of view, for the sample subjected to laser induced plasma formation. This feature enables overcoming the limitation of the time span required for acquiring spectral image data of a sample being orders of magnitude higher than the lifetimes of plasma plumes.

The preferred embodiment of the method of on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma according to the present invention features the following principle steps: (1) Provide a sample divided into Rj regions, with each region having S_j subregions; (2) Provide an elemental analysis spectroscopic imaging system, including a scanning interferometer with an adjustable scanning element, for example, a gated laser beam, a gated CCD (charge coupled detector), an optical system, control/data links, and a control system; (3) Adjust and set the interferometer scanning element to a position over a subregion in a region of the sample via control system signal Pi; (4) Generate a laser pulse via control system signal P₂, onto the subregion, for a duration of a few sub-microseconds, including (a) producing a plasma plume over the subregion, and (b) waiting a finite time (10 - 100 microseconds) following the laser pulse; (5) Open gated CCD via control system signal P₃, following completion of the finite waiting time, including (a) obtaining an interferogram image of the subregion, via the optical system; (6) Repeat steps (3) through (5) for M subregions in the same region of the same sample, using M fields of view, each field of view at another OPD; (7) Perform quantitation of the spectral data obtained from the selected 6 region; (8) Generate a spectral image (image cube) from the M interferogram images, including (a) FFT (Fast Fourier Transform) of the pixels of the M two-dimensional interferogram images, and (b) constructing the three-dimensional spectral image of the same region; (9) Perform classification process of the spectral data obtained from the region, to produce initial results of the elemental analysis; (10) Repeat steps (3) through (9) for N regions of the same sample; and (11) Perform scenario analysis of the spectral data of the N regions to produce final results of the elemental analysis.

The preferred embodiment of the system of on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma according to the present invention features the following principle components: (1) A sample divided into R regions, with each region having S_j subregions; (2) An elemental analysis spectroscopic imaging system, including a scanning interferometer with an adjustable scanning element for application to multiple fields of view of the subregions within each region of the sample, a gated laser beam, a gated CCD, an optical system, control/data links, and a control system; and (3) Data processing equipment featuring algorithms for (a) performing quantitation of spectral data, including generation of three-dimensional spectral images, involving operations of FFTs on two-dimensional interferogram image pixels, (b) performing a classification process on the generated spectral image data, and (c) performing scenario analysis of the spectral data obtained from a sufficient number of regions of the sample, in order to produce final results of the elemental analysis.

According to the present invention there is provided a method of elemental analysis by temporal gated imaging of atomic emissions, the method comprising the steps of: (a) providing a sample divided into a plurality of regions, each of the plurality of regions further divided into a plurality of subregions; (b) providing an elemental analysis spectroscopic imaging system, the imaging system including a temporal gated CCD camera; (c) for at least one of the plurality of regions of the sample: (i) setting the spectroscopic imaging system for acquisition of one wavelength of atomic emission of one of the plurality of subregions, the setting corresponding to one of a plurality of single fields of view of the spectroscopic imaging system in the at least one of the plurality of regions, (ii) inducing a plasma plume over the one subregion by irradiating the one subregion, following completion of setting the spectroscopic imaging system, (iii) waiting a finite time for the plasma plumto thermally cool, whereby the thermal spectrum of the plasma plume decays, to form a nonthermal atomic emission, (iv) activating and opening of the temporal gated CCD camera for acquisition of a 7 two dimensional image of the one wavelength of the nonthermal atomic emission of the one subregion, following completion of the finite time for the plasma plume to thermally cool, (v) successively repeating steps (i) through (iv) for a number of the subregions in the at least one region, to form a plurality of the two dimensional images, each of the two dimensional images corresponding to the acquisition of a different one wavelength of the nonthermal atomic emission of a different one subregion using a different one of a plurality of single fields of view of the spectroscopic imaging system in the at least one of the plurality of regions, (vi) generating a spectral image from the plurality of the two dimensional images, the spectral image featuring a plurality of voxels, whereby each of the plurality of voxels corresponds to a plurality of the different wavelengths of the nonthermal atomic emissions of the number of the subregions of the at least one of the plurality of regions, the spectral image including a plurality of observed spectra, and (vii) comparing the observed spectra with a database of atomic emission spectra of elements to obtain estimates of amounts of the elements present in the at least one region of the sample. According to the present invention there is provided a method of elemental analysis by temporal gated imaging of atomic emissions, the method comprising the steps of: (a) providing a sample divided into a plurality of regions, each of the plurality of regions further divided into a plurality of subregions; (b) providing an elemental analysis spectroscopic imaging system, the imaging system including a temporal gated CCD camera; (c) for each of the plurality of regions of the sample: (i) setting the spectroscopic imaging system for acquisition of one wavelength of atomic emission of one of the plurality of subregions, the setting corresponding to one of a plurality of single fields of view of the spectroscopic imaging system in each of the plurality of regions, (ii) inducing a plasma plume over the one subregion by irradiating the one subregion, following completion of the setting the spectroscopic imaging system, (iii) waiting a finite time for the plasma plume to thermally cool, whereby the thermal spectrum of the plasma plume decays, to form a nonthermal atomic emission, (iv) activating and opening of the temporal gated CCD camera for acquisition of a two dimensional image of the one wavelength of the nonthermal atomic emission of the one subregion, following completion of the finite time for the plasma plume to thermally cool, (v) successively repeating steps (i) through (iv) for a number of the subregions in each region, to form a plurality of the two dimensional images, each of the two dimensional images corresponding to the acquisition of a different one wavelength of the nonthermal atomic emission of a different one subregion using a different one of a plurality of single fields of 8 view of the spectroscopic imaging system in the at least one of the plurality of regions, (vi) generating a spectral image from the plurality of the two dimensional images, the spectral image featuring a plurality of voxels, whereby each of the plurality of voxels corresponds to a plurality of the different wavelengths of the nonthermal atomic emissions of the number of the subregions of each of the plurality of regions, the spectral image including a plurality of observed spectra; and (d) classifying the regions according to a minimum number of the elements in each of the regions, as inferred from inter-regional comparisons of the observed spectra.

According to the present invention there is provided a method of controlling elemental emissions from an industrial process by temporal gated imaging of atomic emissions, the method comprising the steps of: (a) providing a sample of emission of the industrial process, the sample divided into a plurality of regions, each of the plurality of regions further divided into a plurality of subregions; (b) providing an elemental analysis spectroscopic imaging system, the imaging system including a temporal gated CCD camera; (c) for at least one of the plurality of regions of the sample: (i) setting the spectroscopic imaging system for acquisition of one wavelength of atomic emission of one of the plurality of subregions, the setting corresponding to one of a plurality of single fields of view of the spectroscopic imaging system in the at least one of the plurality of regions, (ii) inducing a plasma plume over the one subregion by irradiating the one subregion, following completion of setting the spectroscopic imaging system, (iii) waiting a finite time for the plasma plume to thermally cool, whereby the thermal spectrum of the plasma plume decays, to form a nonthermal atomic emission, (iv) activating and opening of the temporal gated CCD camera for acquisition of a two dimensional image of the one wavelength of the nonthermal atomic emission of the one subregion, following completion of the finite time for the plasma plume to thermally cool, (v) successively repeating steps (i) through (iv) for a number of the subregions in the at least one region, to form a plurality of the two dimensional images, each of the two dimensional images corresponding to the acquisition of a different one wavelength of the nonthermal atomic emission of a different one subregion using a different one of a plurality of single fields of view of the spectroscopic imaging system in the at least one of the plurality of regions, (vi) generating a spectral image from the plurality of the two dimensional images, the spectral image featuring a plurality of voxels, whereby each of the plurality of voxels corresponds to a plurality of the different wavelengths of the nonthermal atomic emissions of the number of the subregions of the at least one of the plurality of regions, the spectral image including a 9 plurality of observed spectra, and (vii) comparing the observed spectra with a database of atomic emission spectra of elements to obtain estimates of amounts of the elements present in the at least one region of the sample; and (d) adjusting a control parameter of the industrial process based on the estimates. According to the present invention, there is provided a system of elemental analysis by temporal gated imaging of atomic emissions, the system comprising: (a) a sample divided into a plurality of regions, each of the plurality of regions further divided into a plurality of subregions; (b) a spectroscopic imaging system, the imaging system including: (i) an excitation energy source for inducing atomic emissions of the sample, (ii) a temporal gated CCD camera, and (iii) a means of setting the spectroscopic imaging system for acquisition of two dimensional images of nonthermal atomic emissions of the plurality of the subregions, the setting corresponding to a plurality of single fields of view of the spectroscopic ^• imaging system in at least one of the plurality of regions; and (d) data processing equipment including algorithms for: (i) generation of a plurality of three-dimensional spectral images from the two dimensional images, whereby each of the spectral images features a plurality of voxels, whereby each of the plurality of voxels corresponds to a plurality of different wavelengths of the nonthermal atomic emissions of the plurality of the subregions of the at least one of the plurality of regions, whereby each of the spectral images includes a plurality of observed atomic emission spectra, (ii) comparing the observed spectra with a database of atomic emission spectra of elements to obtain estimates of amounts of the elements present in the at least one region of the sample, (iii) performing a classification process on data of the spectral images, and (iv) performing scenario analysis of the data of the spectral images to produce final results of the elemental analysis.

Implementation of thmethod and system of the present invention involves performing or completing tasks or steps manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of a given elemental analysis system, several steps of the present invention could be implemented by hardware or by software on any operating system of any firmware or a combination thereof. For example, as hardware, indicated steps of the invention could be implemented as a chip or a circuit. As software, indicated steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, indicated steps of the method of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions. 10

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 is a diagram of a portion of the surface of an exemplary sample, showing division of the surface into regions and subregions;

FIG. 2 is a flow diagram of a preferred embodiment of the method of on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma according to the present invention; FIG. 3 is a schematic diagram of an exemplary system for implementing the preferred embodiment of the method of the present invention described in Fig. 2;

FIG. 4 is an overall flow diagram of the detection and quantitation of spectral data according to the preferred embodiments of the method and system of the present invention;

FIG. 5 is a flow diagram of the classification process according to the preferred embodiments of the method and system of the present invention; and

FIG. 6 is a generalized intensity curve for illustrating fuzzy logic description parameters relating to the classification process of Fig. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is of a method and system of real-time on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma. The present invention is used in applications of elemental analysis of small samples of industrial processes, for example, requiring detection and quantitation of targeted elements in chemical feeds, intermediates, effluents, or finished products. The scope of the present invention includes the chemical analysis of any suitable sample that is spatially extended in two dimensions, including, for example, aerosols and particulates collected on filter paper, as well as soil and sludge samples. Moreover, the present invention is applicable to such analytical samples containing one or more atomic elements capable of exhibiting an atomic emission spectrum induced by a temporally gated, excitation energy source. This includes samples containing elements capable of undergoing luminescence, in general, and fluorescence or phosphoresence, in particular, where the gated excitation energy source can be light of the electromagnetic spectrum in general, including from a gated laser beam, or from a gated heat source, in particular. Furthermore, the present invention is applicable to imaging systems 11 having the possibility of including temporally gated acquisition of atomic emission data, for example by using a temporal gated CCD camera synchronized with a gated excitation energy source.

Steps, components, and implementation of the method and system of on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma according to the present invention are better understood with reference to the following drawings and the accompanying descriptions. It is to be noted that illustrations of the present invention shown here are for illustrative purposes only and are not meant to be limiting. For example, the following drawings and accompanying description of a preferred embodiment of the method and system of the present invention refer to a spectroscopic imaging system featuring a scanning interferometer. An alternative spectroscopic imaging system used for implementing the preferred embodiment of the method of the present invention could feature a set of interchangeable optical bandpass filters.

Figure 1 shows a portion of a surface of an exemplary sample 10 divided into an arbitrary number, Rj, of regions 12, each region 12 being of size on the order of a few millimeters by a few millimeters. One of regions 12 is shown divided into an arbitrary number, S_j, of disjoint subregions 14, each subregion being of size several tens of microns by several tens of microns. According to the present invention, one subregion 14 at a time is excited in each region 12 to produce a plasma. For example, if a scanning interferometer is used to acquire the spectral images, then at each position of the scanning element of the interferometer, corresponding to a different OPD, and to a single field of view, only one subregion 14 of each region 12 is excited to produce a plasma. It is assumed that regions 12 are sufficiently homogeneous that all subregions 14 within the same region 12 produce plasmas of the same elemental composition when excited. Because a given subregion 14 of any region 12 is excited only once, alteration of the geometry and composition of that same subregion 14 induced by the excitation of the plasma does not affect the accuracy of the analysis of multiple subregions or regions of the sample.

In Fig. 1, a plasma is formed above a subregion 14 by focusing a suitably intense laser beam onto that subregion- 14. The plasma as formed exhibits black body thermal radiation influences, but after several microseconds the plasma cools and the thermal radiation decays, leaving a population of nonthermal electronically excited elemental atoms that decay to their ground states .during the course of the next several tens of microseconds, while emitting a spectrum that consists of pronounced atomic lines. According to the preferred embodiment of 12 the present invention, there is a programmed waiting period of a finite time of on the order of tens of microseconds, corresponding to decay of the black body radiation of each plasma plume, prior to opening of the gated CCD for acquisition of atomic emission data from the plasma plume. Elemental analysis of sample 10 is based on analysis of a plurality of regions 12, whereby each region 12 features a plurality of subregions 14. Implementation of the method and system of the present invention is such that each field of view corresponds to a single position of the interferometer scanning element over a single subregion 14. In terms of providing final estimates of elemental analysis of sample 10, results are based on a plurality of fields of view corresponding to a plurality of spectral images, where each spectral image relates to the chemical composition of a single region 12.

There are several ways to acquire spectral images of regions 12, from subregions 14, by generating laser induced plasmas of a sample. When using a scanning interferometer, or, as described below, when using a set of bandpass filters, several plumes are sequentially excited per region 12, one plume for each linear combination of wavelengths in the case of the scanning interferometer, or one plume per filter in the case of the bandpass filters. In either case, the initial spectral image, or image cube, consists of a set of a plurality of two- dimensional interferogram images, featuring two-dimensional pixels, acquired from a plurality of laser induced plasmas, at a corresponding set of optical path differences (OPDs). FFT (Fast Fourier Transform) is carried out on each two-dimensional pixel, resulting in a full spectrum (i.e., ca. 100 - 200 wavelengths) corresponding to that pixel. The ultimate spectral image, or image cube, of the sample as a whole, consists of three-dimensional voxels, where each voxel, having a spectral intensity, represents a full spectrum of a given two-dimensional interferogram image pixel. One voxel of the spectral image, as a whole, corresponds toseveral pixels of the two-dimensional interferogram images.

Figure 2 is a flow diagram of a preferred embodiment of the method of on-line elemental analysis by temporal gated imaging of atomic emissions induced by laser plasma according to the present invention. In Fig. 2, each generally applicable, principle step of the method of the present invention is numbered and enclosed inside a frame. Substeps representing further of an indicated principle step of the method are indicated by a letter in parentheses. Terminology appearing in the following description is consistent with that used in Fig. 2.

In Step 1, there is provision of a sample divided into Rj regions, with each region 13 having S_j subregions, as shown in Fig. 1. Regions and/or subregions of the sample can be geometrcially uniform or nonuniform.

In Step 2, an elemental analysis spectroscopic imaging system is provided, including a scanning interferometer with an adjustable scanning element, a gated laser beam, a gated CCD, an optical system, control/data links, and a control system.

In Step 3, there is adjustment and setting of the interferometer scanning element to a position over a subregion in a region of the sample via control system signal Pi. Each setting of the interferometer scanning element corresponds to another OPD.

In Step 4, there is generation of a laser pulse via control system signal P₂, onto the subregion, for a duration of a few sub-microseconds. Typically, laser pulse duration is of the order of nanoseconds. In step (a), a plasma plume is produced over the subregion as a result of the laser pulse. In step (b), a finite waiting time, e.g.,- 10 - 100 microseconds, following completion of the laser pulse, takes place. This time interval corresponds to the approximate time duration required for the initial plasma plume to exhibit thermal decay of black body thermal influences. Moreover, this time interval varies according to characteristics of a given sample, and of a given matrix holding the sample. The method of the present invention allows for optimization of this time interval in order to achieve high quality spectral information based on actual atomic emission of various targeted elements of a given sample, separate from thermal and/or matrix influences. In Step 5, there is temporal gating of the CCD, whereby it is activated and opened for a specified time interval via control system signal P₃, following completion of the finite waiting time described in Step 4. In step (a), an interferogram image of the subregion is obtained, via the optical system. As for the time interval of Step 4, the method of the present invention allows for optimization of the CCD gating time interval in order to achieve high quality spectral information based on actual atomic emission of various targeted elements of a given sample, separate from thermal and/or matrix influences.

In Step 6, Steps 3 through 5 are repeated for M subregions in the same region of the same sample, using M different fields of view of the optical system, each field of view at another OPD. This step results in generation of a spatial set of sequential interferogram images.

In Step 7, there is quantitation of spectral data obtained from the selected region under analysis. In this step there is digitation, alignment, summation, and blanking of the image data, according to algorithms featuring specific criteria set at the beginning of the imaging 14 procedure. Further details of this step are shown in Fig. 4, and described in the accompanying description.

In Step 8, there is generation of a spectral image (image cube) from the spatial set of M two-dimensional interferogram images obtained from the same region. In step (a), FFT (Fast Fourier Transform) is carried out on each two-dimensional pixel of each interferogram image, resulting in a full spectrum (i.e., ca. 100 - 200 wavelengths) corresponding to that pixel. In step (b), the complete spectral image, or image cube, of the sample as a whole, is constructed as full spectrum three-dimensional voxels, where each voxel, having a spectral intensity, represents a full spectrum of two-dimensional pixels in the same selected region of the sample under analysis.

In Step 9, classification process of the spectral data obtained from the same region is performed, in order to produce initial estimates of the elemental analysis of the sample. Further details of this step are shown in Figures 5 and 6, and are described in the accompanying descriptions. In Step 10, Steps 3 through 9 are repeated for N regions of the same sample.

In Step 11, scenario analysis of the spectral data of the N regions is performed to produce final results of the elemental analysis of the entire sample. This step is performed by applying scenario analysis algorithms to spectral data surviving the classification process of Step 9. Figure 3 is a schematic diagram of an exemplary system for implementing the preferred embodiment of the method of the present invention described in Fig. 2. Such a system could be, for example, an automatic real time, on-line system for monitoring heavy elements (e.g., metals) in soot. A roll of a porous, thermally stable substrate 16 such as PTFE or fiberglass is mounted on a pair of rollers 18 which move substrate 16 from left to right. Exhaust gases bearing particulates from an industrial process (e.g., combustion) are directed by a flue 20 to traverse substrate 16 so that a sample 10 of particles is deposited on substrate 16. Rollers 18 move sample 10 to a field of view position for viewing under a spectroscopic imaging system 36. Spectroscopic imaging system 36 includes a gated laser 26, an optical system 28, a scanning interferometer 30, and a gated CCD camera 32 that has a suitable sensitivity and dynamic range. Optical system 28 includes components such as prisms or mirrors that direct an output beam 27 from laser 26 sequentially to subregions 14 within regions 12 of sample 10. Components of optical system 28 are represented symbolically in Fig. 3 by a scanning mirror 29. Optical system 28 also includes components such as lenses 15 that focus the output beam onto subregions 14 of regions 12 of sample 10, and components such as lenses that direct the light emitted by the plasmas thus created above subregions 14 to scanning interferometer 30.

The wavelength of the light emitted by laser 26 may be from the near infrared to the near ultraviolet. Suitable lasers 26 include a nitrogen gas laser emitting light having a wavelength of 337 nanometers, a Q-switched neodymium YAG laser, emitting light having a wavelength of 1064 nanometers, the same Q-switched neodymium YAG laser in conjunction with a frequency doubler that produces a second harmonic output beam 27 having a wavelength of 532 nanometers, and an XeCl excimer laser emitting light having a wavelength of 318 nanometers. Typically, the laser pulses are about 5 to 20 nanoseconds in duration, whereby optical system 28 focuses laser beam 27 to a spot, i.e., a subregion 14 (Fig. 1), of about 50 microns in diameter, to achieve a power density between 10² and 10⁴ J/cm².

Gated CCD camera 32, scanning interferometer 30, optical system 28, and laser 26, are connected by suitable control/data links 38 to a control system 40. In particular, activation of gated CCD camera 32 is synchronized as follows: the scanning element of scanning interferometer 30 is positioned over a subregion 14 (Fig. 1) of sample 10 by control system signal Pi , followed by a pulse of laser beam 27 over subregion 14 by control system signal P₂, followed by activation of gated CCD camera 32 by control system signal P₃. In other words, control system 40 activates gated CCD camera 32, by control system signal P₃, to receive light from scanning interferometer 30 only in a time window which starts after a suitable delay, typically in the range of 10 to 100 microseconds, after termination of each pulse from laser 26. The plasma as formed following each pulse from laser 26 has a black body thermal spectrum, but after several microseconds the plasma cools and the thermal spectrum decays, leaving only a nonthermal population of eexcited heavy metal atoms that decay to their ground states during the course of the next several tens of microseconds, while emitting a spectrum that consists of pronounced atomic lines. It is this spectrum of atomic lines which is recorded by using the scanning interferometer, enabling _. generation of an interferometer image for the subregion 14. This synchronization is repeated as necessary for each of M subregions in each of N regions of the same sample. The system of the present invention allows for optimization of the synchronization among the setting of the interferometer scanning element 29 via signal P-i, the laser beam pulse via signal P₂, and the CCD gating time interval via signal P₃, in order to achieve high quality spectral information based on actual atomic emission of various targeted elements of a 16 given sample, separate from thermal and/or matrix influences.

Rollers 18 also are connected by a control/data link 38 to control system 40 so that substrate 16 can be advanced under the control of control system 40, such that completion of obtaining spectral imaging data of one sample is followed by delivery of another sample. Rollers 18 are mounted on a stage 22 which has two lateral degrees of freedom of motion: left-right, like rollers 18, and also into and out of the plane of Fig. 3. Stage 22 also is controlled by control system 40 via a control/data link 38. Rollers 18 are activated by electric motors, for gross lateral motion. Stage 22 is based on both stepping motors and piezoelectric activators, for fine control of the aiming of laser beam 27. Preferably, rollers 18 are used to move substrate 16 to the right, as seen in Fig. 3, in a stepwise fashion, so that while control system 40 is acquiring and analyzing images of one sample 10, flue 20 is delivering the next sample 10. Optical system 28 is provided with a sufficiently low numerical aperture that vertical motion for focusing is unnecessary.

Control system 40 is based on a personal computer, and includes a frame grabber, for acquiring images from gated CCD camera 32, as well as other hardware interface boards for controlling rollers 18, stage 22, and the other components 26, 28 and 30 of spectroscopic imaging system 36. The software of control system 40 includes a database of atomic emission spectra, for a variety of sample matrices, and code for implementing image processing, quantitation, and classification algorithms described below. In a variant of the system of Fig. 3, scanning interferometer 30 is replaced by a set of interchangeable optical bandpass filters. These filters may be made easily interchangeable by mounting them on a filter wheel. For each subregion 14, a two-dimensional image is acquired via a different filter, and the corresponding wavelength is the central wavelength of the filter's bandpass. Figure 4 is an overall flow diagram of the detection and quantitation of spectral data according to the preferred embodiments of the method (Steps 3 through 11 of Fig. 2) and system (Fig. 3) of the present invention. The general structure of the flow is a loop (block 60) over regions 12. In each region 12, a preliminary set of M two-dimensional interferogram images, featuring pixels, is acquired (block 62) as described above (Step 6 of Fig. 2), i.e., one two-dimensional interferogram image is obtained per field of view per subregion, at each position (i.e., OPD) of the scanning element of interferometer 30 of Fig. 3. These two- dimensional images are aligned (block 64) by translating them relative to each other to maximize their mutual cross-correlations. This is necessary because for this system, each 17 image is of a different plasma plume, so that in general the various images do not necessarily overlap exactly, if only because each plasma plume is created by exciting a different subregion 14 of sample 10 (Fig. 1).

The two-dimensional interferogram images are summed (block 66) to give a summed, or gray level, image, featuring three-dimensional voxels, which is checked (oval 68) for gray level voxels whose intensities exceed a preset threshold related to background intensity. Note that, like voxels of a spectral image, each gray level image features voxels, and, in fact, the intensity value of a gray level voxel represents the sum of the intensities of the two- dimensional pixels featured in the set of two-dimensional interferogram images that share a common location, where the common location is defined by a particular OPD or wavelength. The criterion for a sufficiently high amount of targeted (e.g., heavy or metallic) elements being present in a region 12 of sample 10 (Fig. 1), is that the fraction of gray level image voxels whose intensities exceed the, threshold be sufficiently high. If the criterion is not satisfied, another region 12 of sample 10 is selected (oval 68). Intensities of two-dimensional pixels of the preliminary set of two-dimensional images that correspond to below-threshold intensities of gray level voxels in the summed images are blanked (block 70).

Following blanking of appropriate image data, the remaining set of interferogram images are then linearly transformed to produce a spectral image of a particular target region 12 (Step 8 of Fig. 2). This spectral image is classified (block 72 of Fig. 4, and Step 9 of Fig. 2), i.e., compared to the atomic emission spectra in the database to assay targeted elements present in region 12. The classification process is followed by a consistency check (Fig. 4, block 74). When elemental detection, quantitation, and classification, has been performed on a large enough number of regions 12 (Fig. 4, block 76), the initial data are analyzed by a scenario analysis algorithm to convert them to final estimates of absolute elemental amounts (Fig. 4, block 78, and Fig. 2, Step 11).

Figure 5 is a flow diagram of the classification process according to the preferred embodiments of the method and system of the present invention (block 72 of Fig. 4, and Step 9 of Fig. 2). There are well-established methods for comparing spectral intensities of voxels, i.e., pixels of two-dimensional images, that share a common location (i.e., I), to a database of atomic emission spectra, to determine the elemental composition of a region 12 of exemplary sample 10 (Fig. 1). The most powerful of these is multivariate analysis in general, and principal component regression (PCR) or least squares analysis (for example, partial least squares analysis (PLS) or non-linear least squares fitting) in particular. See, for example, H. 18

Martens and T. Naes, Multivariance Calibration (John Wiley & Sons, 1989). Another such method is fuzzy logic analysis. See, for example, J. C. Bezdek and S. K. Pal (eds.), Models for Pattern Recognition, IEEE Press, 1992, and R. R. Yager and L. A. Zadeh (eds.), An Introduction to Fuzzy Logic Applications in Intelligent Systems, Kluwer Academic Publications, 1992.

In the preferred embodiments of the method and system of the present invention, both multivariate regression (e.g., principle component regression) and fuzzy logic analysis are used, to exploit the redundancy inherent in using two independent methods. Essentially, the classification process is a matter of looking for a linear combination of the spectra that matches the intensities. The coefficients of the linear combination then are proportional to the amounts of the various elemental species at the location sampled. In Fig. 5, the linear combination is determined by two methods, fuzzy logic analysis (block 80) and principal component regression (block 82). Both of these methods yield both estimates of elemental species amounts and uncertainty measures for those estimates. The two sets of estimates are reconciled (block 84) to give a final set of estimated amounts of the targeted elements of the sample.

In the absence of a matrix dependent database of laser induced plasma atomic emission spectra, the observed spectra of the various regions 12 (Fig. 1) can be compared to each other by other well-established methods, such as cluster analysis, to determine minimum numbers of targeted elemental species that are conwith these spectra. For example, if a spectral line is present in one set of regions and absent in another set of regions, then there is at least one targeted elemental specie that is present in the first set of regions and absent in the second set of regions.

Figure 6 is a generalized intensity curve 86 (plotted as intensity I as a function of wavelength I), illustrating five of the description parameters used in the fuzzy logic analysis, relating to the classification process of Fig. 5. Although in principle the spectral lines of atomic elements in the plumes are sharp, in practice these lines are broadened, as shown,, for example by thermal broadening. Curve 86 has two peaks, one with a peak intensity Ii at wavelength l_{l s} and the other with a peak intensity I₂ at wavelength l₂. The minimum intensity between the two peaks is I₃, corresponding to a wavelength l₃. The full width at half amplitude of the first peak is designated by Di. The full width at half amplitude of the second peak is designated by D₂. The difference between \_\ and l₃ is D₃. The five description parameters illustrated in Fig. 6 are: 19 peak height ratio I]/I₂ peak full width at half amplitude ratio Dι/D₂ number of peaks peak to minimum ratio Dι/D₃ peak wavelength ratio I ι/l₂

Elemental species amounts having been estimated for each voxel of the spectral image, the estimates are analyzed for mutual consistency (Fig. 4, block 74), based on the criterion that neighboring voxels are expected to feature similar elemental compositions. It is unlikely that a voxel (i ,λ) will feature a different composition than a neighboring voxel (k,l,λ), where i - l ≤ k ≤ i + l and j - l ≤ l ≤ j + 1 (neighborhood decision concept), for the same wavelength, I. Voxels not satisfying the criterion are culled from final spectral image.

Estimates of intensities ^"of the surviving voxels are assumed to be valid measurements of local elemental amounts in region 12 of sample 10 (Fig. 1).

When elemental detection, quantitation, and classification, has been performed on a large enough number of regions 12 (Fig. 4, block 76), the initial data are analyzed by a scenario analysis algorithm to convert them to final estimates of absolute elemental amounts

(Fig. 4, block 78, and Fig. 2, Step 11).

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.

Claims

20WHAT IS CLAIMED IS:

1. A method of elemental analysis by temporal gated imaging of atomic emissions, the method comprising the steps of:

(a) providing a sample divided into a plurality of regions, each of said plurality of regions further divided into a plurality of subregions;

(b) providing an elemental analysis spectroscopic imaging system, said imaging system including a temporal gated CCD camera;

(c) for at least one of said plurality of regions of said sample:

(i) setting said spectroscopic imaging system for acquisition of one wavelength of atomic emission of one of said plurality of subregions, said setting corresponding to one of a plurality of single fields of view of said spectroscopic imaging system in said at least one of said plurality of regions,

(ii) inducing a plasma plume over said one subregion by irradiating said one subregion, following completion of said setting said spectroscopic imaging system,

(iii) waiting a finite time for said plasma plume to thermally cool, whereby the thermal spectrum of said plasma plume decays, to form a nonthermal atomic emission, (iv) activating and opening of said temporal gated CCD camera for acquisition of a two dimensional image of said one wavelength of said nonthermal atomic emission of said one subregion, following completion of said finite time for said plasma plume to thermally cool, (v) successively repeating steps (i) through (iv) for a number of said subregions in said at least one region, to form a plurality of said two dimensional images, each of said two dimensional images corresponding to said acquisition of a different said one wavelength of said nonthermal atomic emission of a different said one subregion using a different said 21 one of a plurality of single fields of view of said spectroscopic imaging system in said at least one of said plurality of regions,

(vi) generating a spectral image from said plurality of said two dimensional images, said spectral image featuring a plurality of voxels, whereby each of said plurality of voxels corresponds to a plurality of said different wavelengths of said nonthermal atomic emissions of said number of said subregions of said at least one of said plurality of regions, said spectral image including a plurality of observed spectra, and

(vii) comparing said observed spectra with a database of atomic emission spectra of elements to obtain estimates of amounts of the elements present in said at least one region of said sample.

2. The method of claim 1, wherein said irradiating said one subregion is effected by using a temporal gated excitation energy source for inducing atomic emission, said excitation energy source is synchronized with said temporal gated CCD camera.

3. The method of claim 1, wherein each of said plurality of said two dimensional images features a plurality of pixels, each of said plurality of said pixels having an intensity corresponding to said one wavelength of said nonthermal atomic emission of a said one subregion.

4. The method of claim 3, wherein said plurality of said two dimensional images are acquired using a scanning interferometer, so that said intensity of said each of said plurality of said pixels corresponds to a linear combination of a plurality of said wavelengths.

5. The method of claim 3, wherein said each of said plurality of said two dimensional 22 images is acquired via a filter that passes a different one of said one wavelength.

6. The method of claim 3, further comprising the step of, in said at least one region:

(viii) aligning said two dimensional images.

7. The method of claim 1, wherein said comparing of said observed spectra with said database spectra is effected only for said observed spectra that have a summed intensity greater than a certain threshold.

8. The method of claim 1, wherein said comparing of said observed spectra with said database spectra is effected by multivariate analysis, said.multivariate analysis includes at least one algorithm selected from the group consisting of principal component regression and partial least squares analysis.

9. The method of claim 1, wherein said comparing of said observed spectra with said database is effected by fuzzy logic analysis based on at least one description parameter, said at least one description parameter is selected from the group consisting of peak height ratio, peak full width at half amplitude ratio, number of peaks, peak to minimum ratio and peak wavelength ratio.

10. The method of claim 1, wherein, for said at least one region, the method further includes the step of:

(viii) checking neighboring said voxels for mutual consistency.

11. The method of claim 1 , further comprising the step of performing scenario analysis of said spectrimaging data acquired for said plurality of said regions, to generate final results of the elemental analysis of said sample.

12.. A method of elemental analysis by temporal gated imaging of atomic emissions, 23 the method comprising the steps of:

(c) for each of said plurality of regions of said sample:

(i) setting said spectroscopic imaging system for acquisition of one wavelength of atomic emission of one of said plurality of subregions, said setting corresponding to one of a plurality of single fields of view of said spectroscopic imaging system in said each of said plurality of regions,

(iii) waiting a finite time for said plasma plume to thermally cool, whereby the thermal spectrum of said plasma plume decays, to form a nonthermal atomic emission, (iv) activating and opening of said temporal gated CCD camera for acquisition of a two dimensional image of said one wavelength of said nonthermal atomic emission of said one subregion, following completion of said finite time for said plasma plume to thermally cool, (v) successively repeating steps (i) through (iv) for a number of said subregions in said each region, to form a plurality of said two dimensional images, each of said two dimensional images corresponding to said acquisition of a different said one wavelength of said nonthermal atomic emission of a different said one subregion using a different said one of a plurality of single fields of view of said spectroscopic imaging system in said at least one of said plurality of regions, (vi) generating a spectral image from said plurality of said two dimensional 24 images, said spectral image featuring a plurality of voxels, whereby each of said plurality of voxels corresponds to a plurality of said different wavelengths of said nonthermal atomic emissions of said number of said subregions of said each of said plurality of regions, said spectral image including a plurality of observed spectra; and

(d) classifying said regions according to a minimum number of the elements in each of said regions, as inferred from inter-regional comparisons of said observed spectra.

13. The method of claim 12, wherein said irradiating said one subregion is effected by using a temporal gated excitation energy source for inducing atomic emission, said excitation energy source is synchronized with.said temporal gated CCD camera.

14. The method of claim 12, wherein each of said plurality of said two dimensional images features a plurality of pixels, each of said plurality of said pixels having an intensity corresponding to said one wavelength of said nonthermal atomic emission of a said one subregion.

15. The method of claim 14, wherein said plurality of said two dimensional images are acquired using a scanning interferometer, so that said intensity of said each of said plurality of said pixels corresponds to a linear combination of a plurality of said wavelengths.

16. The method of claim 14, wherein said each of said plurality of said two dimensional images is acquired via a filter that passes a different one of said one wavelength. 25

17. The method of claim 14, further comprising the step of, in said at least one region:

(vii) aligning said two dimensional images.

18. The method of claim 12, wherein said classifying is effected only for said observed spectra that have a summed intensity greater than a certain threshold.

19. The method of claim 12, wherein, for said at least one region, the method further includes the step of:

(vii) checking neighboring said voxels for mutual consistency.

20. The method of claim 12, further comprising the step of performing scenario analysis of said spectral imaging data acquired for said plurality of said regions, to generate final results of the elemental analysis of said sample.

21. A method of controlling elemental emissions from an industrial process by temporal gated imaging of atomic emissions, the method comprising the steps of:

(a) providing a sample of emission of the industrial process, said sample divided into a plurality of regions, each of said plurality of regions further divided into a plurality of subregions;

(c) for at least one of said plurality of regions of said sample:

(ii) inducing a plasma plume over said one subregion by irradiating said one 26 subregion, following completion of said setting said spectroscopic imaging system,

(iii) waiting a finite time for said plasma plume to thermally cool, whereby the thermal spectrum of said plasma plume decays, to form a nonthermal atomic emission,

(iv) activating and opening of said temporal gated CCD camera for acquisition of a two dimensional image of said one wavelength of said nonthermal atomic emission of said one subregion, following completion of said finite time for said plasma plume to thermally cool,

(v) successively repeating steps (i) through (iv) for a number of said subregions in said at least one region, to form a plurality of said two dimensional images, each of said two dimensional images corresponding to said acquisition of a different said one wavelength of said nonthermal atomic emission of a different said one subregion using a different said one of a plurality of single fields of view of said spectroscopic imaging system in said at least one of said plurality of regions,

(vii) comparing said observed spectra with a database of atomiemission spectra of elements to obtain estimates of amounts of the elements present in said at least one region of said sample; and

(d) adjusting a control parameter of the industrial process based on said estimates.

22. The method of claim 21, wherein said irradiating said one subregion is effected by 27 using a temporal gated excitation energy source for inducing atomic emission, said excitation energy source is synchronized with said temporal gated CCD camera.

23. The method of claim 21, wherein each of said plurality of said two dimensional images features a plurality of pixels, each of said plurality of said pixels having an intensity corresponding to said one wavelength of said nonthermal atomic emission of a said one subregion.

24. The method of claim 23, wherein said plurality of said two dimensional images are acquired using a scanning interferometer, so that said intensity of said each of said plurality of said pixels corresponds to a linear combination of a plurality of said wavelengths.

25. The method of claim 23, wherein said each of said plurality of said two dimensional images is acquired via a filter that passes a different one of said one wavelength.

26. The method of claim 23, further comprising the step of, in said at least one region:

(viii) aligning said two dimensional images.

27. The method of claim 21, wherein said comparing of said observed spectra with said database spectra is effected only for said observed spectra that have a summed intensity greater than a certain threshold.

28. The method of claim 21, wherein said comparing of said observed spectra with said database spectra is effected by multivariate analysis, said multivariate analysis includes at least one algorithm selected from the group consisting of principal component regression and partial least squares analysis. 28

29. The method of claim 21, wherein said comparing of said observed spectra with said database is effected by fuzzy logic analysis based on at least one description parameter, said at least one description parameter is selected from the group consisting of peak height ratio, peak full width at half amplitude ratio, number of peaks, peak to minimum ratio and peak wavelength ratio.

30. The method of claim 21, wherein, for said at least one region, the method further includes the step of:

(viii) checking neighboring said voxels for mutual consistency.

31. The method of claim 2\; further comprising the step of performing scenario analysis of said spectral imaging data acquired for said plurality of said regions, to generate final results of the elemental analysis of said sample of emission of the industrial process.

32. A system of elemental analysis by temporal gated imaging of atomic emissions, the system comprising:

(a) a sample divided into a plurality of regions, each of said plurality of regions further divided into a plurality of subregions;

(b) a spectroscopic imaging system, said imaging system including: (i) an excitation energy source for inducing atomic emissions of said sample, (ii) a temporal gated CCD camera, and (iii) a means of setting said spectroscopic imaging system for acquisition of two dimensional images of nonthermal atomic emissions of said plurality of said subregions, said setting corresponding to a plurality of single fields of view of said spectroscopic imaging system in at least one of said plurality of regions; and (d) data processing equipment including algorithms for: 29 (i) generation of a plurality of three-dimensional spectral images from said two dimensional images, whereby each of said spectral images features a plurality of voxels, whereby each of said plurality of voxels corresponds to a plurality of different wavelengths of said nonthermal atomic emissions of said plurality of said subregions of said at least one of said plurality of regions, whereby each of said spectral images includes a plurality of observed atomic emission spectra,

(ii) comparing said observed spectra with a database of atomic emission spectra of elements to obtain estimates of amounts of the elements present in said at least one region of said sample,

(iii) performing a classification process on data of said spectral images, and

(iv) performing scenario analysis of said data of said spectral images to produce final results of the elemental analysis.

33. The system of claim 32, wherein, said excitation energy source for said inducing said atomic emissions is synchronized with said temporal gated CCD camera.

34. The system of claim 32, wherein said means of said setting said spectroscopic imaging system is selected from the group consisting of using a scanning interferometer and using a filter that passes a different one of said one wavelength.

35. The system of claim 32, wherein each of said plurality of said two dimensional images features a plurality of pixels, each of said plurality of said pixels having an intensity corresponding to one of said plurality of said different wavelengths of one of said nonthermal atomic emissions of one of said subregions.

36. The system of claim 35, wherein the intensity of said each of said plurality of said pixels of said plurality of said two dimensional images acquired by using a scanning interferometer corresponds to a linear combination of a said different wavelengths. 30

37. The system of claim 32, said system is used for controlling emissions of an industrial process, said controlling effected by adjusting a control parameter of said industrial process based on said final results of the elemental analysis.