Optics: measuring and testing – By dispersed light spectroscopy – With sample excitation
Patent
1993-12-06
1995-08-29
McGraw, Vincent P.
Optics: measuring and testing
By dispersed light spectroscopy
With sample excitation
G01N 2163
Patent
active
054465389
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
This application is a national phase of PCT/DE92/00447 filed 2 Jun. 1992 and based, in turn, upon German national application P41 18 518.8 filed 6 Jun. 1991 under the International Convention.
FIELD OF THE INVENTION
The invention relates to a process for emission spectroscopy, particularly laser emission spectroscopy, wherein the radiation emitted by the laser-induced plasma of the material to be analyzed is broken down by a spectrometer and at least one fraction of the found spectrum is transferred to a processing device for element analysis.
BACKGROUND OF THE INVENTION
Exemplified by laser emission spectroscopy and spark emission spectroscopy, emission spectroscopy serves for material analysis, whereby the laser beam or the sparks are used for the vaporization of minimal amounts of material, so that the vaporized material can be analyzed. According to FIG. 1A at (1) a laser beam is focussed on the workpiece to be analyzed. Based on the natural absorption of the laser beam by the workpiece 4 an energy coupling as per FIG. 1B occurs at 2 in a localized area, wherefrom a part of the material is vaporized according to FIG. 1A-1D, the vapor being seen at 3. The amount of the vaporized material depends on the energy, the output and the output density, the local output distribution and the wavelength of the laser beam. The generation and the state of the vaporized material are also influenced by the characteristics themselves and by the surrounding atmosphere.
The laser beam is coupled into the vaporized material, so that the latter is brought into a plasma state or a plasma-like state. As a result of the energy coupling, the components of the plasma are induced to emit radiation. The thereby emitted radiation 40 according to FIG. 1D is characteristic of the composition of the material to be analyzed.
The beam 40 emitted by the plasma 6 is directed towards a spectrometer and is there spectrally decomposed. For instance the dependency of the radiation intensity I.sub.S =f(.lambda.) can be obtained as shown in FIG. 3. This information is fed to a processing unit, which for instance is equipped with a computer and an output device. In the processing unit, intensity, or line ratios, are calculated with the aid of calibrating curves, in order to determine the element concentration of the material. For instance a ratio between the intensity I.sub.1 of an emission line .lambda..sub.1 in relation to the intensity I.sub.2 of an emission line .lambda..sub.2 is established, whereby the emission line .lambda..sub.2 serves as reference line and for instance originates from the element which is most often present in the examined material. With the aid of the ratio I.sub.1 /I.sub.2 it is possible to determine in percentage the content C.sub.1 of a first element of the entire material with the aid of a calibration curve I.sub.1 /I.sub.2 =f(C) according to FIG. 3a.
Such material analyses with laser beams are contactless methods, which can practically be carried out without sample taking. Being performed with fast components, they afford the possibility of high measuring speeds. Therefore they can be incorporated in processing and machining production lines, without impairing the flow of workpieces by taking samples and transporting the samples to the analyzing device. It is possible to perform elemental and multi-elemental analyses. Through on-line analysis, it is possible for instance to survey quantitatively and qualitatively the production processes of workpieces. Furthermore it is even possible to intervene in a controlled manner in the production of workpieces, when high measuring speeds make possible an on-line analysis. For instance it is possible to control the introduced raw materials, to test the identity of workpieces and to sort out mixed materials and workpieces. However these basic possibilities can be limited by the fact that accuracy of measurement and the reproducibility are low because the changes in the plasma state with time are not sufficiently considered. FIG.
REFERENCES:
patent: 4645342 (1987-02-01), Tanimoto et al.
patent: 4839493 (1989-06-01), Herziger et al.
Dubno Herbert
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
McGraw Vincent P.
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