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Compact cross-dispersed spectrometer for extended spectral range

Compact cross-dispersed spectrometer for extended spectral range description/claims

The present application claims priority from U.S. Provisional Patent Application No. 60/891,408, titled “Hand-Held, Self-Contained Optical Emission Spectroscopy (OES) Analyzer,” filed Feb. 23, 2007, which is incorporated in its entirety by reference herein.

The contents of commonly-assigned U.S. patent application Ser. No. 12/035,477, by Denis Baiko, et al., titled “Fast and Precise Time-Resolved Spectroscopy with Linear Sensor Array,” filed Feb. 22, 2008, is incorporated in its entirety by reference herein.

The contents of commonly-assigned U.S. patent application Ser. No. ______ (to be supplied), by John E. Goulter, et al., titled “Hand-Held, Self-Contained Optical Emission Spectroscopy (OES) Analyzer,” filed Feb. 22, 2008, is incorporated in its entirety by reference herein.

The present invention relates to spectrometers and, more particularly, to compact spectrometers that remain dimensionally stable and accurate over a temperature range without heating or cooling.

Analyzing chemical composition of samples is important in many contexts, including identifying and segregating metal types (particularly various types of iron and steel) in outdoor metal recycling facilities, quality control testing in factories and forensic work. Several analytical methods are available.

Optical emission spectroscopy (OES) is a mature, robust technology for the elemental analysis of materials. In OES, a small quantity of sample material is vaporized and excited above atomic ground state. Emissions characteristic of elements in the vaporized sample are captured by a light guide, which sends the light to a spectrometer, which produces and analyzes a spectrum from the light, so as to yield the elemental composition.

For metal samples, the prevalent techniques for generating an emission spectra use either an electric arc or a spark, or both, to vaporize a small quantity of the sample to be analyzed. Alternatively, laser-induced breakdown spectroscopy (LIBS) or glow discharge (GD) may be used to vaporize and excite an emission sample. A survey of OES analytical techniques may be found in Slickers, Automatic Atomic-Emission Spectroscopy, Second Edition (1993), which is incorporated by reference as if fully set forth herein.

In order to be confident that the composition deduced from a measurement, which typically tests a miniscule portion of the sample, is representative of the composition of the entire sample, minimizing effects from, for example, inclusions, matrixes and surface contaminants, it is standard practice to average the spectra from as many as several thousand arcs/sparks that have struck an area as large as 100 square mm in a few seconds of a measurement.

Some OES analyzers are large, non-portable units intended for use in laboratories. Other OES analyzers are “portable,” in that they can be moved about. However, prior art “portable” OES analyzers that can identify carbon or other common constituents in iron or steel require two separate components interconnected by a fiber optic/electric cable. For example, an analyzer available from Spectro A. I., Inc. under the trade name Spectroport includes a hand-held probe connected via a 10-foot cable to a suitcase-sized, 33-pound analysis unit. The Spectro iSort analyzer, also from Spectro A. I., Inc., includes a hand-held probe connected by a cable to an analysis unit housed in a 10-pound backpack.

To cover a spectral range required to detect carbon, phosphorous, sulfur and other elements necessary to identify common materials, such as cast iron and various alloys, these prior art analyzers include fixed-wavelength detectors in the hand-held probes for carbon, phosphorous, sulfur and iron, as well as a spectrometer in the analysis unit for other elements. This awkward, two-part structure makes these analyzers difficult to use and move about.

An two-part analyzer available from Metorex, Ewing, N.J., under the trade name ARC-MET 8000 MobileLab, includes a hand-held “probe” connected by a ten-foot cable to a roll-around “main unit.” The probe contains a spectrometer with an advertised spectral range of 175-370 nm; however, the roll-around main unit is required to provide power and cooling to the probe and to analyzes the output from the spectrometer. At least some users would prefer to use a hand-held OES analyzer that is fully self-contained.

The Spectrosort analyzer, also from Spectro A. I., Inc., is a one-piece, battery-powered, hand-held analyzer. However, spectral limitations of the spectrometer in this analyzer make it incapable of detecting carbon, phosphorous and sulfur, thus severely limiting the utility of this analyzer.

Users of self-contained, hand-held OES analyzers would prefer analyzers that are capable of detecting carbon and other key elements, so the analyzers can identify a wide range of common materials. However, various roadblocks have thus far prevented construction of such a full-range, self-contained, hand-held analyzer. Among these roadblocks is an inability to construct a spectrometer that exhibits the wavelength range and temperature stability needed for the above-described analysis under typical environmental conditions, in a size and weight appropriate for a hand-held analyzer,

An embodiment of the present invention provides an analyzer for analyzing composition of a portion of a sample. The analyzer includes a hand-held, self-contained, test instrument. The test instrument includes an exciter for exciting the portion of the sample, the excitation producing an optical signal and a first dispersive element disposed within the hand-held instrument for receiving the optical signal and creating an intermediate optical signal dispersed in a first plane. A second dispersive element disposed within the hand-held instrument disperses the intermediate optical signal so as to place a first resolved optical order on a corresponding first plurality of detector elements and a second resolved optical order on a corresponding second plurality of detector elements. A processor is coupled to receive signals from the first and second pluralities of detector elements and is programmed to process the signals. A battery powers the exciter and the processor.

At least one of the optical orders placed on the corresponding plurality of detector elements may extend to wavelengths shorter than about 193 nm, or shorter than about 178 nm, or at least as short as about 170 nm.

Each plurality of detector elements may be configured so as to receive a continuous spectral range of the resolved optical order placed on the plurality of detector elements. The spectral range placed on the first and second pluralities of detector elements may extend at least from about 178 nm to about 400 nm.

The instrument may include a structure defining an aperture, through which the intermediate optical signal passes. The optical signal may be focused on the structure.

The exciter may include an electrode for sustaining an electrical potential with respect to the portion of the sample and a voltage supply for establishing the electrical potential on the electrode with respect to the portion of the sample. The exciter may include a laser.

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