Hadamard spectrometer

Details Hadamard spectrometer Hadamard spectrometer

1999-09-10

2001-03-27

Evans, F. L. (Department: 2877)

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

C356S310000, C356S330000

Reexamination Certificate

active

06208413

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a Hadamard spectrometer which enables the detection of a number of polyatomic gases or liquids using, for example, infrared absorption. Such devices are utilized, in particular, for emission control, workplace inspection, and environmental monitoring.
With respect to prior art related to the invention, reference is made to a spectrophotometer disclosed in U.S. Pat. No. 5,257,086 which enables a mathematical evaluation of detected spectral data and, hence, a spectral analysis under use of the Hadamard transformation. The spectrophotometer described therein is provided with a radiation source array, which is typically an essential unit for spectrometers. The individual radiation sources of the radiation source array provide different wavelengths which can be controlled in accordance with the Hadamard method. The spectrophotometer includes an imaging diffraction grating with a detector arranged behind a slit for detecting spectral signals, and electronic units which ensure a very fast spectral analysis of a sample to be examined. The essential advantage resulting from the Hadamard transformation is a considerable improvement of the signal-to-noise ratio. A disadvantage of the arrangement described in U.S. Pat. No. 5,257,086 is that at first LEDs have to be available as radiation sources which correspond to the frequency spectrum to be examined, and this at present limits the arrangement to a wavelength spectrum of from 250 nm to about 2.5 &mgr;m. Another significant disadvantage of this device is that considerable expenditures have to be spent in order to stabilize the intensities of the individual LEDs in order to obtain spectra which can be analyzed quantitatively.
Furthermore, spectrometers are known, namely the monolithic miniature spectrometer designated MMS 1 manufactured by Carl Zeiss, Business Field for Special Engineering, Sales Department for Optical Components, D-73446 Oberkochen, Germany, in which diode rows are employed as detecting elements. In this case, it is required to image a spectral line onto at least three adjacent detector elements. Only the three measurement signals obtained permit a precise detection of the wavelength. Hence, the resolution power of such spectrometers with respect to a wavelength interval is limited by the number of the detector elements employed and their mutual distance.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a Hadamard spectrometer which, under application of conventional detector rows, ensures an increased resolution power, an improved wavelength accuracy, and an enhanced signal-to-noise ratio, and has a small and compact construction.
The object is realized by providing a Hadamard spectrometer with a detector row having individual detector elements spaced from one another by a set distance and a unit for the light emitting and reflecting having three or more adjacent identical luminous sources. The luminous sources are individually controllable in accordance with the Hadamard principle and arranged apart from one another at a set distance related to the distance between the detector elements.
An important feature of the invention is that row-shaped units, i.e., units having a row of constituent elements, are employed both, for a detector unit for registering spectra and for a light emitting and reflecting unit. The detecting unit includes a plurality of individual detecting ranges or elements and the light emitting and reflecting unit includes a plurality of individual luminous sources. Therefore the designation “double array” is used hereinafter, and the Hadamard principle, known per se, finds application herein.
When within the scope of the invention the Hadamard principle is referred to, then multiplexing in the spectroscopy including entry switching matrices after Hadamard is intended to be encompassed within the meaning of the term.


REFERENCES:
patent: 5050989 (1991-09-01), Van Tassel et al.
patent: 5257086 (1993-10-01), Fateley et al.
patent: 5488474 (1996-01-01), Fateley et al.

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