Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
1999-11-22
2003-09-02
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
Reexamination Certificate
active
06614528
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCED COMPUTER PROGRAM LISTINGS
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates to analytical spectrometry. In particular this invention relates to compact high resolution spectrometry by the simultaneous use of two gratings with either solid-state sensors or photomultiplier tubes.
2. Description of the Related Art
For some time now, the Paschen-Runge setup has been used in analytical spectrometry On the whole it appears due to the fact that diffraction and image formation is accomplished by a single optical element—a concave grating.
With a given number of grooves per mm and entrance angle a specific spectral section is imaged on the Rowland circle. At the same time the spectral resolution which strongly affects the lower detection limit in spectrometry is determined by the diameter of the Rowland circle and the dispersion of the grating.
The application of large Rowland diameters is in contrast to the demands for a modem compact spectrometer design. Therefor, the spectral resolution needed is preferably achieved by using a large number of grooves per mm. The available spectral range then results from the chosen length of the Rowland circle arc.
Current Paschen-Runge spectrometers using a single diffraction grating retain some drawbacks because of the following facts:
1. Image distortions strongly increase at high diffraction angles deteriorating the spectral resolution. The useable length of the Rowland circle arc and resulting spectral range will thus be reduced.
2. Only a continuous, coherent spectral section can be imaged, so that areas along the Rowland curve may be occupied by wavelength regions which are of no interest for analytical purposes.
The restrictions stated in 1 and 2 often lead to a division of the entire spectral range applying several spectrometer units.
3. Commercial solid-state linear array sensors come in standardized chip carrier packages, the dimensions of which are much larger than the radiation “sensitive” part of the chips. In order to avoid substantial gaps in the detection of the spectrum the sensors must overlap along the focal curve. This can be done either by inclination of the linear arrays to the plane of dispersion (see Deutsches Patentamt, Offenlegungschrift DE 195 23 140 A1, “Mehrkanal-Spektrometer mit Zeilensensor”) or by overlapping of horizontally oriented sensor chip carriers. In both cases, the array sensors with regard to the entire detect radiation several millimeters above or below the plane of dispersion. However, in these regions the imaging physics of the Rowland setup causes increased aberrations, resulting in a reduction of the spectral resolution.
BRIEF SUMMARY OF THE INVENTION
Consequently, the features of the invention are;
1. Realization of a single spectrometer unit in which different spectral ranges and corresponding dispersions can be adapted to the requirements of the analytical task.
2. Realization of a detector arrangement along the focal curve through which
(a) only the radiation close to the dispersion plane will be detected thus optimum spectral resolution is guaranteed,
(b) a nearly complete detection of the available spectrum is possible using commercial solid-state linear array sensors.
REFERENCES:
patent: 4571074 (1986-02-01), Thevenon
patent: 4697924 (1987-10-01), Akiyama
patent: 5228103 (1993-07-01), Chen et al.
patent: 5274435 (1993-12-01), Hettrick
patent: 5371813 (1994-12-01), Artigue
patent: 1106518 (1961-05-01), None
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patent: 36 21 464 (1987-01-01), None
patent: 44 10 036 (1995-09-01), None
patent: 195 23 140 (1997-01-01), None
patent: 196 09 916 (1997-09-01), None
Japan Abstract JP 0110014570 AA. vol. 8, No. 38.
Japan Abstract JP 0060102399 AA. vol. 8, No. 38.
Bartoe eta l., “New Stigmatic, Coma-Free Concave-grating spectrograph”, Journal of the Optical Society of America, vol. 65, No. 1, Jan. 1975; 13-20.
Font Frank G.
Nguyen Tu T.
Onka Thomas J.
SAI Gesellschaft fur analytische MeBgerate mbH
Woodbridge Richard C.
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