Echelle polychromator

Details Echelle polychromator Echelle polychromator

1994-05-16

1995-09-05

Evans, F. L.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356332, 356334, 359615, 359832, G01J 314, G01J 318, G02B 506

Patent

active

054483514

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to an Echelle polychromator.
A polychromator is a spectrometer in which a spectrum is produced on a detector array by a dispersion element, i.e. a row of detector elements closely arranged next to one another. In this way the spectral intensities are simultaneously measured at the different wavelengths of a wavelength range detected by the detector array. By contrast, a monochromator generates a spectrum on the plane of an exit slit. Then, light of a particular, relatively narrow wavelength range will emerge from that exit slit. The light emerging from the exit slit may then impinge onto a single detector, e.g. a photomultiplier. However, the light passing through the exit slit may be directed onto a further monochromator or polychromator. In the latter case one talks about a pre-monochromator. Pre-monochromators serve the reduction of interfering light. With grating monochromators pre-monochromators have the function of eliminating light of interfering orders.
An Echelle grating is a grating having a triangular groove profile, the spacing of the grooves thereof being large with respect to the wavelength. An Echelle grating uses high interference orders. A polychromator which operates with an Echelle grating is an Echelle polychromator.


BACKGROUND ART

Different types of monochromators and polychromators are described in a book by J. Sternberg "The Design of Optical Spectrometers", Chapman and Hall, 1969, and in a book by Y. Talmi "Multichannel Image Detectors", American Chemical Society, 1979.
U.S. Pat. No. 4,820,048 describes an Echelle polychromator combined with a novel solid-state detector array. A separation of the orders within the Echelle polychromator is performed for a simultaneous detection of the complete wavelength range. This results in a limitation in the entrance slit height. Furthermore, imaging errors arise at the end portions of the spectrum. The level of scattered light is relatively high.
GB-A-2 204 964 describes an Echelle polychromator for multiple element analysis. A light source produces a light bundle defined by two crossed entrance slits. The light bundle impinges onto a collimator mirror. The collimator mirror directs the light bundle directed in parallel through a dispersion prism onto an Echelle grating. The light bundles diffracted by the Echelle grating repass through the dispersion prism and are collected by a camera mirror onto a two-dimensional detector array. The dispersion prism effects dispersion in a direction vertical to the direction of dispersion of the Echelle grating, and thus a separation of the different orders of the Echelle grating. The detector array comprises detector elements at the locations of characteristic spectrum lines of the various chemical elements to be determined.
An Echelle monochromator is known in which the orders are separated by a pre-monochromator. The pre-monochromator produces a spectrum on the plane of an entrance slit of the high-resolution Echelle monochromator. Only a limited wavelength range of that spectrum enters into the Echelle monochromator. Then, the Echelle monochromator takes from this wavelength range a more narrow wavelength range by means of an exit slit and a detector positioned downstream thereof. Such dual Echelle monochromators achieve a high spectral resolution at an extremely small amount of stray light. A high light guide number results from the larger height of the slits. However, only one spectral position within the total spectrum can be investigated at a time (P. W. J. M. Boumans and J. J. A. M. Vrakking, "Spectrochimica Acta" Bd. 39B No. 9-11, 1239).
DE-C-3 634 485 describes a liquid prism having a variable prism angle for producing spectrally distorted photographs and projections.


DISCLOSURE OF THE INVENTION

It is the object of the present invention to provide a spectral apparatus by means of which it is possible to analyse not only a particular spectral position with high resolution but also the vicinity thereof at the same time.
According to the invention

REFERENCES:
patent: 4575243 (1986-03-01), Witte
patent: 4820048 (1989-04-01), Barnard
patent: 4995721 (1991-02-01), Krupa et al.
"High-resolution spectroscopy using an echelle spectrometer w/predisperser -I. Characteristics of instru. & approach for measurng physl line widths in inductivly coupled plasma", Spectrochimica Acta, vol. 39B, Nos. 9-11, pp. 1239-1260, 1984, P. W. J. M. Boumans and J. J. A. M. Vrakking.
"High-resolution spectroscopy using echelle spectrometer w/predisperser--II. Analytical optimization for inductively coupled plasma atomic emission spectromtry" Spectrochimica Acta. vol. 39B Nos. 9-11, pp. 1261-1290, 1984, P. W. J. M. Boumans and J. J. A. M. Vrakking.
"High-resolution spectroscopy using a echelle spectrometer w/predisperser--III. A study of line wings as a major contribution to the background in line-rich spectra emitted by a inductively coupled plasma", Spectrochimica Acta. vol. 39B. Nos. 9-11, pp. 1291-1305, 1984, P. W. J. M. Boumans and J. J. A. M. Vrakking.

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