Optics: measuring and testing – By dispersed light spectroscopy – With monochromator structure
Patent
1988-07-21
1991-02-26
Evans, F. L.
Optics: measuring and testing
By dispersed light spectroscopy
With monochromator structure
G01J 318
Patent
active
049957252
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a monochromator arrangement with an adjustable grid monochromator whose path of rays features an entrance focus and an exit focus which relative to the entrance focus is offset sideways.
Known from the German patent application No. 34 00 299 C 2 and Fresenius Z Anal. Chemi (1984) 317:347-349, such monochromator arrangements are employed in the use of adjustable infrared diode lasers for high-resolution spectroscopy, for instance in the quantitative gas analysts, in order to separate the spectrum emitted by the diode laser in individual laser modes respectively laser frequencies while blanking out the remaining modes. High-resolution grid monochromators are used for mode selection.
In prior monochromator arrangements it is for adjustment purposes necessary to move a plane mirror within the monochromator arrangement before the diffraction grid. Since such a mirror is of necessity arranged before the diffraction grid, the illumination of the following lenses will change when the mirror is moved in. An optimization of the lighting is thus not achievable for all cases.
Basing on this prior art, the problem underlying the invention is to provide a monochromator arrangement which retroactively can be inserted in an external path of rays of a spectrometer that features an intermediate focus, after the spectrometer has already been adjusted, where this adjustment is fully retained.
This problem is inventionally solved in that with the grid monochromator there is coordinated a reversing device that features a flat reversing mirror through which the entrance focus and the exit focus are reproduced in one and the same intermediate focus of an external path of rays that extends transverse to the connecting line between the entrance focus and the exit focus of the grid monochromator.
In the inventional monochromator arrangement, adjustment and operation of the entire spectrometer arrangement are possible without monochromator.
In the inventional monochromator arrangement, the entrance and exit ray are so reversed by the reversing mirror that the entrance focus and the exit focus will coincide, with the entrance and exit directions being identical. In this way it is possible to operate the monochromator arrangement in transparency in an intermediate focus of an optical laser spectrometer setup, without influencing the external path of rays.
In accordance with the instant invention, the diffraction grid is utilized twice, and under a large angle in the monochromator arrangement, for increasing the dispersion. Accomplished thereby is a sufficiently high resolution for mode selection also with a small grid of only about 30 mm edge length. Owing to the possibility of requiring only a small grid, the monochromator arrangement can be built very small, enabling a closely spaced serial arrangement. An extra-axial parabolic mirror is used in the monochromator as a collimator in order to obtain a reproduction that is limited in diffraction and free of astigmatism.
Owing to the reversing device of the monochromator arrangement it is possible to move the entrance focus of the monochromator at the place of an intermediate focus of the external path of rays and to reproduce the exit focus of the monochromator, by reflection, as well in the same intermediate focus in such a way that the monochromator will restore the external path of rays and appears from outside the same as an aperture with a spectral filter effect. The reversing device is an integral part of the monochromator arrangement. By means of a centering pin it is possible to introduce the monochromator arrangement in reproducibly accurate fashion in a free intermediate focus of the external spectrometer arrangement.
Suitable developments and designs of the invention are characterized in the subclaims.
The invention will be more fully described hereafter with the aid of an embodiment illustrated in the drawing.
FIG. 1 shows a monochromator arrangement according to the invention in a lateral view, partly in section;
FIG. 2, the reversing device of the mo
REFERENCES:
patent: 3069967 (1962-12-01), White et al.
patent: 3700898 (1972-10-01), Macleod
patent: 3749498 (1973-07-01), Shimomura
patent: 3753618 (1973-08-01), Haley
Fresenius Zeitsthrift publication "Gas Analysis with IR-Diode Laser Specteters", 1984, pp. 347-349.
Grisar Roland
Knothe Manfred
Preier Horst M.
Riedel Wolfgang
Wolf Helmut
Evans F. L.
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forshung E
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