Optics: measuring and testing – By dispersed light spectroscopy – With monochromator structure
Patent
1984-05-02
1987-11-10
McGraw, Vincent P.
Optics: measuring and testing
By dispersed light spectroscopy
With monochromator structure
356334, G01J 314, G01J 318
Patent
active
047053968
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an image monochromator, by which is meant an instrument which is capable of producing a picture by selecting light in one narrow wavelength band only for the imaging process. The invention is concerned with the provision of such an image monochromator which can give a view as seen in essentially only one spectral line and which can be used, for instance, in fluorescent analysis to obtain a picture of the spatial distribution of a particular substance on a test surface, or in plasma diagnostics, as a simple alternative to the classical spectroheliograph.
BACKGROUND ART
The spectroheliograph, as invented by George Ellery Hale in 1891, is an instrument which consists, essentially, of a prism between synchronously moving input and output slits. By means of, say, a telescopic lens, an image of an object to be studied is projected onto the plane of the moving input slit and an image is produced in turn on a photographic plate immediately beyond the moving output slit. As the input slit moves over the image projected by the telescopic lens, a picture is produced by the co-moving output slit at a narrow wavelength band determined by the positioning of the output slit relative to the input slit and the prism. In the spectrohelioscope, a modification of the spectroheliograph developed by Hale in 1924 but originally suggested by C. A. Young in 1870, an image for direct viewing is produced by rapidly oscillating the images of the slits, usually by means of two synchronously rotating prisms, so that the impression of a static picture is given to the eye.
Also known are image quality interference filters which are frequently employed in various applications to produce pictures in predetermined, narrow wavelength bands. Interference filters are of special interest in applications where the mechanical complexity of the spectroheliograph cannot be justified.
British Patent Specification No. 1,577,198 describes a system for microscopic analysis which utilises a monochromator with gratings. However, the object plane is imaged on the gratings and this is disadvantageous since imperfections, dust particles etc. on the gratings will show up in the final picture.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an image monochromator which is mechanically simpler than the conventional spectroheliograph and which can be used to produce good quality pictures in a very narrow band with the possibility of allowing for tuning over a wide spectral range, in contrast to the fixed wavelength band of conventional interference filters.
According to the invention therefore is provided an image monochromator arranged to receive light at an input thereof simultaneously from an entire object field to be viewed and to transmit a viewable image of the entire object field simultaneously through an output thereof at a selected wavelength band, said monochromator having inner and outer optical systems, said inner system comprising an input slit which is projected on an output slit through imaging means (lenses or mirrors) and via a dispersive means (such as a diffraction grating or prism) operable to transmit light at a tunable narrow wavelength band, and said outer optical system comprising an objective system, in which a picture of the object field is imaged on a picture plane by imaging means (lenses or mirrors), characterised in that the inner optical system is inserted within the objective system so that said dispersive means receives slightly divergent to convergent rays from each object point. To compensate for the small radiance in the selected narrow band under terrestial conditions the optical system may incorporate an image intensifier.
With the monochromator of the invention a good quality picture of an entire object field to be viewed can be produced at a narrow selected wave band in a particularly simple manner.
The means used with the instrument of the invention for the selection of the desired wave band may be of customary design in that it c
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Johnson et al, "Video Fluorometer", American Institute of Physics, Rev. Sci. Instrum., 50(1), Jan. 1979, pp. 118-129.
Olesik and Hieftje, "Optical Imaging Spectrometers", Analytical Chemistry, vol. 57--pp. 2049-2055 (1985).
Letter (dated Feb. 24, 1986), from Dr. Gary H. Hieftje, author of above article.
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