Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1997-02-18
2000-01-18
Turner, Samuel A.
Optics: measuring and testing
By particle light scattering
With photocell detection
356352, G01B 902
Patent
active
06016199&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device for carrying out spectroscopic measurements by the principle of interferometry, with a matrix of photodetectors.
The current state of spectroscopy includes methods operating on the dispersive and the interferometric principles.
In the dispersive method, various dispersion agents, such as prisms and diffraction gratings (scratched or holographically etched) and in some cases wedge filters are used. The key element of this method is a spectrograph or a monochromator. A spectrograph is designed so that the entire wavelength range to be measured is detected in one step, and the complete spectrum is shown at the output. The spectrum is recorded with a photographic film, video camera, reticon or a CCD (charge coupled device). In the monochromator, light of only one wavelength at a time is delivered to the output. In order to pick up a spectrum, the prism or reflection grating is rotated, so that all the wavelengths are admitted in succession over time. For recording, a photodiode, photomultiplier, or bolometer is typically used.
In the interference method, a Michelson interferometer is often used, in which the light to be measured is carried through two partially transparent mirrors, and the spacing of the mirrors from one another is varied in order to move all the wavelengths through. The recording of the light at the output is done by means of a photodiode. The resultant course over time of the output signal of the photodiode is then subjected to a Fourier, Hadamard or similar transform, in order to obtain the spectrum.
A modified Michelson interferometer is disclosed in WO 85/03122, which makes do without a moving mirror. This is attained in that one of the mirrors is tilted, so that a two dimensional interference pattern is produced. This interference pattern is read out by means of a photodetector matrix.
From German Patent Application DE 39 28 001 A1, a multi-beam interferometer for distance measurement is known, having a monochromatic light source and one fixed and one movable mirror. One of the two mirrors has a stepped profile.
Monochromators, spectrographs and interferometers are as a rule large, expensive, and heavy and usually includes parts that have to be moved mechanically, which always entails problems with respect to accuracy. The efficiency of dispersive elements is moreover very greatly dependent on the wavelength.
SUMMARY OF THE INVENTION
The object of the invention is to create a measuring device of the type referred to at the outset which is distinguished by improved spectral measurement properties, low weight, and small dimensions, and which assures high reliability even over a relatively long period of time and a wide temperature range, and which moreover is invulnerable to even strong mechanical shaking.
This object is attained, in a measuring device of the type referred to at the outset, in accordance with the invention in which a plurality of interferometers are provided, which each comprise two partially transparent parallel mirrors and are arranged in the form of a rectangular matrix in such a way that the mirrors of all the interferometers are spaced apart by different spacings from one another, such that for each arbitrary wavelength to be measured, a plurality of reflection phase relations are present in the array, and that the different spacings are distributed uniformly between the smallest and largest spacing, and that the matrix of the photodetectors is disposed downstream of the interferometers in such a way that each interferometer is assigned at least one photodetector for receiving the light that is to be measured and that strikes the interferometer perpendicularly, and that for displaying the spectrum, a device for transforming the output signals of the matrix of photodetectors is provided.
In one embodiment the invention provides that the many interferometers are formed by two disks disposed parallel to one another, whose sides remote from one another are embodied as flat, while their sides toward one anot
REFERENCES:
patent: 4822998 (1989-04-01), Yokota et al.
patent: 5128798 (1992-07-01), Bowen et al.
Striker Michael J.
Turner Samuel A.
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