Optics: measuring and testing – By polarized light examination
Patent
1986-07-22
1989-04-18
Rosenberger, Richard A.
Optics: measuring and testing
By polarized light examination
G01J 404, G01N 2221
Patent
active
048221694
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a measuring assembly for analyzing electromagnetic radiation.
Important fields of application of the measuring assembly designed in accordance with the invention are: radiation, radiation,
STATE OF THE ART
The measurement of the wavelength of light is the basis of a great number of physical examinations, for instance in spectroscopy of photometry. Another field of application of the measurement of wavelengths is the quality control in the technical field, e.g. the measurement of the center of gravity wavelength of semiconductor lasers.
Usually so-called monochromators are used for this purpose. They permit only light of a certain wavelength to pass in response to the position of a diffraction grating at an outlet slit. Such instruments are of very complicated structure in order to obtain the necessary resolution of the result of measurement. Furthermore, this operating principle does not permit the analysis of light at quickly varying wavelength or short-term pulses because the balancing time for positioning the diffraction grating is rather long. Consequently measurement values cannot be detected in real time. With conventional monochromators another disadvantage resides in the fact that, apart from other parameters, the resolution in the first place is determined by the width of the outlet slit. If high resolution is to be obtained, long paths within the monochromators and small slit widths are required, and this again involves high losses in intensity. In the analysis of weak signals which, among others, are the rule in the Raman spectroscopy, therefore, monochromators are useful with limitations only, e.g. by putting up with long integration times. As monochromators because of their principle, furthermore integrate across the spectral band width passing the outlet slit, as regards the intensity, the determination proper of the energy content of the radiation to be analyzed is impossible, and yet this would be required in many areas of chemical and physical elucidation of structures.
In numerous fields of application in research and technical quality control the radiation to be examined is available only in the form of pulses of short duration. As an example in this respect the manufacture and use of pulse semiconductor lasers and solid body lasers may be mentioned. In chemical analysis, moreover, it is observed that increasing use is being made, in the optical analysis, of radiation sources which emit shorter light pulses. Among others this has the advantage that the sample is treated with care and, at the same time, higher optical outputs are available. Monochromators usually are not suitable in this case for determining the wavelength or evaluating the spectral characteristic because, as explained above, the dispersing element cannot cover the entire spectrum within the short pulse duration because of the balancing principle.
Often serious problems are encountered in all fields of chemical and physical analyses making use of the means of spectroscopy of photometry if substances are to be identified selectively which have very similar emission or absorption spectra. The reason is that with such measuring tasks the outlet slit of the monochromator provided in the customary spectrometers would have to be infinitely small if the necessary resolution is to be reached for differentiating between substances having very similar spectra. A reduction of the outlet slit, however, involves the great disadvantage of considerably lowering the sensitivity of the measuring system. Thus the outlet slit cannot be reduced at random. Rather, conventional spectrophotometers are dependent on the substances contained in mixtures to be analyzed having characteristics peaks based on which the substances are easily identified. The problems described are touched on, for instance, in the application print DE-AS 24 30 011 "Zweistrahl-Photometer mit Iterferenzfilter". For examining coherent light, there are so-called wavemeters which determine the wavelength based on interferometric me
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Distl Richard
Schmidt Ulrich
Rosenberger Richard A.
Sjoquist Paul L.
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