Optics: measuring and testing – By polarized light examination – With polariscopes
Patent
1984-10-23
1987-10-13
Rosenberger, R. A.
Optics: measuring and testing
By polarized light examination
With polariscopes
G01N 2121
Patent
active
046995145
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL AREA
The invention concerns a multibeam measuring device for the real time polarimetric analysis of samples, wherein a linearly polarized measuring beam, after having traversed the sample, is separated by means of a first beam separator into at least two partial beams representing the total beam cross-section of the measuring beam, namely a reference beam and at least one test beam. With this measuring arrangement, the intensity of the reference beam is detected by means of a first photosensitive sensor and the intensity of the test beam by means of a second photosensitive sensor. For doing this, connected in ahead of the second photosensitive sensor is an analyzer whose direction of throughpass has a predetermined, fixed orientation that is different from that of the polarizer. The signal outputs of the two photosensitive sensors are connected, for determining the polarimetric magnitudes capable of being interpreted by the sample, in particular the optical activity (e.g. the rotational value) of the sample, with the inputs of a measuring circuit.
UNDERLYING STATE OF THE ART
The aforementioned multibeam measuring device is known from the German patent DE No. 27 24 543 C2 (MULLER). In the case of the known multibeam measuring device, used as the beam separator is a dielectric separator element, namely a semi-pervious mirror. Accordingly, separation of the measuring beam into a reference and a test beam is accomplished here by reflection and transmission. Use of a beam separator of this type has the disadvantage that, because of the phase shift, the linearly polarized light impinging on the semiperviously reflected layers is changed relative to its status of polarization, namely being converted into elliptically polarized light. Accordingly, the change of polarization status of the test beam capable of being detected by means of the analyzer stems not only from the optical activity of the sample, but rather also from the reflection at the beam separator. This has as a consequence a first systematic measurement error. Secondly, the ratio of transmitted to reflected energy in the case of a beam separator of this type is dependent upon the direction of polarization of the impinging radiation. The direction of polarization of the measuring beam impinging on the beam separator is, however, in consequence of the unknown optical activities of the sample, undefined, otherwise it would not be necessary to first determine rotation of the plane of polarization of the measuring beam by a measurement.
In the case of the multibeam measuring device known from the abovementioned German patent No. 27 24 543, the measuring circuit consists of a differential circuit disposed on the input side, with an amplifier connected downstream and an indicating and/or recording contrivance. The signal outputs of the two photosensitive sensors are here connected with the inputs of the differential circuit. However, this circuit has the disadvantage that the output signal of the differential circuit is not only a function of the angle of rotation of the plane of polarization (evoked by the optical activity of the sample), but also a function of the output intensity of the light source. Hence, it is basically not possible to determine whether a change of the output signal from the differential circuit is to be ascribed to a change in the light intensity of the light source or a change in the optical activity of the sample.
Therefore, in total, the measured value determined by means of the multibeam measuring device described is burdened with at least three systematic errors of measurement.
However, the multibeam measuring device described in the patent mentioned does have the advantage that analog signal processing apparently occurs without delay and, therefore, there is available a quasi-real time measurement. However, because of the pointertype measuring instrument apparently used in the patent that has been mentioned, slight fluctuations in measured value are no longer capable of being determined because of the inertia of th
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Distl Richard
Schmidt Ulrich
Rosenberger R. A.
Sjoquist Paul L.
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