Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1997-11-14
1999-12-21
Evans, F. L.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
356328, G01J 314, G01J 320
Patent
active
060056614
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a control device, in particular for spectroscopy, endoscopy and/or radiometry systems, and a wavelength selection device, in particular for spectroscopy, endoscopy and/or radiometry systems as well as the optical systems comprised thereof for spectroscopy, endoscopy and/or radiometry.
A known spectroscopic system in which a spectrometer or a simultaneous spectrometer, respectively, is used, conventionally comprises an illumination device, a sample and a simultaneous spectrometer. The radiation emitted by the illumination device permeates the sample and is incident upon the entrance slit of the simultaneous spectrometer, which spectrally splits and, by a receiver unit, detects the incident radiation. In this way, for example, the absorption of the sample can be determined as a function of the frequency of the radiation.
The core concept of a frequently used simultaneous spectrometer is the use of rows of self-scanning diodes developed by Snow in 1975 and which comprise for example 512 discrete diodes on a length of 1.27 cm. The application, developed by the applicant, of these diode rows in a spectrometer is determined by the row geometry, wherein one diode width of 25 .mu.m defines simultaneously the width of the exit slit of the spectrometer. In an image with the smallest error rate, i.e. 1:1, this represents also the width of the entrance slit. As a dispersive element in such a simultaneous spectrometer a holographically generated concave grating is used, which permits saving an additional focusing element.
Frequently an illumination device adapted to the structure of the simultaneous spectrometer is used. Light is emitted by a preferably point-form light source and focused into an object space. In order for the spectrometer to be utilized with maximum efficiency, the same configuration is basically used in the illumination device as in the spectrometer with the highly-open hologram grating being replaced by an aspherical (ellipsoidal) mirror of identical aperture. In order for a "complete representation" being attained, thus the strictly conjugated sequence of source diaphragm-objective diaphragm etc., the mirror has the dimension of the grating of the spectrometer. Of the light source and the image of the light source, which simultaneously is the entrance diaphragm into the measuring instrument, is required that they are very small. Instead of the light source L a maximally high luminous intensity is required. This condition is met for example by xenon lamps of the lowest power class of 30 to 75 W at a radiant field diameter of 0.3 to 0.5 mm. For the ultraviolet region deuterium lamps with radiant field diameters of 0.5 mm with high luminous intensity and 35 W power consumption are available.
Between the light source image and the entrance slit of the spectrometer is located the object space in which the directional illumination of an object or a sample is required. The sample is disposed for example in a cell which is transilluminated at slight radiation inclination against the optical axis, in the ideal case with telecentric illumination. To meet this, on both sides of the sample one aperture converter each can be disposed which comprises a coaxial conical optical waveguide or mirror, with a light entrance and a light exit opening and a mirroring or totally reflecting inner surface.
Such optical system is distinguished by very good energy efficiency, i.e. a large portion of the radiation emitted by the illumination device is incident upon the sample and proceeds from the sample to the simultaneous spectrometer. Furthermore, such system is distinguished by good utilization of the capabilities of the simultaneous spectrometer. To attain high spectral resolution, the spectrometer requires at the entrance slit radiation having a very large aperture. This is made available through the aperture converters.
In such system, however, a number of difficulties occur which make further improvements desirable.
In order to utilize the capabilities of the simultaneous spectrometer as well a
REFERENCES:
patent: 5223715 (1993-06-01), Taylor
patent: 5675411 (1997-10-01), Brooks et al.
Evans F. L.
Hewlett--Packard Company
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