Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1995-03-27
1997-06-10
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250216, 2504844, 2504845, G01N 2100, G03B 4200
Patent
active
056378670
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for the optical scanning of a recording medium, especially a phosphor storage plate, with a scanning head which can move in relation to the recording medium and contains a scanning beam path along which a scanning beam impinges on a prescribed scanning location past which the recording medium is movable by the relative movement, and a mirror-optical imaging system which focuses the useful radiation produced by the scanning beam at the scanning location substantially in an imaging plane, together with a photo-detector arranged in the path of the useful radiation spaced behind the imaging plane, which are known from a publication by Mori et al., J. Electron. Miscrosc. 39; 433-436 (1990).
BACKGROUND OF THE INVENTION
The device ("IP reading device") known from the aforementioned publication contains an He-Ne laser for producing a scanning beam which along a scanning beam path through a partially transparent mirror impinges on a deflecting mirror and is then focussed by a lens on a scanning location, past which the phosphor storage plate is moved by a coordinate table. The scanning beam produces at the point of the phosphor storage plate housing the scanning location a fluorescent radiation representing the stored information which following collimation by the focussing lens is reflected by the deflection mirror and by the partially transparent mirror and is focussed by a second lens in the aperture of a diaphragm, downstream of which a photomultiplier is arranged. The diaphragm is necessary to laterally distinguish the luminescence signal from the storage plate, thus increasing the resolution of the reading system.
Due to the relatively limited aperture of the focussing lens and the optical losses caused by the lenses and mirrors in the beam path of the reading beam and lastly due to the diaphragm itself, only a relatively small proportion of the fluorescent radiation arrives at the photomultiplier so that the ratio of the wanted signal to the unwanted signal at the output of the photomultiplier needs to be improved.
SUMMARY OF THE INVENTION
On the basis of this prior art the present invention is based on the object of defining a device for the optical scanning of a recording medium, especially a phosphor storage plate, with a scanning head which can move in relation to the recording medium and contains a scanning beam path along which a scanning beam impinges on a prescribed scanning location past which the recording medium is movable by the relative movement, and a mirror-optical imaging system which focuses the useful radiation produced by the scanning beam at the scanning location substantially in an imaging plane, together with a photo-detector arranged in the path of the useful radiation spaced behind the imaging plane, in which a substantially greater proportion of the useful radiation generated by the scanning beam at the scanning location may be detected by the photodetector whilst simultaneously achieving a very high lateral localized resolution.
This object is achieved by the device as characterized in claim 1. Further developments and advantageous embodiments of this device according to the invention are the subject matter of sub-claims.
The present invention is charactized by a substantially confocal optical system of mirrors of a very high aperture which detects a very large proportion of the useful radiation generated in reading and passes it on to the photodetector practically loss-free. Due to the imaging property of the mirror system the laser radiation reflected or backscattered by the inlet window of the photodetector (SEV) or by a colored glass filter upstream of the latter may be absorbed in a further concave mirror designed as a beam trap, at the output of the system of mirrors forming the actual imaging system. Sensitivity and resolution are high.
In one preferred device for scanning the information stored in a phosphor storage plate a laser scanning beam is used, the intensity of which is substantially higher than that of
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Electron Microscopy 1986. Proceedings of the XIth Int. Cong. on Electron roscopy. 7 Sep. 1986, Kyoto, JP, vol. 1, pp. 29 -34.
Mori et al., "Development of the Imaging Plate for the Transmission Electron Microscope and Its Characteristics." J Electron Microsc 39:433-436 (1990).
Schroder, Gottfried, "Technische Optik." Vogel-Verlag, Wurzburg, 1974.
Burmester Christoph
Schroder Rasmus
Lee John R.
Max-Planck-Gesellschaft zur Forderung der Wissenschaften e.v.
Murray William H.
Rosenthal Robert E.
Westin Edward P.
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