Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1996-05-16
1998-03-03
Phan, James
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359209, 359211, 359226, 358493, G02B 2608
Patent
active
057241716
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally to optical scanning apparatus, more especially in the field of phosphor image-storage plate scanning and secondarily to the optical scanning of gels. However, the invention also has general application to scanning microscopy and the optical scanning of materials for electronic or photographic purposes.
BACKGROUND TO THE INVENTION
In many types of scanning apparatus, a lens or other light transmitting device is placed close to the subject and moved over its surface, usually in a raster fashion. This device, which is referred to herein as a reading head, serves both to concentrate a light beam to form a small spot on the specimen and to receive radiation emitted from or reflected by the specimen in the region of the spot. The value of placing the reading head close to the subject is to increase the solid angle of acceptance of radiation emitted by the specimen (thus increasing the sensitivity of detection), to improve the resolution of the focussed spot of incident illumination and to increase the efficiency of confocal optics, assuming suitable other optical apparatus is present.
In order to scan, the reading head must be moved over the subject or vice versa or a combination of such movements employed. Thus Amemiya, in Physics Research A 266 (1988), pages 645 to 653, describes an arrangement in which the subject, a flexible phosphor image plate, is wrapped around a drum. The drum is then rotated and the reading head moved in a linear fashion parallel to the axis of rotation. Different apparatus is produced by the MAC Company (Japan) and by Marresearch (Germany), in which a planar phosphor image plate is rotated about an axis perpendicular to its surface while a reading head is moved across the surface towards the centre of rotation, thus executing a spiral scan. Neither of these arrangements is satisfactory, since the subject has to be either folded or rotated to be scanned. Particularly with phosphor image plates, it is desirable for the plate (i.e. the subject) to remain stationary during the scan. Brearley, in Patent Specification GB 2152697A, describes a way in which this could potentially be done, by causing the reading head to move linearly. However, Brearley's apparatus also requires the subject to move to produce the frame scan, and provides no special means of conveying the incident radiation to the reading head. The light is conveyed, in Brearley's apparatus, by bathing the entire area of movement of the reading head in incident radiation, with the result that only a small part of this radiation is transmitted to the subject.
The present invention aims to overcome the two problems mentioned above by providing scanning while allowing the subject to be stationary and by directing the incident beam into a reading head in an optically efficient manner.
SUMMARY OF THE INVENTION
According to the invention, there is provided optical scanning apparatus comprising a support having an axis of rotation, a plurality of reading heads mounted on the support to rotate therewith when the support is rotated at uniform angular speed about its axis, at least one optical source, and optical beam-switching means also movable in rotation at uniform angular speed for switching the beam from the source or sources between the reading heads so that successive reading heads are in turn continuously operational over a predetermined segment of a circular line scan, whereby a subject relative to which at least the reading head support of the assembly has a linear translational movement may be read by the reading heads.
Preferably, the return beam from the subject is passed reversely through the beam-switching means to a stationary detector.
The subject may be an image-beating element, such as a phosphor image-storage element, which is either planar or part-cylindrical. In the former case the scanning path is of circular form; in the latter case the scanning path lies in a plane normal to the axis of the part-cylinder. Thus, at least the reading head support, but po
Amos William Bradshaw
Henderson Richard
Mallett John Francis William
Medical Research Council
Phan James
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