Radiant energy – Ionic separation or analysis – Static field-type ion path-bending selecting means
Patent
1988-03-03
1991-02-12
Lee, John D.
Radiant energy
Ionic separation or analysis
Static field-type ion path-bending selecting means
2503272, 264 15, 350 9624, B29D 1100, G02B 600
Patent
active
049919180
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to light collectors for stimulable phosphor imaging apparatus and more particularly to such light collectors comprising a sheet of transparent material.
DESCRIPTION TO THE PRIOR ART
U.S. Pat. No. 4,346,295 issued Aug. 24, 1982 to Tanaka et al. discloses a stimulable phosphor radiation image readout apparatus having a light collector 10 as shown in FIG. 2 comprising a transparent sheet having a linear end 12 arranged adjacent a scan line 14, on a stimulable phosphor sheet 16 and an annular end 18 arranged at the face of a light detector such as a photomultiplier tube 20. Emitted light entering the linear end of the light collector is directed by total internal reflection within the light collector to the light detector. The light collector is formed by heating a sheet of thermoplastic resin in an oven while holding one edge of the sheet in a fixture. After heating to a temperature where the thermoplastic is pliable, the other end of the sheet is formed by hand into a substantially cylindrical output end having a cylindrical axis 21 normal to the output face of the collector. The annular end is held in a collar (not shown) while cooling, then it is cut off, squared, ground, and polished. A problem arises when forming a light collector in this manner, for when the cylindrical output end is formed, the thermoplastic sheet undergoes some stretching and is thereby thinned in regions 22 near the output end. The thinning in the sheet has a deleterious effect on the light collection efficiency of the light collector. This effect is explained with reference to FIGS. 3 a, and b, where a cross section of a tapered light collector 24 and a untapered light collector 26 are shown respectively. It is noted that each time a light ray 28 undergoes an internal reflection in the light collector, a small portion of the light is lost. In theory, the internal reflection is "total" if the surface of the collector is optically perfect; in practice this is difficult or impossible to achieve. Furthermore, there are also higher absorption losses due to a longer optical path through the transparent collector when the light experiences more reflections. Therefore, to maximize the light collection efficiency of the light collector it is desirable to minimize the number of internal reflections experienced by a light ray on its path to the detector
FIG. 3a shows a light ray 28 entering a tapered light collector 24. The tapered light collector is thicker at the entrance end and thinner at the exit end. As the light ray 28 progresses through the light collector, the angles of reflection .THETA..sub.1,.THETA..sub.2 . . . from the surface of the light collector progressively increase due to the taper, thereby causing the light ray 28 to experience more and more reflections between the surfaces of the collector and consequently to traverse a longer path in the collector. FIG. 3b shows a light collector 26 with no taper. It is readily seen by comparing FIG. 3a and FIG. 3b that the number of reflections of the light ray 28 in the non tapered collector is less than in the tapered collector. It is the object of the present invention to provide a light collector of the type discussed above, having improved light collection efficiency.
DISCLOSURE OF THE INVENTION
The light collector according to the present invention is characterized by having a thickness that is constant or increasing from the linear input edge to the annular output edge, thereby minimizing the number of internal reflections experienced by a ray of collected light in its path through the light collector. In a preferred mode of practicing the invention, the light collector is formed by heating a rectangular sheet of thermoplastic material and forming the sheet on a mold that comprises a triangular section, with two half circular cylinders arranged along two edges of the triangular section such that the surfaces of the half circular cylinders are tangent to the surface of the triangular section. When the sheet is formed on such a mold, th
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patent: 4222630 (1980-09-01), Delignieres
patent: 4346295 (1982-08-01), Tanaka et al.
patent: 4409477 (1983-10-01), Carl
patent: 4485302 (1984-11-01), Tanaka et al.
patent: 4636641 (1987-01-01), Mori et al.
patent: 4749861 (1988-06-01), Watanabe
Boutet John C.
Garbe William F.
Kessler David
Kulpinski Robert W.
Lubinsky Anthony R.
Close Thomas H.
Eastman Kodak Company
Lee John D.
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