Radiant energy – Photocells; circuits and apparatus – Housings
Reexamination Certificate
2003-11-07
2004-11-16
Luu, Thanh X. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Housings
C250S370150, C313S011000
Reexamination Certificate
active
06818885
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cooling type photodetector in which at least a cooling device is built inside a housing for accommodating a photoelectric tube.
2. Related Background Art
A cooling type photodetector of this kind is disclosed, for example, in Japanese Patent Laid-Open No. 6-88747 (Reference 1), which describes the configuration of a cooling type photodetector comprising a cooling device composed of a Peltier element, and an annular cooling block attached to the low temperature side (heat absorbing portion) of the cooling device, both being built inside a box for accommodating a photomultiplier. Further, Japanese Patent Laid-Open No. 5-312638 (Reference 2) discloses the configuration of an infrared optical apparatus comprising an infrared image detector, a cooling device composed of a Peltier element, and a cooling framework attached to the heat absorbing side (heat absorbing portion) of the cooling device, all being built inside a lens barrel of an optical system for forming an infrared image.
In the the cooling type photodetector described in Reference 1, the annular cooling block surrounds and cools down one end portion on the photoelectric surface side of a photomultiplier and one end portion of a vacuum cell type light entrance window facing the photomultiplier. The portion of the photomultiplier other than the one end portion is supported within the box via a heat insulating material, and the other end portion of the vacuum cell type light entrance window is supported such as to be fitted into a wall portion of the box. Then, the other end portion of the vacuum cell type light entrance window is heated through the wall portion of the box by a heat radiating plate to which a high temperature side (heat radiating portion) of the cooling device is attached.
On the other hand, in the infrared optical apparatus described in Reference 2, an auxiliary lens of the optical system is solely supported on the cooling framework so as to be cooled down. The infrared image detector is cooled down through a holding portion by another cooling portion filled with liquid nitrogen or the like.
SUMMARY OF THE INVENTION
The inventors have studied conventional photodetectors in detail and, and as a result, have found problems as follows. Namely, in the cooling type photodetector described in Reference 1, the annular cooling block surrounds and cools down indirectly the one end portion on the photoelectric surface side of the photomultiplier. This causes a poor cooling efficiency, and hence has a possibility that the occurrence of noise is not sufficiently suppressed in the photomultiplier. Further, the vacuum cell type light entrance window that is heated generates background light (thermal radiation), so that the background light is incident on the photomultiplier and can increase the dark current of the photomultiplier. This creates drawbacks in precision detection of weak light.
On the other hand, the infrared optical apparatus described in Reference 2 needs two separate systems of cooling means constituted by the cooling means comprising the cooling portion and the retaining portion for cooling the infrared image detector, and the auxiliary cooling means having the cooling device and the cooling framework for cooling the auxiliary lens of the optical system. This creates drawbacks in the size reduction of the apparatus configuration.
The invention has been devised in order to resolve these problems. An object of the invention is to provide a photodetector capable of detecting even weak light with precision and having a structure permitting size reduction.
The photodetector according to the present invention comprises a housing, a photoelectric tube accommodated in the housing, a heat conductive supporting member accommodated in the housing, and a cooling device accommodated in the housing and arranged between the heat conductive supporting member and an inner surface of the housing. The housing has a light entrance window for introducing light to be measured into inside thereof. The photoelectric tube has a light receiving faceplate and a photoelectric surface located on one surface of the light receiving faceplate. The heat conductive supporting member has a supporting protrusion piece for fixing the photoelectric tube, and the supporting protrusion piece has an aperture stop for introducing light to be measured, which is transmitted through the light entrance window of the housing, to the photoelectric surface of the photoelectric tube through the light receiving faceplate of the photoelectric tube. The cooling device has a heat radiating portion being in contact with the inner surface of the housing and a heat absorbing portion being in contact with the heat conductive supporting member. In particular, in the photodetector according to the present invention, it is preferable that the photoelectric tube is fixed only to the supporting protrusion piece while the light receiving faceplate of the photoelectric tube is aligned with the aperture stop.
In this case, when the cooling device begins cooling operation, the photoelectric tube is cooled down starting from the light receiving faceplate side via the supporting protrusion piece of the heat conductive supporting member fixed to the heat absorbing portion of the cooling device. At that time, the photoelectric tube is fixed only to the supporting protrusion piece, so that heat inflow through other members is prevented. Thus, the photoelectric surface of the photoelectric tube is efficiently cooled down through the light receiving faceplate by the cooling device serving as a cooling source, so that a stable cooling temperature is obtained. This suppresses the emission of thermal electrons from the photoelectric surface of the photoelectric tube, and hence sufficiently suppresses the occurrence of noise in the photoelectric tube. In this state, light to be measured, which is transmitted through the light entrance window of the housing, is incident on the photoelectric surface of the photoelectric tube via the aperture stop of the supporting protrusion piece, while background light emitted from the housing is shielded by the supporting protrusion piece around the aperture stop so as not to be incident on the photoelectric surface.
The photodetector according to the present invention may comprises a housing, a photoelectric tube accommodated in the housing, a heat conductive supporting member accommodated in the housing, a cooling device accommodated in the housing and arranged between the heat conductive supporting member and an inner surface of the housing, and an optical system for collecting light to be measured which is transmitted through the light entrance window of the housing. The housing has a light entrance window for introducing light to be measured into inside thereof. The photoelectric tube has a light receiving faceplate and a photoelectric surface located on one surface of the light receiving faceplate. The heat conductive supporting member has a supporting protrusion piece for fixing the photoelectric tube, and the supporting protrusion piece has an aperture stop for introducing light to be measured, which is transmitted through the light entrance window of the housing, to the photoelectric surface of the photoelectric tube through the light receiving faceplate of the photoelectric tube. The cooling device has a heat radiating portion being in contact with the inner surface of the housing and a heat absorbing portion being in contact with the heat conductive supporting member. The optical system has a lens barrel located between the light entrance window of the housing and the supporting protrusion piece of the heat conductive supporting member. In particular, in the photodetector according to the present invention, it is preferable that the photoelectric tube is fixed to one surface of the supporting protrusion piece of the heat conductive supporting member while the light receiving faceplate of the photoelectric tube is aligned with the aperture stop. A
Hirohata Toru
Negi Yasuharu
Luu Thanh X.
Sohn Seung C.
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