Radiant energy – Invisible radiant energy responsive electric signalling – Ultraviolet light responsive means
Reexamination Certificate
2000-03-27
2002-01-01
Mack, Ricky (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Ultraviolet light responsive means
Reexamination Certificate
active
06335529
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ultraviolet detector that converts the incident amount of ultraviolet radiation into a different wavelength by a wavelength conversion element for detection.
BACKGROUND ART
An ultraviolet detector employing a wavelength conversion element of interest to the present invention is disclosed in, for example, Japanese Patent Laying-Open No. 64-47921.
FIG. 12A
is a sectional view of the detection unit disclosed in this publication, and
FIG. 12B
is a diagram of the entire structure of the ultraviolet detector. Referring to
FIGS. 12A and 12B
, the detection unit of the ultraviolet detector includes a casing
107
having an upper opening
105
provided at the upper portion of the detection unit and a lower opening
106
, in which a plate-like phosphor (wavelength conversion element)
108
is provided between openings
105
and
106
. An optical fiber
109
is arranged at an end face of phosphor
108
. An interference filter
110
is provided in the passage of optical fiber
109
. A light receiving element
104
receives the fluorescence input via optical fiber
109
and interference filter
110
. In this ultraviolet detector, the incident ultraviolet through opening
105
is converted into visible light by phosphor
108
to enter optical fiber
109
from the end face. However, most of the ultraviolet is output through opening
106
without being converted.
Another ultraviolet detector of interest to the present invention is disclosed in, for example, Japanese Patent Laying-Open No. 6-317463. This publication discloses an ultraviolet detector provided with a bandpass filter and a photodetector in a direction orthogonal to the traveling direction of the ultraviolet radiation to be measured.
As a conventional ultraviolet detector employing a wavelength conversion element, Japanese Patent Laying-Open No. 5-231929 discloses the structure in which a light receiving element is arranged at the rear of a wavelength conversion element.
In the aforementioned conventional ultraviolet detectors with the structure in which the light receiving element is located at the rear of a wavelength conversion element, there was a problem that the disturbance light cut filter must be formed of a separate member in order to prevent introduction of disturbance light of high transmittance into the wavelength conversion element. There was also the problem that the light receiving element is degraded when thin in thickness since the wavelength conversion element generally has a low conversion efficiency. In order to prevent the exit of unconverted UV (ultraviolet) light, it is desirable to set the thickness of the direction in which UV light is transmitted great to allow complete conversion internally. It is also to be noted that complete conversion cannot be implemented if the incident power is great. In the conventional optical system, the light receiving element will be degraded. If the wavelength conversion element is made thick, the absorption ratio of the wavelength-converted light increases to result in lower detection sensitivity of ultraviolet radiation.
Furthermore, in the case where visible light is provided to the optical fiber via the end face of a plate-like phosphor as in the ultraviolet detector shown in
FIGS. 12A and 12B
, sufficient quantity of light could not be obtained. As a result, sensitivity could not be achieved.
The present invention is directed to the above problems. An object of the present invention is to provide an ultraviolet detector with reliable ultraviolet detection sensitivity and with less degradation of the light receiving element.
DISCLOSURE OF THE INVENTION
An ultraviolet detector of the present invention is formed of a material that converts ultraviolet into light of a different wavelength, and includes a wavelength conversion element having a first plane on which ultraviolet is incident and a second plane from which converted light is output, and a light receiving element receiving the converted light output from the second plane. In the wavelength conversion element, the first plane and the second plane are non-parallel with each other, and the dimension in the direction perpendicular to the first plane is greater than the dimension in the direction perpendicular to the second plane.
According to the present invention, the wavelength conversion element has a relatively large dimension in the travelling direction of the ultraviolet, and a relatively small dimension in the direction towards the light receiving element. Therefore, the amount of ultraviolet arriving at the light receiving element after being output from the wavelength conversion element to become disturbance light is small, and the amount of ultraviolet arriving at the light receiving element after being incident on the first plane and output from the second plate is small. Thus, degradation of the light receiving element caused by the ultraviolet is small. Also, the ratio of the converted light absorbed by the wavelength conversion element is small since the travelling distance of the converted light through the wavelength conversion element before arriving at the light receiving element is short.
Preferably, the first plane is orthogonal to the second plane. Since the light receiving element is in the direction orthogonal to the incident direction, there is the advantage of being impervious to disturbance light.
Preferably, the wavelength conversion element is plate-like, and one of the end plane is the first plane, and either the front plane or back plane sandwiching the first plane and having a region of the largest area is the second plane. It is preferable to set one of opposite end planes having the region of the smallest area as the first plane.
Further preferably, at least the second plane of the wavelength conversion element is planar with respect to the ultraviolet wavelength. By setting the side plane of the wavelength conversion element located at the light receiving element side as a mirror plane, the diffusion component at the surface can be eliminated to suppress the output of the ultraviolet or disturbance light. The second plane and the plane opposite to the second plane can be set planar with respect to the ultraviolet wavelength. All the planes adjacent to the first plane can be set planar with respect to the ultraviolet wavelength.
Further preferably, the light receiving element is arranged so that its center is located opposite to the position closer to the first plane than the center position of the second plane.
Further preferably, incident angle restriction means is further provided for restricting the incident angle of the ultraviolet entering the first plane. The incident angle restriction means restricts the incident angle of ultraviolet entering the first incident plane including the normal of the second plane to be within a predetermined angle, and allows the ultraviolet in the second incident plane perpendicular to the first incident plane to be incident at an incident angle greater than the predetermined angle.
Here, the incident angle refers to the angle between the normal of the plane of the point where the ray is incident and the ray.
The incident plane refers to the plane that includes the travelling direction of the wave incident on the surface and the perpendicular line of the surface.
Preferably, “predetermined angle” corresponds to an angle at which the ultraviolet incident at an incident angle within that angle is totally reflected at the second plane and does not reach the light receiving element. As to the ultraviolet in the second incident plane, it is not necessary to intentionally restrict the incident angle since the ultraviolet radiation, even if entering at a large angle, will not reach the light receiving element assuming that the influence of irregular reflection within the casing of the ultraviolet detector is neglected. Rather, allowing incidence at a large incident angle will cause a larger amount of ultraviolet to be directed towards the wavelength conversion element to provide the advantage of inc
Matsuyama Akihisa
Sekii Hiroshi
Mack Ricky
Morrison & Foerster / LLP
Omron Corporation
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