Abstract:
A method and apparatus involve collection of radiation with a radiation collector that allows entry of external radiation. The exterior of the collector has mutually exclusive first, second, third and fourth surface portions oriented so that they each effect total reflection of the majority of radiation within a waveband that impinges thereon while propagating within the collector. The first and second surface portions are spaced and approximately parallel. The third and fourth surface portions extend at a first angle with respect to each other, and respectively extend at second and third angles with respect to end portions of the first and second surface portions.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates in general to techniques for providing illumination and, more particularly, to devices for collecting ambient radiation. 
     BACKGROUND OF THE INVENTION 
     There are various applications in which there is a need to collect radiation. As one example, a sight or scope is often mounted on a weapon to help a person aim the weapon at an intended target. Many sights superimpose a reticle on the image of the target. It can be advantageous if the reticle is illuminated. Therefore, some existing sights collect ambient radiation, and use it to illuminate the reticle. Devices have previously been developed to collect ambient radiation. Although these devices have been generally adequate for their intended purposes, they have not been completely satisfactory in all respects. 
     SUMMARY OF THE INVENTION 
     One of the broader forms of the invention involves: permitting radiation to enter a radiation collector from externally thereof, the collector having mutually exclusive first, second, third and fourth surface portions on an exterior thereof; permitting radiation within a waveband to propagate within the collector; and causing a majority of radiation within the waveband that is propagating within the collector and that impinges on any of the surface portions to be substantially total reflected, including: orienting the first and second surface portions to be spaced and extend approximately parallel to each other; orienting the third and fourth surface portions to extend at a first angle with respect to each other; orienting the third surface portion to extend at a second angle with respect to an end portion of the first surface portion, and orienting the fourth surface portion to extend at a third angle with respect to an end portion of the second surface portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic view of an apparatus that is an optical sight, and that embodies aspects of the present invention. 
         FIG. 2  is a diagrammatic view that shows a portion of  FIG. 1  in an enlarged scale, and that also shows some components of the apparatus that are not visible in  FIG. 1 . 
         FIG. 3  is a diagrammatic perspective view showing a radiation collector and an optical fiber that are components of the embodiment of  FIG. 1 . 
         FIG. 4  is a diagrammatic top view of the structure shown in  FIG. 3 . 
         FIG. 5  is a diagrammatic fragmentary sectional view taken along the section line  5 - 5  in  FIG. 3 . 
         FIG. 6  is a diagrammatic perspective view of an optical fiber and a radiation collector that are an alternative embodiment of the arrangement shown in  FIGS. 1-5 . 
         FIG. 7  is a diagrammatic perspective view of a radiation collector that is an alternative embodiment of the radiation collector shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagrammatic view of an apparatus that is an optical sight  10 , and that embodies aspects of the present invention. The sight  10  is designed to be mounted on a not-illustrated weapon, such as a rifle or pistol. A person uses the sight  10  to accurately aim the weapon. In particular, radiation from a remote scene  11  travels through the sight  10  along a path of travel  13  to the eye  12  of the person who is using the sight. 
     The sight  10  has a housing that is represented diagrammatically in  FIG. 1  by a broken line  16 . An optical system is provided within the housing  16 , and includes an objective lens  17 , a prism assembly  18 , and an eyepiece lens  21 . When radiation from the scene  11  is traveling along the path of travel  13 , it passes successively through the objective lens  17 , prism assembly  18 , and eyepiece lens  21 . In the illustrated embodiment, the prism assembly  18  is a configuration of a known type, and includes three prisms  26 ,  27 , and  28 . The prism assembly  18  includes several prism surfaces that reflect the radiation as it travels through the prism assembly  18  along the path of travel  13 . One of these surfaces is identified by reference numeral  31  in  FIG. 1 . 
     An optical coating  32  of a known type is provided on the prism surface  31 . The coating  32  is reflective to visible radiation that is traveling along the path of travel  13 . In a known manner, the coating  32  has at least one not-illustrated opening etched through it, in the shape of a reticle. For example, the reticle may have the form of crosshairs of a known type. The sight  10  further includes a reticle illuminating portion  41 , which is represented diagrammatically in  FIG. 1  by a broken line. 
       FIG. 2  is a diagrammatic view showing a portion of  FIG. 1  in an enlarged scale, including a portion of the prism  28 , a portion of the coating  32 , and the internal structure of the reticle illuminating portion  41 . The reticle illuminating portion  41  includes an internal light source which, in the disclosed embodiment, is a tritium light source  51 . The tritium light source  51  is a radioluminescent device of a type known in the art. More specifically, tritium is a radioactive isotope of hydrogen, with atoms having three times the mass of ordinary light hydrogen atoms. The tritium material is provided within a capsule that is made from glass or some other suitable material, and that has a phosphor coating on its inner surface. As the tritium material decays, it emits soft beta rays that, when they strike the phosphor coating, are converted into visible light. The half life of tritium is approximately 12.5 years, and thus the tritium light source  51  has a usable life of more than 15 years. Consequently, the tritium light source glows continuously for a long time, thereby providing a safe and reliable source of light, without any need for a power source such as a battery. 
     The reticle illuminating portion  41  also includes two small lenses  52  and  53  that are supported at spaced locations. A beam splitter  54  of a known type is disposed optically between the lenses  52  and  53 . The beam splitter is transmissive to radiation having one wavelength or color, and is reflective to radiation at a different wavelength or color. Light  56  emitted by the tritium light source  51  has a wavelength for which the beam splitter  54  is transmissive. Thus, the light  56  passes through the lens  52 , and then some or all of this light then passes through the beam splitter  54  and the lens  53  in a direction toward the coating  32 , where some of this radiation then passes through the not-illustrated opening(s) in coating  32  that define the reticle. 
     Referring again to  FIG. 1 , a radiation collector  61  is fixedly supported on the exterior of the housing  16 . An optical fiber  62  of a known type extends from the radiation collector  61  to the reticle illuminating portion  41 . The fiber  62  has a core that is made from a material such as polystyrene, and the core is surrounded by a cladding made from a material such as a clear acrylic. Due to differences in the refractive indexes of the cladding and core, most of the visible light within the core of the fiber is optically trapped there, and is successively reflected within the core in a manner that causes it to travel lengthwise within the core. 
     Ambient radiation  63  impinges on and enters the radiation collector  61 . In the disclosed embodiment, the ambient radiation  63  encompasses a relatively wide range of wavelengths, including both visible light and ultraviolet light. The radiation collector  61  internally converts non-visible light (such as ultraviolet light) into visible light, in a manner discussed later. Some of the visible light from within the radiation collector  61  is then transmitted through the core of the optical fiber  62  to the reticle illuminating portion  41 . 
     One end of the optical fiber  62  is visible in the lower portion of  FIG. 2 . A small lens  64  is provided between the beam splitter  54  and the illustrated end of the fiber  62 . Visible light emitted from this end of the fiber  62  includes a wavelength as to which the beam splitter  54  is reflective. Consequently, this light from the fiber passes through the lens  64  and travels at  66  to the beam splitter  54 , where at least part of it is reflected by the beam splitter  54 . The reflected light then passes through the lens  53  and propagates toward the coating  32 , where at least some of it serves to illuminate the reticle. 
       FIG. 3  is a diagrammatic perspective view of the radiation collector  61  and also an end portion of the optical fiber  62 .  FIG. 4  is a diagrammatic top view of the structure shown in  FIG. 3 . In the disclosed embodiment, the radiation collector  61  is a single integral part that is plate-like and generally rectangular. The radiation collector  61  has parallel top and bottom surfaces  81  and  82  that are polished and that are each rectangular and planar. Along each of its four edges, the radiation collector  61  has two planar edge surfaces that are polished, that extend parallel to that edge, and that converge outwardly with respect to each other. Two of these edge surfaces are designated by reference numerals  86  and  87 . 
       FIG. 5  is a diagrammatic fragmentary sectional view of the radiation collector  61 , taken along the section line  5 - 5  in  FIG. 3 . As shown in  FIG. 5 , the surfaces  86  and  87  form an angle  88  of 90° with respect to each other. The surface  86  forms an angle  91  of 135° with respect to the top surface  81 , and the edge surface  87  forms an angle  92  of 135° with respect to the bottom surface  82 . The edge surfaces  86  and  87  intersect each other along a line  96  that extends perpendicular to the plane of  FIG. 5 . Similarly, the edge surface  86  intersects the top surface  81  along a line  97 , and the edge surface  87  intersects the bottom surface  82  along a line  98 . 
     In the disclosed embodiment, the radiation collector  61  is a single integral part that is made of a material such as polystyrene, and that has an index of refraction different from the indexes of refraction of almost everything adjacent to the radiation collector  61 , including ambient air. Due to the differing refractive indexes, if visible radiation is propagating within the radiation collector  61  and impinges on any external surface thereof at an angle greater than what is commonly called the “critical” angle, the visible radiation will experience total internal reflection. In this regard, as is known in the art, the critical angle is measured from an imaginary reference line that is perpendicular to the surface at the point where the radiation in question impinges on the surface. The illustrated shape of the radiation collector  61 , including the arrangement of external surfaces, is intended to ensure that visible radiation propagating within the radiation collector  61  will impinge on any external surface it may reach at an angle greater than the critical angle, and will therefore always experience total internal reflection. As a result, most of the visible radiation within the collector  61  will not be able to escape from the radiation collector  61  through any external surface thereof. 
     In addition, the material of the radiation collector  61  is doped with a special fluorescent dye of a type known in the art. When certain wavelengths of non-visible light (such as ultraviolet light) enter the radiation collector  61 , the fluorescent dye absorbs that light and then emits visible light. In essence, the fluorescent dye converts the received optical energy from an initial wavelength outside the visible spectrum to a different wavelength within the visible spectrum. The material of the dye determines the wavelength and thus the color of the visible light that is emitted. The visible light produced by the fluorescent dye is then effectively trapped within the radiation collector  61 , in the manner discussed above. Due to the fact that much of the visible radiation within the radiation collector  61  is not able to escape, the radiation collector  61  is relatively efficient at collecting visible radiation. In addition, to the extent that the fluorescent dye converts ultraviolet or other non-visible radiation into visible radiation, the radiation collector  61  is more efficient at collecting visible radiation than if the dye were not present. Stated differently, when the dye is present, the amount of visible radiation within the radiation collector  61  will be greater than the amount of visible radiation that enters the collector from externally thereof. thus, the radiation collector  61  effectively provides a degree of gain in regard to the collection of visible radiation. 
     As best seen in  FIG. 4 , a horizontal cylindrical opening  106  extends a short distance into the radiation collector  61  from one corner thereof. One end of the optical fiber  62  is disposed within the opening  106 , and is fixedly secured there by a commercially-available adhesive, or in any other suitable manner. Visible light that is trapped within the radiation collector  61  will effectively be bouncing around therein in virtually all directions. Some of this visible radiation will enter the core of the optical fiber  62  at the end surface  108 , and then will propagate through the optical fiber  62  to the reticle illuminating portion  41  ( FIG. 1 ), in order to illuminate the reticle. 
     With reference to  FIGS. 1-2 , when the weapon sight  10  is in an environment where the ambient light includes sunlight or some other strong source of visible and/or non-visible radiation (such as ultraviolet radiation), the visible light emitted from the fiber  62  within the radiation illumination portion  61  will be significantly brighter than the light emitted by the tritium light source  51 . Thus, in this type of situation, the illumination of the reticle is effected primarily by the light produced by the radiation collector  61  and transmitted through the optical fiber  62 . In contrast, when the weapon sight  10  is being used in darkness or in some other environment with little or no ambient light, the optical fiber  82  will be emitting little or no visible light within the reticle illumination portion  41 , but the tritium light source  51  will still be active, and will provide suitable illumination for the reticle. 
       FIG. 6  is a diagrammatic perspective view of the optical fiber  62  and a radiation collector  131  that is an alternative embodiment of the radiation collector in  FIGS. 1-5 . The radiation collector  131  is cylindrical, and has polished exterior surfaces, including a polished conical surface  132  or  133  at each end. All portions of the conical surfaces  132  and  133  extend at an angle of 45 degrees with respect to a central axis of the radiation collector  131 . The cylindrical opening  106  extends a short distance coaxially into the radiation collector  131  from one end, such that the conical surface  133  is actually frustoconical rather than fully conical. An end portion of the optical fiber  62  extends into the opening  106 , and is fixedly secured there by a suitable adhesive. 
     The radiation collector  131  is made of the same material as the radiation collector  61 , and is doped with a fluorescent dye. Visible and non-visible radiation can enter the radiation collector  131  from externally thereof (including ultraviolet radiation), and the fluorescent dye will convert at least some of the non-visible radiation into visible radiation of a certain wavelength or color. As with the radiation collector  61 , the arrangement of external surfaces on the radiation collector  131  (including the conical end surfaces  132  and  133 ) ensures that when visible radiation propagating within the collector  131  impinges on any external surface, it will do so at an angle greater than the critical angle. Consequently, most of the visible radiation within the radiation collector  131  will be effectively trapped there. 
       FIG. 7  is a diagrammatic perspective view of a radiation collector  141  that is an alternative embodiment of the radiation collector  131  of  FIG. 6 . The embodiment of  FIG. 7  is effectively identical to the embodiment of  FIG. 6 , with one difference. The radiation collector  141  has the conical surface  132  at one end, but its other end extends all the way to the reticle illuminating portion  41 , and has a planar end surface  144  that is perpendicular to the central axis of the radiation collector  141 . When visible light that is propagating within the radiation collector  141  reaches the end surface  144 , it will impinge on the surface  144  at an angle less than the critical angle. Consequently, this radiation will pass through the end surface  144  and into the reticle illuminating portion  41 , where it will illuminate the reticle in a manner similar to that described earlier for the radiation  66  in  FIG. 2 . 
     Although several selected embodiments have been illustrated and described in detail, it will be understood that they are exemplary, and that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the following claims.