Abstract:
An internal portion of a photomultiplier tube (PMT) having a reflective photocathode array, and a method for manufacturing the same, are provided. The internal portion of the PMT comprises the reflective photocathode array and at least one dynode structure corresponding to the array of reflective photocathodes. Each reflective photocathode receives light and from the light, generates photoelectrons which then travel towards the at least one dynode structure. Upon the photoelectrons making contact with the at least one dynode structure, the photoelectrons are multiplied.

Description:
RELATED APPLICATION(S) 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/079,985 filed Nov. 14, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to photomultiplier tubes (PMTs). 
       BACKGROUND 
       [0003]    Photomultiplier tubes (PMTs) are devices utilized to detect light. They convert light to photoelectrons that are then multiplied and detected. In the past, one particular type of PMT has been formed from a transmission photocathode and a chain of dynodes. An example of the internal structure of a PMT in accordance with the prior art is shown in  FIG. 1 . As shown in  FIG. 1 , light  102  makes contact with one side of a transparent photocathode  104  and as a result photoelectrons  106  are emitted from the other side of the transparent photocathode  104 . The photoelectrons  106  then make contact with a dynode structure  108  which in turn multiplies the photoelectrons  106 . 
         [0004]    Unfortunately, prior art PMTs (such as that illustrated in  FIG. 1 ) have exhibited various limitations. For example, use of a transmission photocathode, as compared to a reflective photocathode, generally results in lower quantum efficiency and a shorter useful lifetime. However, the use of reflective photocathodes has sometimes been avoided in PMT devices for mainly geometric reasons (for instance, needing to have a compact PMT in order to have high bandwidth). 
         [0005]    There is thus a need for addressing these and/or other issues associated with the prior art PMTs. 
       SUMMARY 
       [0006]    An internal portion of a photomultiplier tube (PMT) having a reflective photocathode array, and a method for manufacturing the same, are provided. The internal portion of the PMT comprises the reflective photocathode array and at least one dynode structure corresponding to the array of reflective photocathodes. Each reflective photocathode receives light and from the light, generates photoelectrons which then travel towards the at least one dynode structure. Upon the photoelectrons making contact with the at least one dynode structure, the photoelectrons are multiplied. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows an internal portion of a photomultiplier tube (PMT) having a transparent photocathode, in accordance with the prior art. 
           [0008]      FIG. 2  shows an internal portion of a PMT having a reflective photocathode array, in accordance with an embodiment. 
           [0009]      FIG. 3A  illustrates a reflective photocathode/dynode sub-structure of the PMT of  FIG. 2  having a housing with light incident head-on, in accordance with an embodiment. 
           [0010]      FIG. 3B  illustrates a reflective photocathode/dynode sub-structure of the PMT of  FIG. 2  having a housing with light incident at an angle, in accordance with an embodiment. 
           [0011]      FIG. 4  illustrates a method for manufacturing an internal portion of a PMT having a reflective photocathode array, in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 2  shows an internal portion of a PMT having a reflective photocathode array, in accordance with an embodiment. As shown, the internal portion of the PMT includes a reflective photocathode array  204 A-C where each of the reflective photocathodes  204 A-C are for receiving light  202  and where photoelectrons  206 A-C are generated from the received light  202  by the reflective photocathodes  204 A-C. The internal portion of the PMT further includes at least one dynode structure corresponding to the array of reflective photocathodes  204 A-C for multiplying the photoelectrons  206 A-C generated by the array of reflective photocathodes  204 A-C. 
         [0013]    In the embodiment shown, a separate dynode structure  208 A-C corresponds to each of the reflective photocathodes  204 A-C for multiplying the photoelectrons  206 A-C generated by the corresponding reflective photocathode  204 A-C. In another contemplated embodiment (not shown), a single dynode structure may correspond to multiple of (e.g. all of) the reflective photocathodes  204 A-C in the array for multiplying the photoelectrons  206 A-C generated by the entire reflective photocathode  204 A-C array. Of course, the PMT may also include other sub-structures as is known in the art. 
         [0014]    Gaps are provided between the reflective photocathodes  204 A-C in order to allow the photoelectrons  206 A-C from each of the reflective photocathodes  204 A-C to pass through to the dynode structure  208 A-C. It should also be noted that while only three sub-structures comprising a reflective photocathode and corresponding dynode structure are shown in the array (i.e. sub-structure  204 A and  208 A, sub-structure  204 B and  208 B, sub-structure  204 C and  208 C), any number of such sub-structures may be included within the PMT, as desired. In other embodiments, the array of reflective photocathodes  204 A-C may be any number larger than one, and the reflective photocathodes  204 A-C may be utilized in combination with any number of dynode structures  208 A-C (i.e. one or more). 
         [0015]    Each reflective photocathode  204 A-C may be positioned at an angle within the PMT, so as to send the photoelectrons  206 A-C towards the dynode structure  208 A-C. Further, each dynode structure  208 A-C may be at a position within the PMT to be able to receive the photoelectrons  206 A-C from the corresponding reflective photocathode(s)  204 A-C. In an embodiment with the aforementioned sub-structures, each of the sub-structures within the PMT comprising the reflective photocathode  204 A-C and corresponding dynode structure  208 A-C may be identical (e.g. in position, material, etc.). 
         [0016]    It should be noted that each reflective photocathode  204 A-C may be any photocathode with at least a reflective top surface capable of reflecting photoelectrons the  206  A-C from the light  202  that is incident thereto. For example, the reflective photocathode  204  A-C may be any existing reflective photocathode known in the art. 
         [0017]    Further, each dynode structure  208 A-C may include a plurality of dynodes, each capable of multiplying photoelectrons received thereby. For example, the dynodes may be positioned in a chain for passing the photoelectrons  206 A-C therebetween. Again, the dynode structure  208 A-C may be that which is well known in the art with regard to PMTs. 
         [0018]    By using the reflective photocathode array  204 A-C in the PMT, higher quantum efficiency may be provided (than that provided by the transparent photocathodes used in the prior art, as shown in  FIG. 1  for example), particularly because the reflective property of the reflective photocathodes  204 A-C allows for more photoelectrons  206 A-C to be captured from the light  202  and transmitted to the dynode structure  208 A-C than amount of the photoelectrons otherwise captured and emitted by the transparent photocathode of the prior art). 
         [0019]    Furthermore, the reflective photocathode  204 A-C is capable of being formed from a more robust material than the traditional transparent photocathode. In particular, the reflective photocathode  204 A-C may be formed from any desired material that is then coated with a reflective surface. This may accordingly increase the lifetime of the PMT when the PMT includes the reflective photocathode  204 A-C as described in the present embodiment, as opposed to the prior art PMT having the transparent photocathode. 
         [0020]    More illustrative information will now be set forth regarding various optional architectures and features with which the foregoing framework may or may not be implemented, per the desires of the user. It should be strongly noted that the following information is set forth for illustrative purposes and should not be construed as limiting in any manner. Any of the following features may be optionally incorporated with or without the exclusion of other features described. 
         [0021]      FIG. 3A  illustrates a reflective photocathode/dynode sub-structure of the PMT of  FIG. 2  having a housing with light incident head-on, in accordance with an embodiment. While only one sub-structure comprising a single reflective photocathode  204  and corresponding dynode structure  208  is shown within the housing  300 , it should be noted that the context of the present description the housing  300  would enclose the array of reflective photocathodes  204 A-C and corresponding dynode structure(s)  208 A-C as described above with respect to  FIG. 2 . 
         [0022]    As shown, the reflective photocathode  204  and the dynode structure  208  are included within the housing  300 . The housing  300  may be a tube or any other enclosed structure as is known in the art with respect to PMTs. Additionally, the reflective photocathode  204  is positioned at a diagonal angle from an end side of the housing  300 . The end side of the housing may be, at least in a part, a window through which the light  202  can pass. In the embodiment shown, the light  202  is directed perpendicularly to the end side of the housing  300  and is incident with the reflective photocathode  204  at an angle. In this case, the PMT may be considered a head-on PMT. 
         [0023]      FIG. 3B  illustrates a reflective photocathode/dynode sub-structure of the PMT of  FIG. 2  having a housing with light incident at an angle, in accordance with an embodiment. Again, while only one sub-structure comprising a single reflective photocathode  204  and corresponding dynode structure  208  is shown within the housing  300 , it should be noted that the context of the present description the housing  300  would enclose the array of reflective photocathodes  204 A-C and corresponding dynode structure(s)  208 A-C as described above with respect to  FIG. 2 . 
         [0024]    As shown, the reflective photocathode  204  and the dynode structure  208  are included within the housing  300 . The housing  300  may be a tube or any other enclosed structure as is known in the art with respect to PMTs. Additionally, the reflective photocathode  204  is positioned at a diagonal angle from an end side of the housing  300 . The end side of the housing may be, at least in a part, a window through which the light  202  can pass. In the embodiment shown, the light  202  may be directed toward the end side of the housing  300  at an angle and is perpendicularly incident with the reflective photocathode  204 , in which case the PMT may not be considered a head-on nor a side-on PMT. As an option, the end side of the housing  300  and window included therein may be positioned such that it is perpendicular to the incident light in order to minimize reflection resulting from the window (not shown). 
         [0025]    To this end, the light can be incident, at an angle, to the array of reflective photocathodes shown in  FIG. 2 , or in another embodiment can be perpendicularly incident to the array of reflective photocathodes shown in  FIG. 2 . Optionally, the angle at which the reflective photocathode  204  is positioned within the housing  300  may differ depending on whether the light is incident at an angle with respect to the array of reflective photocathodes (as in the embodiment shown in  FIG. 3A ) or is incident perpendicular to the array of reflective photocathodes (as in the embodiment shown in  FIG. 3B ). 
         [0026]      FIG. 4  illustrates a method for manufacturing an internal portion of a PMT having a reflective photocathode array, in accordance with an embodiment. It should be noted that the present method described in  FIG. 4  may be implemented in the context of the aforementioned figures and associated descriptions. 
         [0027]    The method includes, in operation  402 , providing, within a housing, an array of reflective photocathodes, each of the reflective photocathodes being at a position capable of receiving light. The method further includes, in operation  404 , providing, within the housing, at least one dynode structure corresponding to the array of reflective photocathodes, the at least one dynode structure being at a position capable of receiving photoelectrons when generated by the array of reflective photocathodes from the received light. 
         [0028]    While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.