REFLECTIVE PHOTOCATHODE ARRAY

RELATED APPLICATION(S)

[0001] This application claims the benefit of U.S. Provisional Patent

Application No. 62/079,985 filed November 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 Figure 1 . As shown in Figure 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 Figure 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] Figure 1 shows an internal portion of a photomultiplier tube (PMT) having a transparent photocathode, in accordance with the prior art.

[0008] Figure 2 shows an internal portion of a PMT having a reflective photocathode array, in accordance with an embodiment.

[0009] Figure 3A illustrates a reflective photocathode/dynode sub-structure of the PMT of Figure 2 having a housing with light incident head-on, in accordance with an embodiment.

[0010] Figure 3B illustrates a reflective photocathode/dynode sub-structure of the PMT of Figure 2 having a housing with light incident at an angle, in accordance with an embodiment.

[001 1] Figure 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] Figure 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 204A-C where each of the reflective photocathodes 204A-C are for receiving light 202 and where photoelectrons 206A-C are generated from the received light 202 by the reflective photocathodes 204A-C. The internal portion of the PMT further includes at least one dynode structure corresponding to the array of reflective photocathodes 204A-C for multiplying the photoelectrons 206A-C generated by the array of reflective photocathodes 204A-C.

[0013] In the embodiment shown, a separate dynode structure 208A-C corresponds to each of the reflective photocathodes 204A-C for multiplying the photoelectrons 206A-C generated by the corresponding reflective photocathode 204A-C. In another contemplated embodiment (not shown), a single dynode structure may correspond to multiple of (e.g. all of) the reflective photocathodes 204A-C in the array for multiplying the

photoelectrons 206A-C generated by the entire reflective photocathode 204A- 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 204A-C in order to allow the photoelectrons 206A-C from each of the reflective photocathodes 204A-C to pass through to the dynode structure 208A-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 204A and 208A, sub-structure 204B and 208B, substructure 204C and 208C), any number of such sub-structures may be included within the PMT, as desired. In other embodiments, the array of reflective photocathodes 204A-C may be any number larger than one, and the reflective photocathodes 204A-C may be utilized in combination with any number of dynode structures 208A-C (i.e. one or more). [0015] Each reflective photocathode 204A-C may be positioned at an angle within the PMT, so as to send the photoelectrons 206A-C towards the dynode structure 208A-C. Further, each dynode structure 208A-C may be at a position within the PMT to be able to receive the photoelectrons 206A-C from the corresponding reflective photocathode(s) 204A-C. In an

embodiment with the aforementioned sub-structures, each of the substructures within the PMT comprising the reflective photocathode 204A-C and corresponding dynode structure 208A-C may be identical (e.g. in position, material, etc.).

[0016] It should be noted that each reflective photocathode 204A-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 208A-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 206A-C therebetween. Again, the dynode structure 208A-C may be that which is well known in the art with regard to PMTs.

[0018] By using the reflective photocathode array 204A-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 Figure 1 for example), particularly because the reflective property of the reflective photocathodes 204A-C allows for more photoelectrons 206A-C to be captured from the light 202 and transmitted to the dynode structure 208A-C than amount of the photoelectrons otherwise captured and emitted by the transparent photocathode of the prior art).

[0019] Furthermore, the reflective photocathode 204A-C is capable of being formed from a more robust material than the traditional transparent photocathode. In particular, the reflective photocathode 204A-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 204A-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] Figure 3A illustrates a reflective photocathode/dynode sub-structure of the PMT of Figure 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 204A-C and corresponding dynode structure(s) 208A-C as described above with respect to Figure 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] Figure 3B illustrates a reflective photocathode/dynode sub-structure of the PMT of Figure 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 204A-C and corresponding dynode structure(s) 208A-C as described above with respect to Figure 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 Figure 2, or in another embodiment can be perpendicularly incident to the array of reflective photocathodes shown in Figure 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 Figure 3A) or is incident perpendicular to the array of reflective photocathodes (as in the embodiment shown in Figure 3B).

[0026] Figure 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 Figure 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 ofreflective 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.