Hybrid gated microchannel plate photomultiplier

Abstract

The application provides a hybrid gated microchannel plate photomultiplier, which is characterized in that a mesh electron pre-multiplication electrode structure is arranged behind a gating grid electrode, the mesh electron pre-multiplication electrode structure collects and initially amplifies photoelectrons passing through the gating grid electrode by means of the material characteristics of a high secondary electron emission coefficient of the surface of the mesh electron pre-multiplication electrode, compensates for the loss of photoelectrons caused by the grid interception and electron absorption at the input end of the microchannel plate, and enables more electrons to enter the channels of the microchannel plate, so that the high collection efficiency characteristics of the gated microchannel plate photomultiplier are finally realized. The photomultiplier simultaneously has the characteristics of the gating function, the high extinction ratio, the high collection efficiency and the high gain, and can meet different high-energy experimental detection requirements.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection technology, and relates to photomultiplier tubes, specifically to a hybrid gated microchannel plate photomultiplier tube. Background Technology

[0002] A photomultiplier tube (PMT) is a vacuum photodetector that converts extremely weak light signals into electrical signals and amplifies them. Its basic working principle is as follows: incident photons strike a photocathode, generating photoelectrons. These photoelectrons are focused by an electron optics system and enter a multiplication system. Secondary electron emission within the multiplication system amplifies the signal, ultimately outputting a measurable electrical signal from the anode. The high sensitivity of PMTs to weak light signals makes them a core photodetector in important applications such as lidar, high-energy particle physics detection experiments, biomedical imaging, and fluorescence spectroscopy.

[0003] However, in applications such as neutron detection, lidar, and transient fluorescence detection, the weak target signal is usually not isolated but accompanied by background noise of varying degrees. Therefore, in environments with strong background noise, photomultiplier tubes (PMTs) are required to have gating functionality. When strong light interference signals arrive, the PMT is "turned off," thus blocking signal amplification and effectively avoiding strong light background noise interference. When the target signal arrives, the PMT is "turned on," enabling amplification and effective detection of the weak signal. Existing gated PMTs are mainly divided into two types: gated dinter photomultiplier tubes based on dinter multiplication systems and gated microchannel plate photomultiplier tubes based on microchannel plate multiplication systems. However, gated dinter photomultiplier tubes have a relatively large dinter component structure and a large number of stages, resulting in a slower time response. Compared to gated dinter photomultiplier tubes, gated microchannel plate photomultiplier tubes typically adopt a close-fitting focusing structure design, featuring a compact structure, high gain, and fast time response.

[0004] However, in traditional gated microchannel plate photomultiplier tubes (MSPs), their collection efficiency is often significantly constrained by two key structural factors: first, the gate grid electrodes introduced to achieve the gating function inevitably intercept some photoelectrons emitted by the photocathode, resulting in photoelectron loss; second, the inherently limited aperture area ratio of the microchannel plate, typically around 60%-70%, means that about 30%-40% of the incident photoelectrons are absorbed by the metal electrode surface at the input end of the microchannel plate and cannot enter the microchannel plate channel for effective multiplication. Under the combined effect of these two physical mechanisms, the collection efficiency of the microchannel plate photomultiplier system is significantly weakened, limiting the collection efficiency of the gated MSPs to below the maximum theoretical value of the microchannel plate aperture area ratio. This low collection efficiency severely limits the detection efficiency, signal gain, and signal-to-noise ratio performance of the gated MSPs. Therefore, how to fundamentally improve the collection efficiency of gated microchannel plate photomultiplier tubes while achieving fast, high extinction ratio gating is a pressing technical challenge in this field. Some researchers have proposed using flared microchannel plate structures to maximize the aperture area ratio; however, the fabrication of such special configurations significantly increases the complexity and cost of device fabrication. Other researchers have used alumina material with secondary electron emission capabilities to be vapor-deposited on the input end surface of the microchannel plate to improve photoelectron collection efficiency. However, during the vapor deposition process, alumina material inevitably enters the microchannel at the input end of the microchannel plate, reducing the aperture area ratio and causing material spillage during the deposition process to contaminate the original functional layer on the inner wall of the channel, thus affecting the consistency of device performance. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention proposes a hybrid gated microchannel plate photomultiplier tube. By placing a mesh-like electron pre-multiplier structure after the gated grid electrodes, and leveraging the high secondary electron emission coefficient of the pre-multiplier surface, the photoelectrons passing through the gated grid electrodes are collected and initially amplified. This compensates for photoelectron losses caused by grid interception and electron absorption at the microchannel plate input, allowing more electrons to enter the microchannel plate channels. Ultimately, this achieves the high collection efficiency of the gated microchannel plate photomultiplier tube. This photomultiplier tube simultaneously possesses gated functionality, high extinction ratio, high collection efficiency, and high gain, meeting the detection needs of various high-energy experiments.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A hybrid gated microchannel plate photomultiplier tube includes a glass window 1, a tube shell 12, and a base 11. The glass window 1, tube shell 12, and base 11 are sealed together to form a vacuum cavity. Along the incident direction of light, a photocathode 2, a gated grid electrode 3, an electron premultiplier electrode 4, a microchannel plate assembly 6, and an anode 9 are sequentially arranged inside the cavity. The photocathode 2, gated grid electrode 3, electron premultiplier electrode 4, microchannel plate assembly 6, and anode 9 are connected to an external power supply circuit through electrode leads, and the external power supply circuit provides operating voltage to each electrode.

[0007] Furthermore, the photocathode 2 is deposited on the inner surface of the glass window 1. The gated grid electrode 3, electron premultiplier electrode 4, microchannel plate assembly 6, and anode 9 are arranged sequentially along the central axis of the vacuum cavity. The glass window 1 and the base 11 are located at opposite ends of the central axis. The tube shell 12 is located circumferentially and connects the glass window 1 and the base 11. Several parallel insulating ceramic rings 7 are arranged axially within the vacuum cavity for assembling different components at the edges, thus separating the different components axially. Each insulating ceramic ring 7 is connected to a ceramic support frame 8 on its outer side for support. The ceramic support frame 8 is located near the inner wall of the tube shell 12 and extends through the vacuum cavity along the base 11. The ceramic support frame 8 has pre-drilled through holes for electrode leads to pass through and connect to an external power supply circuit.

[0008] Furthermore, the cathode material of the photocathode 2 is: Sb-K-Cs dual-alkali cathode or Sb-Na-K-Cs multi-alkali cathode that respond to visible light; or, Cs2Te, Rb2Te, or CsI materials that respond to ultraviolet light.

[0009] Furthermore, the axial distance between the gated grid electrode 3 and the photocathode 2 is 0.3mm~2mm; the gated grid electrode 3 is made of stainless steel with a thickness of 0.05mm~0.5mm, and the grid mesh is a periodically arranged circular, square or hexagonal structure.

[0010] Furthermore, the electron premultiplier 4 has a mesh structure, and its surface is made of copper-beryllium alloy material with secondary electron emission function, with a thickness of 0.05mm~0.5mm, and the axial distance between it and the gated grid electrode 3 is 0.3mm~2mm.

[0011] Furthermore, the opening shape of the electron premultiplier 4 is circular, square, or hexagonal, and the grid wire is cylindrical, rectangular, or triangular prism. The grid wire of the electron premultiplier 4 is aligned with the mesh of the gated grid electrode 3. When the gated grid electrode 3 is in the open state, the potential of the electron premultiplier 4 is set to be 50V~300V higher than the potential of the gated grid electrode 3. Photoelectrons emitted from the surface of the photocathode 2 pass through the mesh of the gated grid electrode 3 and hit the grid wire of the premultiplier 4, where they are collected by the grid wire and premultiplied by the secondary electron emission material on its surface.

[0012] Furthermore, depending on different gain requirements, the microchannel plate assembly 6 can be a single microchannel plate or multiple microchannel plates stacked together. When stacking is used, each microchannel plate is separated by an insulating ceramic ring 7.

[0013] Furthermore, the microchannel plate is a thin plate-like structure with a thickness of 0.4 to 3 millimeters, composed of millions of microchannels with a diameter of 2 to 20 micrometers and an inclination angle of 5 to 15 degrees. The side near the cathode is called the input end, and the side near the anode is called the output end. Metal electrodes are deposited on the surfaces of both the input end and the output end.

[0014] Furthermore, the anode 9 is located 0.5mm to 1mm below the output end of the microchannel plate assembly 6, and its potential is 100V to 600V higher than the electrode potential of the output end of the microchannel plate assembly 6; the anode 9 is connected to the output pin 10, and the gain signal collected by it is output to the outside of the cavity through the output pin 10.

[0015] Furthermore, the anode 9 can be a flat single anode, multiple anodes, or a conical anode structure.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention employs a hybrid multiplication structure combining an electron premultiplier and a microchannel plate assembly after the gated grid electrode. Through structural design, the grid wires of the electron premultiplier, coated with secondary electron emission material, are precisely matched with the mesh of the gated grid electrode, reducing electron divergence and loss during interstage transmission. This not only achieves effective collection of photoelectrons but also provides primary gain, enabling the overall collection efficiency of photoelectrons from the photocathode to the input end face of the microchannel plate to be increased to over 95%.

[0017] 2. The present invention can set the first gate electrode (between the cathode and the gated grid electrode) and the second gate electrode (between the gated grid electrode and the electron premultiplier electrode) through external circuits. Compared with the traditional single gate structure, the synergistic effect of the dual gate design can effectively improve the extinction ratio characteristics of the gated microchannel plate photomultiplier tube, solve the problem of incomplete gate "closing" under strong noise background environment, and ensure the reliability of detecting weak target signals.

[0018] 3. The combination of the electron premultiplier electrode and the gated grid electrode proposed in this invention further effectively suppresses ion feedback noise from the microchannel plate, improving the lifespan of the photocathode and the signal-to-noise ratio of the device.

[0019] 4. The electronic premultiplier structure design in this invention can be applied to different types of gated photomultiplier tubes.

[0020] 5. The hybrid gated microchannel plate photomultiplier tube proposed in this invention has a simple structure, is easy to assemble, and has excellent performance characteristics such as gated function, high collection efficiency, and fast time response. It is suitable for high-energy particle detection in environments with strong background noise and has high commercial application value. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the hybrid gated microchannel plate photomultiplier tube structure of the present invention.

[0022] Figure 2a This is a three-dimensional schematic diagram of the arrangement structure of the gated grid electrodes and electron premultiplier electrodes in an embodiment of the present invention.

[0023] Figure 2b This is a cross-sectional view of the arrangement structure of the gated grid electrodes and electron premultiplier electrodes in an embodiment of the present invention.

[0024] Figure 2c This is a side view of the gated grid electrode and electron premultiplier electrode arrangement structure in an embodiment of the present invention.

[0025] Figure 3 This is a simulation result of the electron trajectory between the photocathode inside the photomultiplier tube of the hybrid gated microchannel plate of the present invention and the input surface of the microchannel plate assembly.

[0026] In the diagram: 1-glass light window, 2-photocathode, 3-gated grid electrode, 4-electron premultiplier, 5-schematic electron trajectory, 6-microchannel plate assembly, 61-first microchannel plate, 62-second microchannel plate, 7-insulating ceramic ring, 8-ceramic support frame, 9-anode, 10-anode output pin, 11-base, 12-tube shell. Detailed Implementation

[0027] To more clearly illustrate the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the present invention is not limited to the following embodiments.

[0028] like Figure 1As shown, the present invention discloses a hybrid gated microchannel plate photomultiplier tube, comprising a glass window 1, a tube shell 12, and a base 11. The glass window 1, the tube shell 12, and the base 11 are indium-sealed together to form a cavity with an internal vacuum environment, the vacuum degree of which is less than 10. -4 The light window 1 is made of low-background quartz glass, magnesium fluoride glass or borosilicate glass, and its shape can be circular or square; the base 11 and the tube shell 12 can be made of metal or ceramic materials.

[0029] Along the direction of light incidence, the cavity contains, in sequence, a photocathode 2, a gated grid electrode 3, an electron premultiplier electrode 4, a microchannel plate assembly 6, and an anode 9. The gated grid electrode 3, electron premultiplier electrode 4, microchannel plate assembly 6, and anode 9 are arranged sequentially and positioned on the central axis of the vacuum cavity. A glass window 1 and a base 11 are located at opposite ends of the central axis. A tube shell 12 is circumferentially positioned and connects the glass window 1 and the base 11 to form the vacuum cavity. Several parallel insulating ceramic rings 7 are arranged axially within the vacuum cavity to assemble different components at the edges, ensuring that the components are axially separated and parallel to each other. Each insulating ceramic ring 7 is connected to a ceramic support frame 8 on its outer side for support. The ceramic support frame 8 is positioned near the inner wall of the tube shell 12 and extends through the vacuum cavity along the base 11. Through holes are provided on the ceramic support frame 8 for electrode leads to pass through and connect to an external power supply circuit, providing external voltage input to the photocathode 2, gated grid electrode 3, electron premultiplier electrode 4, microchannel plate assembly 6, and anode 9. The external voltage regulation methods for each electrode are mature existing technologies in this field, and will not be elaborated further in this article.

[0030] Photocathode 2 is deposited on the inner surface of glass window 1, and its shape is consistent with that of glass window 1, being circular or square. Incident light passes through glass window 1 and strikes photocathode 2, triggering the photoelectric effect and exciting photocathode 2 to emit photoelectrons, thus converting light radiation into photoelectrons. The cathode material of photocathode 2 is selected from Sb-K-Cs dual-alkali cathode or Sb-Na-K-Cs multi-alkali cathode materials that respond to visible light, or Cs2Te, Rb2Te, and CsI materials that respond to ultraviolet light. In electron multiplication mode, the potential of photocathode 2 is set to the minimum potential; that is, if a positive bias is used, the potential of photocathode 2 is generally zero; if a negative bias is used, the potential of photocathode 2 is generally a negative high voltage. The effective detection diameter of this photocathode 2 can be between 10mm and 80mm, adaptable to photomultiplier tubes of different area sizes.

[0031] The gated grid electrode 3 is made of stainless steel, has the same shape as the photocathode 2, and a thickness of 0.05mm to 0.5mm. The grid mesh consists of periodically arranged circular, square, or hexagonal openings. It is positioned below the photocathode 2, with an axial distance of 0.3mm to 2mm between them. When the potential of the gated grid electrode 3 is higher than that of the photocathode 2, it is in the open state; when the potential of the gated grid electrode 3 is lower than that of the photocathode 2, it is in the closed state. By applying rapidly switching voltage pulses to the gated grid electrode 3, with a gate pulse voltage amplitude of -100V to +20V, the ability of photoelectrons emitted from the photocathode 2 to pass smoothly through the gated grid electrode mesh is controlled.

[0032] The electron premultiplier electrode 4 is a specially designed mesh structure. Its surface is made of a copper-beryllium alloy material with secondary electron emission capability, with a thickness of 0.05mm~0.5mm. The opening shape can be circular, square, or hexagonal. The grid wires are cylindrical, rectangular, or triangular prism-shaped, and are placed between the gated grid electrode 3 and the microchannel plate assembly 6, with an axial distance of 0.3mm~2mm between them. Figure 2a , Figure 2b , Figure 2c As shown, the grid wire of the electron premultiplier 4 is aligned with the mesh of the gated grid electrode 3. When the gated grid electrode 3 is in the open state, the potential of the electron premultiplier 4 is set to be 50V~300V higher than the potential of the gated grid electrode 3. Photoelectrons emitted from the surface of the photocathode 2 pass through the mesh of the gated grid electrode 3 and strike the grid wire of the premultiplier 4, where they are collected and premultiplied using the secondary electron emission material on its surface. The electron trajectory is as follows: Figure 1 As shown in Figure 5. When the gated grid electrode 3 is in the closed state, the potential of the electron premultiplier electrode 4 is 0V to 100V lower than the potential of the gated grid electrode 3, forming a negative potential barrier, effectively blocking electron transport, further improving the gate-closing capability of the gated microchannel plate photomultiplier tube, and effectively improving the extinction ratio characteristics of the device.

[0033] The microchannel plate assembly 6 can be configured as a single microchannel plate, two microchannel plates, or multiple stacked microchannel plates, depending on different gain requirements. The operating voltage of each microchannel plate is set between 700V and 1100V. A microchannel plate is a thin plate-like structure 0.4 to 3 mm thick, composed of millions of microchannels with diameters of 2 to 20 micrometers and tilt angles of 5 to 15 degrees. The side closest to the cathode is called the input terminal, and the side closest to the anode is called the output terminal. Metal electrodes are deposited on the surfaces of both the input and output terminals. When using two or more microchannel plates, such as... Figure 1Microchannel plates 61 and 62 are separated by insulating ceramic rings 7. The multiplied secondary electrons undergo avalanche multiplication in the microchannels of the microchannel plate assembly 6, thereby achieving current gain of up to 10⁻⁶. 4 ~10 7 Electron multiplication is achieved. Anode 9 is located 0.5mm to 1mm below the output terminal of the microchannel plate assembly 6, with a potential 100V to 600V higher than the output electrode potential of the microchannel plate assembly 6. It is used to collect the electron flow multiplied by the multiplication system and output current or voltage signals. Anode 9 can be designed as a flat single anode, multi-anode, or conical anode, made of copper sheet or other metal materials. The gain signal collected by anode 9 is led out to the outside of the vacuum chamber through output pin 10.

[0034] When the micro-light signal to be measured arrives, the hybrid gated microchannel plate photomultiplier tube is in the open operating state. At this time, the potential of the gated grid electrode 3 is higher than that of the photocathode 2. The incident photon passes through the glass window 1 and irradiates the photocathode 2. Utilizing the photoelectric effect, the photocathode 2 converts the light signal into photoelectrons. Under the action of the accelerating electric field, the photoelectrons pass through the mesh of the gated grid electrode 3, strike the grid wire of the pre-multiplication electrode 4, and excite secondary electrons. High voltage is applied to both ends of the microchannel plate 6, forming a strong electric field distribution along the axis inside the channel. When the pre-multiplied electrons enter the microchannel, they collide with the inner wall of the channel, generating secondary electrons. Under the action of the electric field inside the microchannel plate, the secondary electrons are accelerated again and collide with the inner wall of the channel, exciting more secondary electrons. This cycle repeats, forming an avalanche-like electron multiplication. Finally, a large number of multiplied electrons output from the output end of the microchannel plate 6 continue to drift under the action of the electric field and are collected by the anode 9, thereby achieving effective signal detection.

[0035] Based on the above embodiments, the performance of this high-collection-efficiency hybrid gated microchannel plate photomultiplier tube was simulated using the finite integration method, Monte Carlo method, and electron trajectory tracking method. After photoelectrons are emitted from the cathode surface, they pass through the gated grid electrodes, undergo preliminary electron multiplication at the electron pre-multiplication electrode, and finally reach the input end face of the microchannel plate assembly, as shown in the complete trajectory. Figure 3 As shown in the figure. Statistical results show that the ratio of the number of electrons arriving at the input channel of the microchannel plate assembly 6 to the number of photoelectrons emitted from the photocathode is higher than 95%, which is significantly better than the 60%-70% collection efficiency of traditional gated microchannel plate photomultiplier tubes.

[0036] The above are merely preferred embodiments of the present invention. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A hybrid gated microchannel plate photomultiplier tube, comprising a glass window (1), a tube shell (12), and a base (11), wherein the glass window (1), the tube shell (12), and the base (11) are indium-sealed to form a vacuum cavity, characterized in that, Along the direction of light incidence, a photocathode (2), a gated grid electrode (3), an electron premultiplier electrode (4), a microchannel plate assembly (6), and an anode (9) are sequentially arranged inside the cavity; the photocathode (2), the gated grid electrode (3), the electron premultiplier electrode (4), the microchannel plate assembly (6), and the anode (9) are connected to an external power supply circuit through electrode leads, and the external power supply circuit provides working voltage to each electrode.

2. The hybrid gated microchannel plate photomultiplier tube according to claim 1, characterized in that, The photocathode (2) is deposited on the inner surface of the glass window (1). The gated grid electrode (3), electron premultiplier electrode (4), microchannel plate assembly (6) and anode (9) are arranged sequentially along the central axis of the vacuum cavity. The glass window (1) and the base (11) are located at the two ends of the central axis, respectively. The tube shell (12) is located circumferentially and connects the glass window (1) and the base (11). Several parallel insulating ceramic rings (7) are arranged along the axial direction in the vacuum cavity for assembling different components at the edge, so that different components are separated along the axial direction. Each insulating ceramic ring (7) is connected to the ceramic support frame (8) on the outside of the ring for support. The ceramic support frame (8) is arranged close to the inner wall of the tube shell (12) and extends through the vacuum cavity along the base (11). The ceramic support frame (8) has a reserved through hole for electrode leads to pass through and connect to the external power supply circuit.

3. The hybrid gated microchannel plate photomultiplier tube according to claim 1, characterized in that, The cathode material of the photocathode (2) is: Sb-K-Cs dual-alkali cathode or Sb-Na-K-Cs multi-alkali cathode that respond to visible light; or, Cs2Te, Rb2Te, or CsI materials that respond to ultraviolet light.

4. The hybrid gated microchannel plate photomultiplier tube according to any one of claims 1-3, characterized in that, The axial distance between the gated grid electrode (3) and the photocathode (2) is 0.3mm~2mm; the gated grid electrode (3) is made of stainless steel with a thickness of 0.05mm~0.5mm, and the grid mesh is a periodically arranged circular, square or hexagonal structure.

5. The hybrid gated microchannel plate photomultiplier tube according to claim 4, characterized in that, The electron premultiplier electrode (4) has a mesh structure and its surface is made of copper-beryllium alloy material with secondary electron emission function. The thickness is 0.05mm~0.5mm and the axial distance between it and the gated grid electrode (3) is 0.3mm~2mm.

6. The hybrid gated microchannel plate photomultiplier tube according to claim 5, characterized in that, The opening shape of the electron premultiplier (4) is circular, square or hexagonal, and the grid wire is cylindrical, rectangular or triangular prism. The grid wire of the electron premultiplier (4) is aligned with the mesh of the gated grid electrode (3). When the gated grid electrode (3) is in the open state, the potential of the electron premultiplier (4) is set to be 50V~300V higher than the potential of the gated grid electrode (3). The photoelectrons emitted from the surface of the photocathode (2) pass through the mesh of the gated grid electrode (3) and hit the grid wire of the premultiplier (4), so that they are collected by the grid wire and premultiplied by the secondary electron emission material on its surface.

7. The hybrid gated microchannel plate photomultiplier tube according to claim 1, characterized in that, Depending on the different gain requirements, the microchannel plate assembly (6) can be a single microchannel plate or multiple microchannel plates stacked together. When stacking is used, each microchannel plate is separated by an insulating ceramic ring (7).

8. The hybrid gated microchannel plate photomultiplier tube according to claim 7, characterized in that, The microchannel plate is a thin plate-like structure with a thickness of 0.4 to 3 millimeters, composed of millions of microchannels with a diameter of 2 to 20 micrometers and an inclination angle of 5 to 15 degrees. The side closer to the cathode is called the input end, and the side closer to the anode is called the output end. Metal electrodes are deposited on the surfaces of both the input end and the output end.

9. The hybrid gated microchannel plate photomultiplier tube according to claim 8, characterized in that, The anode (9) is located 0.5 mm to 1 mm below the output end of the microchannel plate assembly (6), and its potential is 100 V to 600 V higher than the electrode potential of the output end of the microchannel plate assembly (6). The anode (9) is connected to the output pin (10), and the gain signal collected by it is output to the outside of the cavity through the output pin (10).

10. The hybrid gated microchannel plate photomultiplier tube according to claim 9, characterized in that, The anode (9) is a flat single anode, multi-anode, or conical anode structure.

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