An x-ray gated imaging method and system based on a cascade micro-channel plate and hCMOS

Abstract

The application relates to the technical field of gated imaging, and provides an X-ray gated imaging method and system based on a cascade microchannel plate and an hCMOS, which sequentially comprises, along a light incidence direction: a photocathode used for converting an incident X-ray image into a photoelectron image; a first-stage electron transmission microchannel plate coupled with the photocathode and used for time slicing the photoelectron image and outputting an electron beam slice carrying time information; a second-stage high-gain microchannel plate MCP coupled with the first-stage electron transmission microchannel plate and used for electron multiplication of the electron beam slice and outputting an amplified electron image; and an hCMOS image sensor coupled with the second-stage high-gain microchannel plate and used for directly receiving and detecting the amplified electron image, converting the amplified electron image into an electric signal and reading out the electric signal. The application can preferably perform X-ray gated imaging.

Description

Technical Field

[0001] This invention relates to the field of gating imaging technology, and more specifically, to an X-ray gating imaging method and system based on cascaded microchannel plates and hCMOS. Background Technology

[0002] In high-energy-density physics experiments, the evolution of physical processes often occurs on timescales of nanoseconds or even picoseconds, accompanied by intense X-ray radiation, neutron flux, and electromagnetic pulse interference. For example, in the implosion stagnation phase of laser inertial confinement fusion (ICF), high-temperature, high-density plasma evolves and generates a large amount of radiation in an extremely short time. To analyze the evolution of the plasma, the diagnostic system needs to perform multi-frame, short-interval two-dimensional imaging of radiation information in a highly interfering environment, while maintaining stable performance parameters such as time resolution, sensitivity, and dynamic range.

[0003] Single-stage microchannel plate (MCP) framing cameras are core two-dimensional spatially resolved diagnostic devices for transient physics processes. These cameras possess the ability to acquire multiple two-dimensional images in a single exposure, making them crucial tools for studying ultrafast physics processes. As ICF experiments advance towards higher energies and faster ignition, more stringent requirements are placed on diagnostic equipment, demanding not only a temporal resolution exceeding 30 ps but also high detection sensitivity and a high signal-to-noise ratio under extremely strong radiation interference. This is particularly important in environments where neutron yields may exceed 10... 16 When conducting diagnostics in experiments, diagnostic equipment is required to have radiation hardening capabilities. Research on radiation hardening modifications for the NIF (National Institute for Nuclear Research) indicates that traditional circuits are highly susceptible to damage in strong neutron environments, necessitating radiation hardening improvements to ensure data integrity.

[0004] Traditional MCP (Multi-Chip Photocell) cameras are mature in application, but there is a trade-off between their time resolution and signal strength. Using a 0.5 mm thick MCP in a high-gain mode increases transit time dispersion and gain non-uniformity; while using a 0.2 mm thick MCP in a low-gain mode can shorten transit time dispersion, it results in a poor signal-to-noise ratio (SNR) between the fluorescent screen and the back-end optical imaging equipment. Therefore, the sampling process needs to be decoupled structurally. Furthermore, the sampling method of imaging the electronic image on the fluorescent screen through the optical imaging equipment suffers from significant signal coupling loss, so it is necessary to reduce unnecessary conversion steps to enhance the output SNR.

[0005] In recent years, with the advancement of radiation-hardened semiconductor technology, direct electron detection technology based on hCMOS has become a new research hotspot. This technology eliminates the need for fluorescent screens and optical lenses, placing the sensor chip (without a protective window) in a vacuum to directly receive electron bombardment. It utilizes the principle of electrons depositing energy in silicon to generate a large number of electron-hole pairs, achieving high-sensitivity detection. Although direct detection technology holds great promise, the aforementioned contradictions still need to be addressed. If high time resolution is pursued by operating the microchannel plate in a low-gain state, the front-end signal will be weak. Although electron bombardment gain can compensate, the signal-to-noise ratio remains limited under strong radiation background. Conversely, if high signal strength is pursued by increasing the microchannel plate gain, the time resolution will decrease. Summary of the Invention

[0006] Single-stage microchannel plate (MCP) framing cameras struggle to simultaneously achieve both temporal resolution and detection sensitivity. Increasing the MCP thickness increases the gain coefficient, but it also increases the electron multiplication rate and transit time dispersion within the channel, leading to a decrease in temporal resolution. Conversely, decreasing the MCP thickness shortens transit time dispersion, but this results in insufficient gain, failing to meet sensitivity requirements. Traditional indirect imaging methods utilize optical devices to image electrons on a fluorescent screen, resulting in signal coupling losses and poor signal-to-noise ratio (SNR) of the output signal. This invention provides an X-ray gated imaging method and system based on cascaded microchannel plates and hCMOS, which addresses the aforementioned problems and achieves imaging performance that balances temporal resolution and SNR even in environments with strong radiation interference.

[0007] According to the present invention, an X-ray gated imaging system based on a cascaded microchannel plate and hCMOS comprises, in sequence along the light incident direction:

[0008] A photocathode is used to convert incident X-ray images into photoelectron images;

[0009] The first-stage electron transport microchannel plate is coupled to a photocathode and is used to perform time slicing on the photoelectron image and output electron beam slices carrying time information.

[0010] The second-stage high-gain microchannel plate (MCP) is coupled to the first-stage electron transport microchannel plate and is used to perform electron multiplication on the electron beam slice to output an amplified electron image.

[0011] The hCMOS image sensor, coupled to a second-stage high-gain microchannel plate, is used to directly receive and detect amplified electronic images, convert them into electrical signals, and read them out.

[0012] As a preferred embodiment, the surface of the photocathode is coated with a microstrip transmission line, and the port of the microstrip line has an exponential impedance gradient structure.

[0013] The photocathode selects optical signals based on microstrip transmission lines and traveling wave gating pulses, and establishes a spatiotemporal mapping relationship, that is, transforms the temporal distribution of the input signal into a spatial distribution along the microstrip line.

[0014] As a preferred embodiment, the first-stage electron transmission microchannel plate and the photocathode together constitute an ultrafast electron optical shutter. Its channel wall has no secondary electron emission layer and does not have a gain effect. It completes the time slicing of the electronic image within the window. The first-stage electron transmission microchannel plate works in conjunction with picosecond-level ultrashort high-voltage pulses and is in the electronic image time sampling working state.

[0015] The channel axis of the first-stage electron transport microchannel plate has an oblique angle relative to the normal of the substrate. The chamfer angle is set to satisfy the cutoff condition based on the channel geometry parameters, as shown in the following formula:

[0016]

[0017] In the formula For the channel aperture, This represents the channel length.

[0018] As a preferred embodiment, the second-stage high-gain microchannel plate operates in long-pulse bias mode, and its channel wall has a secondary electron emission layer. When high-energy electrons bombard the channel wall, they will transfer some of their kinetic energy to the electrons inside the material, enabling them to overcome the surface barrier and escape.

[0019] Secondary electron emission coefficient Defined as the average number of secondary electrons excited by each incident electron, it is the incident electron energy. and angle of incidence The function can be described by the empirical formula as follows:

[0020]

[0021] in, This reflects the quantum efficiency of the material in exciting secondary electrons. It represents the ratio of the average range of electrons in a material to the average escape depth of secondary electrons; as electrons penetrate deeper into the channel, the number of collisions increases. n Cumulative increase, total electronic gain within a single channel G This is manifested as a geometric progression in the emission coefficient of a single collision:

[0022]

[0023] Within the unsaturated linear operating region, the macroscopic electronic gain is derived by integrating the above physical processes. G Between the applied voltage It follows a significant power-law pattern:

[0024]

[0025] In the formula Characteristic turn-on voltage, The gain coefficient is determined by the channel aspect ratio and material properties; by adjusting the pulse bias voltage of the second-stage high-gain microchannel plate, the electron multiplication factor can be controlled to ensure that the weak signal is amplified to above the detector response threshold.

[0026] Preferably, the system also includes a timing control module, which is used for:

[0027] A full-width pulse (FWHM) is input into the second-stage high-gain microchannel plate to establish a stable electric field environment for electron avalanche and cover the expected occurrence window of the physical event. Within the effective coverage of this window, an ultra-short traveling wave pulse with FWHM on the order of picoseconds is input into the microstrip cathode to complete the gating of the transient physical image.

[0028] Preferably, a vacuum drift region is provided between the second-stage high-gain microchannel plate and the hCMOS image sensor, and a post-acceleration voltage is applied in the vacuum drift region to enable the amplified electronic image to bombard the hCMOS image sensor with higher energy, thereby generating electron bombardment gain.

[0029] As a preferred option, the hCMOS image sensor is a radiation-hardened sensor with in-pixel storage to ensure data integrity in environments with strong background radiation.

[0030] This invention provides an X-ray gated imaging method based on cascaded microchannel plates and hCMOS, which employs the aforementioned X-ray gated imaging system based on cascaded microchannel plates and hCMOS.

[0031] The beneficial effects of this invention are as follows:

[0032] This invention proposes a high spatiotemporal resolution X-ray gated imaging device based on an electron transport microchannel plate and a high-gain MCP cascade structure, employing hCMOS electron detection. The key to this device lies in separating time gating from charge multiplication; the front stage determines the time gate width, while the rear stage provides signal gain, structurally alleviating the contradiction of high gain and large dispersion in a single-stage MCP. After the MCP outputs the electron beam, hCMOS is used to replace the fluorescent screen and subsequent visible optical imaging equipment for direct electron detection, reducing coupling loss and image quality degradation caused by fluorescence scattering. Combined with the wide-gated envelope electron transport microchannel plate of the high-gain MCP and the narrow-gating timing configuration, the effective signal ratio within the target event window can be increased.

[0033] Compared to traditional single-stage high-gain MCP schemes, this invention utilizes a first-stage electron transmission microchannel board design to reduce time dispersion in the multiplication process, improving the time resolution from the conventional 60-100 ps to within 29 ps. Furthermore, by adding a second-stage high-gain MCP as an amplifier and hCMOS electron bombardment gain, the signal-to-noise ratio of the output signal is improved. Simultaneously, compared to traditional optical readout cameras, the use of hCMOS direct detection eliminates optical coupling losses, enhancing data integrity under high background conditions. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of an X-ray gated imaging system based on a cascaded microchannel plate and hCMOS in one embodiment;

[0035] Figure 2 This is a cross-sectional view of the cascaded MCP in the embodiment;

[0036] Figure 3 This is a flowchart illustrating the signal detection and functional decoupling of the cascaded MCP-hCMOS system in the embodiment.

[0037] Figure 4 The figure shows the characteristic curve of the output electronic pulse FWHM of the electronic transmission microchannel board in the embodiment as a function of the driving pulse width.

[0038] Figure 5 The figure shows the characteristic curves of electron transit time and dispersion in the electron transport microchannel plate in the embodiment as a function of the voltage across its two ends.

[0039] Figure 6 This is a graph showing the gain characteristics of the electron transmission microchannel plate under different voltages in the embodiment.

[0040] Figure 7 This is a graph showing the gain characteristics of the high-gain MCP at different voltages in the embodiment.

[0041] Figure 8 The figure shows the characteristic curve of the total electronic gain of the system as a function of the MCP voltage in the embodiment. Detailed Implementation

[0042] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0043] Example

[0044] like Figure 1 As shown, this embodiment provides an X-ray gated imaging system based on a cascaded microchannel plate and hCMOS, which includes the following components along the light incident direction:

[0045] Photocathode 110 is used to convert the incident X-ray 120 image into a photoelectron image;

[0046] The first-stage electron transmission microchannel plate 130 is coupled to the photocathode 110 and is used to perform time slicing on the photoelectron image and output electron beam slices carrying time information.

[0047] The second-stage high-gain microchannel plate (MCP) 140 is coupled to the first-stage electron transport microchannel plate 130 and is used to perform electron multiplication on the electron beam slice and output an amplified electron image.

[0048] The hCMOS image sensor 150 is coupled to the second-stage high-gain microchannel plate 140 to directly receive and detect the magnified electronic image, convert it into an electrical signal, and read it out.

[0049] The aforementioned integrated design can eliminate the photoelectron free drift space between the traditional discrete cathode and multiplier, effectively suppress the time broadening caused by photoelectron initial velocity dispersion and space charge effect, thereby optimizing the intrinsic time response characteristics of the device.

[0050] Photocathode and Spacetime Mapping Principle

[0051] The ICF experiment requires diagnostic equipment with a large imaging field of view and multi-frame imaging capabilities. Therefore, four parallel, 12 mm wide microstrip transmission lines are deposited on the photocathode surface. Since the physical width of the microstrip line is inversely proportional to its characteristic impedance, the characteristic impedance of the microstrip transmission line is lower than the 50 Ω of the external circuit. Without impedance matching, signal reflection and standing wave oscillations will occur at impedance abrupt change points, disrupting the waveform integrity of the gating pulse and leading to uneven gain distribution within the imaging area. To solve the impedance matching problem, the microstrip line ports feature an exponential impedance gradient structure, achieving a smooth impedance change from the external circuit to the SMA connector to the microstrip line. This reduces the reflection coefficient and ensures that the picosecond-level gating signal can be transmitted through the imaging area without distortion.

[0052] The photocathode 110 uses microstrip transmission lines and traveling wave gating pulses to select optical signals and establish a spatiotemporal mapping relationship, transforming the temporal distribution of the input signal into a spatial distribution along the microstrip line. When the traveling wave pulse propagates along the microstrip line, it excites photoelectrons within the pulse's coverage area, acting like a shutter whose spatial position changes over time. Electrons synchronously within the pulse's spatiotemporal window gain sufficient energy to overcome their work function, enter the MCP channel, and are output from the first-stage electron transport microchannel plate to participate in subsequent imaging. Electrons outside the window are blocked. Since X-rays form multiple discrete images along the wave propagation direction on the microstrip line after passing through the pinhole array, sequentially gating these regions during traveling wave pulse transmission maps the temporal position sequence of the images to a spatial sampling sequence; that is, the spatiotemporal mapping relationship of the images is related to the traveling wave propagation speed. An external timing controller delays the triggering of four microstrip lines, allowing the microstrip lines to image during the imaging intervals of the other three microstrip lines, reducing the device's sampling interval.

[0053] Functional decoupling principle of cascaded microchannel boards

[0054] This embodiment employs a two-stage MCP cascade architecture. Through fine segmentation of the physical structure and differentiated configuration of operating modes, the movement of electrons within the microchannel is divided into two electron dynamics stages: collimated transport and avalanche multiplication. For example... Figure 2 The diagram shows a two-stage cascaded MCP architecture, comprising an input electrode 210, a microchannel 220, and an output electrode 230. The input electrode is typically tightly coupled to the microstrip line of the photocathode and is used to receive and transmit picosecond-level ultrashort gating high-voltage pulses. In the second-stage high-gain MCP, it is used to apply a wide-pulse bias voltage, thereby establishing an axial accelerating and multiplying electric field within the microchannel. The input electrode not only covers the end face but also extends inwards to a certain depth along the microchannel aperture wall. The output electrode of the electron transport microchannel plate serves to establish the electric field, responsible for smoothly and efficiently guiding the gating electron beam to the next stage for multiplication. In the second-stage high-gain MCP, its output electrode is used to establish a strong post-accelerating electric field with the downstream hCMOS sensor. The electron transmission microchannel board has no secondary electron emission layer and is only used as a channel. The second-stage high-gain MCP microchannel has a conductive layer with a high secondary electron emission coefficient. When the primary electrons entering the channel accelerate towards the output end, they collide with the inner wall of the channel to generate secondary electrons, forming a cascade avalanche amplification effect, thereby achieving a high amplitude linear gain for weak electronic signals.

[0055] The first-stage electron transport microchannel plate and photocathode together constitute an ultrafast electron optical shutter. Its channel walls lack a secondary electron emission layer and do not provide gain; their purpose is to perform time-slicing of the electron image within the window. This stage works in conjunction with picosecond-level ultrashort high-voltage pulses, operating in electron image time-sampling mode. The trajectory of electrons within the electron transport microchannel plate is primarily influenced by the axial electric field component, with relatively low radial drift velocity. In this mode, photoelectrons mainly fly along a large-curvature parabola, and electrons colliding with the channel walls during passage are absorbed. Electrons output from the electron transport microchannel plate do not undergo multiple scattering and multiplication processes, thus significantly reducing the uncertainty introduced by these processes. Furthermore, the differences in flight trajectories of electrons with different initial energies and incident angles within the channel are effectively reduced. By eliminating the accumulated uncertainty caused by multiple collisions, this stage of the electron transport microchannel plate can suppress the transit time dispersion of electrons within the channel to a low level, achieving high-fidelity transmission of the incident signal's temporal characteristics.

[0056] The channel axis of the first-stage electron transport microchannel plate has an oblique angle relative to the normal of the substrate. To achieve geometric occlusion of background radiation, the chamfer angle is set to satisfy the cutoff condition based on the channel geometry parameters, as shown in the following formula:

[0057]

[0058] In the formula For the channel aperture, This represents the channel length. The chamfer angle is typically set between 5° and 13°. In electron transport microchannel plate design, this chamfer angle not only effectively blocks background stray light and direct X-ray interference using geometric blocking effects, improving the signal-to-noise ratio of the image, but also ensures that the initial photoelectrons emanating from the photocathode can enter the channel at a better incident angle. For example... Figure 3 As shown, driven by ultrashort traveling wave pulses, this stage of the electron transport microchannel plate can achieve time slicing and gating, truncating continuous input signals into extremely narrow time segments and outputting electron beam slices carrying high-fidelity time information, providing a high-quality input basis for subsequent entry into the second-stage high-gain MCP. Although the electron gain is less than 1 in the gain-free mode, the spatiotemporal information of the photoelectron image is preserved, and the temporal resolution of the device is improved.

[0059] After being time-sliced ​​by the first-stage electron transport microchannel plate, the electron beam then enters the second-stage high-gain microchannel plate. The second-stage high-gain microchannel plate is the core linear amplifier of the system, operating in long-pulse bias mode. Unlike the ballistic transport of the electron transport microchannel plate, electrons undergo multiple collisions within the high-gain MCP channel, triggering an electron avalanche process.

[0060] The channel wall of the second-stage high-gain microchannel plate has a secondary electron emission layer. When high-energy electrons bombard the channel wall, they transfer some of their kinetic energy to electrons inside the material, enabling them to overcome the surface barrier and escape.

[0061] Secondary electron emission coefficient Defined as the average number of secondary electrons excited by each incident electron, it is the incident electron energy. and angle of incidence The function can be described by the empirical formula as follows:

[0062]

[0063] in, This reflects the quantum efficiency of the material in exciting secondary electrons. It represents the ratio of the average range of electrons in a material to the average escape depth of secondary electrons; as electrons penetrate deeper into the channel, the number of collisions increases. n Cumulative increase, total electronic gain within a single channel G This is manifested as a geometric progression in the emission coefficient of a single collision:

[0064]

[0065] Within the unsaturated linear operating region, the macroscopic electronic gain is derived by integrating the above physical processes. G Between the applied voltage It follows a significant power-law pattern:

[0066]

[0067] In the formula Characteristic turn-on voltage, The gain coefficient is determined by the channel aspect ratio and material properties; by adjusting the pulse bias voltage of the second-stage high-gain microchannel plate, the electron multiplication factor can be controlled to ensure that the weak signal is amplified to above the detector response threshold.

[0068] Time-domain gain decoupling mechanism and nested gating strategy

[0069] The advantage of this architecture lies in achieving physical decoupling between time resolution and signal gain. In traditional single-stage MCP framing cameras, a thicker MCP (e.g., 0.5 mm) is required to achieve high gain. However, a thicker MCP leads to an increase in the number of electron collisions and energy dispersion, resulting in a degradation in time resolution and preventing the breakthrough of the 60 ps time resolution limit. Reducing the MCP thickness to 0.2 mm can improve the time resolution to 35 ps, but this results in a decrease in gain and insufficient signal-to-noise ratio. The mutual constraint between time resolution and gain coefficient makes it difficult for single-stage MCP-based framing cameras to achieve high-gain detection while obtaining a time resolution better than 30 ps.

[0070] In contrast, the cascaded MCP architecture achieves parametric decoupling of system performance by distributing time slicing and signal amplification to two independent devices. Image sampling is performed by a first-stage electron transport microchannel board operating in low-gain mode. These electron beams carrying high-fidelity time information enter a second-stage high-gain MCP for high-gain avalanche amplification. The first-stage electron transport microchannel board samples the input signal to obtain a time resolution of 29 ps, and then increases the pulse voltage of the second-stage high-gain MCP to obtain higher electron gain, ensuring effective capture of weak transient signals.

[0071] Based on this decoupling characteristic, the system needs to construct a nested gated timing control module to further optimize the signal-to-noise ratio under complex radiation environments. The timing control module is used for:

[0072] A wide pulse (nanosecond pulse) with a full width at half maximum (FWHM) of approximately 80 ns is input into the second-stage high-gain microchannel plate to establish a stable electric field environment for electron avalanche and cover the expected occurrence window of the physical event. Within the effective coverage of this window, an ultrashort traveling wave pulse (picosecond pulse) with a FWHM of 50 ps is input into the microstrip cathode to gating the transient physical image. This dual-gating mechanism of wide-window envelope and narrow-window can thus function as a highly efficient time-domain filter. Outside the effective signal window, the second-stage high-gain MCP is in a closed or low-gain state, effectively blocking the thermal neutron flux and long-lifetime fluorescence scattering background in fusion experiments. Simultaneously, the gating window of the first-stage electron transport microchannel plate minimizes the integration time of dark current and background noise. Utilizing the synergistic effect of the two-stage gating, the system can significantly improve signal purity and image contrast under strong radiation interference. The complete signal detection and processing flow under this decoupled mechanism is as follows: Figure 3 As shown.

[0073] hCMOS electron bombardment direct detection mechanism

[0074] The system uses a radiation-resistant hCMOS sensor at the end to directly detect electrons, replacing the readout method based on fluorescent screen and CCD, reducing efficiency loss and image quality degradation caused by the conversion process.

[0075] In traditional readout methods, the electron beam is first converted into visible light on a fluorescent screen, and then transmitted to a CCD camera via a lens or fiber optic taper to complete a secondary photoelectric conversion. This link suffers from two main losses: fluorescence emission is approximately isotropic, and due to limitations in the numerical aperture of the optical system, the proportion of photons that can be collected is relatively low; scattering within the fluorescent layer and optical system aberrations broaden the point spread function, limiting spatial resolution and reducing contrast.

[0076] In direct detection mode, amplified electrons are directly incident on the hCMOS photosensitive layer under the accelerating electric field of the high-gain MCP output. Energy is deposited in the silicon to generate electron-hole pairs, which are then collected by the pixel potential well. Compared to the traditional indirect readout method described above, this approach reduces optical coupling losses. Furthermore, because spatial resolution is primarily affected by the electron scattering volume in silicon and the pixel size, rather than by scattering within the phosphor layer and optical system aberrations which broaden the point spread function, combining the radiation-hardened technology and shutter storage structure of hCMOS can improve data integrity under high background conditions.

[0077] A vacuum drift region is set between the second-stage high-gain microchannel plate and the hCMOS image sensor, and a post-acceleration voltage is applied in the vacuum drift region to enable the amplified electronic image to bombard the hCMOS image sensor with higher energy, thereby generating electron bombardment gain.

[0078] This embodiment provides an X-ray gated imaging method based on cascaded microchannel plates and hCMOS, which adopts the aforementioned X-ray gated imaging system based on cascaded microchannel plates and hCMOS.

[0079] Simulation model construction and parameter setting

[0080] This embodiment utilizes the Monte Carlo particle tracking algorithm to construct a three-dimensional electron optics simulation model covering photoelectric conversion, electronic transport, and signal readout. The model's geometry is designed to perfectly match the actual size of the physical entity. For multi-frame imaging requirements, the simulation employs a 16-hole pinhole array, corresponding to independent imaging regions on the microstrip cathode, to simulate the real multi-frame input process.

[0081] The photocathode assembly consists of four parallel microstrip lines, each 12 mm wide and 3 mm apart. To optimize the transmission quality of the ultrashort pulse, an exponential impedance gradient line is integrated between the SMA interface and the microstrip body. This structure helps mitigate signal attenuation caused by impedance mismatch and ensures the temporal integrity of the gating pulse on the cathode surface.

[0082] The core processing unit consists of two cascaded microchannel plates, each 0.5 mm thick, with a microchannel diameter of 12 μm. To ensure effective photoelectron capture and suppress background noise while maintaining temporal characteristics, the first-stage electron transport microchannel plate operates in a gain-free gating mode to time-slice the electron beam; the second-stage MCP operates in a high-gain amplification mode to multiply the electrons. Both microchannel plates have an 8° bevel angle. To balance electron imaging quality and device withstand voltage, the system's backend is coupled to the hCMOS detector via a 1.5 mm vacuum drift region. A 1024 CMOS detector is selected within the hCMOS detector. A 1024-pixel array, an hCMOS chip with a pixel pitch of 25μm.

[0083] During the simulation, a Gaussian gating pulse with a full width at half maximum (FWHM) of 50 ps is applied to the input surface of the electron transport microchannel plate and propagates on the microstrip cathode, directly determining the transient exposure characteristics of the system. This is complemented by an 80 ns wide-gated pulse applied across the high-gain MCP, whose window covers all sampling times and provides a stable charge multiplication environment.

[0084] The post-acceleration effect of the electron beam is achieved by applying a 3000 V DC voltage to the vacuum drift region. This strong field drives electrons to bombard the sensor's photosensitive layer at high speed, exciting the generation of sufficient signal charge. The sensor bias voltage is set to 3.3 V to ensure that the charge collection process conforms to the electrical logic of standard semiconductor devices.

[0085] Based on the constructed simulation model, this section conducts an in-depth quantitative analysis of the electron transit time dispersion and cascaded electron gain that affect the imaging quality of the system. These two indicators determine the system's limiting time resolution and detection sensitivity, respectively.

[0086] Electron transit time dispersion is one of the key physical factors limiting time resolution. This study investigates the response characteristics of an electron transport microchannel plate under different driving pulse widths using the Monte Carlo method, and evaluates the time-domain fidelity of the system.

[0087] Figure 4 The linear curve of the output electronic pulse FWHM evolution with driving pulse width is shown. The data shows a positive correlation between the output signal pulse width and the input gating pulse width, indicating a low level of intrinsic dispersion. Therefore, it can be inferred that the system's time resolution primarily depends on the external pulse driving capability. This high time-domain fidelity ensures the system achieves a dynamic time resolution of 29 ps.

[0088] Besides the driving pulse width, the operating voltage of the MCP is also a key factor affecting the electronic transport characteristics. Figure 5The relationship between electron transit time and time dispersion as a function of the applied voltage of the MCP is shown. The curves in the figure reveal that as the operating voltage increases, the axial acceleration of electrons within the channel increases, leading to a non-linear decrease in transit time. Furthermore, a high field strength effectively suppresses path differences caused by electron initial velocity and emission angle distribution, resulting in a significant reduction in time dispersion. This result demonstrates that using a higher operating voltage in MCP design not only improves gain but also further reduces the time response width, optimizing the system's time resolution.

[0089] This embodiment focuses on verifying the system's ability to detect transient X-ray signals and analyzing the independent gain response and overall detection sensitivity of each MCP stage. Figure 6 and Figure 7 Gain curves of the electron transport microchannel plate (EMB) and the high-gain MCP at different bias voltages are presented. The results show that, due to the absence of a secondary electron emission layer in the EMB, the response modes of the two stages differ significantly. The gain growth curve of the first-stage EMB is relatively flat, indicating that it is mainly in the unsaturated linear transport region. In contrast, the second-stage high-gain MCP exhibits typical exponential avalanche multiplication characteristics, with the gain increasing exponentially with voltage. Around 1400 V, the dynamic range of the MCP is somewhat limited by the electron compensation capability of the conductive layer on the inner wall of the channel for the secondary electron emission layer—a self-saturation phenomenon—and the gain curve gradually deviates from the exponential law, showing a saturation trend. This design allows the system to flexibly adjust the back-end gain according to requirements without changing the gating conditions at the front end, effectively resolving the contradiction between gain and resolution in traditional technologies.

[0090] When the first-stage electron transport microchannel plate is loaded with a voltage of 1500 V, and the voltage of the second-stage high-gain MCP is changed, the overall gain characteristic of the cascaded system is as follows: Figure 8 As shown. This index is defined as the product of the electronic gains of the two microchannel plates, representing the intensity of the electron beam ultimately bombarding the sensor. The total electronic gain variation characteristic curve shows that when the high-gain MCP operates in the 500V to 1400V range, the total system gain still increases exponentially, and the signal charge output by the system is sufficient to exceed the noise floor of the hCMOS sensor. When the first-stage electron transport microchannel plate is loaded with 1500V and the second-stage high-gain MCP is loaded with 1500V, the total gain of the cascaded system is 7503. The pulse voltages applied to the two microchannel plates generally have amplitudes above 2000V, thus the system has a high total gain.

[0091] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. An X-ray gated imaging system based on cascaded microchannel plates and hCMOS, characterized in that: Along the direction of light incidence, the following are included in sequence: A photocathode is used to convert incident X-ray images into photoelectron images; The first-stage electron transport microchannel plate is coupled to a photocathode and is used to perform time slicing on the photoelectron image and output electron beam slices carrying time information. The first-stage electron transmission microchannel plate and the photocathode together constitute an ultrafast electron optical shutter. Its channel wall has no secondary electron emission layer and does not have a gain effect. It completes the time slicing of the electronic image within the window. The first-stage electron transmission microchannel plate works in conjunction with picosecond-level ultrashort high-voltage pulses and is in the electronic image time sampling working state. The channel axis of the first-stage electron transport microchannel plate has an oblique angle relative to the normal of the substrate. The chamfer angle is set to satisfy the cutoff condition based on the channel geometry parameters, as shown in the following formula: ； In the formula For the channel aperture, This refers to the channel length; The second-stage high-gain microchannel plate (MCP) is coupled to the first-stage electron transport microchannel plate and is used to perform electron multiplication on the electron beam slice to output an amplified electron image. The second-stage high-gain microchannel plate operates in long-pulse bias mode. Its channel wall has a secondary electron emission layer. When high-energy electrons bombard the channel wall, they will transfer some of their kinetic energy to the electrons inside the material, enabling them to overcome the surface barrier and escape. Secondary electron emission coefficient Defined as the average number of secondary electrons excited by each incident electron, it is the incident electron energy. and angle of incidence The function can be described by the empirical formula as follows: ； in, This reflects the quantum efficiency of the material in exciting secondary electrons. It represents the ratio of the average range of electrons in the material to the average escape depth of secondary electrons; as electrons penetrate deeper into the channel, the number of collisions n increases cumulatively, and the total electron gain G in a single channel exhibits a geometrical increase in the emission coefficient of a single collision: ； Within the non-saturated linear operating region, by integrating the above physical process, the relationship between the macroscopic electronic gain G and the applied voltage can be derived. It follows a significant power-law pattern: ； In the formula Characteristic turn-on voltage, The gain coefficient is determined by the channel aspect ratio and material properties; by adjusting the pulse bias voltage of the second-stage high-gain microchannel plate, the electron multiplication factor can be controlled to ensure that the weak signal is amplified to above the detector response threshold. The hCMOS image sensor, coupled to a second-stage high-gain microchannel plate, is used to directly receive and detect amplified electronic images, convert them into electrical signals, and read them out.

2. The X-ray gated imaging system based on cascaded microchannel plates and hCMOS according to claim 1, characterized in that: The photocathode is fabricated into a microstrip transmission line structure, and the port of the microstrip line has an exponential impedance gradient structure. The photocathode selects optical signals based on microstrip transmission lines and traveling wave gating pulses, and establishes a spatiotemporal mapping relationship, that is, transforms the temporal distribution of the input signal into a spatial distribution along the microstrip line.

3. The X-ray gating imaging system based on cascaded microchannel plates and hCMOS according to claim 2, characterized in that: The system also includes a timing control module, which is used for: A nanosecond-level full width at half maximum (FWHM) pulse is input into the second-stage high-gain microchannel plate to establish a stable electric field environment for electron avalanche and cover the expected occurrence window of the physical event. Within the effective coverage of this window, a picosecond-level ultrashort traveling wave pulse with FWHM of full width is input into the microstrip cathode to complete the gating of the transient physical image.

4. The X-ray gating imaging system based on cascaded microchannel plates and hCMOS according to claim 3, characterized in that: A vacuum drift region is set between the second-stage high-gain microchannel plate and the hCMOS image sensor, and a post-acceleration voltage is applied in the vacuum drift region to enable the amplified electronic image to bombard the hCMOS image sensor with higher energy, thereby generating electron bombardment gain.

5. The X-ray gating imaging system based on cascaded microchannel plates and hCMOS according to claim 4, characterized in that: hCMOS image sensors are radiation-hardened sensors with in-pixel storage to ensure data integrity in environments with high background radiation.

6. An X-ray gated imaging method based on cascaded microchannel plates and hCMOS, characterized in that: It employs an X-ray gated imaging system based on cascaded microchannel plates and hCMOS as described in any one of claims 1-5.

Images