Lens coupling X-ray imaging detector based on photonic crystal enhanced scintillator

Abstract

The invention discloses a lens coupling X-ray imaging detector based on a photonic crystal enhanced scintillator. The lens coupling X-ray imaging detector comprises a scintillation wafer assembly, an objective lens, an imaging lens and an image sensor, the scintillation wafer assembly comprises a scintillation wafer substrate and a photonic crystal layer located on a light-emitting surface of the scintillation wafer substrate, the photonic crystal layer is a regularly-arranged medium ball array, the medium ball array can provide reciprocal lattice vector compensation for a waveguide mode in the scintillation wafer substrate through a diffraction effect, the waveguide mode is coupled into a radiation mode, and the radiation mode is used for emitting light to the scintillation wafer substrate. Total internal reflection is destroyed; the objective lens is arranged on one side of the light emitting surface and is used for collecting the signal light enhanced by the photonic crystal layer; the imaging lens is used for receiving and focusing the signal light; the image sensor is arranged at the focal plane of the imaging lens and used for converting the signal light into an electric signal. According to the invention, not only is the light collection efficiency improved, but also the emergent light distribution is improved, the comprehensive imaging performance of low dosage, high sensitivity and high resolution is realized, and compared with the prior art, the system has remarkable advantages.

Description

Technical Field

[0001] This invention relates to the field of X-ray imaging detection technology, and more specifically to a lens-coupled X-ray imaging detector based on a photonic crystal enhanced scintillator. Background Technology

[0002] In the fields of X-ray microscopy and non-destructive testing, indirect conversion detectors are widely used. These detectors typically first expose X-rays to a scintillator, which converts the X-rays into visible light. The visible light is then coupled to an image sensor (such as a CCD or CMOS) via an optical lens system for imaging. Optical lens coupling is particularly favored due to its ability to achieve high spatial resolution and flexible system configuration. However, existing lens-coupled X-ray detectors still have some limitations.

[0003] High-performance scintillators (such as inorganic scintillators) typically have a high refractive index. According to optical principles, when light enters air with a low refractive index from a scintillator with a high refractive index, if the angle of incidence is greater than the critical angle, the light will be trapped inside the scintillator and unable to escape. This significantly reduces the system's light collection efficiency, thus affecting the detector's sensitivity. To improve sensitivity, the thickness of the scintillator is usually increased to allow more X-rays to be absorbed. However, thick crystals cause severe lateral light diffusion inside, reducing image resolution. Conversely, making the crystal very thin can improve resolution, but it absorbs fewer X-rays, resulting in a weaker signal, especially in low-dose imaging. This creates a contradiction between achieving high resolution and high sensitivity simultaneously.

[0004] This shows that existing lens-coupled X-ray imaging detectors still have significant technical bottlenecks in terms of light extraction efficiency, resolution, and sensitivity balance, and further improvements are needed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a lens-coupled X-ray imaging detector based on a photonic crystal enhanced scintillator that can improve light extraction efficiency and improve imaging sensitivity while ensuring high resolution.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A lens-coupled X-ray imaging detector based on a photonic crystal-enhanced scintillator includes a scintillator assembly, an objective lens, an imaging lens, and an image sensor. The scintillator assembly includes a scintillator substrate and a photonic crystal layer located on the light-emitting surface of the scintillator substrate. The photonic crystal layer is a regularly arranged array of dielectric microspheres. The dielectric microsphere array can provide reciprocal lattice compensation for waveguide modes in the scintillator substrate through diffraction, coupling the waveguide modes into radiation modes and destroying total internal reflection. The objective lens is disposed on one side of the light-emitting surface and is used to collect the signal light enhanced by the photonic crystal layer and convert it into parallel light. The imaging lens is used to receive and focus the parallel light. The image sensor is disposed at the focal plane of the imaging lens and is used to convert the signal light into an electrical signal.

[0008] In this invention, the diffraction effect of the photonic crystal layer provides reciprocal lattice vector compensation for the waveguide modes in the scintillator substrate, coupling the waveguide modes that were originally trapped inside the scintillator due to total internal reflection into radiation modes, thus solving the problem of low light extraction efficiency in thick scintillators. The regularly arranged array of dielectric microspheres forms a periodic structure that generates reciprocal lattice vectors, achieving efficient momentum compensation. The objective lens, imaging lens, and image sensor constitute a complete infinity-corrected imaging optical path, transmitting and converting the enhanced signal light into an electrical signal. Therefore, without increasing the thickness of the scintillator (and thus without sacrificing resolution), the light extraction efficiency is significantly improved, achieving a balance between sensitivity and resolution.

[0009] As an optimization, the scintillator substrate is an inorganic scintillator with a refractive index of 1.85-2.5.

[0010] As an optimization, the dielectric microsphere array is a single-layer hexagonal stack, and the diameter of the dielectric microspheres is 400-600 nm. The dielectric microspheres are any one of polystyrene microspheres, silica microspheres, or polymethyl methacrylate microspheres. Single-layer hexagonal stacking is the most compact and regular arrangement, capable of forming a well-defined photonic crystal periodic structure and generating precise reciprocal lattice vectors for momentum compensation.

[0011] As an optimization, the detector also includes a reflective element disposed between the objective lens and the imaging lens to deflect the signal light path to avoid the direct path of X-rays. By deflecting the signal light path through the reflective element, the X-rays are absorbed along their original straight-line propagation direction, completely avoiding direct damage to the downstream image sensor from X-rays. This protects the sensor and reduces background noise caused by direct X-ray exposure. Moreover, the reflective element's placement in the optical path between the objective lens and the imaging lens does not affect image quality, achieving a balance between radiation protection and high-fidelity imaging.

[0012] As an optimization, the reflective element includes a reflector placed at a 45° angle. The 45° angle can bend the optical path by 90°, making the signal light imaging branch perpendicular to the X-ray direct path, avoiding radiation damage to the sensor caused by direct X-ray exposure, and maximizing the use of space.

[0013] As an optimization, the scintillation wafer assembly further includes a reflective film located on the X-ray incident surface of the scintillation wafer substrate. The reflective film can reflect the scintillation light propagating in the direction of the incident surface back to the exit surface, realizing the secondary utilization of light energy.

[0014] As an optimization, the reflective film is an aluminum film with a thickness of 25-500 nm.

[0015] As an optimization, the photonic crystal layer is prepared using a gas-liquid interface self-assembly process. This self-assembly process offers significant advantages such as low cost, large-area fabrication capability, and suitability for mass production. Through gas-liquid interface self-assembly, a large-area, low-defect hexagonal close-packed monolayer structure can be formed on the scintillator surface, ensuring the optical quality of the photonic crystal layer.

[0016] As an optimization, the detector also includes a housing with an entrance window mounted on it. The position of the entrance window corresponds to the X-ray incident surface of the scintillation crystal assembly. A positioning part is provided on the inner wall of the housing for positioning and fixing the scintillation crystal assembly, the objective lens, the imaging lens, and the image sensor. The housing integrates all optical components into one unit, and the positioning part precisely fixes the scintillation crystal assembly, objective lens, imaging lens, and image sensor, ensuring the optical axis consistency of each component and avoiding image quality degradation due to assembly errors. The entrance window is installed on the X-ray incident side, directly opposite the scintillation crystal assembly, allowing X-rays to enter the detector while shielding external visible light and reducing stray light interference.

[0017] As an optimization, the outer shell is made of tungsten alloy, and the entrance window is made of carbon fiber plate. Tungsten alloy has high density and good absorption capacity for X-rays, while carbon fiber plate has high X-ray transmittance, which can ensure effective X-ray incidence, provide structural support, and shield external visible light.

[0018] Compared with existing technologies, this invention improves light collection efficiency and output light distribution through structural design and optical coupling optimization, achieving comprehensive imaging performance with low dose, high sensitivity and high resolution, which has significant advantages over existing technologies. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall optical path structure of the present invention;

[0020] Figure 2 This is a schematic diagram of the cross-sectional structure of the scintillation wafer assembly in this invention;

[0021] Figure 3 This is a schematic diagram of the physical mechanism of photonic crystal momentum compensation and light extraction in this invention;

[0022] Figure 4 This is a bar chart comparing the imaging signal-to-noise ratio (SNR) of the present invention with that of a conventional GAGG:Ce detector;

[0023] Figure 5 This is a comparison curve of the modulation transfer function (MTF) of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] like Figure 1 and Figure 2 As shown, the lens-coupled X-ray imaging detector based on a photonic crystal enhanced scintillator in this specific embodiment includes a scintillator wafer assembly, an objective lens 1, an imaging lens 2, and an image sensor 3. The scintillator wafer assembly includes a scintillator wafer substrate 4 and a photonic crystal layer 5 located on the light-emitting surface of the scintillator wafer substrate 4. The photonic crystal layer 5 is a regularly arranged array of dielectric microspheres. The dielectric microsphere array can provide reciprocal lattice compensation for the waveguide modes in the scintillator wafer substrate 4 through diffraction, coupling the waveguide modes into radiation modes and destroying total internal reflection. The objective lens 1 is disposed on one side of the light-emitting surface and is used to collect the signal light enhanced by the photonic crystal layer 5 and convert it into parallel light. The imaging lens 2 is used to receive and focus the parallel light. The image sensor 3 is disposed at the focal plane of the imaging lens 2 and is used to convert the signal light into an electrical signal.

[0026] The scintillator substrate 4 is an inorganic scintillator with a refractive index of 1.85-2.5.

[0027] The dielectric microsphere array is a single-layer hexagonal stack, the diameter of the dielectric microsphere is 400-600 nm, and the dielectric microsphere is any one of polystyrene microsphere, silica microsphere or polymethyl methacrylate (PMMA) microsphere.

[0028] The detector also includes a reflective element 6, which is disposed between the objective lens 1 and the imaging lens 2 to deflect the signal light path to avoid the direct path of X-rays.

[0029] The reflective element 6 includes a reflector, which is placed at a 45° angle.

[0030] The scintillation wafer assembly also includes a reflective film 7 located on the X-ray incident surface of the scintillation wafer substrate 4.

[0031] The reflective film 7 is an aluminum film with a thickness of 25-500nm.

[0032] The photonic crystal layer 5 is prepared by a gas-liquid interface self-assembly process.

[0033] The detector also includes a housing 8, on which an entrance window 9 is mounted. The position of the entrance window 9 corresponds to the X-ray incident surface in the scintillation crystal assembly. A positioning part is provided on the inner wall of the housing 8 for positioning and fixing the scintillation crystal assembly, the objective lens 1, the imaging lens 2, and the image sensor 3.

[0034] The outer shell 8 is made of tungsten alloy, and the entrance window 9 is made of carbon fiber plate.

[0035] Regular arrangement refers to the periodic and orderly arrangement of dielectric spheres in a two-dimensional plane, including but not limited to hexagonal close packing and tetragonal arrangement. Periodic structures can generate definite reciprocal lattice vectors, providing momentum compensation for waveguide modes. Among these, hexagonal close packing is the preferred arrangement due to its ease of self-assembly and fewer defects.

[0036] The scintillation crystal substrate uses a high-refractive-index inorganic scintillator, specifically a GAGG:Ce single crystal with a refractive index of 1.9. The substrate thickness can be selected within the range of 100-300 μm to balance X-ray absorption efficiency and resolution.

[0037] The reflective film is made by vacuum evaporation to deposit an aluminum film on the incident surface of the substrate, with a specific thickness of 100 nm and a reflectivity greater than 98%.

[0038] The photonic crystal layer uses a gas-liquid interface self-assembly method to prepare a single-layer hexagonal close-packed polystyrene microsphere array on the light-emitting surface of the substrate. The microsphere diameter is specifically selected as 500 nm. It can provide reciprocal lattice vector compensation for waveguide modes through diffraction effect, couple waveguide modes into radiation modes, and destroy total internal reflection.

[0039] The objective lens is an infinity-corrected plan apochromatic objective lens, operating in the scintillator emission band (400-750nm). The numerical aperture can be 0.2-0.5, and the magnification can be 2x, 5x, or 10x. In this embodiment, the numerical aperture is 0.28, and the magnification is 10x. The objective lens collects and converts the signal light emitted from the scintillator crystal assembly into parallel light.

[0040] The reflective element is a mirror placed at a 45° angle between the objective lens and the imaging lens, which deflects the parallel light path by 90° to avoid the direct path of X-rays while maximizing space utilization. The mirror's operating wavelength is matched to the objective lens, and its surface is coated with a protective silver or aluminum film to improve reflectivity.

[0041] The imaging lens is an apochromatic tube with a focal length of 200mm. It is matched with the objective lens to form an infinity-corrected imaging system that focuses parallel light onto the photosensitive surface of the image sensor.

[0042] The image sensor uses a scientific-grade CMOS or CCD camera, which has high quantum efficiency and low readout noise, and converts light signals into digital images.

[0043] The outer shell is made of tungsten alloy with a wall thickness of 3mm, providing excellent X-ray absorption and shielding residual X-rays. The entrance window is made of a 500μm thick carbon fiber plate, fixed to the outer shell.

[0044] The specific fabrication steps of the photonic crystal layer include:

[0045] Substrate preparation: Select double-sided polished GAGG:Ce single crystal wafer with a thickness of 150μm;

[0046] Backside coating: A high-reflectivity aluminum film is deposited on the X-ray incident surface (backside) of the wafer by vacuum evaporation. The aluminum film with a reflectivity of over 98% is used as an anti-reflection film. This reflective film can reflect the photons transmitted backward back to the light surface, realizing the secondary utilization of light energy.

[0047] Photonic crystal self-assembly: A photonic crystal layer is prepared on the light-emitting surface (front side) of the wafer using a gas-liquid interface self-assembly method. In the substrate treatment, plasma treatment is used to make the substrate superhydrophilic. In this embodiment, a contact angle of <5° is selected to ensure the firm adhesion of the colloidal monolayer. Monodisperse polystyrene nanospheres are used as building blocks in the liquid surface self-assembly process. The prepared polystyrene suspension is dropped onto a tilted clean silicon wafer, which is partially immersed in a deionized water subphase (18.2 MΩ·cm). After a certain amount of suspension is added, the interface is saturated, and a trace amount of surfactant solution (0.1 wt% sodium dodecyl sulfate solution, SDS) is introduced into the water subphase. The resulting surface tension gradient induces a significant lateral capillary force, compressing the loosely packed suspended islands into centimeter-scale hexagonal close-packed (HCP) monolayers. Then, deionized water is slowly pumped out using a peristaltic pump to lower the liquid level and transfer the assembled monolayer to the scintillator substrate, and it is dried at 45°C to remove residual moisture. Finally, a large-area, complete, and ordered photonic crystal monolayer film is formed.

[0048] like Figure 3As shown, the photonic crystal enhancement principle is as follows: A hexagonal stacked monolayer nanophotonic interface, formed by the self-assembly of polystyrene microspheres, is designed on the surface of the scintillator. This periodic dielectric fluctuation is designed to provide the necessary momentum compensation, coupling the originally trapped guided mode into a radiating mode through the diffraction effect. When the in-plane wave vector component of the photon... When equation (1) is satisfied, energy is prohibited from entering the air side.

[0049] ( Equation (1);

[0050] in, As the vacuum wave vector, this constraint only produces a rapidly decaying evanescent field of the form (2), and the light energy is locked into the waveguide mode in the high refractive index substrate.

[0051] Equation (2);

[0052] In stark contrast, a monolayer structure (D=500nm, nPhC≈1.59) composed of self-assembled polystyrene microspheres acts as a diffraction grating, fundamentally altering this boundary condition. The periodicity of the lattice introduces reciprocal lattice vectors. This compensates for the momentum mismatch between the trapped mode and the vacuum light cone. The extraction mechanism follows the basic Bragg conservation law (3):

[0053] Equation (3);

[0054] Therefore, the trapped guiding mode, which originally had a large momentum, was folded back into the radiation cone. The light is coupled into the microsphere and scattered to form a propagable radiation wavefront. This process effectively tunnels light energy from the guided state into free space, resulting in increased light output, i.e., improved brightness, from a macroscopic perspective.

[0055] Working principle: X-rays first pass through the entrance window and irradiate the scintillation crystal assembly. The scintillation crystal assembly converts the X-rays into visible light, which is then enhanced by the photonic crystal layer and emitted as signal light carrying sample information. The signal light is collected by the objective lens, emitted as parallel light, deflected by the reflective element, and focused by the imaging lens onto the photosensitive surface of the image sensor, where it is converted into an electrical signal output. The residual X-rays propagate along the original straight line, are absorbed by the outer casing, and do not enter the imaging branch.

[0056] The detector was fabricated according to the above structure, and tested under X-ray source excitation (80kV, 24W).

[0057] (1) The scintillation crystal substrate is GAGG:Ce (150μm thick), the reflective film is aluminum film (100nm thick), the photonic crystal layer is a hexagonal close-packed monolayer of polystyrene microspheres with a diameter of 500nm; the objective lens is a 10× / 0.28 plan apochromatic objective lens, the reflector is a silver mirror placed at 45°, the imaging lens is an apochromatic tube lens with a focal length of 200mm, and the image sensor is a scientific-grade CMOS camera;

[0058] Optical Output Comparison: Compared to a GAGG:Ce wafer of the same thickness without photonic crystal, the center wavelength optical output of the photonic crystal scintillator wafer of this invention increases by 5.0 times, the overall optical output increases by 4.7 times, and the signal-to-noise ratio of the image acquired by the detector increases from 25.35dB to 38.31dB. Figure 4 As shown.

[0059] Spatial resolution: The modulation transfer function (MTF) curve is measured by photographing a standard resolution test chart, such as... Figure 5 As shown, when MTF=0.1, the corresponding spatial resolution is 22.1 lp / mm, indicating that the present invention maintains high resolution and high imaging clarity while improving sensitivity.

[0060] (2) The scintillation crystal substrate is GAGG:Ce (100μm thick), and the photonic crystal layer is a hexagonal close-packed monolayer of polystyrene microspheres with a diameter of 500nm.

[0061] Optical output comparison: Compared with a GAGG:Ce wafer of the same thickness (100μm) without photonic crystals, the center wavelength optical output of the photonic crystal scintillator wafer increased by 4.95 times, and the overall optical output increased by 4.5 times. The signal-to-noise ratio of the image acquired by the detector increased from 23.42dB to 35.79dB.

[0062] (3) The scintillation crystal substrate is GAGG:Ce (150μm thick), and the photonic crystal layer is a hexagonal close-packed monolayer of polystyrene microspheres with a diameter of 400nm.

[0063] Optical output comparison: Compared with a GAGG:Ce wafer of the same thickness (150μm) without photonic crystals, the center wavelength optical output of the photonic crystal scintillator wafer increased by 2.5 times, and the overall optical output increased by 1.9 times. The detector signal-to-noise ratio increased from 25.35dB to 28.86dB.

[0064] (4) The scintillation crystal substrate is GAGG:Ce (150μm thick), and the photonic crystal layer is a hexagonal close-packed monolayer of polystyrene microspheres with a diameter of 600nm.

[0065] Optical output comparison: Compared with a GAGG:Ce wafer of the same thickness (150μm) without photonic crystals, the center wavelength optical output of the photonic crystal scintillator wafer increased by 4.0 times, and the overall optical output increased by 3.47 times. The signal-to-noise ratio of the image acquired by the detector increased from 25.35dB to 35.44dB.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A lens-coupled X-ray imaging detector based on a photonic crystal scintillator, characterized in that: It includes a scintillation wafer assembly, an objective lens, an imaging lens, and an image sensor; the scintillation wafer assembly includes a scintillation wafer substrate and a photonic crystal layer located on the light-emitting surface of the scintillation wafer substrate. The photonic crystal layer is a regularly arranged array of dielectric microspheres. The array of dielectric microspheres can provide reciprocal lattice compensation for the waveguide modes in the scintillation wafer substrate through diffraction effects, coupling the waveguide modes into radiation modes and destroying total internal reflection. The objective lens is positioned on one side of the light-emitting surface and is used to collect the signal light enhanced by the photonic crystal layer and convert it into parallel light; the imaging lens is used to receive and focus the parallel light; the image sensor is positioned at the focal plane of the imaging lens and is used to convert the signal light into an electrical signal.

2. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 1, characterized in that: The scintillator substrate is an inorganic scintillator with a refractive index of 1.85-2.

5.

3. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 1, characterized in that: The dielectric microsphere array is a single-layer hexagonal stack, the diameter of the dielectric microsphere is 400-600 nm, and the dielectric microsphere is any one of polystyrene microsphere, silica microsphere or polymethyl methacrylate microsphere.

4. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 1, characterized in that: The detector also includes a reflective element disposed between the objective lens and the imaging lens, which is used to deflect the signal light path to avoid the direct path of X-rays.

5. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 4, characterized in that: The reflective element includes a reflector, which is placed at a 45° angle.

6. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 1, characterized in that: The scintillation wafer assembly also includes a reflective film located on the X-ray incident surface of the scintillation wafer substrate.

7. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 6, characterized in that: The reflective film is an aluminum film with a thickness of 25-500nm.

8. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 1, characterized in that: The photonic crystal layer is prepared by a gas-liquid interface self-assembly process.

9. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 1, characterized in that: The detector also includes a housing with an entrance window installed on it. The position of the entrance window corresponds to the X-ray incident surface in the scintillation crystal assembly. The inner wall of the housing is provided with a positioning part for positioning and fixing the scintillation crystal assembly, the objective lens, the imaging lens, and the image sensor.

10. The lens-coupled X-ray imaging detector based on a photonic crystal scintillator according to claim 9, characterized in that: The outer shell is made of tungsten alloy, and the entrance window is made of carbon fiber plate.

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