X-ray refractive focusing and detection system

Abstract

The application discloses an X-ray refraction focusing and detecting system, which collects and detects X-ray signals through a refraction focusing mode and comprises an array type X-ray refraction lens, an array type diaphragm and an X-ray detector. The array type X-ray refraction lens is used for focusing high-gain X-ray photons in parallel incidence; the array type diaphragm is used for limiting the size of a focal spot, improving the angular resolution and filtering out spatial noise particles irradiated in a non-array type diaphragm square hole area; and the X-ray detector converts the focused X-ray photons into electric signals and reads out information such as the energy, time and position of the photons. The application realizes the detection of light-weight and short-focus X-ray pulsar signals and can be modularly spliced to form a large detection area.

Description

Technical fields:

[0001] This invention belongs to the field of X-ray detection and application technology, and relates to an X-ray refraction focusing and detection system. Background technology:

[0002] X-ray refraction focusing and detection systems are novel systems that utilize the principle of refraction to focus and detect X-ray photons. When X-rays penetrate materials and are refracted, material absorption and attenuation are significant factors; the lower the energy, the greater the attenuation. X-ray pulsar radiation exhibits a power-law spectrum distribution and has weak radiative flux. To detect low-energy X-ray photons, a large X-ray focusing and detection area is required, which can be formed by splicing multiple array-type lens units. In 2019, M. Wujun et al. from the Royal Institute of Technology in Sweden proposed the concept of constructing a hard X-ray telescope using arrayed refraction lenses. Based on the focusing performance of a single composite refraction lens for 13.5 keV X-rays, they designed an array-type telescope structure. This invention targets the detection of soft X-ray signals in the low-energy range. It utilizes beryllium, a low-attenuation X-ray material, instead of photoresist materials unsuitable for space environments, and silicon, a material widely used in synchrotron radiation sources and exhibiting greater X-ray attenuation, to design a low-attenuation refraction lens structure and develop corresponding fabrication techniques. This is one of the main innovative points that distinguishes this invention from related international work; there is currently no literature on array-type X-ray refraction lenses in China.

[0003] The concept of X-ray compound refractive lenses was proposed in 1996, and various materials and corresponding fabrication techniques have since been developed. However, apart from materials compatible with semiconductor processes, array-type compound refractive lenses have not yet been fabricated more efficiently on other materials (such as beryllium). The array-type X-ray lens involved in this invention can be mass-produced from beryllium materials using hot pressing technology. The use of beryllium materials and the development of lens fabrication methods are a comprehensive manifestation of the lightweight and low X-ray attenuation characteristics of X-ray telescope focusing units.

[0004] X-ray refraction focusing and detection systems for pulsar navigation require high angular resolution, such as 1 arcminute or even higher. This invention provides technical support for angular resolution telescopes. However, for the soft X-ray detection band (0.5-10 keV) required for pulsar navigation, X-ray refraction focusing and detection systems cannot focus all energy simultaneously at a single point. In fact, broadband detection would result in a large focal spot on the focal plane, reducing angular resolution if most photons of high energy are detected. Therefore, a balanced approach is taken between photon detection efficiency and angular resolution, with an aperture structure placed on the focal plane at the optimal energy design value. Corresponding to the characteristics of array focusing, this aperture is also array-type. Furthermore, to prevent X-rays from entering from non-lens regions on the lens array plane, X-ray blocking layers need to be deposited in these regions. This design differs from the concept proposed by M. Wujun et al., effectively improving the angular resolution of the telescope and making the system more lightweight.

[0005] Currently, X-ray refraction focusing and detection systems are mainly used for focusing and microscopic imaging of X-ray bands from synchrotron radiation sources. The beam size of synchrotron radiation dictates that the lens size must be within 1 mm. In recent years, foreign countries have conducted research on using refraction lenses for the detection of hard X-ray photons, proposing the concept of constructing an array of X-ray refraction lenses using photoresist and combining them with high-energy detectors to form an X-ray telescope structure. Compared with the existing X-ray telescope satellite projects NuSTAR and ASTRO-H, which are based on reflection-based X-ray focusing and detection systems, they have significantly reduced weight, greatly shortened focal length, and significantly reduced the payload requirements for X-ray space detection. However, due to the inherent properties of photoresist materials, they are difficult to use in the actual space environment for extended periods. Currently, this technology is still in the conceptual stage abroad, and there are no reports of its application in space. Domestically, it is in the technology tracking stage.

[0006] Research on X-ray refractive lenses has been conducted in China for over a decade, primarily using materials such as aluminum, silicon, PMMA, and photoresist. The corresponding processing techniques include laser drilling, deep reactive ion etching, extreme ultraviolet (EUV) or X-ray lithography. These lenses are mainly used for focusing hard X-ray photons on synchrotron radiation sources. The concept of using refractive lenses for detecting soft X-ray signals from pulsars has not yet been proposed or implemented in China. Summary of the Invention:

[0007] The purpose of this invention is to provide an X-ray refraction focusing and detection system that can achieve lightweight design, short focal length, and modular splicing to form a large detection area.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] An X-ray refraction focusing and detection system is characterized by comprising an array-type X-ray refraction lens, an array-type aperture, and an X-ray detector; the array-type X-ray refraction lens is used to focus parallel X-rays with high gain; the array-type aperture is used to limit the focal spot size, improve angular resolution, and filter out spatial noise particles irradiating the non-aperture region of the array-type aperture; the X-ray detector converts the focused X-ray photons into electrical signals and reads out the energy, time, and position information of the photons.

[0010] The array-type X-ray refraction lens is made of a light element material, with Be being chosen as the material. The array-type X-ray refraction lens consists of a large number of tiny parabolic lenses, each of which can focus parallel-incident X-rays.

[0011] An array-type aperture is placed between the array-type refractive lens and the X-ray detector to limit the focal spot size and improve angular resolution. The array-type aperture is made by etching, coating and bonding silicon wafers. The number of aperture holes is the same as the number of refractive lenses, and the optical axes of the two are accurately aligned during installation.

[0012] The rear end of the array aperture is close to the X-ray detector, and the light spot formed after passing through the array aperture can be detected by the X-ray detector; the X-ray detector is a silicon-based detector with high time resolution, high energy resolution and position information readout.

[0013] After passing through an array of refractive lenses, the X-ray photons emitted by the pulsar are focused, then pass through an array of apertures and converge on the focal plane of the X-ray detector, where they are captured by the detector.

[0014] The distance between the array-type refractive lens and the X-ray detector is set to 25cm to ensure high transmittance of 2keV X-ray photons. For higher-energy X-ray photons, the focal length of the array-type refractive lens is greater than 25cm; for lower-energy X-ray photons, the focal length of the array-type refractive lens is less than 25cm. By adjusting the aperture size of the array-type aperture, the highest efficiency detection of soft X-ray photons emitted by pulsars can be achieved across the entire energy range.

[0015] Compared with the prior art, the advantages and effects of the present invention are as follows:

[0016] 1. This invention is a lightweight, short-focal-length, modularly assembled X-ray refraction focusing and detection system. Its technological innovation lies in:

[0017] (1) Beryllium, a light element material, is used to make an X-ray refraction lens, which is more than half the weight of the existing X-ray detection system.

[0018] (2) A design and optimization method for a low-attenuation array-type X-ray composite refraction focusing system is proposed, which can achieve high-efficiency detection of soft X-ray photons.

[0019] (3) The array-type composite refractive lens is mass-produced using hot pressing forming technology, and an array-type aperture and silicon-based X-ray detector are configured to achieve modular splicing.

[0020] (4) The X-ray refraction lens adopts an array micro structure, and the focal length can be controlled within 25cm. The short focal length is conducive to the miniaturization of the X-ray refraction focusing and detection system.

[0021] 2. Lightweight design is an essential feature for X-ray telescopes designed for pulsar navigation. Compared to the traditional Wolter-I type X-ray telescope based on a multi-layered nested structure, the array-type compound refractive lens significantly reduces the weight and volume of the X-ray telescope by using lightweight materials and a short focal length, while ensuring the detection area.

[0022] 3. One of the development directions for X-ray refraction focusing and detection system payloads in space engineering applications is to simplify the manufacturing technology and reduce costs. Traditional X-ray telescopes used for pulsar navigation, namely the Wolter-I type focusing system, require a large number of high-precision nested reflective mirrors. The requirements for mirror roughness and surface accuracy are extremely high, resulting in high technical complexity, manufacturing difficulty, and high cost. Composite refraction lens focusing systems utilize relatively mature micro-nano fabrication technology to significantly reduce manufacturing costs by reducing the difficulty of implementation.

[0023] 4. Currently, X-ray pulsar navigation technology is still in the development stage, and there are no practical and mature pulsar navigation terminals at home and abroad. The X-ray refraction focusing and detection system involved in this invention is suitable for pulsar navigation engineering applications. It has the advantages of small size, light weight, and short focal length, and can effectively suppress background and reduce power consumption. Attached image description:

[0024] Figure 1 This is a structural diagram of the X-ray refraction focusing and detection system of the present invention;

[0025] Figure 2 This is a schematic diagram of the cross-section of an array-type aperture.

[0026] Figure 3 This is a schematic diagram of the principle of refractive X-ray focusing;

[0027] Figure 4 This is a schematic diagram illustrating the collimation-type X-ray focusing principle.

[0028] Figure 5 This is a schematic diagram illustrating the working principle of the Wolter-I type X-ray focusing mirror. Detailed implementation method:

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. For ease of understanding, the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0030] This invention relates to an X-ray refraction focusing and detection system, comprising an array-type X-ray refraction lens, an array-type aperture, and an X-ray detector; the array-type X-ray refraction lens is used to focus parallel X-rays with high gain; the array-type aperture is used to limit the focal spot size, improve angular resolution, and filter out spatial noise particles irradiating the non-aperture region of the array-type aperture; the X-ray detector converts the focused X-ray photons into electrical signals and reads out information such as the photon's energy, time, and position.

[0031] Array-type X-ray refraction lenses are made of lightweight materials, which have a lower attenuation coefficient for soft X-rays, making them ideal for X-ray refraction lenses. Be is typically chosen as the material. An array-type X-ray refraction lens consists of numerous tiny parabolic lenses, each capable of focusing parallel-incident X-rays.

[0032] An array-type aperture is placed between the array-type refractive lens and the X-ray detector to limit the focal spot size and improve angular resolution. The array-type aperture is etched from a single thin silicon wafer, with the same number of aperture holes as the refractive lens, and the optical axes of the two are precisely aligned during installation.

[0033] The rear end of the array-type aperture is close to the X-ray detector, and the light spot formed after passing through the array-type aperture can be detected by the X-ray detector. The X-ray detector is a silicon-based detector with high time resolution, high energy resolution, and position information readout.

[0034] X-ray photons emitted by pulsars are focused after passing through an array of refractive lenses, then pass through an array of apertures and converge on the focal plane of the X-ray detector, where they are captured by the detector.

[0035] To achieve the highest detection efficiency of the X-ray refraction focusing and detection system for X-ray pulsars in the soft X-ray energy range, while ensuring a small spatial volume, the distance between the array-type refraction lens and the X-ray detector is set to 25 cm to guarantee high transmittance for 2 keV photons. For higher-energy X-ray photons, the focal length of the array-type refraction lens is greater than 25 cm; for lower-energy X-ray photons, the focal length is less than 25 cm. The highest efficiency detection of soft X-ray photons emitted by pulsars can be achieved by adjusting the aperture size of the array-type aperture. This invention's X-ray refraction focusing and detection system consists of an array-type X-ray refraction lens, an array-type aperture, and an X-ray detector.

[0036] Arrayed X-ray refractive lenses (e.g., each with a diameter of 100 micrometers) enable the focusing of parallel-incident X-ray photons;

[0037] Arrayed apertures are used to limit the focal spot size, improve angular resolution, and shield spatial noise particles in the non-aperture region of the arrayed aperture.

[0038] An X-ray detector converts focused X-ray photons into electrical signals, and reads out information such as the photon's energy, time, and position.

[0039] The working principle of an X-ray refraction focusing and detection system: An array-type refraction lens is used to collect X-ray photons emitted by pulsars. This lens is optimized for 2keV X-rays. 2keV X-ray photons are focused by the array-type refraction lens, pass through the micro-aperture of the array aperture, and converge at the focal point (25cm behind the lens). The array aperture is placed at the focal point, and the X-ray detector is placed close to it. X-ray photons can be captured by the X-ray detector through the micro-aperture of the array aperture. For higher-energy X-rays, the focusing effect of the lens is not ideal, resulting in a longer focal length and a focal spot at the 25cm focal position. The higher the energy, the larger the focal spot. This is where the array aperture becomes effective. Since angular resolution can be expressed by dividing the focal spot size by the focal length, controlling the aperture of the array aperture limits the focal spot size, thus controlling the angular resolution. If the aperture is 30 micrometers, the angular resolution is 20 arcseconds. Similarly, for X-rays with energies lower than 2keV, the focal length after passing through the lens is shorter than 25cm, so a focal spot will also be formed at 25cm. High resolution can also be achieved by controlling the aperture size of the array aperture. At the same time, the array aperture can also prevent non-parallel X-ray photons from passing through the non-lens positions on the array lens and entering the X-ray detector, thereby suppressing background noise and improving the detection signal-to-noise ratio.

[0040] The following is a comparative analysis of the existing collimating type and Wolter-I type soft X-ray telescopes and the X-ray refraction focusing and detection system involved in this invention.

[0041] 1. Comparison of this invention with the collimation type

[0042] In terms of physical structure, both refractive lenses and collimating systems are relatively simple. Their principle of collecting X-ray photons is illustrated in the diagram. Figure 3 , Figure 4As shown, refractive X-ray detection systems use lens arrays to focus X-ray photons over a large area, forming a multifocal structure on the focal plane. A focal plane detector with the same area as the lens array receives the X-ray photon signal. Collimating detection systems, on the other hand, limit the field of view of the X-ray photons to be received using a collimator. X-ray photons falling within the field of view are received by the detector. The detector area of ​​both types of detection systems represents the upper limit of the system's detection area.

[0043] The following compares the performance of the two types of X-ray detection systems in terms of field of view, angular resolution, detection efficiency, and noise level. First, the field of view of a collimating system is determined by the aspect ratio of the collimator structure; for example, the field of view of my country's HXMT satellite low-energy telescope is 1.6° × 6°. The field of view of a refractive system, however, is related to the lens aperture size and system size, generally selected in the range of arcminutes or even arcseconds, capable of covering the pulsar's line-of-sight direction. If the X-ray detectors used in both systems have the same area, their background noise levels are comparable. This is because large-field-of-sight systems collect signals from a wider range of pulsar nebulae while simultaneously collecting pulsar photon signals, which significantly affects the signal-to-noise ratio (SNR) of the pulsar signal. Refractive systems, with their smaller field of view, can better shield various types of space particle noise, resulting in a higher SNR. Second, regarding angular resolution, the focusing structure of the refractive detection system, combined with a specially designed system structure, can significantly improve angular resolution. The angular resolution of this invention can reach within 1 arcminute, an order of magnitude improvement compared to the collimating system. Finally, regarding detection efficiency, assuming both types of detection systems use the same X-ray detectors, the refractive type requires X-rays to pass through a lens array for focusing, which causes some attenuation of the X-rays. For 2keV X-ray photon energy, approximately 61.8% of X-ray photons will pass through. The collimating type, however, has a soft X-ray shielding film above the collimator to remove visible light and ultraviolet signals from space, allowing soft X-rays to pass through, thus reducing detection noise. The HXMT satellite's low-energy telescope uses a three-layer structure of aluminum / polyimide / nickel mesh. The aluminum film is approximately 200nm thick, used to block visible light, while the polyimide film is approximately 400nm thick, mainly to enhance the mechanical properties of the shielding film. The transmittance of both materials for 2keV X-rays is approximately 85%. Duty cycle data for the nickel mesh is currently unavailable, so the final transmittance cannot be determined. If a duty cycle of 80% is considered, the transmittance for 2keV X-rays is approximately 68%.

[0044] 2. Comparison of this invention with Wolter-I type

[0045] Working principle of the Wolter-I X-ray detection system Figure 5It focuses X-rays via grazing incidence and increases the receiving area through multi-layer nesting. As the aperture of the focusing lens increases, the grazing incidence angle of the X-rays also increases, and the reflection efficiency decreases. If a shorter focal length is required, the aperture of the focusing lens must be limited to ensure efficiency.

[0046] The following is a comparative analysis of the Wolter-I and refractive lens systems in terms of structure and performance. First, based on the previous analysis, structurally, the Wolter-I lens is very difficult to manufacture due to its large lens area and the extremely high surface roughness requirement (approximately 0.5 nm) needed to achieve grazing incidence focusing of X-ray photons. The large lens area requires a significant amount of material, and the addition of multi-layered nested auxiliary structures, such as hubs, further increases the overall weight of the detection system. In contrast, the refractive focusing lens uses a lightweight material lens that is thin and has a low material density. Even with a detection area of ​​100mm × 100mm, the beryllium lens weighs less than 2g, and the polyimide lens has a similar weight, making it significantly lighter than the Wolter-I focusing lens. Furthermore, the two focusing structures have different surface roughness requirements; the refractive lens requires a surface roughness 1000 times lower than the reflective focusing lens. Moreover, the refractive focusing method can control the focal length by changing the lens aperture size and the number of lens units, making it easy to achieve a focal length of less than 0.5m, which is much lower than the focal length of several meters for the Wolter-I type focusing lens. Therefore, it has a greater advantage in terms of size.

[0047] Secondly, a comparison was made in terms of indicators such as field of view, angular resolution, and detection efficiency. The refractive telescope achieves a resolution of 30″ at 2keV energy with a field of view of 2.75′, smaller than the Wolter-I type. Regarding resolution, the Chandra telescope, based on a directly polished glass focusing lens, still holds the record for 0.5″ resolution, while a focusing lens based on nickel-electroformed lenses can also achieve a resolution better than 30″. Overall, both focusing lenses can achieve an angular resolution of 30″, but the Wolter-I type performs better.

[0048] Regarding detection efficiency, for the Wolter-I type, it mainly depends on the specular reflectivity; for the refractive type, it mainly depends on the lens transmittance. The Wolter-I type uses two reflections: a paraboloid of revolution and a hyperboloid of revolution. Assuming the focusing efficiency of the first reflection is 80%, the total focusing efficiency of the two reflections is 64%. The transmittance of the refractive lens is related to the lens material, the lens aperture size, and the selected operating wavelength. The refractive lens designed in this invention uses beryllium with an aperture size of 100 μm and a photon energy of 2 keV. According to calculations, the transmittance of the refractive lens is approximately 61.8%. It can be seen that the focusing efficiency of the Wolter-I type lens is basically equivalent to that of the refractive lens. The detection area of ​​the Wolter-I type lens also depends on the lens aperture and the number of nesting layers; the detection area of ​​the refractive lens, in addition to being related to the lens aperture, is also related to the size of the lens array.

[0049] In fact, compared with the collimating type, the Wolter-I type has significant advantages in terms of noise level and angular resolution, but its main drawbacks are that its size and weight are difficult to adapt to navigation payload requirements, and it is also difficult to manufacture. To address these issues, this invention proposes a solution using a refractive focusing and detection system. Its main significance lies in:

[0050] (1) Lightweight is a necessary feature for X-ray detection systems for pulsar navigation. Compared with the Wolter-I type X-ray detection system based on a multi-layer nested structure, the array-type refractive lens, due to the use of lightweight materials and short focal length, significantly reduces the weight and volume of the space X-ray detection system while ensuring the detection area.

[0051] (2) Reducing technical difficulty is one of the important directions for the development of pulsar navigation terminals. The Wolter-I type focusing system requires multiple layers of nested lenses, and the lens roughness requirements are very strict. The technical process is complex, difficult to manufacture, and costly. The refractive lens system uses relatively mature micro-nano fabrication technology to reduce manufacturing costs by reducing processing difficulty.

[0052] Compared to the Wolter-I X-ray detection system, the X-ray refraction lens has significant advantages in weight and size, can be modularly assembled to achieve the required area, and high angular resolution is easily achieved. The reduction in weight and size also lowers the cost of satellite launch. Furthermore, the reduced manufacturing difficulty also lowers economic costs, which is conducive to its widespread application.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. All equivalent structural changes made based on the description and drawings of the present invention should be included within the scope of patent protection of the invention.

Claims

1. An X-ray refraction focusing and detection system, characterized in that: It includes an array-type X-ray refraction lens, an array-type aperture, and an X-ray detector; the array-type X-ray refraction lens is used to focus parallel X-rays with high gain; the array-type aperture is used to limit the focal spot size, improve angular resolution, and filter out spatial noise particles that irradiate the non-aperture region of the array-type aperture. X-ray detectors convert focused X-ray photons into electrical signals, and read out the photon's energy, time, and position information; The array-type X-ray refraction lens is made of a light element material, with Be being chosen as the material. The array-type X-ray refraction lens consists of a large number of tiny parabolic lenses, each of which can focus parallel-incident X-rays. An array-type aperture is placed between the array-type refractive lens and the X-ray detector to limit the focal spot size and improve angular resolution. The array-type aperture is made by etching, coating and bonding silicon wafers. The number of aperture holes is the same as the number of refractive lenses, and the optical axes of the two are accurately aligned during installation. The rear end of the array aperture is close to the X-ray detector, and the light spot formed after passing through the array aperture can be detected by the X-ray detector. The X-ray detector is a silicon-based detector with high temporal resolution, high energy resolution, and position information readout. The distance between the array-type refractive lens and the X-ray detector is set to 25cm to ensure high transmittance of 2keV X-ray photons. For higher-energy X-ray photons, the focal length of the array-type refractive lens is greater than 25cm; for lower-energy X-ray photons, the focal length of the array-type refractive lens is less than 25cm. By adjusting the aperture size of the array-type aperture, the highest efficiency detection of soft X-ray photons emitted by pulsars can be achieved across the entire energy range.

2. The X-ray refraction focusing and detection system according to claim 1, characterized in that: After passing through an array of refractive lenses, the X-ray photons emitted by the pulsar are focused, then pass through an array of apertures and converge on the focal plane of the X-ray detector, where they are captured by the detector.

Images