Backlit X-ray diffraction imaging device based on bent crystal coupling

Abstract

A backlit X-ray diffraction imaging device based on bent crystal coupling includes a high-power pulsed laser source, a metal target, a spherical bent crystal, a dual-focus photon sieve and a detector. The present invention utilizes a spherical bent crystal to converge the divergent X-rays generated by the high-power pulsed laser source loaded on the metal target to perform X-ray backlighting on the object to be measured, and then diffracts and images through the dual-focus photon sieve, and the detector receives the amplified imaging results. Compared with the existing backlit diffraction imaging, the present invention can increase the light flux in the imaging system by three orders of magnitude, increase the detection efficiency of the imaging system, and can achieve two-level zoom, making it simple to change the imaging magnification in experimental detection. Combined with the imaging characteristics of high time / space resolution and large field of view of backlit diffraction imaging, the present invention can be applied to research fields such as plasma fluid dynamics instability imaging and ultrafast biological living cell imaging.

Description

Technical Field

[0001] The invention relates to diffraction optical imaging technology, in particular to a backlit X-ray diffraction imaging device based on bent crystal coupling. Background Art

[0002] In laser-driven inertial confinement fusion, small-scale plasma fluid instabilities induced by laser inhomogeneities can develop into larger-scale inhomogeneities through nonlinear growth and coupling, which in turn affects the driving symmetry and reduces the implosion gain. Experimental and theoretical studies have shown that these small-scale fluid instabilities are usually near the critical density, with lateral dimensions in the micrometer range and movement speeds of up to tens of micrometers per nanosecond. In experiments, X-rays are generally used for diagnostic imaging, which places high demands on diagnostic technology.

[0003] At present, the main methods used for X-ray imaging at home and abroad include pinhole imaging, Wolter X-ray imaging, KB mirror imaging, curved crystal imaging, diffraction imaging, etc. The spatial resolution of pinhole imaging is limited by the pinhole aperture, which is generally 10 microns, and the light collection efficiency is extremely low; Wolter X-ray imaging requires precise mirror surface shape and is difficult to process; the resolution of KB mirror imaging is several microns, but it requires grazing incidence and is difficult to adjust; and although curved crystal imaging can achieve energy spectrum resolution and obtain X-ray two-dimensional spatial information, the optimal resolution is generally also several microns. The flat plate geometry of the diffraction optical element used in diffraction imaging occupies a small space volume and is flexible in optical path arrangement. The diffraction optical element manufactured by nano-processing is not limited by the optical aperture, and the resolution can reach the sub-micron level, which is suitable for experimental research requiring a large field of view and high resolution. At present, including the Lawrence Livermore National Laboratory (LLNL) in the United States, diffraction imaging is used in many fields such as fusion energy, space lasers, and high-end laser equipment. In 2021, the LLNL laboratory in the United States [Rev. Sci. Instrum. 92, 053511 (2021)] conducted a plasma imaging experiment using a Fresnel zone plate. The experiment used 24 beams of laser-excited X-rays with a pulse width of 600ps and a total energy of 20kJ as the backlight source of the Fresnel zone plate, achieving sub-micron spatial resolution. However, due to the low diffraction efficiency of the Fresnel zone plate and the extremely high brightness requirements of the backlight source, this experimental scheme cannot be widely used.

[0004] The present invention proposes a backlit X-ray diffraction imaging device based on bent crystal coupling, which can improve the light collection capacity by 3 orders of magnitude while improving the monochromatic performance of the backlight source, and is expected to solve the problem of low detection efficiency of X-ray diffraction imaging on laser-excited X-ray backlight illumination. The present invention can be applied to fields with strong demands for high time / space resolution measurement and large field of view detection, such as plasma hydrodynamic instability imaging, ultrafast biological living cell imaging, etc. Summary of the invention

[0005] The object of the present invention is to provide a backlit X-ray diffraction imaging device based on bent crystal coupling to achieve diagnostic imaging with submicron spatial resolution and a field of view of hundreds of microns under low laser energy.

[0006] The technical solution of the present invention is as follows:

[0007] A backlit X-ray diffraction imaging device based on bent crystal coupling, characterized in that it includes a high-power pulsed laser source, a metal target, a spherical bent crystal, a dual-focus photon sieve and a detector;

[0008] The high-power pulsed laser source emits laser pulses loaded on the metal target to generate X-rays, which are incident on the spherical curved crystal at a Bragg angle. After being collected and reflected by the spherical curved crystal, monochromatic X-rays satisfying the Bragg condition 2dsinθ=nλ converge in front of the object to be measured to achieve backlighting, wherein d is the lattice spacing of the spherical curved crystal, θ is the Bragg angle, n is the diffraction order, and λ is the wavelength of the incident X-rays;

[0009] Then, the dual-focus photon sieve performs diffraction imaging. After the X-rays are diffracted by the dual-focus photon sieve, multiple diffraction orders are generated. The detector receives the +1 order diffraction of the dual-focus photon sieve, which is the magnified imaging of the object being measured.

[0010] When the dual-focus photon sieve performs diffraction imaging, two images with different magnifications are formed on the axis.

[0011] The dual-focus photon sieve uses nanogold columns with the same diameter as the photon sieve holes as the phase control unit of X-rays. The centers of the nanogold columns are located on the even Greek ladder orbits encoded using the Greek ladder number sequence. There are no nanogold columns on the odd Greek ladder orbits, thus designing a dual-focus photon sieve.

[0012] The object to be measured is placed behind the focal spot of the X-rays where the spherical curved crystals converge, so as to avoid irreversible damage to the object to be measured due to excessive power density of the X-rays at the focal spot.

[0013] The dual-focus photon sieve is used for focusing and imaging of X-rays. To increase the light flux in the imaging system, the optical path should be adjusted so that the X-rays in the optical path can participate in diffraction imaging to the greatest extent.

[0014] The detector is placed on the image plane of the dual-focus photon sieve and is used to collect diffraction patterns. Different magnifications are selected according to specific needs in actual diagnostic imaging.

[0015] Compared with the prior art, the technical effects of the present invention are:

[0016] 1) The solution of using bent crystal coupling not only improves the monochromaticity of X-rays, but also enhances the light collection ability of the optical path, increases the light flux of the entire detection system, and is expected to reduce the energy demand for high-power pulsed laser sources and expand the scope of application of X-ray diffraction imaging. In addition, compared with the existing backlit diffraction imaging, the use of spherical bent crystals can also arrange the optical path more reasonably, avoid the contamination and damage of the measured object and diffraction element by the plasma or target splashes that emit X-rays, and better protect the measured object and diffraction element under backlit illumination.

[0017] 2) The present invention uses a dual-focus photon sieve for diffraction imaging, which is not limited by the wavelength of traditional refractive lenses and can achieve higher resolution. Nanogold pillars replace the sieve holes of the photon sieve. When the aspect ratio is too large, nanogold pillars are easier to process than sieve holes. While ensuring micron-level spatial resolution, the dual-focus photon sieve can simultaneously form two images with different magnifications in the axial direction, and can achieve secondary zoom. The detector can select different image planes according to different actual needs, making it simple to change the imaging magnification in experimental detection.

[0018] 3) The backlight + diffraction imaging method can achieve high time / space resolution measurement and large field of view detection. After construction, it can expand applications beyond plasma fluid dynamics instability imaging, such as ultrafast biological living cell imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a light path diagram of the backlit X-ray diffraction imaging device based on bent crystal coupling of the present invention.

[0020] Figure 2 This is the optical path diagram of the bent crystal coupled X-ray backlighting.

[0021] Figure 3 is a comparison diagram of the X-ray diffraction imaging light path, where: Figure 3 (a) is the X-ray diffraction imaging optical path in the present invention, Figure 3 (b) is the prior art.

[0022] Figure 4 This is the front view of the dual-focus photon sieve.

[0023] Figure 5 This is the on-axis light intensity distribution diagram of the dual-focus photon sieve.

[0024] Figure 6 is the light intensity distribution diagram of the dual-focus photon sieve on two focal planes. Among them, Figure 6 (a) is the light intensity distribution at the focal plane where the focus F1 is located, Figure 6 (b) is the light intensity distribution on the focal plane where the focus F2 is located.

[0025] In the figure, 1 is a high-power pulsed laser source, 2 is a metal target, 3 is a spherical curved crystal, 4 is an object to be measured, 5 is a dual-focus photon sieve, and 6 is a detector; 1' is a high-power pulsed laser source, 2' is an object to be measured, 3' is a diffraction element, and 4' is a detector. F1 is the first focus of the dual-focus photon sieve, and f1 is its corresponding focal length. F2 is the second focus of the dual-focus photon sieve, and f2 is its corresponding focal length. R1 is the radius of curvature of the spherical curved crystal, and R2 is the radius of the Rowland circle corresponding to the spherical curved crystal. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with the accompanying drawings and specific implementation examples, but this should not limit the scope of protection of the present invention.

[0027] The present invention is a backlit X-ray diffraction imaging device based on bent crystal coupling, which aims to reduce the energy demand of X-ray diffraction imaging for high-power pulsed laser sources, expand the scope of application of X-ray diffraction imaging, and improve the monochromaticity of X-rays and the light collection ability of the optical path while increasing the luminous flux of the entire detection system, greatly enhancing the feasibility of using the diffraction element photon sieve for diagnostic imaging.

[0028] See also Figure 1 , a backlit X-ray diffraction imaging device based on bent crystal coupling, the optical path is as follows Figure 1 As shown. A high-power pulsed laser source emits laser pulses loaded on a metal target to generate plasma, which is excited by reverse bremsstrahlung absorption to generate X-rays. After being collected and reflected by the spherical curved crystal, the monochromatic X-rays incident at the Bragg angle converge in front of the object to be measured for backlighting, and then diffracted by the dual-focus photon sieve for imaging. After diffraction by the dual-focus photon sieve, the X-rays generate multiple diffraction orders, and the detector receives the +1 order diffraction of the dual-focus photon sieve, which is the magnified image of the object to be measured.

[0029] See also Figure 2 The X-rays are focused in front of the object to be measured through the spherical curved crystal for backlighting. Figure 2As shown. A high-power laser is loaded on a metal target to stimulate the generation of divergent X-rays, which are then collected and converged by a spherical curved crystal. The spherical curved crystal can be regarded as an X-ray monochromator. Only monochromatic X-rays that meet the Bragg condition can be interfered and enhanced and reflected in front of the object being measured. The spherical curved crystal performs spectral diffraction based on the Rowland circle principle, and the circle inscribed in the midpoint of the spherical curved crystal is the Rowland circle. The radius R2 of the Rowland circle is half of the radius of curvature R1 of the spherical curved crystal. At this time, the metal target is placed on the Rowland circle. After the laser pulse hits the target, the X-ray spectrum converged by the spherical curved crystal will also appear on the Rowland circle, and the object being measured behind the X-ray spectrum will be backlit.

[0030] See also Figure 3 , X-ray diffraction imaging optical path comparison diagram as shown Figure 3 As shown, a is the X-ray diffraction imaging optical path in the present invention, and b is the prior art. The X-rays generated by the laser pulse loaded on the metal target can be considered as a divergent point light source. In the prior art, the X-rays are directly irradiated on the object to be measured, the received X-ray flux is small, and the detector image brightness is low. The present invention adds spherical curved crystals to the backlight illumination optical path. The spherical curved crystals have a larger spatial solid angle for receiving X-rays than the diffraction elements, and can converge more X-rays, thereby improving the light flux and image brightness of the entire imaging system. Assume Figure 3 (a) The distance between the metal target and the spherical curved crystal Figure 3 In (b), the distance between the metal target and the diffraction element is the same, which is 100 mm. The diameter of the diffraction element is 0.495 mm, and the diameter of the spherical curved crystal is 25 mm. At this time, the solid angle of the diffraction element is 6.1256×10 -6 πsr, the solid angle of the spherical curved crystal is 0.0154πsr, which is about 2514 times the solid angle of the diffraction element. If a spherical curved crystal with a diameter of 50mm is used, the solid angle is 0.0597πsr, which is about 9745 times the solid angle of the diffraction element. Although this situation is an ideal situation, it does not take into account the actual pupil connection and requires Figure 3 In (a), all the light rays converged by the spherical curved crystal are incident on the photon sieve, but the use of spherical curved crystals can still increase the light flux in the system by three orders of magnitude, which is expected to reduce the energy demand of diffraction imaging for high-power pulsed laser sources. The method of curved crystal coupling not only improves the monochromaticity of X-rays, but also enhances the light collecting ability of the optical path, thereby increasing the light flux of the entire detection system. In addition, compared with the existing technology, the use of spherical curved crystals can also arrange the optical path more reasonably, avoiding contamination and damage of the X-ray emitting plasma or target splashes to the object being measured and the diffraction element, so that the object being measured and the diffraction element under backlighting can be better protected.

[0031] See also Figure 4 , the front view of the double-focus photon sieve is shown as Figure 4As shown. In the process of constructing the photon sieve, nanogold columns with the same diameter as the photon sieve holes are used as the phase control unit of X-rays. The center of the nanogold column is located on the even Greek ladder track encoded by the Greek ladder sequence formation law, and there is no nanogold column on the odd Greek ladder track. The diameter of the dual-focus photon sieve is D = 495μm, the height of the nanogold column is h = 700nm, and the minimum diameter of the nanogold column is d min =59.5nm. When the aspect ratio is too large, the nanogold column is easier to process than the sieve hole.

[0032] See also Figure 5 , Figure 6 The light intensity distribution on the axis of the dual-focus photon sieve and the light intensity distribution on the two focal planes are as follows: Figure 5 , Figure 6 As shown. The incident energy of the X-ray is 4.75keV, and the expected value of the optical focal length ratio of the dual focus is The two focal points appear at 89.72mm and 126.88mm respectively, and the sum of the object distance p and the image distance q is 1360mm. The light intensity distribution on the focal plane where the focus F1 is located is as follows: Figure 6 (a), at this time p = 96.6mm, q = 1263.4mm, M = 13.1, f1 = 89.72mm. The light intensity distribution on the focal plane where the focus F2 is located is as follows Figure 6 (b) shows that at this time p = 141.6mm, q = 1218.4mm, M = 8.6, f2 = 126.88mm. Among them, M is the magnification. Using a dual-focus photon sieve for X-ray diffraction imaging, two-stage zoom can be achieved while ensuring micron-level spatial resolution, making it simple to change the imaging magnification in experimental detection and facilitating diagnostic imaging of the object being measured.

[0033] In summary, the present invention improves the monochromaticity of X-rays and the light collecting ability of the optical path while ensuring micron-level spatial resolution and hundreds of micron field of view through bent crystal coupling and dual-focus photon sieve diffraction imaging, thereby increasing the light flux of the entire detection system, reducing the energy demand for high-power pulsed laser sources, and expanding the scope of application of X-ray diffraction imaging. Combined with the imaging characteristics of high time / space resolution and large field of view of backlit diffraction imaging, the present invention can be applied to research fields such as plasma hydrodynamic instability imaging and ultrafast biological living cell imaging.

[0034] The contents not described in the present invention are common knowledge to those skilled in the art.

[0035] The specific implementation examples described above further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation example of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement or improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A backlit X-ray diffraction imaging device based on bent crystal coupling, characterized in that: It comprises a high-power pulsed laser source (1), a metal target (2), a spherical curved crystal (3), a double-focus photon sieve (5) and a detector (6); The high-power pulse laser source (1) emits laser pulses loaded on the metal target (2) to generate X-rays. The X-rays are incident on the spherical curved crystal (3) at a Bragg angle. After being collected and reflected by the spherical curved crystal (3), monochromatic X-rays satisfying the Bragg condition 2dsinθ=nλ converge in front of the object to be measured (4) to achieve backlighting, wherein d is the lattice spacing of the spherical curved crystal (3), θ is the Bragg angle, n is the diffraction order, and λ is the wavelength of the incident X-rays. Then, the dual-focus photon sieve (5) performs diffraction imaging. After the X-rays are diffracted by the dual-focus photon sieve (5), a plurality of diffraction orders are generated. The detector (6) receives the +1 order diffraction of the dual-focus photon sieve (5), i.e., the magnified image of the object to be measured (4); When the dual-focus photon sieve (5) performs diffraction imaging, two images with different magnifications are formed on the axis.

2. The backlit X-ray diffraction imaging device based on bent crystal coupling according to claim 1, characterized in that: The dual-focus photon sieve (5) uses nanogold columns with the same diameter as the photon sieve holes as X-ray phase control units, the centers of the nanogold columns are located on even Greek ladder tracks encoded using the Greek ladder sequence, and there are no nanogold columns on odd Greek ladder tracks.

3. The backlit X-ray diffraction imaging device based on bent crystal coupling according to claim 1, characterized in that: The object to be measured (4) is placed behind the focal spot of the X-rays converged by the spherical curved crystal (3).

4. The backlit X-ray diffraction imaging device based on bent crystal coupling according to claim 1 or 2, characterized in that: The dual-focus photon sieve (5) is used for focusing and imaging of X-rays, and when adjusting the optical path, it should be placed at a position where the X-rays in the optical path can participate in diffraction imaging to the greatest extent.

5. The backlit X-ray diffraction imaging device based on bent crystal coupling according to claim 1, characterized in that: The detector (6) is placed on the image plane of the dual-focus photon sieve (5) and is used to collect diffraction patterns. Different magnification factors are selected according to specific needs in actual diagnostic imaging.

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