Preparation method of diamond two-dimensional X-ray Kinoform type refractive lens

Abstract

The invention discloses a preparation method of a diamond two-dimensional X-ray Kinofm type refraction lens. The preparation method comprises the following steps: 1) designing an X-ray refraction lens CRL and converting the X-ray refraction lens CRL into a bidirectional Kinofm refraction lens BKL; the incident plane and the emergent plane of the BKL are both short Kinform type refraction lenses SKL; (2) respectively etching the two surfaces of the diamond sample original sheet to form SKL by adopting a layer-by-layer infinitesimal etching method and a high-repetition-frequency ultraviolet femtosecond laser three-dimensional etching technology; (3) optimizing the step error on the side wall of the SKL to obtain a diamond two-dimensional X-ray Kinoform type refraction lens; the optimization method comprises the following steps: calculating the height of each step as the step error removal depth corresponding to the step, and optimizing the step according to the step error removal depth corresponding to each step and the processing position. The diamond machining efficiency and accuracy can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the fields of precision optical element preparation and X-ray optical technology, and relates to a method for preparing a diamond two-dimensional Kinoform X-ray refractive lens used in focusing X-rays from a high-energy synchrotron radiation light source. Background Art

[0002] The X-rays provided by the fourth-generation synchrotron radiation source have the advantages of high brightness, high coherence and low emissivity, and have huge application space in cutting-edge research in many fields such as physics, chemistry, biophysics and protein crystallography, material dynamics and structure, geophysics and environmental science.

[0003] Since their inception, X-ray refractive lenses (CRLs) have been crucial beam-focusing and shaping devices in synchrotron radiation sources. Their robust and compact structure, easy adjustment, stable performance, and wide applicable energy range have made them highly popular in synchrotron radiation sources. Currently, over 50% of beamlines at the European Synchrotron Radiation Facility (ESRF) utilize refractive lenses, and the first phase of the Beijing Huairou High Energy Synchrotron Source (HEPS), currently under construction, plans to use them in 73% of the beamlines.

[0004] Compared to traditional refractive lens materials (beryllium, aluminum, silicon, SU-8 photoresist, etc.), single-crystal diamond has a superior X-ray refraction-absorption ratio (δ / μ). It also possesses unique properties such as low thermal expansion coefficient, high thermal conductivity, high mechanical hardness, and radiation resistance. Single-crystal diamond is the perfect refractive lens material for fourth-generation synchrotron radiation sources, which have high thermal loads and high radiation levels.

[0005] Traditional X-ray refractive lenses are concave mirrors with circular or parabolic surfaces. In order to improve the numerical aperture and transmission efficiency of the X-ray refractive lens, a portion that has no effect on focusing and causes a phase change of 2π integer multiples can be removed from the original lens surface. This type of lens is called a Kinoform X-ray refractive lens. Previously, due to the lack of effective high-precision diamond three-dimensional cutting and etching technology, only one-dimensional Kinoform X-ray refractive lenses could be made on flat single-crystal diamond materials. For example, a metal chromium mask was made using electron beam lithography and a diamond one-dimensional long Kinoform X-ray refractive lens was made using reactive ion beam etching technology. B, Hoszowska J, Freund AK, et al. Diamondplanar refractive lenses for third-and fourth-generation X-ray sources[J]. Journal of Synchrotron Radiation, 2003, 10(2): 168-171.], or by depositing a double-layer mask on the diamond surface using metal gold and metal chromium, and using mixed gas circulation assisted ion beam etching technology to fabricate diamond one-dimensional short Kinoform X-ray refractive lenses[Isakovic AF, Stein A, Warren JB, et al. DiamondKinoform hard X-ray refractive lenses: design, nanofabrication and testing[J]. Journal of Synchrotron Radiation, 2009, 16(1): 8-13.].

[0006] For electron beam lithography and ion beam etching technologies, the processing aspect ratio is limited, making it difficult to process deep structures with a depth of more than 200μm on single crystal diamond samples while maintaining good mirror sidewall verticality, which greatly limits the aperture and surface quality of the lens. At the same time, the above methods are complex and have high requirements for the physical and chemical environment of the manufacturing process. In addition, the economic cost of ion beam etching technology is high and the processing efficiency is low. Finally, the above methods can only realize the development of two-dimensional kinoform X-ray refractive lenses on metals and the production of one-dimensional Kinoform X-ray refractive lenses on flat diamond samples. It cannot realize the processing of two-dimensional Kinoform lenses. Summary of the Invention

[0007] To address the challenges of the prior art, the present invention aims to provide a method for fabricating diamond X-ray Kinoform refractive lenses for use in high-energy synchrotron radiation sources. This method utilizes ultraviolet femtosecond laser three-dimensional processing technology to develop a diamond bidirectional Kinoform refractive lens (BKL). This type of diamond lens has never been developed before, and compared to long-wavelength or ultrafast lasers such as picosecond and nanosecond lasers, ultraviolet femtosecond lasers can significantly improve the efficiency and accuracy of diamond processing.

[0008] This invention utilizes high-repetition-rate ultraviolet femtosecond laser 3D processing technology to etch a two-dimensional Kinoform-type X-ray refractive lens on a diamond surface. First, ultraviolet femtosecond laser 3D processing technology has a large processing range and depth, capable of etching lens structures with diameters exceeding 1 mm and depths greater than 500 μm on diamond samples. Second, ultraviolet femtosecond laser processing of diamond can be performed at room temperature and in a non-vacuum environment, with low environmental requirements and high processing efficiency. Finally, ultraviolet femtosecond laser 3D etching technology can complete the processing of three-dimensional structures on diamond samples, making it possible to produce two-dimensional Kinoform-type X-ray refractive lenses.

[0009] The technical solution of the present invention is:

[0010] A method for preparing a diamond two-dimensional X-ray Kinoform refractive lens, comprising the following steps:

[0011] 1) Designing an X-ray refractive lens CRL and converting it into a bidirectional Kinoform refractive lens BKL; the incident surface and the exit surface of the bidirectional Kinoform refractive lens BKL are both short Kinoform refractive lenses SKL;

[0012] 2) Using a layer-by-layer microelement etching method and high-repetition-rate ultraviolet femtosecond laser three-dimensional etching technology, short Kinoform refractive lenses (SKLs) were etched on both sides of the diamond sample.

[0013] 3) Optimizing the step error on the sidewall of the short Kinoform refractive lens SKL to obtain a diamond two-dimensional X-ray Kinoform refractive lens; wherein the step error optimization method is: calculating the height of each step as the step error removal depth corresponding to the layer, and optimizing the step layer according to the step error removal depth and processing position corresponding to each step using high repetition rate ultraviolet femtosecond laser three-dimensional etching technology; wherein ΔH n is the height of the nth step, R0 n is the radius of the aperture corresponding to the n-th step, and the processing position of the n-th step is determined according to the radius of the aperture corresponding to the n-th step.

[0014] Furthermore, the method for converting the designed X-ray refractive lens CRL into a bidirectional Kinoform refractive lens BKL is as follows: based on the principle of removing the thickness that causes a phase of an integer multiple of 2π of the wavelength, the surface shape of the X-ray refractive lens CRL is converted into a long Kinoform refractive lens LKL, and the tooth length w of each level on the obtained long Kinoform refractive lens is the same, which is the ratio of the wavelength of the focused light to the corresponding diamond refractive attenuation rate; then, using the projection principle, all the lens structures left after removing the integer multiple of 2π phase are translated to the same plane, thereby realizing the conversion of the long Kinoform refractive lens into a short Kinoform refractive lens SKL; then, the teeth are arranged alternately on both sides, with adjacent teeth separated by a tooth width, to obtain a bidirectional Kinoform refractive lens BKL.

[0015] Furthermore, R0 n =R0-(n-1)dR; where dR is the difference in radius between adjacent single-layer microelements, and 2R0 is the receiving aperture of the two-dimensional X-ray Kinoform refractive lens.

[0016] Furthermore, an X-ray refractive lens CRL is designed according to the energy of the focused X-rays, the receiving aperture of the two-dimensional X-ray Kinoform refractive lens, and the target focusing position.

[0017] Furthermore, in the process of etching the diamond sample original sheet using high-repetition-rate ultraviolet femtosecond laser three-dimensional etching technology, the scanning speed of the ultraviolet femtosecond laser was 0.035 mm / s, the scanning line distance was 1 μm, the laser power was 0.72 W, and the number of cycles was 10 times.

[0018] Furthermore, the etching depth of each step is 1 μm.

[0019] Furthermore, the thickness distance between the two short Kinoform refractive lenses SKLT is T.

[0020] Furthermore, the etching order for etching the short Kinoform refractive lens SKL is first the center and then the periphery.

[0021] Furthermore, the X-ray refractive lens CRL is an X-ray refractive lens CRL having a double rotating parabola.

[0022] The advantages of the present invention are as follows:

[0023] 1. Compared with the two-dimensional diamond CRL, the two-dimensional Kinoform lens produced by the present invention can effectively improve the transmission efficiency when the lens is used in combination.

[0024] 2. Compared with metals (Au, W, etc.) produced by electron beam or ion beam etching technologies, the diamond two-dimensional Kinoform lens developed in this invention can be used in extreme environments such as high-temperature irradiation, and is more suitable for the application scenarios of the fourth-generation light source.

[0025] 3. Compared with photolithography, reactive ion etching, and focused ion beam processing methods, the present invention uses laser etching instead of photolithography and reactive ion etching, which simplifies the processing process, improves processing efficiency and the light aperture of the transmission element.

[0026] 4. The present invention combines processing characteristics and proposes for the first time an optimization strategy for the step error of the mirror surface, which can effectively reduce the surface error of the mirror surface and improve the quality of the lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Flow chart of the method of the present invention.

[0028] Figure 2 Schematic diagram of the lens structure in the present invention.

[0029] Figure 3 Schematic diagram of the layer-by-layer micro-element etching method.

[0030] Figure 4 Schematic diagram of step error generated on the side wall of the lens.

[0031] Figure 5 It is a circular metal exterior tooling structure diagram. DETAILED DESCRIPTION

[0032] The present invention will be described in further detail below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0033] The present invention is not limited to the embodiments, and those skilled in the art may make various modifications thereto, such as changing the laser processing parameters, the shape and size of the diamond, the shape, size and material of the external tooling, etc. However, as long as these modifications do not deviate from the spirit and intention of the present invention, they are still within the scope of protection of the present invention.

[0034] The preparation process of the present invention includes four parts: lens structure design, processing strategy design, and processing and cleaning characterization. The process is as follows: Figure 1 As shown, the specific method is:

[0035] 1) Lens structure design. First, a CRL is designed based on factors such as the energy of the focused X-ray, the required receiving aperture, and the target focusing position. For example, a CRL with a double-rotated paraboloid is designed based on a curvature radius R of 0.1 mm, a receiving aperture 2R0 of 0.44 mm, and a focused light energy of 30 keV. The surface equation is y 2=2Rx, where x is the distance of the lens surface along the optical axis, y is the distance of the lens surface perpendicular to the optical axis, and R is the vertex curvature radius. Where T is the length of the lens along the optical axis. The focal length of the lens Where σ is the refractive index, which is related to the X-ray energy and the lens material.

[0036] like Figure 2 As shown, according to the principle of removing the thickness that causes the phase of an integer multiple of 2π wavelength, the surface shape of the CRL is converted into a long Kinoform refractive lens (LKL). At this time, the tooth length (w) of each level on the obtained long Kinoform refractive lens is the same, which is the ratio of the wavelength of the focused light to the corresponding diamond refractive attenuation rate (such as 50μm). And using the projection principle, all the lens structures left after removing the integer multiple of 2π phase are translated to the same plane, that is, the long Kinoform refractive lens is converted into a short Kinoform refractive lens (SKL). In the actual processing process, the movement error and thermal effect of the laser will cause the collapse of the teeth. In order to avoid collapse, there needs to be a certain distance between the teeth. Therefore, the present invention adopts the design of a two-way Kinoform refractive lens (BKL), that is, the teeth are arranged alternately on both sides, separated by a tooth width distance (such as Figure 2 ).

[0037] 2) Processing strategy design. The present invention adopts the strategy of layer-by-layer microelement etching to process the short Kinoform, that is, etching a single layer of microelement with a certain depth and inner and outer diameters, and stacking the etching layer by layer, such as Figure 3 As shown in the figure, the underlined area represents the etched portion, with the same spacing (dH) between each layer. The blank area represents the lens structure, T represents the thickness of the center section, and the dashed line represents the original diamond boundary. First, based on processing and inspection capabilities, an appropriate single-layer microelement depth (e.g., 0.25 μm) is determined. Based on this depth, the Kinoform lens surface is segmented along the optical axis from the lens entrance to the bottom. For lens teeth of the same level, the single-layer microelement appears as concentric rings. The single-layer microelement at the center level of the lens is circular, with the inner and outer diameters varying according to the designed lens structure. Finally, each layer has a fixed depth (e.g., 0.25 μm). After each single-layer microelement is etched, the laser focal spot is adjusted to the diamond sample surface, ultimately achieving the desired lens surface shape. To minimize errors introduced by laser movement and start-stopping, the etching sequence is from the center to the periphery. Theoretically, the thinner the center of the lens, the less X-ray absorption the lens structure will have. However, to maintain the rigidity and stability of the lens structure, a certain thickness (e.g., 50 μm) is required in the center.

[0038] Since the processing is carried out by using a layer-by-layer micro-element etching strategy, step errors (such as Figure 4As shown in Figure 2), in order to optimize this type of error, a correction for step error needs to be added to the machining strategy. Figure 4 It can be seen that where ΔH n is the height of the nth step, that is, the step error removal depth corresponding to this layer, R0 n is the radius of the aperture corresponding to the nth step, that is, the processing position corresponding to this layer that needs to be optimized, which can be calculated according to the formula R0 n = R0-(n-1)dR, where dR is the radius difference of adjacent single-layer micro-elements. According to the above formula, the processing position and removal depth of the step error optimization strategy can be determined.

[0039] 3) Processing process: The present invention utilizes high-repetition-rate ultraviolet femtosecond laser three-dimensional etching technology (such as 343nm, 200fs, 600kHz) to perform lens etching. Single-layer micro-elements with different inner and outer diameters are etched on the original diamond sample and the parameters related to the laser power density, such as the scanning speed, scanning line distance, laser power, and number of cycles of the processing system are adjusted until the single-layer micro-elements etched corresponding to the laser power density meet the requirements of the depth and inner and outer diameters in the processing strategy, and then the parameter combination corresponding to the etching of the single-layer micro-elements with the same depth and different inner and outer diameters is determined (such as a set of parameter combinations: scanning speed 0.035mm / s, scanning line distance 1μm, laser power 0.72W, number of cycles 10 times; the corresponding single-layer etching depth is 1μm). The lens structure is etched using an ultraviolet femtosecond laser three-dimensional processing system. The specific steps are as follows: The cut diamond disc or square is embedded in a metal outer tooling (such as a circular oxygen-free copper outer tooling, such as Figure 5 The sample is positioned at the center of the lens (as shown) and placed on the processing system's sample stage. Coaxial vision is used to locate the sample's geometric center. Based on the previously determined processing strategy and parameters, the first single layer of microelements in the strategy is etched. After each single layer is etched, the sample stage is raised by a fixed single layer depth (e.g., 1 μm) to ensure that the laser focal spot remains centered on the sample surface. Once one side of the lens structure is etched, the sample is flipped over and the other side is etched using the same process.

[0040] 4) Cleaning, Characterization, Evaluation, and Process Optimization: The etched lens is cleaned with 20 kHz ultrasound in anhydrous alcohol. After natural drying, it is scanned under a 20X laser confocal microscope to obtain the three-dimensional structure of a single surface. The surface error is calculated based on the ideal structure. The process level is evaluated and optimized based on the numerical value and distribution of the error. The surface shape of the entire lens or the composite lens will be inspected using X-ray far-field speckle imaging technology based on a synchrotron radiation source to obtain the lens wavefront and convert it into lens structure information based on the refractive index of diamond, thereby enabling the inspection of the entire lens or the composite lens surface.

[0041] While specific embodiments of the present invention have been disclosed for illustrative purposes, intended to facilitate understanding and implementation of the present invention, those skilled in the art will appreciate that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the disclosure of the preferred embodiments, and the scope of protection claimed in the present invention shall be determined by the scope of the claims.

Claims

1. A method for preparing a diamond two-dimensional X-ray Kinoform refractive lens, comprising: 1) Design an X-ray refractive lens (CRL) and convert it into a bidirectional Kinoform refractive lens (BKL); The incident surface and the exit surface of the bidirectional Kinoform refractive lens BKL are both short Kinoform refractive lenses SKL; 2) Using a layer-by-layer microelement etching method and high-repetition-rate ultraviolet femtosecond laser three-dimensional etching technology, short Kinoform refractive lenses (SKLs) were etched on both sides of the diamond sample. 3) Optimizing the step error on the sidewall of the short Kinoform refractive lens SKL to obtain a diamond two-dimensional X-ray Kinoform refractive lens; wherein the step error optimization method is: calculating the height of each step as the step error removal depth corresponding to the layer, and optimizing the step layer according to the step error removal depth and processing position corresponding to each step using high repetition rate ultraviolet femtosecond laser three-dimensional etching technology; wherein ΔH n is the height of the nth step, R0 n is the radius of the aperture corresponding to the n-th step, and the processing position of the n-th step is determined according to the radius of the aperture corresponding to the n-th step.

2. The method according to claim 1, characterized in that The method for converting the designed X-ray refractive lens CRL into a bidirectional Kinoform refractive lens BKL is as follows: based on the principle of removing the thickness that causes a phase of an integer multiple of 2π of the wavelength, the surface shape of the X-ray refractive lens CRL is converted into a long Kinoform refractive lens LKL. The tooth length w of each stage on the obtained long Kinoform refractive lens is the same, which is the ratio of the wavelength of the focused light to the corresponding diamond refractive attenuation rate; then, using the projection principle, all the lens structures left after removing the integer multiple of 2π phase are translated onto the same plane to realize the conversion of the long Kinoform refractive lens into a short Kinoform refractive lens SKL; then, the teeth are arranged alternately on both sides, with adjacent teeth separated by a tooth width, to obtain a bidirectional Kinoform refractive lens BKL.

3. The method according to claim 1, characterized in that R0 n =R0-(n-1)dR; where dR is the difference in radius between adjacent single-layer microelements, and 2R0 is the receiving aperture of the two-dimensional X-ray Kinoform refractive lens.

4. The method according to claim 1, wherein An X-ray refractive lens (CRL) is designed based on the energy of the focused X-rays, the receiving aperture of the two-dimensional X-ray Kinoform refractive lens, and the target focusing position.

5. The method according to claim 1, characterized in that In the process of etching the diamond sample original piece using high-repetition-rate ultraviolet femtosecond laser three-dimensional etching technology, the scanning speed of the ultraviolet femtosecond laser is 0.035mm / s, the scanning line distance is 1μm, the laser power is 0.72W, and the number of cycles is 10 times.

6. The method according to claim 5, characterized in that The etching depth of each step is 1 μm.

7. The method according to claim 1, characterized in that The thickness distance between the two short Kinoform refractive lenses SKLT is T.

8. The method according to claim 1, characterized in that The etching order for etching the short Kinoform refractive lens SKL is first the center and then the periphery.

9. The method according to claim 1, characterized in that The X-ray refractive lens CRL is an X-ray refractive lens CRL having a double rotation parabola.

Images