A high frequency fast-scan monochromator with circular motion and a scanning method thereof

Abstract

The application discloses a high-frequency fast-scan monochromator with circular motion and a scanning method thereof. The high-frequency fast-scan monochromator with circular motion is characterized in that it comprises a rotatable multi-surface prism and multiple groups of light splitting crystals; one group of light splitting crystals is fixed on each side surface of the multi-surface prism and used for diffracting an incident light beam to output a scanning light beam. The monochromator is designed based on high-speed circular rotation, and through integration of multiple groups of slotting crystal structures, the surface heat load of the crystals is effectively dispersed and reduced while the time resolution of sub-millisecond level is achieved; the multi-surface alternating working mode makes the heat load no longer concentrated on a single crystal, thereby simplifying the traditional system depending on liquid nitrogen cooling into a conventional water cooling scheme, and remarkably reducing the operation cost. In addition, the rotary multi-slotting crystal configuration overcomes the problem of low duty cycle of the traditional full-circumferential rotation monochromator, and improves the light flux utilization efficiency.

Description

Technical Field

[0001] This invention belongs to the field of synchrotron radiation technology and relates to a circular motion high-frequency fast-scan monochromator and its scanning method. Background Technology

[0002] The X-rays produced by synchrotron radiation facilities are characterized by wide wavelength range, high collimation, high polarization, high brightness, and high stability, providing users with ultra-high-quality experimental beams. Currently, more than 50 synchrotron radiation sources are operating simultaneously worldwide. These large scientific facilities have become important tools for cutting-edge scientific research and technological innovation in physics, chemistry, materials science, energy, environment, biomedicine, and high technology. Based on synchrotron radiation facilities, researchers have developed numerous precision analytical methods. Among them, X-ray absorption fine structure spectroscopy (XAFS), as a local structure analysis technique with element-specific properties, has been widely applied. Especially in the hard X-ray band, XAFS can detect samples in different states of matter without a vacuum environment and can be flexibly coupled with in-situ conditions such as acidic / alkaline atmospheres, temperature, and pressure, thereby accurately characterizing the structural features of samples under real-world conditions. This makes it one of the most widely used and interdisciplinary experimental methods in synchrotron radiation facilities, playing an irreplaceable role in fields such as catalysis chemistry, materials science, and environmental science.

[0003] Since the beginning of the 21st century, the study of the real-time evolution of material structures in situ, under working conditions, and in service has become a hot topic in the field. Time-resolved XAFS technology, by tracking dynamic structural changes during chemical reactions, has achieved a leap from static structural characterization to dynamic process analysis. Its technological evolution is comparable to the upgrade from still photography to motion picture, and it has become an important development trend in the XAFS field. However, traditional XAFS technology is limited by light source intensity, requiring long integration times to obtain high signal-to-noise ratio data. It typically employs a monochromator point-by-point energy scanning mode, with testing cycles of 10–1000 seconds for conventional samples, which is insufficient to meet the time-resolved requirements for dynamic process studies. The emergence of Quick-Scan X-ray Absorption Fine Structure Spectroscopy (QXAFS) has significantly improved time-resolved capabilities; currently, its single-spectrum acquisition time has been shortened to the order of 1 second to 20 milliseconds. With the iteration of synchrotron radiation facilities and the continuous improvement of light source brightness, developing X-ray monochromators that combine high-speed scanning performance with high thermal load tolerance has become a core technological requirement for further optimizing the time resolution of QXAFS. Examples include liquid nitrogen-cooled grooved crystal fast scanning monochromators, which have been successfully applied in third- and fourth-generation synchrotron radiation facilities. Typical examples include SLS's Super XAS, NSLS's X18B, SPring-8's BL40XU, SSRF's BL11B, and HEPS's ID46. Grooved crystal monochromators achieve multiple diffractions by machining specific grooves in a single crystal and using the groove walls as diffraction surfaces. Compared to dual-crystal monochromators with a fixed exit height, this structure exhibits superior performance in maintaining spot stability, and its mechanical clamping structure is simpler, significantly improving reliability. Since the two diffraction surfaces originate from the same crystal and are spatially adjacent, their physical properties can be considered identical, resulting in a high degree of overlap between the two diffraction curves, which helps to improve the integrated reflectivity. After multiple diffractions, the half-width at half-maximum (FWHM) of the rocking curve decreases, and the curve becomes steeper with increasing diffraction order, thus enhancing the resolving power of the emitted light. The core design concept of this type of monochromator is that the spectroscopic crystal reciprocates with an amplitude of about 1° around a specific angle. Due to the use of a single slotted crystal, the first crystal of the slotted crystal faces the problem of high thermal load from synchrotron white light in this motion mode. Due to the high power density of the light source in the insert of third- and fourth-generation synchrotron radiation devices, liquid nitrogen is generally used as the cooling medium to ensure the performance of the monochromator.

[0004] Current fast-scan monochromators mainly suffer from the following limitations: 1. Reciprocating rotary fast-scan monochromator These monochromators use servo motors or direct-drive motors as driving units. A magnetohydrodynamic sealing device transfers the rotational torque from outside the vacuum to inside, driving a single slotted beam-splitting crystal to perform periodic reciprocating rotation within a small angle range, thus achieving high-speed scanning of the target energy region. Due to the high power density, the beam-irradiated area on the beam-splitting crystal carries a large amount of heat, forming a temperature gradient field. This causes surface undulations and subsurface lattice distortion, directly affecting the monochromator's dispersive accuracy and stability. Therefore, its cooling system typically consists of a copper cooler block tightly attached to the crystal and a liquid nitrogen circulation pipeline loop. This design can suppress the temperature gradient while maintaining the crystal's high stability.

[0005] Although the solution has been engineered, it still has two structural defects: First, the reciprocating periodic motion, especially at high frequencies, exhibits unsteady motion patterns. It requires extremely high acceleration and deceleration to be completed in a very short time, and it is difficult to adapt to high-speed precision drive of large-mass or large-volume components. This results in the highest spectral scanning speed of existing equipment being limited to within 500Hz (corresponding to 2ms / spectrum), and the monochromator in actual application can only reach a maximum of 10ms / spectrum, with limited room for further improvement. Second, long-term high-frequency reciprocating motion causes severe wear and tear on the mechanical structure and motor, and it is difficult to guarantee motion accuracy during long-term service. Third, the reciprocating rotation mode concentrates high heat load in a very small area of ​​the crystal, which must rely on high-cost liquid nitrogen cooling technology, significantly increasing the manufacturing and operating costs of the equipment.

[0006] 2. Direct-drive multi-channel fast-scan monochromator This technical solution uses a direct-drive motor as the driving unit, connecting the atmospheric end and the vacuum end through a magnetohydrodynamic sealing device, driving a multi-channel dicing and spectroscopic crystal placed in a vacuum to achieve circumferential rotation. Compared with the reciprocating rotation mode, the full-circumferential rotation design improves structural stability and increases the number of crystal light-receiving surfaces from the traditional 1 to 6, thereby improving the scanning frequency and time resolution, while reducing the thermal load per unit area of ​​the crystal.

[0007] However, due to the lattice symmetry of single-crystal silicon, for example, the (220) crystal plane with the highest symmetry has only 6 times of symmetry, resulting in only 6 effective light emission cycles per rotation of the crystal, and the effective emission angle for each cycle is approximately 1°, with a photon utilization rate of only about 1 / 60. For crystal planes with even lower symmetry, such as (111) and (311), the photon utilization rate decreases further, and the range of selectable photon energy is also significantly limited. Although this design has advantages in terms of motion and thermal management, its low duty cycle (the ratio of effective luminous flux to total luminous flux) results in serious luminous flux waste, limiting the monochromator's application potential in high-sensitivity detection. See the patent title "A Multichannel Crystal Monochromator and Its Fabrication and Operation Methods". 3. Other related technical solutions Besides the aforementioned mainstream solutions, another type of fast-scan X-ray absorption fine-structure spectroscopic monochromator related to this patent in the prior art employs a polygonal faceted spectroscopic crystal design (refer to the patent document entitled "A Fast-Scan X-ray Absorption Fine-Structure Spectroscopic Monochromator"). This structure mainly includes a rotating component and its first and second drive shafts. A hollow polygonal faceted spectroscopic crystal is installed at one end of the drive shaft that extends into the vacuum cavity. The drive shaft itself is a hollow water-cooled structure with an internal water inlet pipe that sprays cooling water onto the hollow inner wall of the crystal, which then flows back and is discharged through the return water pipe. The sidewalls of the vacuum cavity are respectively provided with light inlets and outlets for white light incident and monochromatic light emitting, respectively. When the first and second drive shafts rotate, each of the two polygonal faceted spectroscopic crystals has a dispersive surface that forms a set of dynamically parallel diffraction surfaces, achieving synchronous diffraction.

[0008] The crystal configuration of this scheme can be divided into two forms: one is to process polygonal facets on a single crystal, but due to the lattice symmetry of single-crystal silicon, there are problems of low light flux utilization and narrow selectable photon energy range; the other is to bond flat crystals to the surface of the polygonal prism to form a composite beam splitting prism. Although this can alleviate the limitations of light flux and energy range, the orientation of the diffraction planes of the two crystals needs to be matched to a degree close to one-thousandth of an arcsecond to achieve effective light output, which brings great difficulties to the adjustment and fixation of the device.

[0009] In contrast, grooved crystals, by machining specific grooves in a single crystal, allow the two diffraction planes to naturally maintain lattice parallelism without the need for complex subsequent alignment, and are therefore more widely used in fast-scan monochromators. Summary of the Invention

[0010] To address the problems existing in the prior art, the present invention aims to provide a high-frequency fast-scanning monochromator with circular motion and its scanning method, which can be used for X-ray absorption fine structure (QXAFS) spectroscopy research. This monochromator is based on a high-speed circular rotation design and integrates multiple sets of slotted crystal structures to effectively disperse and reduce the thermal load on the crystal surface while achieving sub-millisecond time resolution. The alternating working mode of multiple working surfaces ensures that the thermal load is no longer concentrated on a single crystal, thus simplifying the traditional liquid nitrogen cooling system to a conventional water cooling solution, significantly reducing operating costs. Furthermore, this rotating multi-slotted crystal configuration overcomes the problem of low duty cycle in traditional full-circular rotating monochromators, improving luminous flux utilization efficiency.

[0011] The technical solution of this invention is as follows: A high-frequency fast-scan monochromator with circular motion is characterized by comprising a rotatable multifaceted prism and a multi-component optical crystal; a component optical crystal is fixed on each side of the multifaceted prism for diffracting the incident beam to output a scanning beam.

[0012] Preferably, each component crystal performs Bragg diffraction on obliquely incident light to output a scanning beam with a set characteristic energy.

[0013] Preferably, each group of optical crystals is a single-celled crystal, including single-celled and double-celled crystals with the same crystal plane index.

[0014] Preferably, the range of Bragg diffraction angle θ is changed by adjusting the angle α between the incident light and the side edge of the grooved crystal along its length direction, thereby adjusting the energy scanning range of the scanning beam.

[0015] A scanning method based on the circular motion high-frequency fast-scan monochromator is characterized in that the multifaceted prism is driven to rotate, the incident light beam acts on each component optical crystal in sequence, and the diffracted scanning light beam scans the sample.

[0016] Preferably, the multifaceted prism is driven to rotate in an alternating "high speed-low speed-high speed-low speed" operating mode: when the pitch angle deviates far from the Bragg angle θ, the motor drives the multifaceted prism to rotate at high speed, thereby shortening the ineffective illumination time; when the pitch angle is close to the Bragg angle θ, the motor drives the multifaceted prism to run at low speed to match the limited resolution capability of the detector.

[0017] Preferably, during the rotation of the multifaceted prism, the characteristic energy is changed by altering the Bragg angle θ of the spectroscopic crystal, thereby achieving energy tunability.

[0018] The advantages of this invention are as follows: This invention achieves efficient adaptation to high-power synchrotron radiation sources with low manufacturing and maintenance costs, and significantly improves the time resolution capability of XAFS, providing a key technological foundation for the development of a new generation of ultra-high time resolution, high stability, and easy-to-maintain X-ray absorption spectroscopy experimental stations. Attached Figure Description

[0019] Figure 1 Design diagram of a three-dimensional structure for a fast-scan monochromator with multiple grooves for circular motion.

[0020] Figure 2 This represents the orientation relationship between the optical path and the grooved crystal. (a) Front view of the crystal, (b) Back view of the crystal, (c) Side view of the crystal.

[0021] Figure 3 This is a diagram showing the orientation relationship between the central angle, the grooved crystal, and the optical path.

[0022] Wherein, 1—incident light, 2—outcrystal light, 3—grooved crystal, and 4—multifaceted prism rotation axis. Detailed Implementation

[0023] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0024] To address the low duty cycle issue in fully circular rotating monochromators, this paper proposes a novel multi-component optical crystal array structure. This design utilizes multiple sets of slotted crystals fixed on various sides of a multifaceted prism, with each set acting as a beam-splitting crystal element, forming multiple beam-splitting crystal units, significantly improving the luminous flux utilization efficiency of the device. In this structure, the fully circular rotation mode allows the incident beam to be sequentially utilized by the multi-component optical crystals distributed on different sides of the prism, effectively distributing the thermal power load of the incident beam and avoiding localized concentration of high power load. Thanks to the uniform distribution of the thermal load, the system can be cooled using conventional water cooling methods, eliminating the need for costly liquid nitrogen cryogenic cooling technology.

[0025] Furthermore, the scheme of using multi-faceted prisms to fix multiple sets of slotted crystals constitutes a beam-splitting crystal prism structure, which can significantly increase the light emission frequency per revolution of the monochromator, thereby improving the overall utilization rate of the beamline luminous flux. For example, when using a slotted crystal group with 50 facets, its luminous flux utilization rate is significantly higher than that of a traditional integrated multi-channel slotted fast-scan monochromator. In addition, the crystal orientation index of the slotted crystals in this design can be flexibly selected, without being limited by the lattice symmetry of single-crystal silicon, thus breaking through the constraints on crystal orientation of traditional integrated slotted monochromators (which can usually only achieve a maximum of six channels).

[0026] Specifically, when the system is equipped with a 50-facet grooving crystal assembly and operates at a conventional speed of 3000 rpm, its time resolution can reach 0.4 ms. Furthermore, as the speed increases or the number of grooving crystals increases, the system's time resolution will be further improved.

[0027] Figure 1 This is a 3D structural design of a circular motion multi-grooved crystal fast scanning monochromator. It contains 50 groups of grooved crystals, evenly distributed on the sides of a multifaceted prism. The central angle of each grooved crystal is 7.2°, and R is the circumcircle diameter of the multifaceted prism. During operation, the multifaceted prism carrying multiple groups of grooved crystals rotates around the Y-axis under the drive of a direct-drive motor. Therefore, the scanning angle range of a single grooved crystal rotating around the Y-axis is 7.2°. The grooved crystals have a specific azimuth angle with the incident beam, such as... Figure 3 As shown.

[0028] The crystal face of the grooved crystal is a specific single crystal face, such as (111), (220), (311), etc. The grooved crystal shown in the figure is located at the top of the polyhedral prism. The orientation relationship between the grooved crystal and the incident light is represented by α and θ, where α is the angle between the incident light and the side edge along the length direction of the crystal. It can be seen that unlike the case of normal incidence in a traditional monochromator (the incident light is parallel to the side edge along the length direction of the crystal), this invention is oblique incidence. The size of the α angle determines the range of the θ angle. For example, as shown in Table 1, when the selected characteristic energy is 8.978keV, the Bragg angle is 12.72°, and the central angle is scanned from 0 to 7.2°. When the value of α is different, the range of θ is different. Note that when the central angle is rotated to 3.6°, the θ angle is adjusted to 12.72° Bragg angle. Figure 3 As shown, as the central angle rotates around the Y-axis, the θ angle scans within a certain range around the Bragg angle and obtains energy spectrum information. Furthermore, it can be seen that when the value of α increases, a larger θ angle scanning range can be obtained, improving angular resolution, which is something that traditional monochromators cannot achieve.

[0029] Table 1 shows the scanning range of θ for different values ​​of α when the characteristic energy is 8.978 keV. In this scheme, scanning of the θ angle is achieved by rotating a multifaceted prism. With a constant prism rotation speed, the emission frequency remains stable. By adjusting the value of the α angle, the scanning range of the θ angle can be flexibly adjusted, thereby expanding the energy scanning range. In contrast, traditional fast-scan monochromators can only expand the energy range by increasing the scanning range of the Bragg angle (θ), but this leads to a longer single-scan time, thus reducing the emission frequency and time resolution. Furthermore, with a central angle of 3.6°, by changing the value of θ, different energies can be obtained when the central angle rotates, enabling spectroscopic analysis of different elements.

[0030] To further improve temporal resolution and beam utilization efficiency, an alternating "high-speed-low-speed-high-speed-low-speed" operating mode can be introduced. Specifically, when the pitch angle deviates significantly from the Bragg angle θ, the motor rotates at high speed to shorten the ineffective illumination time; when the pitch angle approaches the Bragg angle θ, the motor switches to low speed to match the detector's limited resolution, ensuring data acquisition accuracy near critical angles, effectively reducing ineffective illumination time, and improving overall experimental efficiency.

[0031] During rotation, the Bragg angle θ of the crystal can be changed by adjusting the high-precision turntable along the Y-axis, thereby altering the characteristic energy and achieving adjustable energy.

[0032] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-frequency fast-scan monochromator for circular motion, characterized in that, It includes a rotatable multifaceted prism and a multi-component optical crystal; a component optical crystal is fixed on each side of the multifaceted prism for diffracting the incident beam to output a scanning beam.

2. The circular motion high-frequency fast-scan monochromator according to claim 1, characterized in that, Each optical crystal performs Bragg diffraction on obliquely incident light to output a scanning beam with a set characteristic energy.

3. The circular motion high-frequency fast-scan monochromator according to claim 1 or 2, characterized in that, Each group of optical crystals is a slotted crystal, including single crystals and double crystals with the same crystal plane index.

4. The circular motion high-frequency fast-scan monochromator according to claim 3, characterized in that, The range of Bragg diffraction angle θ is changed by adjusting the angle α between the incident light and the side edge of the grooved crystal along its length direction, thereby adjusting the energy scanning range of the scanning beam.

5. A scanning method based on the circular motion high-frequency fast-scan monochromator as described in claim 1, characterized in that, The multifaceted prism is driven to rotate, and the incident light beam acts on each component optical crystal in sequence, and the diffracted scanning beam scans the sample.

6. The method according to claim 5, characterized in that, The sampling operates in an alternating "high speed - low speed - high speed - low speed" mode to drive the multifaceted prism to rotate: when the pitch angle deviates far from the Bragg angle θ, the motor drives the multifaceted prism to rotate at high speed, thereby shortening the invalid illumination time; when the pitch angle is close to the Bragg angle θ, the motor drives the multifaceted prism to run at low speed to match the limited resolution capability of the detector.

7. The method according to claim 6, characterized in that, During the rotation of the multifaceted prism, the characteristic energy is changed by altering the Bragg angle θ of the spectroscopic crystal, thus achieving energy tunability.

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