Beam Positioning System and Method for X-ray Free-Electron Laser Based on Visible Light Laser

Abstract

This invention provides a beam positioning system and method for X-ray free electron lasers based on visible light lasers. This invention uses visible light lasers to directly indicate the beam direction instead of XFELs, reducing the radiation risk associated with direct beam adjustment using XFELs. It can be used for beam adjustment in an atmospheric environment and is easy to operate. Through the combination of various components, it can work stably on the beamline station for a long time, effectively improving the optical path adjustment efficiency of XFEL experiments.

Description

Technical Field

[0001] This invention relates to the field of synchrotron radiation and free-electron laser instruments and equipment, and in particular to a beam positioning system and method for X-ray free-electron lasers based on visible light lasers. Background Technology

[0002] Currently, hard X-ray free-electron lasers can provide high-brightness, high-repetition-rate, femtosecond-level ultrashort pulses of coherent X-ray light. A total of three beamlines and ten experimental stations have been designed. Since each beamline is over 1 km long, and the experimental stations are connected in series, each station has a limited allocated time. Therefore, it is necessary to minimize the setup time of the experimental stations to allow users more time for experiments. Because X-rays cannot be directly observed, adjusting the light transmission elements of the experimental stations typically requires using photodiodes or imagers at the sample points to detect X-rays, which increases the risk of damage to some radiation-sensitive materials. Summary of the Invention

[0003] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a beam positioning system and method for X-ray free electron lasers based on visible light lasers, in order to solve the problem that X-rays cannot be directly observed and that adjusting the light transmission elements of the experimental station usually requires the use of photodiodes or imagers at the sample point to detect X-rays, which will increase the risk of damage to some radiation-sensitive materials.

[0004] To achieve the above and other related objectives, a first aspect of the present invention provides a beam positioning system for an X-ray free-electron laser based on visible light laser, comprising: a visible light laser source for emitting visible light laser; a beam adjustment mechanism located on the optical path of the visible light laser for adjusting the size of the laser beam; a beam pointing adjustment mechanism located on the optical path of the visible light laser emitted from the beam adjustment mechanism after reflection by a first planar reflector, for guiding the laser beam from the atmospheric environment into the vacuum cavity containing the XFEL beam and adjusting the pointing of the laser beam to coincide with the XFEL beam; a first fluorescent target vacuum insertion cavity connected to the XFEL vacuum flight pipe for inserting a fluorescent crystal target into the XFEL beamline pipe so that both the visible light laser and the XFEL beam can generate detectable fluorescent spots; and a first beam two-dimensional imaging detection device located at one of the viewing flanges of the first fluorescent target vacuum insertion cavity outside the vacuum environment for observing and acquiring the two-dimensional morphology of the fluorescent spot generated on the fluorescent crystal target in the first fluorescent target vacuum insertion cavity and calibrating the centroid position of the first beam.

[0005] In some embodiments of the first aspect of the present invention, the invention further includes: a second fluorescent target vacuum insertion cavity and a second spot two-dimensional imaging detection device; the second fluorescent target vacuum insertion cavity is connected to the XFEL vacuum flight pipe and located in the optical path of the laser beam emitted through the first fluorescent target vacuum insertion cavity, and a second crystal fluorescent target is disposed therein; the second spot two-dimensional imaging detection device is located at the viewing flange of the second fluorescent target vacuum insertion cavity outside the vacuum environment, and is used to observe and collect the two-dimensional morphology of the fluorescent spot generated on the fluorescent crystal target in the second fluorescent target vacuum insertion cavity and to mark the centroid position of the second spot; wherein, whether the centroid position of the first spot and the centroid position of the second spot coincide simultaneously is used to determine whether the laser beam and the XFEL beam are completely collinear.

[0006] In some embodiments of the first aspect of the present invention, the spot adjustment mechanism includes: a collimating lens, a neutral density filter, a beam expander group, a zoom lens group, and a laser shutter; the laser beam emitted by the visible light laser source passes through the collimating lens and the beam expander group, and the roundness of the laser beam is corrected to obtain a parallel beam with a preset spot diameter; the intensity of the parallel beam is adjusted by the neutral density filter; the parallel beam with intensity adjusted by the neutral density filter is directed towards the zoom lens group; the zoom lens group is composed of positive and negative lenses, and the convergence degree of the parallel beam is controlled by adjusting the distance between the positive and negative lenses; the beam emitted from the zoom lens group is reflected by a first plane mirror and then directed to the laser shutter; the laser shutter is used to control whether the visible laser light is emitted.

[0007] In some embodiments of the first aspect of the present invention, the beam pointing adjustment mechanism is composed of a second plane mirror and a third plane mirror, the two plane mirrors using an electrically controlled mirror frame for multi-dimensional directional adjustment.

[0008] In some embodiments of the first aspect of the present invention, the first fluorescent target vacuum insertion cavity includes: a first viewing flange, a second viewing flange, a first insertion flange, and a second insertion flange; the first viewing flange serves as the entrance for the laser beam; the laser beam enters the vacuum environment through the first viewing flange; the first insertion flange is connected to a vacuum one-dimensional transmission rod, through which a fourth reflecting mirror set at a preset angle is connected, so as to drive the fourth reflecting mirror to insert and retract from the XFEL optical path; the fourth reflecting mirror is disposed on the optical path of the laser beam, and its reflecting surface is in contact with the XFEL optical path. The path is angled at 45° to redirect the propagation direction of the visible laser beam perpendicular to the XFEL optical path by 90°, making it align with the propagation direction of the XFEL beam. A vacuum one-dimensional transfer rod is connected to the second insertion flange, which is connected to the crystal fluorescence target to facilitate the insertion and withdrawal of the crystal fluorescence target from the XFEL optical path. The crystal fluorescence target is set at the same preset angle as the fourth reflector and is located on the light exit path of the fourth reflector. The second window flange faces the crystal fluorescence target, and a first spot two-dimensional imaging detection device is connected to the outside of the window.

[0009] In some embodiments of the first aspect of the present invention, the first spot two-dimensional imaging detection device comprises a fixed-distance variable magnification microscope lens and a CMOS two-dimensional array detector.

[0010] In some embodiments of the first aspect of the present invention, the first and second window flanges are quartz windows coated with an antireflective film.

[0011] In some embodiments of the first aspect of the present invention, the visible light laser source includes a 450nm laser diode with an output power of 30mW, which generates diverging light with divergence angles of 7° and 21° in the horizontal and vertical directions, respectively.

[0012] In some embodiments of the first aspect of the present invention, the crystal fluorescent target includes a Ce:YAG crystal fluorescent target and a pBN crystal fluorescent target.

[0013] In some embodiments of the first aspect of the present invention, the Ce:YAG crystal fluorescent target is selected from Ce. 3+ YAG crystals with doping concentrations ranging from 0.5% to 0.8 mol%.

[0014] To achieve the above and other related objectives, a second aspect of the present invention provides a visible light laser-based X-ray free-electron laser beam positioning method, applied to the visible light laser-based X-ray free-electron laser beam positioning system of the first aspect described above; the positioning method includes: opening the XFEL shutter, causing the XFEL beam to strike a crystal fluorescent target and generate a visible light fluorescent spot; locating the centroid position of the visible light fluorescent spot of the XFEL beam using a first spot two-dimensional imaging device and recording the spot position under different fields of view; closing the XFEL shutter and turning on the visible light laser source, causing the laser beam generated to enter the vacuum insertion cavity of the first fluorescent target through a beam pointing adjustment mechanism; the laser beam striking the crystal fluorescent target also generates a visible light fluorescent spot. The visible fluorescence spot of the XFEL beam is located using a two-dimensional imaging device, and the position of the spot under different fields of view is recorded. The orientation of the two plane mirrors in the beam pointing adjustment mechanism is adjusted so that the positions of the visible fluorescence spot of the XFEL beam and the visible fluorescence spot of the laser beam initially coincide. The laser shutter is closed and the plane mirror in the vacuum insertion cavity of the first fluorescence target is removed. The XFEL shutter is opened, and the position of the visible fluorescence spot of the XFEL beam is determined again. After the centroid of the spot is located and recorded, the XFEL shutter is closed. The visible laser source is turned on and the above steps are repeated multiple times until the positions of the visible fluorescence spot of the XFEL beam and the visible fluorescence spot of the laser beam completely coincide.

[0015] As described above, the X-ray free-electron laser beam positioning system and method based on visible light laser of the present invention has the following beneficial effects:

[0016] (1) The present invention uses visible light laser to directly indicate the beam direction instead of XFEL, thereby reducing the radiation risk caused by direct adjustment using XFEL beam.

[0017] (2) The present invention can be used to control the beam in an atmospheric environment and is easy to operate.

[0018] (3) By combining the various parts of the equipment, the present invention can work stably on the beamline station for a long time, which can effectively improve the optical path debugging efficiency of XFEL experiments. Attached Figure Description

[0019] Figure 1 The diagram shown is a structural schematic of an X-ray free-electron laser beam positioning system based on visible light lasers according to an embodiment of the present invention.

[0020] Figure 2 The diagram shown is a schematic representation of the structure of the vacuum insertion cavity for the optical target in one embodiment of the present invention.

[0021] Figure 3The diagram shown is a flowchart illustrating a method for positioning an X-ray free-electron laser beam based on visible light lasers according to an embodiment of the present invention. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0023] It should be noted that in the following description, reference is made to the accompanying drawings, which illustrate several embodiments of the present invention. It should be understood that other embodiments may also be used, and changes in mechanical composition, structure, electrical system, and operation may be made without departing from the spirit and scope of the invention. The following detailed description should not be considered limiting, and the scope of the embodiments of the invention is defined only by the claims of the published patents. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Spatially related terms, such as “upper,” “lower,” “left,” “right,” “below,” “below,” “lower part,” “above,” “upper part,” etc., may be used herein to illustrate the relationship between one element or feature shown in the figures and another element or feature.

[0024] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," and "holding" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] Furthermore, as used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It should be further understood that the terms “comprising,” “including,” indicate the presence of the stated feature, operation, element, component, item, kind, and / or group, but do not preclude the presence, occurrence, or addition of one or more other features, operations, elements, components, items, kinds, and / or groups. The terms “or” and “and / or” as used herein are interpreted as inclusive, or mean any one or any combination thereof. Thus, “A, B, or C” or “A, B, and / or C” means “any one of: A; B; C; A and B; A and C; B and C; A, B, and C.” Exceptions to this definition arise only when combinations of elements, functions, or operations are inherently mutually exclusive in some manner.

[0026] To address the problems mentioned in the background art, this invention provides a beam positioning system and method for X-ray free-electron lasers based on visible light lasers. The aim is to propose a method that utilizes visible light lasers coaxial with X-rays to replace X-rays for beam path pointing during the commissioning phase, achieving rapid alignment of optical components within the station, reducing the radiation dose to components from X-rays, and lowering the risk of damage. The system of this invention is placed close to the experimental station and is used during the beam collimation and equipment alignment phases within the station. It uses visible light lasers to represent the beam spot position instead of XFELs, thereby quickly aligning components within the station, shortening commissioning time, improving the efficiency of the experimental commissioning phase, and reducing the number of times XFELs enter the station, protecting components within the station from damage caused by XFEL radiation.

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the invention.

[0028] Before providing a further detailed description of the present invention, the nouns and terms used in the embodiments of the present invention are explained, and the nouns and terms used in the embodiments of the present invention are subject to the following interpretations:

[0029] <1> XFEL (X-Free Electron Laser) is a novel type of highly coherent radiation source characterized by high power, high efficiency, wide wavelength tuning range, and ultrashort pulse time structure. The physical principle of a free-electron laser utilizes the interaction between a high-speed electron beam passing through a periodically oscillating magnetic field and the optical radiation field, transferring the kinetic energy of the electrons to the optical radiation and thus increasing its intensity.

[0030] <2> KB reflector: A two-dimensional focusing mirror composed of elliptical vertical and horizontal reflectors. KB reflectors are used to focus synchrotron radiation and XFEL beams with two-dimensional divergence angles, and are characterized by high reflectivity and strong focusing ability.

[0031] <3> Grazing incidence: This refers to the propagation of light from an optically less dense medium to an optically denser medium, with an incident angle close to 90 degrees. Focusing an X-ray beam using a KB mirror requires the beam to propagate via grazing incidence.

[0032] This invention provides a method and system for positioning X-ray free-electron laser beams based on visible light lasers. Regarding the implementation of the visible light laser-based X-ray free-electron laser beam positioning system, this invention will describe exemplary implementation scenarios of X-ray free-electron laser beam positioning based on visible light lasers.

[0033] like Figure 1 The diagram illustrates a structural schematic of an X-ray free-electron laser beam positioning system based on visible light lasers according to an embodiment of the present invention. The X-ray free-electron laser beam positioning system based on visible light lasers in this embodiment mainly includes: a visible light laser source 1, a beam spot adjustment mechanism 2, a beam pointing adjustment mechanism 3, a first fluorescent target vacuum insertion cavity 4, and a first beam spot two-dimensional imaging detection device 5.

[0034] The visible light laser source 11 is used to generate a continuous visible light laser for positioning the spot.

[0035] For example, the visible light laser source 11 can be a visible light laser, that is, a laser that directly emits visible light. For example, the visible light laser can be a laser diode (e.g., a red laser diode based on GaInp and AlGaInp), a helium-neon laser (which can emit 632.8nm red light, or 543.5nm green light, 594.1nm yellow light, etc.), a metal vapor laser that emits blue light at 441.6nm, etc.

[0036] Preferably, the visible light source 1 is a 450nm laser diode with an output power of 30mW, producing divergent light with horizontal and vertical divergence angles of 7° and 21° respectively. The laser diode requires TEC (Thermo-Electric Cooling). It should be understood that TEC (Thermo-Electric Cooling) refers to thermoelectric cooling, which is based on the Peltier effect. It typically consists of two materials that transfer heat from one side of the device to the other while a forced direct current flows through them; the side that dissipates heat becomes cooler, and the side that transfers heat becomes hotter.

[0037] The spot adjustment mechanism 2 is located in the optical path of the visible light laser and is used to adjust the size of the laser spot to ensure that the laser spot is smaller than all light-limiting apertures during long-distance transmission and that the spot can be quickly focused at different positions.

[0038] In this embodiment of the invention, the light spot adjustment mechanism 2 includes a collimating lens 201, a neutral density filter 202, a beam expander group 203, a zoom lens group 204, and a zoom lens group 205.

[0039] Specifically, the beam emitted by the visible light laser source 11, after passing through a collimating lens and a beam expander assembly, has its roundness corrected, resulting in a parallel beam with a spot diameter of approximately 3 mm. The parallel beam is then subjected to intensity adjustment via a neutral density filter 202. The zoom lens assembly 204 consists of positive and negative lenses, which are clamped on an electrically controlled frame to achieve one-dimensional electronic adjustment. By adjusting the distance between the positive and negative lenses, the convergence of the beam is controlled, allowing the laser beam to pass completely through the rear KB mirror assembly and other light-limiting elements such as the vacuum differential tube without being blocked.

[0040] It should be understood that a collimating lens 201 refers to an instrument that transforms light rays from each point in the aperture frame into a parallel collimated beam. Reflective and transmissive collimators are used in beam transmission systems to maintain the collimation of the beam between the laser resonator and the focusing optics. Reflective collimators generally use copper total reflection mirrors, while transmissive collimators use zinc selenide lenses. A neutral density filter 202 (also called an optical attenuator) utilizes the light absorption properties of a material, is made into a sheet, and placed in the optical path to attenuate light intensity. The amount of intensity attenuation depends on the material and its thickness. For example, a standard transmittance of 0.02 on a neutral density filter indicates that only 2% of the original light intensity is transmitted after passing through the filter. A zoom lens can change the degree of light focusing, thereby achieving focal length adjustment at different distances. Its principle is to use a special structural design to change the propagation and focusing of light by changing the position or shape of the lens. A beam expander assembly is an optical element assembly capable of changing the diameter and divergence angle of a laser beam, consisting of lenses and circular pinholes.

[0041] The zoom lens group 205 is used to control whether the visible light laser emits light, serving as a safety protection measure during debugging and preventing the visible light laser from illuminating other reflective surfaces during debugging intervals. Specifically, a laser shutter needs to be added to the optical path before the laser can be transmitted over long distances, so that the laser can be remotely switched on and off when the visible light laser source 1 is emitting light stably, ensuring the safe use of the laser during the debugging process.

[0042] After the laser beam is emitted by the beam spot adjustment mechanism 2, it is reflected by the first plane mirror 206 and then enters the beam pointing adjustment mechanism 3. The beam pointing adjustment mechanism 3 is used to guide the laser beam from the atmospheric environment into the vacuum cavity where the XFEL beam is located, and adjust the pointing of the laser beam to coincide with the XFEL beam.

[0043] For example, the beam pointing adjustment mechanism 3 is composed of a second plane mirror 301 and a third plane mirror 302. The two plane mirrors use a five-axis electrically controlled mirror frame, which can realize the adjustment of three-dimensional translation in XYZ and two-dimensional angle in θXθZ.

[0044] The first fluorescent target vacuum insertion cavity 4 is a key part of positioning the laser and XFEL beam. It is a vacuum cavity connected to the XFEL vacuum flight tube and is used to insert a fluorescent crystal target into the XFEL beamline tube so that both the visible light laser and the XFEL beam can produce detectable fluorescent spots.

[0045] In this embodiment of the invention, the structure of the first fluorescent target vacuum insertion cavity 4 is as follows: Figure 2 As shown, it has a first viewing flange 401, a second viewing flange 404, a first insertion flange 402, and a second insertion flange 403. Combined Figure 1 and Figure 2 Explanation:

[0046] The first viewing window flange 401 is the entrance for the laser beam. It is a quartz window coated with a 450nm antireflective film, through which the laser beam enters the vacuum. It should be understood that the antireflective film is a type of anti-reflective coating, whose main function is to reduce or eliminate reflected light from optical surfaces such as lenses, prisms, and plane mirrors, thereby increasing the light transmittance of these components and reducing or eliminating stray light in the system.

[0047] The first insertion flange 402 is connected to a vacuum one-dimensional transmission rod, which is connected to a fourth plane mirror 207 set at a preset angle, so as to drive the fourth plane mirror 207 to insert and withdraw from the XFEL optical path; the fourth plane mirror 207 is located on the optical path of the laser beam, and is used to change the propagation direction of the laser beam so that it is in the same direction as the propagation direction of the XFEL beam; by adjusting the beam pointing adjustment mechanism, the laser beam is not only in the same direction as the propagation direction of the XFEL beam, but also collinear with the XFEL beam.

[0048] The second insertion flange 403 is also connected to a vacuum one-dimensional transmission rod, which is connected to the crystal fluorescence target to drive the crystal fluorescence target to be inserted into and withdrawn from the XFEL optical path. The crystal fluorescence target is set at the same preset angle as the fourth plane mirror 207 and is located on the light output path of the fourth plane mirror 207.

[0049] For example, the crystalline fluorescent target in this embodiment is a Ce:YAG crystalline fluorescent target. Ce:YAG is an important scintillation crystal with excellent scintillation performance, possessing high luminous efficiency and a wide light pulse. Its greatest advantage is its emission center wavelength of 550 nm, which allows for effective coupling with detection devices such as silicon photodiodes. Ce:YAG scintillation crystals have a fast decay time (approximately 70 ns, while CsI has a decay time of approximately 300 ns). Furthermore, Ce:YAG scintillation crystals are non-hygroscopic, heat-resistant, and thermodynamically stable. They are mainly used in light particle detection, alpha particle detection, and gamma ray detection. In addition, they can also be applied to electron detection imaging (SEM) and high-resolution microscopic imaging fluorescent screens.

[0050] The second viewing window flange 404 faces the crystal fluorescence target, and the first spot two-dimensional imaging detection device 5 is connected to the outside of the window.

[0051] For example, the second viewing window flange 404 is sealed with a quartz window coated with a visible light antireflection film, and the first spot two-dimensional imaging detection device 5 connected to the outside of the window is a two-dimensional spot imaging detection microscope system. It should be understood that the antireflection film is an anti-reflection film, whose main function is to reduce or eliminate reflected light from optical surfaces such as lenses, prisms, and plane mirrors, thereby increasing the amount of light transmitted by these components and reducing or eliminating stray light in the system.

[0052] The first spot two-dimensional imaging detection device 5 is used to collect the two-dimensional morphology of the fluorescent spot generated on the fluorescent crystal target in the first fluorescent target vacuum insertion cavity 4 and to calibrate the position of the spot centroid.

[0053] For example, the centroid position of the light spot can be determined based on an image centroid analysis algorithm. The image centroid analysis algorithm includes, but is not limited to, ordinary centroid algorithms, heavily weighted centroid algorithms, and threshold centroid algorithms; this embodiment of the invention does not limit the specific algorithms used.

[0054] For example, the microscope system used in the first spot two-dimensional imaging detection device 5 consists of a commercially available fixed-distance zoom microscope lens and a CMOS two-dimensional array detector. The microscope lens is a zoom lens with a fixed working distance, and the long working distance is over 100 mm. This sufficient working distance allows the microscope system to directly image the fluorescent target outside a vacuum. The microscope system can achieve a zoom effect with a magnification of 0.3 to 2.5 times.

[0055] Furthermore, the collinearity of the laser beam and the XFEL beam needs to be achieved by simultaneously coinciding with two fluorescent spots at different positions. Therefore, the X-ray free-electron laser beam positioning system based on visible light laser provided in this embodiment of the invention also includes a second fluorescent target vacuum insertion cavity 6 and a second spot two-dimensional imaging detection device 7. The second fluorescent target vacuum insertion cavity 6 includes a Ce:YAG crystal fluorescent target, which is inserted and withdrawn from the optical path via a one-dimensional vacuum transfer arm. The second spot two-dimensional imaging detection device 7 includes a microscope system and a CMOS two-dimensional array detector. The microscope system and the CMOS two-dimensional array detector are located outside the vacuum and observe and record the spot position on the Ce:YAG crystal fluorescent target through the viewing flange of the second fluorescent target vacuum insertion cavity 6. It is worth noting that the vacuum cavity designed in the system does not carry an active vacuum acquisition device; a flange port for a vacuum acquisition device is reserved at the bottom of the cavity.

[0056] To facilitate understanding, the present invention is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0057] In this specific embodiment, refer to Figure 1 and Figure 2 The beam positioning system for an X-ray free-electron laser based on visible light lasers mainly includes: a visible light laser source 1, a beam spot adjustment mechanism 2, a beam pointing adjustment mechanism 3, a first fluorescent target vacuum insertion cavity 4, a first beam spot two-dimensional imaging detection device 5, a second fluorescent target vacuum insertion cavity 6, and a second beam spot two-dimensional imaging detection device 7.

[0058] The visible light laser source 1 uses a 450nm laser diode with an output power of 30mW, producing divergent light with horizontal and vertical angles of 7° and 21°, respectively. The crystalline fluorescent target is a Ce:YAG crystalline fluorescent target.

[0059] The collimating lens and beam expander group in the beam spot adjustment mechanism 2 correct the roundness of the beam and obtain a parallel beam with a beam spot diameter of approximately 3mm. The beam passes through a neutral density filter to achieve intensity adjustment. The parallel beam passes through a zoom lens group, which consists of positive and negative lenses. The two lenses are clamped on an electrically controlled frame, enabling one-dimensional electronic adjustment. By adjusting the distance between the two lenses, the convergence of the beam is controlled, allowing the laser beam to pass completely through the rear KB mirror group and other light-limiting elements such as the vacuum differential tube without being blocked. Before long-distance laser transmission, a laser shutter needs to be added to the optical path to enable remote operation of the laser switch when the laser diode output is stable, ensuring safe laser use during the debugging process.

[0060] After passing through the laser beam adjustment mirror group 2, the laser beam enters the beam pointing adjustment mechanism 3, which consists of two plane mirrors. The plane mirrors use an electrically controlled mirror mount, allowing for 5-dimensional adjustment. The laser beam is then guided into the vacuum cavity containing the XFEL through the pointing adjustment mirror group.

[0061] The first fluorescent target vacuum insertion cavity 4 is a key component for positioning the laser and XFEL. It is a vacuum cavity connected to the XFEL vacuum flight pipe, featuring two viewing flanges and two insertion flanges. For example... Figure 2 As shown, the first viewing window flange 401 is the entrance port for the laser beam, and the viewing window flange is a quartz window coated with a 450nm antireflection film.

[0062] The laser enters the vacuum through the first viewing flange 401. The first insertion flange 402 is connected to a 45° reflector via a vacuum one-dimensional transfer rod, enabling the insertion and removal of the reflector from the XFEL optical path. This ensures that the laser propagates in the same direction as the XFEL through the reflector, and the laser and XFEL are strictly collinear through fine adjustment by the beam pointing adjustment mechanism 3. Approximately 10 cm behind the 45° reflector is the second insertion flange 403, connected to a one-dimensional transfer rod, which enables the insertion and removal of the Ce:YAG crystal fluorescent target from the XFEL optical path. The Ce:YAG fluorescent target is at a 45° angle to the beam, and the second viewing flange 404 at 45° faces the Ce:YAG direction. The second viewing flange 404 is sealed with a quartz window coated with a visible light anti-reflection film, and a first spot two-dimensional imaging detection device 5 is connected to the outside of the window.

[0063] The two-dimensional spot imaging detection microscope system 5 consists of a commercially available fixed-distance zoom microscope lens and a CMOS two-dimensional array detector. The microscope lens is a zoom lens with a fixed working distance, and the long working distance is over 100mm. This sufficient working distance allows the microscope system to directly image fluorescent targets outside a vacuum. The microscope system can achieve a zoom magnification of 0.3 to 2.5 times.

[0064] When an XFEL beam strikes a Ce:YAG crystal fluorescent target, it produces a visible fluorescent spot in the vicinity of 530 nm. The position of this spot is located using a two-dimensional imaging detection device 5. Spot searching is achieved at different field-of-view ranges through zooming. The size of the spot produced by the XFEL beam is approximately 3 mm. The centroid of the spot is located using an image centroid algorithm, and the spot position is recorded at different field-of-view ranges.

[0065] After the XFEL beam is turned off, the visible light laser source 1 is turned on, and the 450nm laser generated by it enters the vacuum insertion cavity 4 of the first fluorescent target through the beam pointing adjustment mechanism 3. The 450nm laser irradiates the Ce:YAG crystal fluorescent target, producing the same fluorescence effect and obtaining a visible light fluorescent spot with a wavelength around 450nm. Similarly, the centroid position of the spot is located using the first spot two-dimensional imaging detection device 5, and by adjusting the attitude of the reflector of the beam pointing adjustment mechanism 3, the position of the laser spot is finally made to coincide with the position of the XFEL fluorescent spot.

[0066] Close the laser shutter and remove the 45° reflector. Open the XFEL shutter and re-determine the XFEL spot position. After the centroid positioning and recording are completed, close the XFEL and turn on the laser source. Repeat the above steps multiple times until the centroid positions of the two spots are determined to overlap.

[0067] Preferred choice: Ce 3+ YAG crystals with a doping concentration of 0.5% to 0.8 mol% can achieve an excitation efficiency of over 90% for fluorescent photons, which is beneficial for imaging and detection of fluorescent spots.

[0068] After the collinearity adjustment of the laser and XFEL is completed, the positioning laser now functions to indicate the direction of the XFEL beam. Since the KB mirror is a grazing-incidence reflective element, the beam strikes the element surface at a very small incident angle, resulting in an equivalent aperture of approximately 3 mm. Therefore, the zoom lens group needs to be adjusted to change the divergence of the laser beam, ensuring that the positioning laser spot hits the KB mirror element completely without causing beam jamming. As the attitude of the KB mirror element is adjusted, the positioning laser can be directed to the moving position of the XFEL beam, allowing elements at the rear of the KB mirror, such as the cleaning slit and vacuum differential aperture, to quickly align with the beam position, preventing radiation damage after the XFEL is opened. Further adjustment of the zoom lens group ensures that the size of the positioning laser spot at the sample point within the experimental chamber is less than 1 mm. This laser spot can be detected using an observation microscope within the experimental chamber. After completing the element position adjustments for the entire experimental station, the positioning laser is turned off, and the XFEL is turned on to complete subsequent debugging work.

[0069] like Figure 3 The diagram illustrates a flowchart of a beam positioning method for an X-ray free-electron laser based on visible light lasers, according to an embodiment of the present invention. The positioning method specifically includes the following steps:

[0070] Step S31: Open the XFEL shutter to allow the XFEL beam to strike the crystal fluorescent target and generate a visible light fluorescent spot; locate the centroid of the visible light fluorescent spot of the XFEL beam using the first spot two-dimensional imaging device and record the spot position under different fields of view.

[0071] Step S32: Close the XFEL shutter and turn on the visible light laser source, so that the laser beam generated by it enters the vacuum insertion cavity of the first fluorescent target through the beam pointing adjustment mechanism; the laser beam hits the crystal fluorescent target and also generates a visible light fluorescent spot; the centroid position of the visible light fluorescent spot of the laser beam is located by the first spot two-dimensional imaging device and the spot position under different fields of view is recorded.

[0072] Step S33: Adjust the orientation of the two plane mirrors in the beam pointing adjustment mechanism so that the visible light fluorescence spot of the XFEL beam initially coincides with the visible light fluorescence spot of the laser beam.

[0073] Step S34: Close the laser shutter and remove the plane mirror from the vacuum insertion cavity of the first fluorescent target. Open the XFEL shutter and re-determine the position of the visible light fluorescent spot of the XFEL beam. After the centroid of the spot is located and recorded, close the XFEL shutter.

[0074] Step S35: Turn on the visible light laser source and repeat the above steps multiple times until the visible light fluorescence spot of the XFEL beam and the visible light fluorescence spot of the laser beam are completely aligned.

[0075] It should be noted that the implementation process and principle of the X-ray free electron laser beam positioning method based on visible light laser in this embodiment of the invention are similar to those of the X-ray free electron laser beam positioning system based on visible light laser described above, and therefore will not be repeated here.

[0076] In summary, this invention provides a beam positioning system and method for X-ray free-electron lasers based on visible light lasers. This invention uses visible light lasers to directly indicate the beam direction instead of XFELs, reducing the radiation risks associated with direct beam adjustment using XFELs. It allows for beam control in atmospheric environments and is easy to operate. Through the integration of various components, it can operate stably at a beamline station for extended periods, effectively improving the optical path adjustment efficiency of XFEL experiments. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0077] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A beam positioning system for an X-ray free-electron laser based on visible light lasers, characterized in that, include: Visible light laser source, used to emit visible light laser; The beam adjustment mechanism, located in the optical path of the visible light laser, is used to adjust the size of the laser beam. The beam pointing adjustment mechanism is located on the optical path of the visible light laser emitted by the beam pointing adjustment mechanism after being reflected by the first plane mirror. It is used to guide the laser beam from the atmospheric environment into the vacuum cavity where the XFEL beam is located, and to adjust the pointing of the laser beam to coincide with the XFEL beam. The first fluorescent target vacuum insertion cavity is connected to the XFEL vacuum flight tube and is used to insert a fluorescent crystal target inside the XFEL beamline tube so that both the visible light laser and the XFEL beam can generate detectable fluorescent spots. The first spot two-dimensional imaging detection device is located at one of the viewing flanges of the first fluorescent target vacuum insertion cavity outside the vacuum environment. It is used to observe and collect the two-dimensional morphology of the fluorescent spot generated on the fluorescent crystal target in the first fluorescent target vacuum insertion cavity and to mark the position of the centroid of the first spot. A second fluorescent target vacuum insertion cavity and a second spot two-dimensional imaging detection device; the second fluorescent target vacuum insertion cavity is connected to the XFEL vacuum flight pipe and is located in the optical path of the laser beam emitted through the first fluorescent target vacuum insertion cavity, and a second crystal fluorescent target is disposed therein; the second spot two-dimensional imaging detection device is located at the viewing flange of the second fluorescent target vacuum insertion cavity outside the vacuum environment, and is used to observe and collect the two-dimensional morphology of the fluorescent spot generated on the fluorescent crystal target in the second fluorescent target vacuum insertion cavity and to mark the centroid position of the second spot; wherein, whether the centroid positions of the first spot and the second spot coincide simultaneously is used to determine whether the laser beam and the XFEL beam are completely collinear.

2. The X-ray free-electron laser beam positioning system based on visible light laser as described in claim 1, characterized in that, The light spot adjustment mechanism includes: Collimating lens, neutral density filter, beam expander group, zoom lens group, and laser shutter; The laser beam emitted by the visible light laser source passes through the collimating lens and beam expander group, where the roundness of the laser beam is corrected to obtain a parallel beam with a preset spot diameter. The intensity of the parallel beam is adjusted by the neutral density filter. The parallel beam with intensity adjusted by the neutral density filter is then directed towards the zoom lens group. The zoom lens group consists of positive and negative lenses, and the convergence of the parallel beam is controlled by adjusting the distance between the positive and negative lenses. The beam emitted from the zoom lens group is reflected by the first plane mirror and then directed to the laser shutter. The laser shutter is used to control whether the laser beam is emitted.

3. The X-ray free-electron laser beam positioning system based on visible light laser according to claim 1, characterized in that, The beam pointing adjustment mechanism consists of a second plane mirror and a third plane mirror. The two plane mirrors use an electrically controlled mirror frame for multi-dimensional directional adjustment.

4. The X-ray free-electron laser beam positioning system based on visible light laser according to claim 1, characterized in that, The first fluorescent target vacuum insertion cavity includes: First viewing flange, second viewing flange, first insertion flange and second insertion flange; The first viewing window flange serves as the entrance for the laser beam; the laser beam enters the vacuum environment through the first viewing window flange. The first insertion flange is connected to a vacuum one-dimensional transmission rod, through which a fourth reflector is connected at a preset angle, so as to drive the fourth reflector to insert and retract from the XFEL optical path; the fourth reflector is located on the optical path of the laser beam, and the reflecting surface is at 45° with the XFEL optical path, so as to turn the propagation direction of the visible light laser beam perpendicular to the XFEL optical path by 90°, so that it is in the same direction as the propagation direction of the XFEL beam; The second insertion flange is connected to a vacuum one-dimensional transfer rod, which is connected to the crystal fluorescence target to drive the crystal fluorescence target to be inserted into and withdrawn from the XFEL optical path; the crystal fluorescence target is set at the same preset angle as the fourth reflector and is located on the light output path of the fourth reflector; The second viewing window flange faces the crystal fluorescence target, and the outer side of the window is connected to the first spot two-dimensional imaging detection device.

5. The X-ray free-electron laser beam positioning system based on visible light laser according to claim 1 or 4, characterized in that, The first spot two-dimensional imaging detection device consists of a fixed-distance variable magnification microscope lens and a CMOS two-dimensional array detector.

6. The X-ray free-electron laser beam positioning system based on visible light laser according to claim 4, characterized in that, The first and second viewing flanges are made of quartz windows coated with an anti-reflective film.

7. The X-ray free-electron laser beam positioning system based on visible light laser according to claim 1, characterized in that, The visible light laser source includes a 450nm laser diode with an output power of 30mW, which generates diverging light with divergence angles of 7° and 21° in the horizontal and vertical directions, respectively.

8. The X-ray free-electron laser beam positioning system based on visible light laser according to claim 1, characterized in that, The crystalline fluorescent targets include Ce:YAG crystalline fluorescent targets and pBN crystalline fluorescent targets.

9. The X-ray free-electron laser beam positioning system based on visible light laser according to claim 8, characterized in that, The Ce:YAG crystal fluorescent target is selected from Ce. 3+ YAG crystals with doping concentrations ranging from 0.5% to 0.8 mol%.

10. A method for beam positioning of an X-ray free-electron laser based on visible light laser, characterized in that, The beam positioning system for an X-ray free-electron laser based on visible light lasers, as described in any one of claims 1 to 9, comprises: Open the XFEL shutter to allow the XFEL beam to strike the crystal fluorescent target and generate a visible light fluorescent spot; use a two-dimensional imaging device for the first spot to locate the centroid of the visible light fluorescent spot of the XFEL beam and record the spot position under different fields of view. The XFEL shutter is closed and the visible light laser source is turned on, so that the laser beam generated by it enters the vacuum insertion cavity of the first fluorescent target through the beam pointing adjustment mechanism; the laser beam hits the crystal fluorescent target and also generates a visible light fluorescent spot; the centroid position of the visible light fluorescent spot of the laser beam is located by the first spot two-dimensional imaging device and the spot position under different fields of view is recorded. Adjust the orientation of the two plane mirrors in the beam pointing adjustment mechanism so that the visible light fluorescence spot of the XFEL beam initially coincides with the visible light fluorescence spot of the laser beam; Close the laser shutter and remove the plane mirror from the vacuum insertion cavity of the first fluorescent target. Open the XFEL shutter and re-determine the position of the visible light fluorescence spot of the XFEL beam. After the centroid of the spot is located and recorded, close the XFEL shutter. Turn on the visible light laser source and repeat the above steps multiple times until the visible light fluorescence spot of the XFEL beam and the visible light fluorescence spot of the laser beam are completely aligned.

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