Free electron laser

Abstract

The invention relates to a free electron laser. A free electron laser comprises a tube body, an electron source and an undulator. The tube body is provided with a vacuum chamber, the electron source comprises an optical fiber and an electron emission layer, the light emitting end of the optical fiber is located in the vacuum chamber, the electron emission layer is arranged at the light emitting end of the optical fiber, the electron emission layer at least comprises an electron excitation layer, and the electron excitation layer is arranged on a light emitting path of laser emitted by the optical fiber. Therefore, the electron excitation layer can emit electrons under the excitation of the laser. The undulator is arranged in the vacuum chamber, the light emitting end of the optical fiber and the undulator are arranged at an interval in the extending direction of the optical fiber, and the undulator is provided with a first electron channel through which electrons emitted from the electron excitation layer penetrate. The electron excitation layer comprises at least one of a zero-dimensional material, a one-dimensional material and a two-dimensional material. As the electron emission layer is arranged on the optical fiber, the space in the vacuum chamber can be saved, and the size of the free electron laser can be reduced.

Description

Technical Field

[0001] This application relates to the technical field of free electron lasers, and particularly to free electron lasers. Background Art

[0002] In related technologies, a free electron laser generally includes an electron gun, an accelerator, a deflection magnet, a wiggler magnet, etc. After the electrons emitted by the electron gun are accelerated by the accelerator, the high-energy electrons generated by the accelerator are injected into the wiggler magnet with alternating polarities through the deflection magnet, and the electrons generate electromagnetic radiation due to the wiggling motion. However, the traditional free electron laser is relatively large in volume. Summary of the Invention

[0003] Based on this, it is necessary to provide a free electron laser to address the problem of the relatively large volume of the traditional free electron laser.

[0004] This application provides a free electron laser, comprising:

[0005] A tube body having a vacuum chamber;

[0006] An electron source including an optical fiber and an electron emission layer. The light-emitting end of the optical fiber is located inside the vacuum chamber. The electron emission layer is disposed at the light-emitting end of the optical fiber, and the electron emission layer at least includes an electron excitation layer. The electron excitation layer is disposed on the light path of the laser emitted by the optical fiber so that the electron excitation layer can emit electrons under the excitation of the laser; and

[0007] A wiggler disposed inside the vacuum chamber and along the extending direction of the optical fiber. The light-emitting end of the optical fiber and the wiggler are spaced apart;

[0008] Wherein, the wiggler has a first electron channel for the electrons emitted from the electron excitation layer to pass through;

[0009] The electron excitation layer includes at least one of zero-dimensional materials, one-dimensional materials, and two-dimensional materials.

[0010] In one embodiment, the free electron laser further includes an anode located between the electron source and the wiggler;

[0011] The anode has a second electron channel communicating with the first electron channel;

[0012] There is a first preset electric field between the anode and the electron excitation layer, so that the electrons emitted from the electron excitation layer can pass through the second electron channel and penetrate into the first electron channel under the action of the first preset electric field.

[0013] In one embodiment, the electron source further includes a conductive connection layer, which is at least disposed on the light-emitting end of the optical fiber and is electrically connected to the electron excitation layer;

[0014] The conductive connection layer and the anode are respectively used to externally connect the negative electrode and the positive electrode of a first power source, so that there is a first preset electric field between the anode and the electron excitation layer.

[0015] In one embodiment, the electron source further includes a first wire electrically connected to the conductive connection layer;

[0016] The tube body is provided with a first wire passing hole for the first wire to pass through and communicating with the vacuum chamber, and a first sealant is provided between the side wall of the first wire passing hole and the part of the first wire passing through the first wire passing hole.

[0017] In one embodiment, the free electron laser further includes a second wire electrically connected to the anode. The tube body is provided with a second wire passing hole for the second wire to pass through and communicating with the vacuum chamber, and a second sealant is provided between the side wall of the second wire passing hole and the part of the second wire passing through the second wire passing hole.

[0018] In one embodiment, the anode includes a plurality of spaced metal rings and dielectric rings located between two adjacent metal rings;

[0019] All the metal rings and all the dielectric rings jointly define the second electron channel.

[0020] In one embodiment, the material of the dielectric ring includes a high-K dielectric material.

[0021] In one embodiment, the free electron laser further includes an insulating member disposed between the electron source and the anode;

[0022] The insulating member has a third electron channel communicating with the second electron channel, so that the electrons emitted from the electron excitation layer pass through the third electron channel and penetrate into the second electron channel.

[0023] In one embodiment, the radial cross-section of the second electron channel is circular, and the inner diameter of the second electron channel is D1;

[0024] The outer diameter of the core of the optical fiber is D2;

[0025] Wherein, D1 > 6D2.

[0026] In one embodiment, the optical fiber includes a core for transmitting laser light and a cladding layer wrapped around the core, and the end face of the light-emitting end of the optical fiber is arranged at an angle with respect to the extending direction of the core;

[0027] The electron emission layer is disposed on the end face of the light-emitting end of the optical fiber, and the electron excitation layer covers the core of the optical fiber. The laser light emitted from the core can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the laser light emitted from the core and emits electrons.

[0028] In one embodiment, the optical fiber includes a core for transmitting laser light and a cladding layer wrapped around the core;

[0029] A light leakage notch is formed in the radial direction of the light-emitting end of the optical fiber;

[0030] The electron emission layer is disposed on the bottom wall surface of the light leakage notch. The bottom wall surface of the light leakage notch is configured as a plane, and the projection of the electron excitation layer on the bottom wall surface covers the projection of the core on the bottom wall surface;

[0031] The electron excitation layer further extends to the light-emitting end of the optical fiber.

[0032] In one embodiment, the optical fiber includes a perforated optical fiber, and the perforated optical fiber has a light guiding hole;

[0033] The electron excitation layer is at least disposed on the side wall of the light guiding hole and extends to the light-emitting end of the optical fiber along the extending direction of the light guiding hole.

[0034] In one embodiment, the optical fiber includes a perforated optical fiber, and the perforated optical fiber has a light guiding hole;

[0035] The electron emission layer is disposed on the end face of the light-emitting end of the perforated optical fiber, and the electron excitation layer covers one end of the light guiding hole located at the end face of the light-emitting end;

[0036] The laser light emitted from the perforated optical fiber can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the laser light emitted from the core and emits electrons.

[0037] In one embodiment, a pointed end portion is provided at the light-emitting end of the optical fiber;

[0038] The electron excitation layer covers the surface of the pointed end portion of the optical fiber;

[0039] The optical fiber includes a core for transmitting laser light. The laser light emitted from the core can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the laser light emitted from the core and emits electrons.

[0040] In one embodiment, the tube body is sleeved on the optical fiber.

[0041] In one embodiment, the outer diameter of the tube body is 125 μm - 2000 μm, and the length of the tube body is 3 cm - 9 cm.

[0042] In one embodiment, the thickness of the electron excitation layer is less than or equal to 50 nm.

[0043] In one embodiment, a laser output window is provided on the tube body. Along the longitudinal extension direction of the tube body, the electron source, the undulator, and the laser output window are sequentially arranged at intervals.

[0044] In one embodiment, the free electron laser further includes an annular receiving electrode located between the undulator and the laser output window. The annular receiving electrode has a laser channel for outputting the laser.

[0045] A second preset electric field is provided between the annular receiving electrode and the electron excitation layer, so that the annular receiving electrode can receive the electrons passing out of the first electron channel.

[0046] In one embodiment, a first port is provided on the tube body and is disposed opposite to the laser output window.

[0047] Along the longitudinal extension direction of the tube body, the light output end of the optical fiber extends into the vacuum chamber through the first port, and the outer peripheral wall of the optical fiber is hermetically connected to the inner peripheral wall of the first port.

[0048] In one embodiment, the optical fiber has a light input end disposed opposite to the light output end, and the end face of the light input end is flush with the plane where the first port is located.

[0049] In one embodiment, the undulator includes a plurality of magnet groups arranged at intervals along the extension direction of the optical fiber. The plurality of magnet groups define the first electron channel.

[0050] Each magnet group includes two magnets with opposite magnetic poles disposed on the inner peripheral wall of the tube body. Among adjacent magnet groups, the two magnets located on the same side and adjacent to each other have opposite magnetic poles.

[0051] In the technical solution of the present application, when the free electron laser is in use, the laser can interact with the low-dimensional material of the electron excitation layer, so that the electrons in the low-dimensional material absorb the photons of the laser and undergo an energy transition to escape outside the electron excitation layer, thereby realizing the excitation of electrons. These electrons can penetrate into the first electron channel and perform a wavy motion in the first electron channel under the action of the undulator, and radiate electromagnetic waves during this process. In this free electron laser, since the electron emission layer is provided on the optical fiber, the space in the vacuum chamber can be saved, and structures such as deflection magnets, wiggler magnets, and resonators are omitted, which is beneficial to reducing the volume of the free electron laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 FIG. shows a schematic structural diagram of a free electron laser according to an embodiment of the present application.

[0053] Figure 2 FIG. shows Figure 1 an enlarged schematic diagram of part A of

[0054] Figure 3 FIG. shows Figure 1 an enlarged schematic diagram of part B of

[0055] Figure 4 FIG. shows Figure 1 an enlarged schematic diagram of part C of

[0056] Figure 5 FIG. shows a schematic structural diagram of an electron source according to the first embodiment of the present application.

[0057] Figure 6 FIG. shows a schematic structural diagram of an electron source according to the second embodiment of the present application.

[0058] Figure 7 FIG. shows Figure 6 a side view of

[0059] Figure 8 FIG. shows a schematic structural diagram of an electron source according to the third embodiment of the present application.

[0060] Figure 9 FIG. shows Figure 8 an enlarged schematic diagram of part D of

[0061] Figure 10 FIG. shows a schematic structural diagram of an electron source according to the fourth embodiment of the present application.

[0062] Figure 11 FIG. shows Figure 10 an enlarged schematic diagram of part E of

[0063] Figure 12 FIG. shows a schematic structural diagram of an electron source according to the fifth embodiment of the present application.

[0064] Figure 13 shows Figure 12 an enlarged schematic view at position F of

[0065] Figure 14 shows a schematic structural view of an electron source according to the sixth embodiment of the present application.

[0066] Figure 15 shows a schematic structural view of a free electron laser according to another embodiment of the present application.

[0067] Figure 16 shows a schematic process view of a method for preparing an electron source according to an embodiment of the present application.

[0068] Reference numerals:

[0069] 10, free electron laser;

[0070] 100, electron source; 110, optical fiber; 111, core; 112, cladding; 1101, light incident end; 1102, light output end; 11021, end face; h, light leakage notch; h1, bottom wall surface; h2, side wall surface; k, side wall of light guiding hole; j, tip; j1, surface; 120, electron emission layer; 121, electron excitation layer; 1211, first part; 1212, second part; 130, conductive connection layer; 131, first conductive part; 132, second conductive part; 1301, first wire; 122, auxiliary layer;

[0071] 200, anode; 201, second electron channel; 21, second wire;

[0072] 300, tube body; 301, vacuum chamber; 302, first port; 303, second port;

[0073] 400, undulator; 41, N-type magnet; 42, S-type magnet; 431, first carrier; 401, first electron channel;

[0074] 500, laser output window;

[0075] 600, annular receiving electrode; 61, laser channel;

[0076] 700, insulating member; 701, third electron channel;

[0077] 20, temporary substrate;

[0078] 30, perforated glass slide;

[0079] 40, annular heating sheet. Detailed implementation manners

[0080] To make the above objects, features, and advantages of the present application more apparent and understandable, the following provides a detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings. Many specific details are set forth in the following description to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0081] In the description of the present application, it should be understood that if terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or positional relationship indicated by these terms is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0082] In addition, if terms such as "first" and "second" appear, these terms are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present application, if the term "plurality" appears, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0083] In the present application, unless otherwise clearly specified and limited, if terms such as "install", "connect", "couple", "fix", etc. appear, these terms should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0084] In this application, unless otherwise clearly specified and defined, when a first feature is described as being "on" or "under" a second feature or the like, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or simply indicates that the first feature has a lower horizontal height than the second feature.

[0085] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. If an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. If any, the terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used in this application are only for the purpose of illustration and do not represent the only implementation.

[0086] In the traditional technology, the thermionic electron source mainly selects materials with metallic properties such as tungsten filaments and lanthanum hexaboride. When heated to thousands of degrees Celsius, electrons are thermally excited to escape from the material surface to form vacuum electrons. The field emission electron source mainly selects metal tips such as tungsten. Under the action of a strong electric field applied from the outside, a tip discharge effect is generated. Among them, the electron beam emitted by the thermionic electron source can work in a relatively poor vacuum environment, has good adaptability to the environment and good stability, but has a low brightness and poor coherence. The electron beam of the field emission electron source has a high brightness and good coherence, but has high requirements for the vacuum degree and is very sensitive to vibrations. Whether it is a thermionic electron source or a field emission electron source, the regulation of the electron emission properties is limited, and it is impossible to take into account both the performance and stability of the emitted electrons.

[0087] In the traditional technology, the photoemission electron source uses metal materials such as Au as the material of the electron emission layer, and the thickness is above 50 nm, even reaching hundreds of nanometers. However, the inventors of this application have found through research that the electron emission layer of the metal material has a relatively large thickness, and the distance between the bottom layer directly acting with the laser and the surface layer of electron emission is relatively far (50 nm to hundreds of nanometers). During the process of electrons excited from the bottom layer passing through the electron emission layer, they are easily affected by the scattering of the metal lattice, thereby affecting the emission efficiency. Moreover, the metal material is easily damaged under high-power laser irradiation, affecting the service life of the electron emission layer, and thus affecting the emission efficiency and stability of electrons.

[0088] In the conventional technology, there is also a type of photoemission electron source where electrons are excited by an external laser incident on the surface of a metal tip. Since the size of the metal tip is in the nanometer range, it is difficult to align the laser spot to the metal tip. If a high-magnification microscope is set up to align the external laser to the metal tip, it will lead to an increase in the overall cost.

[0089] In addition, in the conventional technology, graphene is used as a saturable absorber. Graphene has broadband saturable absorption characteristics and a fast recovery time, and is used in the Q-switching and mode-locking of lasers, or the laser spectrum is adjusted by graphene to achieve sensing detection.

[0090] Based on this, it is necessary to provide an electron source that can balance the electron emission efficiency and stability.

[0091] In this application, low-dimensional materials such as zero-dimensional materials, one-dimensional materials, or two-dimensional materials are used as the materials for the electron excitation layer. When irradiated by a laser, the low-dimensional materials emit electrons through effects such as the photoelectric effect, multi-photon emission, and optical field emission. The low-dimensional materials have an atomic thickness, no dangling bonds, and stable properties, thus having good stability and a long service life. Moreover, the low-dimensional materials can be directly integrated with an optical fiber, and the optical fiber can provide a stable excitation source with adjustable wavelength, polarization, and optical mode, and can be applied to different application scenarios, such as being applicable to the free electron laser 10 described below.

[0092] Figure 1 The structural schematic diagram of the free electron laser 10 in an embodiment of this application is shown.

[0093] Please refer to Figure 1 and, in combination with referring to Figures 2 - 4 A free electron laser 10 provided in an embodiment of this application includes an electron source 100, a tube body 300, and an undulator 400.

[0094] The electron source 100 includes an optical fiber 110 and an electron emission layer 120. Among them, if the optical fiber 110 is configured as a solid optical fiber, the optical fiber 110 includes a core 111 for transmitting laser light and a cladding layer 112 wrapped around the core 111. The refractive index of the cladding layer 112 is lower than that of the core 111. Therefore, the laser light can be confined in the core 111 by the cladding layer 112 for propagation. A coating layer is also provided on the outer surface of the cladding layer 112 to protect the cladding layer 112 and the core 111.

[0095] The optical fiber 110 has an incident end 1101 and an output end 1102. The incident end 1101 is used to couple to a laser source so that the laser light emitted by the laser source can be transmitted through the core 111 of the optical fiber 110. Among them, the laser source can be a laser.

[0096] The optical fiber 110 is a transmission medium for the laser and a carrier for the low-dimensional material of the electron excitation layer 121. The optical fiber 110 can be a single-mode optical fiber, a multi-mode optical fiber, a polarization-maintaining optical fiber, a holey optical fiber, a multi-core optical fiber, etc.

[0097] The tube body 300 has a vacuum chamber 301. The light-emitting end 1102 of the optical fiber 110 is located in the vacuum chamber 301. The electron emission layer 120 is arranged at the light-emitting end 1102 of the optical fiber 110, and the electron emission layer 120 at least includes an electron excitation layer 121. The electron excitation layer 121 is arranged on the light-emitting path of the laser emitted by the optical fiber 110, so that the electron excitation layer 121 can emit electrons under the excitation of the laser. Among them, the electron excitation layer 121 includes at least one of zero-dimensional materials, one-dimensional materials, and two-dimensional materials.

[0098] In this way, during the process that the laser transmitted in the core 111 of the optical fiber 110 is transmitted to the light-emitting end 1102 of the optical fiber 110 and emitted, this part of the laser can interact with the electron excitation layer 121, so that the electrons in the electron excitation layer 121 absorb the photons of the laser, and undergo energy transition to escape outside the electron excitation layer 121, and emit electrons outward from the light-emitting end 1102.

[0099] It should be noted that the wavelength of the laser can be the wavelength that enables the electrons in the electron excitation layer 121 to absorb a photon and make a transition. For example, the wavelength is in the visible light-near infrared-ultraviolet range, or it can be the wavelength that enables the electrons in the electron excitation layer 121 to absorb multiple photons and make a transition. For example, the wavelength is outside the visible light-near infrared-ultraviolet range, and no specific limitation is made here.

[0100] The undulator 400 is arranged in the vacuum chamber 301, and along the extending direction of the optical fiber 110, the light-emitting end 1102 of the optical fiber 110 and the undulator 400 are arranged at intervals. Among them, the undulator 400 has a first electron channel 401 for the electrons emitted from the electron excitation layer 121 to pass through.

[0101] In this way, when the free electron laser 10 of the present application is used, the laser can interact with the low-dimensional material of the electron excitation layer 121, so that the electrons in the electron excitation layer 121 absorb the photons of the laser, and undergo energy transition to escape outside the electron excitation layer 121. Furthermore, the excitation of electrons can be realized. This part of the electrons can penetrate into the first electron channel 401, and under the action of the undulator 400, perform a wavy motion in the first electron channel 401, and radiate electromagnetic waves during this process. In this free electron laser 10, since the electron emission layer 120 is arranged on the optical fiber 110, the space in the vacuum chamber 301 can be saved, and structures such as deflection magnets, wiggler magnets, and resonators are omitted, which is beneficial to reducing the volume of the free electron laser 10.

[0102] The electron source 100 of the present application uses low-dimensional materials such as zero-dimensional materials, one-dimensional materials, or two-dimensional materials as the material of the electron excitation layer 121, and the electron excitation layer 121 is disposed on the optical fiber 110 to achieve electron excitation, eliminating the complex spatial light coupling structure set due to the introduction of external lasers, and also eliminating the high-magnification microscope set to solve the alignment problem of metal tips, which can reduce the process cost of the free electron laser 10.

[0103] Compared with setting a metal layer on the optical fiber tip and directly interacting the laser transmitted in the optical fiber with the metal layer to excite electrons (electrons are easily affected by lattice scattering during the process of passing through the metal layer, resulting in low electron emission efficiency, wide energy dispersion, and serious heat accumulation), the present application uses low-dimensional materials such as zero-dimensional materials, one-dimensional materials, or two-dimensional materials as the material of the electron excitation layer 121. The low-dimensional materials have an atomic-level thickness, and the back-incident electrons can be emitted without passing through in-body transmission, with high electron emission efficiency; moreover, the low-dimensional materials have no dangling bonds, are stable in nature and have a high melting point, are not easily damaged, can be applied to high-power excitation scenarios, and have characteristics such as good stability and high service life; in addition, the low-dimensional materials also have strong light-material interaction and rich electron band gaps, enabling the laser to better interact with the electron excitation layer 121 to excite the electrons in the electron excitation layer 121. These electrons are excited and detached into the vacuum, forming an electron beam, and the electron beam tunneling and emitting from the electron excitation layer 121 has the characteristics of small energy dispersion, high brightness, and high stability.

[0104] In addition, the low-dimensional material and the optical fiber 110 can be directly integrated. The optical fiber transmits laser and serves as the carrier of the low-dimensional material, capable of providing a stable excitation source with adjustable wavelength, polarization, and optical mode, being applicable to different application scenarios, and not requiring a complex optical path, with characteristics such as small volume and high integration.

[0105] Optionally, the electron excitation layer 121 may include a zero-dimensional material, which refers to a material whose size in the three-dimensional spatial scale direction is in the nanoscale, such as nanoparticles, atomic clusters, and quantum dots, generally composed of a small number of atoms and molecules. There are many zero-dimensional carbon nanomaterials, such as carbon black, nanodiamonds, diamond color center nanometer fullerenes C 60 or carbon-coated nano-metal particles, etc. The zero-dimensional material has typical discrete energy levels. Under the action of laser excitation, electrons are mainly tunneling-excited from the discrete energy levels, making the electron beam tunneling and emitting from the electron excitation layer 121 have the characteristics of small energy dispersion, high brightness, and high stability.

[0106] In some embodiments, the thickness of the electron excitation layer 121 is less than or equal to 50 nm.

[0107] It can be understood that the thickness of the electron excitation layer 121 is on the nanometer scale and is relatively small. In this way, it is more conducive to reducing the in-body transmission process of the excited electrons within the electron excitation layer 121, more conducive to improving the emission efficiency and emission density of electrons, and thus an electron source 100 can be used to realize an electron beam with ultra-short pulses.

[0108] Optionally, the electron excitation layer 121 may include zero-dimensional materials. Zero-dimensional materials refer to materials whose dimensions in the three spatial scale directions are on the nanometer scale, such as nanoparticles, atomic clusters, and quantum dots, etc., which are generally composed of a small number of atoms and molecules. There are many zero-dimensional carbon nanomaterials, such as carbon black, nanodiamond, diamond color center, nanometer fullerene C 60 or carbon-coated nanometal particles, etc. Zero-dimensional materials have typical discrete energy levels. Under the action of laser excitation, electrons are mainly tunnel-excited from the discrete energy levels, so that the electron beam tunnel-emitted from the electron excitation layer 121 has the characteristics of small energy dispersion, high brightness, and high stability.

[0109] Optionally, the electron excitation layer 121 may also include one-dimensional materials. The electrons in one-dimensional materials can be transmitted along the linear chain of the one-dimensional materials. Combining with the fact that the electron excitation layer 121 is arranged on the light-emitting end 1102 of the optical fiber 110, it is conducive to the efficient emission of the electrons emitted by the electron source 100 along the extension direction of the optical fiber 110. One-dimensional materials have the characteristics of a small radius of curvature (nanoscale), can enhance the light-matter interaction and provide a large field enhancement factor, ensure multi-photon emission, light field emission, etc., and are applied to scenarios requiring a high-brightness electron source.

[0110] One-dimensional materials can be nanotubes, nanorods or nanowires, nanoribbons or coaxial nanocables, etc.

[0111] The nanotube can be a carbon nanotube, which can be regarded as a seamless tubular structure formed by winding single-layer or multi-layer graphite according to certain rules. The nanotube can also be a silicon (Si) nanotube, a selenium (Se) nanotube, a tellurium (Te) nanotube, a bismuth (Bi) nanotube, a boron nitride (BN) nanotube, a boron-nitrogen co-doped carbon nanotube (BCN nanotube), a tungsten disulfide (WS2) nanotube, a molybdenum disulfide (MoS2) nanotube, or a titanium dioxide (TiO2) nanotube, etc.

[0112] The material of the nanowire can be silicon (Si) or germanium (Ge); the nanowire can also be an oxide nanowire, such as tin oxide (SnO) or zinc oxide (ZnO), etc.; of course, the nanowire can also be a nitride nanowire, such as gallium nitride (GaN) or silicon nitride (Si3N4), etc.; the nanowire can also be a sulfide nanowire, such as cadmium sulfide (CdS) and zinc sulfide (ZnS), etc.; the nanowire can also be a ternary compound nanowire, such as barium titanate (BaTiO3) and lead titanate (PbTiO3), etc.

[0113] The nanoribbon is quite different from the above two kinds of nanostructures (nanotubes and nanowires). Its cross-section is not nearly circular like that of nanotubes or nanowires, but quadrilateral, and the aspect ratio generally ranges from several to more than a dozen. The material of the nanoribbon can be an oxide, such as tin oxide (SnO) or zinc oxide (ZnO), etc.

[0114] The nanocoaxial cable can be a graphite / boron nitride (C / BN) nanocoaxial cable or a silicon carbide / sulfur dioxide (CSi / SiO2) nanocoaxial cable, etc.

[0115] In some embodiments, the angle between the axial direction of the one-dimensional material in the electron excitation layer 121 and the emission direction of the emitted laser is 0 to 90°, for example, it can be 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° or 90°.

[0116] In some embodiments, the axial direction of the one-dimensional material is the same as the emission direction of the laser, so that point emission of the electron source 100 can be achieved, and the resolution is high. If a low-density arrangement of one-dimensional materials is adopted, the energy dispersion of the emitted electrons is low and the brightness is high. If a high-density arrangement of one-dimensional materials is adopted, a large electron beam of the electron source 100 can be achieved. Among them, low density refers to the number of one-dimensional materials per unit area. For example, a density less than 1 / nm 2 is low density, and greater than 1 / nm 2 is high density.

[0117] In some embodiments, there is an angle between the axial direction of the one-dimensional material and the emission direction of the laser. The angle can be a right angle or an acute angle, and linear electron sources can be generated by laser exciting the one-dimensional material.

[0118] Optionally, the electron excitation layer 121 may also include a two-dimensional material. The electrons in the two-dimensional material can be transmitted along the two-dimensional plane. Combined with the electron excitation layer 121 being arranged on the light-emitting end 1102 of the optical fiber 110, in this way, it is beneficial for the electrons emitted by the electron source 100 to be emitted efficiently along the extension direction of the optical fiber 110; and compared with setting a thinner metal layer on the optical fiber, it will cause the melting point of the metal layer to decrease, and then lead to the problem that the metal layer is easily damaged. The two-dimensional material selected in this application has no dangling bonds, is relatively stable, has a high melting point, is not easily damaged, and is suitable for high-power excitation and large electron beams of the electron source 100. In addition, the energy levels of the two-dimensional material are more discrete, and the energy of the electron beam emitted by tunneling emission is more concentrated and the energy dispersion is smaller.

[0119] Two-dimensional materials have the characteristic of atomic layer thickness. The thickness of two-dimensional materials can be the thickness of a single atomic layer or the thickness of multiple atomic layers. During the interaction between laser and two-dimensional materials, it hardly affects the light transmission mode and has high stability. Moreover, the excited electrons can be directly emitted without scattering inside the material, ensuring the purity of the properties of the emitted electrons and an extremely narrow pulse width.

[0120] The two-dimensional material can be graphene, transition metal sulfide, two-dimensional perovskite, two-dimensional diamond, boron nitride, etc.

[0121] Taking graphene as an example of the two-dimensional material for illustration, the carbon atoms of graphene are bonded in the plane in the form of covalent bonds to form a hexagonal honeycomb planar structure. The electron excitation layer 121 can have a thickness of one atomic layer, about 0.34 nanometers; the electron excitation layer 121 can also have a thickness of several or dozens of atomic layers.

[0122] In some embodiments, the electron excitation layer 121 includes at least one layer of two-dimensional material.

[0123] Optionally, the electron excitation layer 121 includes at least two layers of two-dimensional materials stacked in sequence along the laser emission direction, or the electron excitation layer 121 includes at least two two-dimensional materials with different materials connected to each other in the same plane.

[0124] In some embodiments, at least two layers of two-dimensional materials are stacked, or the electron excitation layer 121 includes at least two two-dimensional materials with different materials connected to each other in the same plane, thereby forming a vertical heterojunction or a planar heterojunction. The heterojunction structure can enhance the interaction between light and two-dimensional materials, realize efficient electron emission under laser power, and the heterojunction has the function of interfacial energy band regulation. Through material design and twist angle regulation, special interfacial states can be obtained to realize high-brightness and low-energy-dispersion electron emission.

[0125] Of course, this application is not limited thereto. The electron excitation layer 121 also includes two or more of zero-dimensional materials, one-dimensional materials, and two-dimensional materials.

[0126] In some embodiments, the materials in the electron excitation layer 121 include one-dimensional materials and zero-dimensional materials disposed at the ends and / or sides of the one-dimensional materials.

[0127] In this application, by combining zero-dimensional materials with one-dimensional materials and disposing the zero-dimensional materials at the ends and / or sides of the one-dimensional materials, that is, using zero-dimensional materials to modify the surface structure of one-dimensional materials. Both zero-dimensional materials and one-dimensional materials have typical discrete energy levels. Under the action of laser, electrons are mainly excited by tunneling from discrete energy levels, and the emitted electrons have the characteristics of concentrated energy, small energy dispersion, and high emission efficiency.

[0128] In some embodiments, the electron excitation layer 121 includes a zero-dimensional material and a two-dimensional material, and the zero-dimensional material is disposed on the surface of the two-dimensional material.

[0129] In this application, the zero-dimensional material is disposed on the surface of the two-dimensional material. The two-dimensional material can not only serve as a support layer for carrying the zero-dimensional material, but also avoid the addition of the following conductive connection layer 130 by using a conductive two-dimensional material, that is, the two-dimensional material can serve as an auxiliary layer for the zero-dimensional material to achieve the functions of support and conduction.

[0130] In some embodiments, the electron excitation layer 121 includes a one-dimensional material and a two-dimensional material, and the one-dimensional material is disposed on the surface of the two-dimensional material; optionally, the angle between the axial direction of the one-dimensional material and the surface of the two-dimensional material is 0 to 90°.

[0131] In this application, the one-dimensional material is disposed on the surface of the two-dimensional material. The two-dimensional material can not only serve as a support layer for carrying the one-dimensional material, but also avoid the addition of the following conductive connection layer 130 by using a conductive two-dimensional material, that is, the two-dimensional material can serve as an auxiliary layer for the one-dimensional material to achieve the functions of support and conduction.

[0132] In some embodiments, the zero-dimensional material, the one-dimensional material or the two-dimensional material independently includes a doping element.

[0133] In this application, by doping elements into the low-dimensional material, the conductivity of the low-dimensional material is improved, the work function is changed, and the electron emission performance is adjusted. For example, alkali metals and alkaline earth metal elements can improve the conductivity of the low-dimensional material, and at the same time can reduce the work function of the low-dimensional material to increase the emission beam current. Elements such as B, C, N, O, F and rare earths can create discrete energy levels to obtain an electron beam with a narrow energy.

[0134] Optionally, the doping element includes at least one of alkali metals, alkaline earth metals, transition metals, rare earth elements, halogen elements and light elements (B, C, N, O, F).

[0135] In some embodiments, please refer to Figure 5 , the end face 11021 of the light output end 1102 of the optical fiber 110 is arranged at an angle α with the extending direction of the fiber core 111, and the angle α is selected between 0 and 90 degrees. The electron emission layer 120 is disposed on the end face 11021 of the light output end 1102 of the optical fiber 110, and the electron excitation layer 121 covers the fiber core 111 of the optical fiber 110. The laser emitted from the fiber core 111 can directly irradiate the electron emission layer 120, so that the electron excitation layer 121 is excited by the laser emitted from the fiber core 111 and emits electrons.

[0136] It can be understood that the electron excitation layer 121 is located on the light output path of the laser emitted from the fiber core 111.

[0137] In this way, the oblique incidence on the electron excitation layer 121 can be achieved, and the photoelectric field perpendicular to the end face 11021 of the light output end 1102 can be realized. The emission angle of electrons can be changed by changing the angle ɑ, or the emission angle of electrons can be adjusted by adjusting the polarization state of the laser in the optical fiber 110, which is beneficial to broadening the application range of the electron source 100.

[0138] In some embodiments, please refer to Figure 6 and Figure 7 , a light leakage gap h is formed in the radial direction of the optical fiber 110 at the light output end 1102 of the optical fiber 110. The electron emission layer 120 is disposed on the bottom wall surface h1 of the light leakage gap h, and the electron emission layer 120 at least includes an electron excitation layer 121. The bottom wall surface h1 of the light leakage gap h is configured as a plane, and the projection of the electron excitation layer 121 on the bottom wall surface h1 covers the projection of the fiber core 111 on the bottom wall surface h1. The electron excitation layer 121 also extends to the light output end 1102 of the optical fiber 110.

[0139] Optionally, the light leakage gap h further has a side wall surface h2 extending in the radial direction of the optical fiber 110, and the bottom wall surface h1 and the side wall surface h2 together define the light leakage gap h.

[0140] Optionally, the bottom wall surface h1 of the light leakage gap h is configured as a plane, and the bottom wall surface h1 of the light leakage gap h extends along the extending direction of the optical fiber 110.

[0141] It may be that the bottom wall surface h1 of the light leakage gap h is spaced from the fiber core 111, and the bottom wall surface h1 of the light leakage gap h is parallel to the tangent plane of the outer surface of the fiber core 111; or it may be that the bottom wall surface h1 of the light leakage gap h is tangent to the outer surface of the fiber core 111 (as Figure 7 shown); of course, it may also be that the bottom wall surface h1 of the light leakage gap h is configured as a plane partially formed on the fiber core 111. For example, by cutting the fiber core 111 and the cladding 112 simultaneously to form the light leakage gap h, and making a part of the bottom wall surface h1 of the light leakage gap h formed on the fiber core 111 and another part of the bottom wall surface h1 of the light leakage gap h formed on the cladding 112.

[0142] In this way, the laser transmitted in the fiber core 111 of the optical fiber 110 can generate an evanescent wave at the bottom wall surface h1 of the light leakage gap h. Since the electron excitation layer 121 is disposed on the bottom wall surface h1 of the light leakage gap h, and the projection of the electron excitation layer 121 on the bottom wall surface h1 covers the projection of the fiber core 111 on the bottom wall surface h1, therefore, the laser transmitted in the fiber core 111 of the optical fiber 110 can interact with the electron excitation layer 121 through the evanescent wave, so that the electrons in the electron excitation layer 121 absorb the energy of the evanescent wave and transition. These electrons can escape from the electron excitation layer 121, and thus the excitation of electrons can be realized.

[0143] In some embodiments, referring to Figure 8 and Figure 9 , the optical fiber 110 includes a holey optical fiber having a light guiding hole. The holey optical fiber may include a hollow holey optical fiber, and the hollow holey optical fiber may be a single-hole or multi-hole hollow optical fiber. Of course, the holey optical fiber may also include a solid-core holey optical fiber, and the solid-core holey optical fiber may be a single-hole or multi-hole solid-core optical fiber, which is not specifically limited herein. Figures 8 - 9 An example of the hollow optical fiber with a single hole as the holey optical fiber is given.

[0144] Specifically, in the embodiment as shown in Figures 8 - 9 , a core 111 composed of air is provided in the light guiding hole. The holey optical fiber further includes a cladding layer 112 surrounding the core 111. The cladding layer 112 is specifically configured as an annular light guiding tube body, and the side wall k of the light guiding hole is formed on the inner side wall of the annular light guiding tube body. Specifically, the material of the annular light guiding tube body may be borosilicate, glass, quartz, etc. More specifically, the holey optical fiber is a capillary optical fiber.

[0145] The electron excitation layer 121 is at least provided on the side wall k of the light guiding hole, and the electron excitation layer 121 extends along the extending direction of the light guiding hole to the light emitting end 1102 of the optical fiber 110.

[0146] When the electron source 100 is in use, during the process of the laser transmitting in the holey optical fiber by means of the light guiding medium, an evanescent wave can be generated at the side wall k of the light guiding hole. Since the electron excitation layer 121 is provided on the side wall k of the light guiding hole, the laser can interact with the electron excitation layer 121 through the evanescent wave, so that the electrons in the electron excitation layer 121 absorb the energy of the evanescent wave and transition. These electrons can escape outside the electron excitation layer 121, and thus the excitation of electrons can be realized.

[0147] In some embodiments, referring to Figure 10 and Figure 11 , the optical fiber 110 includes a holey optical fiber having a light guiding hole. The holey optical fiber may include a hollow holey optical fiber, and the hollow holey optical fiber may be a single-hole or multi-hole hollow optical fiber. Of course, the holey optical fiber may also include a solid-core holey optical fiber, and the solid-core holey optical fiber may be a single-hole or multi-hole solid-core optical fiber, which is not specifically limited herein. Figures 10 - 11 An example of the hollow optical fiber with a single hole as the holey optical fiber is given.

[0148] Specifically, in the embodiment as shown in Figures 10 - 11 , a core 111 composed of air is provided in the light guiding hole. The holey optical fiber further includes a cladding layer 112 surrounding the core 111. The cladding layer 112 is specifically configured as an annular light guiding tube body, and the side wall k of the light guiding hole is formed on the inner side wall of the annular light guiding tube body. Specifically, the material of the annular light guiding tube body may be borosilicate, glass, quartz, etc. More specifically, the holey optical fiber is a capillary optical fiber.

[0149] The electron emission layer 120 is disposed on the end face 11021 of the light output end 1102 of the holey optical fiber, and the electron excitation layer 121 covers one end of the light guiding hole located at the end face 11021 of the light output end 1102. The laser emitted from the holey optical fiber can directly irradiate on the electron emission layer 120, so that the electron excitation layer 121 is excited by the laser emitted from the holey optical fiber and emits electrons.

[0150] Exemplarily, the holey optical fiber is a capillary optical fiber, and the electron excitation layer 121 covers the fiber core 111 of the holey optical fiber. It can be that the electron excitation layer 121 directly covers the fiber core 111 of the holey optical fiber, or it can be that the electron excitation layer 121 indirectly covers the fiber core 111 of the holey optical fiber, and no specific limitation is made here.

[0151] In this way, during the process that the laser transmitted in the holey optical fiber propagates to the end face 11021 of the light output end 1102 and exits, this part of the laser can interact with the electron excitation layer 121, so that the electrons in the electron excitation layer 121 absorb the photons of the laser and undergo energy transition to escape outside the electron excitation layer 121, realizing the excitation of electrons.

[0152] In some embodiments, please refer to Figure 12 and Figure 13 , the light output end 1102 of the optical fiber 110 is provided with a pointed end portion j, the electron excitation layer 121 covers the surface j1 of the pointed end portion j of the optical fiber 110, and the laser emitted from the fiber core 111 can directly irradiate on the electron emission layer 120, so that the electron excitation layer 121 is excited by the laser emitted from the fiber core 111 and emits electrons.

[0153] During the process that the laser transmitted in the fiber core 111 of the optical fiber 110 transmits to the pointed end portion j and exits, this part of the laser can interact with the electron excitation layer 121, so that the electrons in the electron excitation layer 121 absorb the photons of the laser and undergo energy transition to escape outside the electron excitation layer 121, and thus the excitation of electrons can be realized.

[0154] Optionally, along the extending direction of the fiber core 111, the radial dimension of the pointed end portion j gradually decreases.

[0155] The electron excitation layer 121 of the present application is disposed on the pointed end portion j of the optical fiber 110 and covers the surface j1 of the pointed end portion j of the optical fiber 110. Since the pointed end portion j of the optical fiber 110 has a geometric structure similar to a needle tip, the field emission enhancement factor is improved, and a higher brightness electron source 100 can be obtained.

[0156] Optionally, in this embodiment, along the extending direction of the core 111, the size of the tip portion j is L1, and the size of the electron excitation layer 121 is L2, where L1 is greater than L2. Specifically, the size of the tip portion j and the size of the electron excitation layer 121 satisfy the following relationship: L2 > 1 / 2 * L1.

[0157] The electron excitation layer 121 covers the surface j1 of the tip portion j, and the electron excitation layer 121 is disposed around the tip portion j. Since L2 > 1 / 2 * L1, in this way, the contact area between the electron excitation layer 121 and the surface j1 of the tip portion j can be increased, the bonding strength between the electron excitation layer 121 and the optical fiber 110 can be improved, and it is also beneficial to use the laser transmitted by the core 111 to excite the electron excitation layer 121 to emit electrons outward.

[0158] In some embodiments, the electron source 100 further includes a conductive connection layer 130, and the conductive connection layer 130 is at least disposed on the light-emitting end 1102 of the optical fiber 110 and is electrically connected to the electron excitation layer 121.

[0159] The conductive connection layer 130 may be a conductive thin film. Specifically, the conductive connection layer 130 may be a metal thin film, a graphite thin film, or a low-dimensional material thin film, etc.

[0160] It should be added that the conductive connection layer 130 is not disposed on the light-emitting path of the laser emitted from the core 111.

[0161] In this way, the electron excitation layer 121 can be electrically connected to the negative electrode of the power supply through the conductive connection layer 130. On the one hand, the power supply can be used to supplement electrons to the electron excitation layer 121, which is beneficial for the electron excitation layer 121 to continuously emit electrons under the excitation of the laser. On the other hand, the direction and convergence of the electrons emitted from the electron excitation layer 121 can be regulated by the voltage applied to the conductive connection layer 130 by the power supply. For example, the direction of the electrons emitted from the electron excitation layer 121 can be regulated by the voltage applied to the anode 200 and the conductive connection layer 130 by the following first power supply.

[0162] Optionally, the electron excitation layer 121 includes a first portion 1211 located on the light-emitting path of the laser emitted from the core 111, and a second portion 1212 connected to the periphery of the first portion 1211, and the second portion 1212 is electrically connected to the conductive connection layer 130. Among them, the second portion 1212 can be directly in electrical contact with the conductive connection layer 130 to be electrically connected to the conductive connection layer 130; the second portion 1212 can also be electrically connected to the conductive connection layer 130 through other conductive structures.

[0163] Specifically, such as Figure 5In the illustrated embodiment, the first part 1211 and the second part 1212 are disposed on the end face 11021 of the light output end 1102. The first part 1211 covers the core 111 of the optical fiber 110, and the second part 1212 is disposed around the first part 1211 and is electrically connected to the conductive connection layer 130.

[0164] The first part 1211 may directly cover the core 111 of the optical fiber 110, or may indirectly cover the core 111 of the optical fiber 110, and no specific limitation is made herein.

[0165] Specifically, in Figure 6 and Figure 7 the illustrated embodiment, the first part 1211 and the second part 1212 are disposed on the bottom wall surface h1 of the light leakage gap h. The projection of the first part 1211 on the bottom wall surface h1 covers the projection of the core 111 on the bottom wall surface h1. The second part 1212 is located outside the first part 1211 and is electrically connected to the conductive connection layer 130.

[0166] Specifically, in Figure 8 and Figure 9 the illustrated embodiment, the electron excitation layer 121 includes a first part 1211 that completely covers the side wall k of the light guiding hole, and a second part 1212 that is disposed on the end face 11021 of the light output end 1102 of the fiber with holes. The first part 1211 is connected to the second part 1212, and the second part 1212 is electrically connected to the conductive connection layer 130.

[0167] Specifically, in Figure 10 and Figure 11 the illustrated embodiment, the electron excitation layer 121 includes a first part 1211 and a second part 1212 that are disposed on the end face 11021 of the light output end 1102 and are connected to each other. The first part 1211 covers one end of the light guiding hole located on the end face 11021 of the light output end 1102. The second part 1212 is disposed around the first part 1211 and is electrically connected to the conductive connection layer 130.

[0168] Specifically, in Figure 12 and Figure 13 the illustrated embodiment, the electron excitation layer 121 includes a first part 1211 and a second part 1212 that are connected to each other. The projection of the first part 1211 in the target plane perpendicular to the extending direction of the core 111 covers the projection of the core 111 in the target plane. The projection of the second part 1212 in the target plane is located outside the projection of the first part 1211 in the target plane, and the second part 1212 is overlapped with the conductive connection layer 130.

[0169] In this way, by electrically connecting the conductive connection layer 130 to the second part 1212 of the electron excitation layer 121, and considering that the second part 1212 is located on the periphery of the first part 1211, the conductive connection layer 130 can supply electrons to the electron excitation layer 121 without affecting the interaction between the core 111 and the electron excitation layer 121, which is beneficial for the electron excitation layer 121 to continuously emit electrons outward under the excitation of laser light.

[0170] Optionally, the conductive connection layer 130 includes a first conductive part 131 disposed on the light-emitting end 1102 and a second conductive part 132 disposed on the circumferential side surface of the optical fiber 110. The first conductive part 131 is connected to the second conductive part 132, and the first conductive part 131 overlaps with the second part 1212 of the electron excitation layer 121.

[0171] Specifically, in the embodiments shown in Figure 5 、 Figures 8 - 11 the first conductive part 131 is disposed on the end surface 11021 of the light-emitting end 1102 and overlaps with the second part 1212 of the electron excitation layer 121. Specifically, in the embodiments shown in Figure 6 and Figure 7 the first conductive part 131 is disposed on the bottom wall surface h1 of the light leakage notch h and overlaps with the second part 1212 of the electron excitation layer 121. The first conductive part 131 also extends to the light-emitting end 1102. Specifically, in the embodiments shown in Figure 12 and Figure 13 the first conductive part 131 is disposed on the tip part j on the light-emitting end 1102 and overlaps with the second part 1212 of the electron excitation layer 121.

[0172] In this way, the conductive connection layer 130 can cover more of the optical fiber 110, improving the bonding strength between the conductive connection layer 130 and the optical fiber, and also being beneficial for better using the conductive connection layer 130 to supply electrons to the electron excitation layer 121.

[0173] Optionally, the conductive connection layer 130 includes a first metal layer and a second metal layer stacked. The adhesion of the first metal layer is greater than that of the second metal layer, and the corrosion resistance of the first metal layer is less than that of the second metal layer.

[0174] Exemplarily, the material of the first metal layer is titanium, and the material of the second metal layer is gold.

[0175] In this way, the first metal layer with higher adhesion can make the conductive connection layer 130 better adhere to the optical fiber 110, and the second metal layer with better corrosion resistance is used to protect the first metal layer, improving the bonding strength between the conductive connection layer 130 and the optical fiber 110, and also being beneficial for increasing the service life of the conductive connection layer 130.

[0176] In some embodiments, the electron emission layer 120 further includes an auxiliary layer 122 , which is stacked on a side of the electron excitation layer 121 close to the optical fiber 110 , or stacked on a side of the electron excitation layer 121 away from the optical fiber 110 .

[0177] The auxiliary layer 122 may be stacked on a side of the electron excitation layer 121 close to the end face 11021 of the light output end 1102 of the optical fiber 110 , or may be stacked on a side of the electron excitation layer 121 away from the end face 11021 of the light output end 1102 of the optical fiber 110 .

[0178] Of course, the auxiliary layer 122 may also be stacked on a side of the electron excitation layer 121 close to or far from the bottom wall surface h1 of the light leakage gap h.

[0179] Of course, the auxiliary layer 122 may also be stacked on a side of the electron excitation layer 121 close to or away from the surface j1 of the tip j of the optical fiber 110 .

[0180] Figure 10 , Figure 11 and Figure 14 An example is given in which the auxiliary layer 122 is stacked on one side of the end surface 11021 of the electron excitation layer 121 close to the light output end 1102 .

[0181] In the present application, an auxiliary layer 122 is additionally provided. When the electron excitation layer 121 requires structural support, the auxiliary layer 122 is used to provide structural support for the electron excitation layer 121, that is, the electron excitation layer 121 is provided on the auxiliary layer 122; or, when the electron excitation layer 121 cannot be directly connected to the conductive connection layer 130 for conduction, the conductive auxiliary layer 122 is used to connect the conductive connection layer 130, and the auxiliary layer 122 is used to achieve electronic conduction between the electron excitation layer 121 and the conductive connection layer 130.

[0182] Optionally, the auxiliary layer 122 includes at least one of a conductive support layer and a heat dissipation support layer.

[0183] Optionally, the auxiliary layer 122 has a thickness of 0.1 nm to 100 nm.

[0184] Optionally, the light transmittance of the auxiliary layer 122 is greater than 10%, such as 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

[0185] Optionally, the auxiliary layer 122 includes a conductive supporting layer, and the conductive supporting layer is electrically connected to the conductive connecting layer 130 .

[0186] In some embodiments, the auxiliary layer 122 includes a conductive support layer, the material of the conductive support layer includes a conductive metal, the laser wavelength in the optical fiber 110 is 200 nm to 10 μm, the pulse power is 1 nw to 1 w, and the repetition frequency is 0 Hz to 10 GHz.

[0187] In the present application, the auxiliary layer 122 adopts a conductive metal and controls the laser parameters, so as to avoid the problem of melting caused by laser irradiation of the conductive metal, and ensure that the auxiliary layer has the functions of support and conduction.

[0188] The auxiliary layer 122 may also include a conductive support layer, such as Figure 10 and Figure 11 As shown, the electron excitation layer 121 is disposed on the end face 11021 of the light output end 1102 through the auxiliary layer 122, and the auxiliary layer 122 has a bearing plane for bearing the electron excitation layer 121. The auxiliary layer 122 may be a light-transmitting material; the auxiliary layer 122 may also be selected as a non-light-transmitting material, and the auxiliary layer 122 has an annular structure, and the orthographic projection of the auxiliary layer 122 on the end face 11021 of the light output end 1102 is located outside the core 111 of the optical fiber 110.

[0189] In this way, not only can the bearing plane of the auxiliary layer 122 be used to make the electron excitation layer 121 be disposed more flatly on the end face 11021 of the light output end 1102, but also the interaction between the electron excitation layer 121 and the core 111 of the optical fiber 110 is not affected, which is beneficial to the formation of an electron beam with concentrated energy and small energy dispersion from the electrons tunneling and emitting within the electron excitation layer 121.

[0190] The auxiliary layer 122 may also include a heat dissipation support layer. Exemplarily, the material of the auxiliary layer 122 may be hexagonal boron nitride. Of course, the material of the auxiliary layer 122 may also be selected as other materials that can dissipate heat for the electron excitation layer 121 and enable the electron excitation layer 121 to be disposed flatly on the end face 11021 of the light output end 1102. In this way, the heat dissipation efficiency of the electron excitation layer 121 can be increased by using the auxiliary layer 122, so that the electron excitation layer 121 can emit a larger electron beam current.

[0191] In some embodiments, the free electron laser 10 further includes an anode 200 located between the electron source 100 and the undulator 400. The anode 200 has a second electron channel 201 communicating with the first electron channel 401, and there is a first preset electric field between the anode 200 and the electron excitation layer 121, so that the electrons emitted from the electron excitation layer 121 can pass through the second electron channel 201 under the action of the first preset electric field and penetrate into the first electron channel 401.

[0192] Optionally, the material of the anode 200 may include a metal material, such as materials like copper, platinum or gold.

[0193] Thus, the anode 200 is conducive to forming a uniform electric field in the direction from the electron excitation layer 121 to the anode 200, which is more conducive to the linear acceleration of electrons in the vacuum chamber 301.

[0194] Specifically, the central axes of the first electron channel 401, the second electron channel 201, and the optical fiber 110 are collinear.

[0195] Thus, it is conducive to using the anode 200 to form a uniform electric field in the extending direction of the optical fiber 110, which is more conducive to the linear acceleration of electrons in the vacuum chamber 301 along the extending direction of the optical fiber 110, passing through the second electron channel 201, and penetrating into the first electron channel 401. This can enable this part of the electrons to better perform a wavy motion in the first electron channel 401 under the action of the undulator 400 to radiate uniform electromagnetic waves.

[0196] In some embodiments, the conductive connection layer 130 and the anode 200 are respectively used to externally connect the negative electrode and the positive electrode of the first power supply, so that there is a first preset electric field between the anode 200 and the electron excitation layer 121.

[0197] That is to say, the electron excitation layer 121 can be electrically connected to the negative electrode of the first power supply through the conductive connection layer 130, and the anode 200 can be electrically connected to the positive electrode of the first power supply. On the one hand, the first power supply can be used to supplement electrons to the electron excitation layer 121, which is conducive to the electron excitation layer 121 continuously emitting electrons under the excitation of laser; on the other hand, the direction and convergence of the electrons emitted from the electron excitation layer 121 can be regulated by the voltage applied to the conductive connection layer 130 by the first power supply.

[0198] In this embodiment, there is a first preset electric field between the anode 200 and the electron excitation layer 121, and the anode 200 and the electron excitation layer 121 are spaced apart along the extending direction of the optical fiber 110. Thus, the electrons emitted from the electron excitation layer 121 can pass through the second electron channel 201 of the anode 200 along the extending direction of the optical fiber 110 under the action of the first preset electric field and penetrate into the first electron channel 401. This can enable this part of the electrons to better perform a wavy motion in the first electron channel 401 under the action of the undulator 400 to radiate uniform electromagnetic waves.

[0199] In some embodiments, the electron source 100 further includes a first wire 1301 electrically connected to the conductive connection layer 130. The tube body 300 is provided with a first wire passing hole for the first wire 1301 to pass through and communicating with the vacuum chamber 301. A first sealant is provided between the side wall of the first wire passing hole and the part of the first wire 1301 passing through the first wire passing hole.

[0200] The first wire 1301 on the conductive connection layer 130 can pass through the first via hole and extend outside the vacuum chamber 301. Due to the arrangement of the first sealant, while the conductive connection layer 130 is externally connected to the negative electrode of the first power supply through the first wire 1301 (the first wire 1301 passes through the first via hole and extends outside the vacuum chamber 301 and is connected to the negative electrode of the first power supply), the airtightness of the vacuum chamber 301 can also be maintained.

[0201] In some embodiments, the free electron laser 10 further includes a second wire 21 electrically connected to the anode 200. The tube body 300 is provided with a second via hole for the second wire 21 to pass through and communicate with the vacuum chamber 301. A second sealant is provided between the side wall of the second via hole and the part of the second wire 21 passing through the second via hole.

[0202] Specifically, the anode 200 is electrically connected to the second wire 21 through an electrode (not shown in the figure).

[0203] The second wire 21 on the anode 200 passes through the second via hole and extends outside the vacuum chamber 301. Due to the arrangement of the second sealant, while the anode 200 is externally connected to the positive electrode of the first power supply through the second wire 21 (the second wire 21 passes through the second via hole and extends outside the vacuum chamber 301 and is connected to the positive electrode of the first power supply), the airtightness of the vacuum chamber 301 can also be maintained.

[0204] In some embodiments, the anode 200 includes a plurality of spaced metal rings and dielectric rings located between two adjacent metal rings. All the metal rings and all the dielectric rings together define the second electron channel 201.

[0205] By arranging dielectric rings between two adjacent metal rings, the breakdown performance of the anode 200 can be improved, which is also beneficial to forming a relatively high electric field between the anode 200 and the electron excitation layer 121, and better enabling electrons to penetrate into the first electron channel 401 with a certain kinetic energy.

[0206] In this embodiment, the dielectric ring is made of a high-K dielectric material, such as boron nitride or mica.

[0207] Using the dielectric ring made of a high-K dielectric material can better improve the breakdown performance of the anode 200, and is also beneficial to enabling electrons to penetrate into the first electron channel 401 with a certain kinetic energy under the action of the first preset electric field.

[0208] In some embodiments, please refer to Figure 15 , the free electron laser 10 further includes an insulator 700 disposed between the electron source 100 and the anode 200. The insulator 700 has a third electron channel 701 communicating with the second electron channel 201, so that the electrons emitted from the electron excitation layer 121 can penetrate into the second electron channel 201 through the third electron channel 701.

[0209] In this way, the electron excitation layer 121 and the anode 200 can be electrically isolated through the insulating member 700, improving the safety and reliability of the free electron laser 10. Also, the electrons emitted from the electron excitation layer 121 can sequentially pass through the third electron channel 701 and the second electron channel 201, then penetrate into the first electron channel 401, and under the action of the undulator 400, perform a wavy motion in the first electron channel 401, and radiate electromagnetic waves during this process.

[0210] Specifically, the insulating member 700 is located between the conductive connection layer 130 of the electron source 100 and the anode 200. Along the longitudinal extension direction of the tube body 300, one end of the insulating member 700 abuts against the conductive connection layer 130, and the other end of the insulating member 700 abuts against the anode 200. In this way, the occupied dimensions of the insulating member 700, the conductive connection layer 130, and the anode 200 in the vacuum chamber 301 along the longitudinal extension direction of the tube body 300 can be further reduced, and it is also beneficial to reduce the overall volume of the free electron laser 10.

[0211] Optionally, the radial cross-section of the second electron channel 201 is circular, the inner diameter of the second electron channel 201 is D1, and the outer diameter of the fiber core 111 of the optical fiber 110 is D2, where D1 > 6D2.

[0212] In this way, sufficient space can be reserved in the second electron channel 201, the probability of electrons colliding with the inner wall of the second electron channel 201 can be reduced, the anode 200 can be well protected, and the energy loss of electrons can also be reduced, which is beneficial to increasing the energy of the electrons penetrating into the first electron channel 401, and thus the energy of the electromagnetic waves radiated under the action of the undulator 400 can be increased.

[0213] Optionally, the radial cross-section of the third electron channel 701 is circular, and the inner diameter of the third electron channel 701 is equal to the inner diameter of the second electron channel 201. In this way, sufficient space can be reserved in the third electron channel 701, the probability of electrons colliding with the inner wall of the third electron channel 701 can be reduced, the insulating member 700 can be well protected, and the energy loss of electrons can also be reduced, which is beneficial to increasing the energy of the electrons penetrating into the first electron channel 401, and thus the energy of the electromagnetic waves radiated under the action of the undulator 400 can be increased.

[0214] Optionally, the radial cross-section of the first electron channel 401 is circular, and the inner diameter of the first electron channel 401 is larger than the inner diameter of the second electron channel 201.

[0215] In this way, sufficient space can be reserved in the first electron channel 401, the probability of electrons colliding with the inner wall of the first electron channel 401 can be reduced, which is beneficial to increasing the energy of the electromagnetic waves radiated under the action of the undulator 400.

[0216] In some embodiments, the tube body 300 is sleeved on the optical fiber 110.

[0217] While realizing the assembly of the tube body 300 and the optical fiber 110, the overall occupied size of the free electron laser 10 can be reduced, which is beneficial to reducing the volume of the free electron laser 10, making the occupied space of the free electron laser 10 small and the material utilization rate high, and thus enabling the free electron laser 10 to have the advantage of high integration.

[0218] In this embodiment, the outer diameter of the tube body 300 is 125 μm - 2000 μm, and the length of the tube body 300 is 3 cm - 9 cm.

[0219] Optionally, the tube body 300 can be selected as an optical fiber capillary.

[0220] Combined with the tube body 300 being sleeved on the optical fiber 110, the electron excitation layer 121, the conductive connection layer 130, the insulating member 700, the anode 200, the undulator 400, and the following annular receiving electrode 600, etc. are all arranged in the vacuum chamber 301, making the radial size of the free electron laser 10 small, which can greatly reduce the volume of the free electron laser 10, enabling the electron excitation layer 121 and the anode 200 to accelerate electrons well in the relatively small vacuum chamber 301, and being beneficial to realizing the high integration and miniaturization of the free electron laser 10. In addition, when the tube body 300 is selected as an optical fiber capillary, it is also convenient to observe the installation positions of the anode 200 and the undulator 400, so that there is a first preset distance between the anode 200 and the electron excitation layer 121 in the extending direction of the optical fiber 110, and there can also be a second preset distance between the electron excitation layer 121 and the undulator 400 in the extending direction of the optical fiber 110.

[0221] Optionally, the first preset distance can be 3 cm.

[0222] Optionally, the second preset distance can be 4 cm - 6 cm.

[0223] In some embodiments, please refer to Figure 1 and Figure 15 , a laser output window 500 is provided on the tube body 300, and along the longitudinal extension direction of the tube body 300, the electron source 100, the undulator 400, and the laser output window 500 are arranged at intervals in sequence.

[0224] Specifically, the extending direction of the tube body 300 is parallel to the extending direction of the optical fiber 110.

[0225] Optionally, the material of the laser output window 500 includes but is not limited to glass or other light-transmitting materials, etc.

[0226] Thus, on the one hand, the laser transmitted within the core 111 of the optical fiber 110 of the electron source 100 can excite the electron excitation layer 121 to emit electrons towards the first electron channel 401. This part of the electrons can penetrate into the first electron channel 401 and, under the action of the undulator 400, perform a wavy motion within the first electron channel 401 and radiate electromagnetic waves during this process. On the other hand, the laser transmitted within the core 111 of the optical fiber 110 can be emitted out of the vacuum chamber 301 through the laser output window 500.

[0227] In some embodiments, referring to Figure 15 , the free electron laser 10 further includes an annular receiving electrode 600 located between the undulator 400 and the laser output window 500. The annular receiving electrode 600 has a laser channel 61 for laser output. A second preset electric field is provided between the annular receiving electrode 600 and the electron excitation layer 121 so that the annular receiving electrode 600 can receive the electrons that penetrate out of the first electron channel 401.

[0228] Specifically, the annular receiving electrode 600 is externally connected to the positive electrode of the second power supply, and the electron excitation layer 121 is externally connected to the negative electrode of the second power supply through the conductive connection layer 130 so that a second preset electric field is provided between the annular receiving electrode 600 and the electron excitation layer 121.

[0229] Of course, the present application is not limited thereto. The installation manner of the annular receiving electrode 600 and the laser output window 500 can also be: the annular receiving electrode 600 is provided at the port on the side of the tube body 300 away from the electron source 100, and the laser output window 500 is provided within the laser channel 61.

[0230] Optionally, the second preset electric field can be greater than, less than or equal to the first preset electric field, and no specific limitation is made here.

[0231] Thus, on the one hand, the second power supply can be used to supplement electrons to the electron excitation layer 121, which is beneficial for the electron excitation layer 121 to continuously emit electrons under the excitation of the laser. On the other hand, the electrons emitted from the electron excitation layer 121 can be linearly accelerated along the direction from the electron excitation layer 121 towards the annular receiving electrode 600. The annular receiving electrode 600 can be used to receive the electrons that penetrate out of the first electron channel 401, improving the reliability and safety of the free electron laser 10. Of course, the annular receiving electrode 600 can also be grounded, which can also improve the reliability and safety of the free electron laser 10.

[0232] Specifically, the electron excitation layer 121, the anode 200, the undulator 400, and the annular receiving electrode 600 are sequentially arranged at intervals along the extending direction of the optical fiber 110.

[0233] Combined with the structure of the electron source 100, the electron source 100 can efficiently emit electrons along the extending direction of the optical fiber 110, and can make good use of the anode 200 and the annular receiving electrode 600 to linearly accelerate the electrons emitted from within the electron excitation layer 121 along the extending direction of the optical fiber 110. During the process of these electrons passing through the first electron channel 401, uniform electromagnetic waves can be radiated, and the electrons passing through the first electron channel 401 can also be received by the annular receiving electrode 600, which can well improve the reliability and safety of the free electron laser 10, while the laser exits through the laser channel 61 and the laser output window 500.

[0234] In some embodiments, a first port 302 is provided on the tube body 300 and is disposed opposite to the laser output window 500. Along the longitudinal extension direction of the tube body 300, the light output end 1102 of the optical fiber 110 extends into the vacuum chamber 301 through the first port 302, and the outer peripheral wall of the optical fiber 110 is hermetically connected to the inner peripheral wall of the first port 302.

[0235] In this way, the sealing performance of the vacuum chamber 301 can be improved. The electron excitation layer 121 can emit electrons outward from the light output end 1102 under the excitation of the laser transmitted by the fiber core 111, and can better emit electrons toward the anode 200 and the first electron channel 401 within the vacuum chamber 301, which can improve the reliability of the free electron laser 10.

[0236] Specifically, the assembly of the tube body 300 and the optical fiber 110 can be carried out in a vacuum environment, so that the inner peripheral wall of the tube body 300 is hermetically connected to the outer peripheral wall of the optical fiber 110, which can improve the sealing performance of the vacuum chamber 301.

[0237] In this embodiment, the optical fiber 110 has a light input end 1101 disposed opposite to the light output end 1102, and the end face of the light input end 1101 is flush with the plane where the first port 302 is located.

[0238] The optical fiber 110 can be generally encapsulated within the tube body 300, and the end face of the light input end 1101 of the optical fiber 110 is exposed through the first port 302, so as to couple the laser source to the light input end 1101 of the optical fiber 110. While better protecting the optical fiber 110, it also facilitates the laser emitted by the laser source to be transmitted through the optical fiber 110.

[0239] In some embodiments, the undulator 400 includes multiple groups of magnet groups arranged at intervals along the extending direction of the optical fiber 110. The multiple groups of magnet groups define the first electron channel 401. Each magnet group includes two magnets with opposite magnetic poles disposed on the inner peripheral wall of the tube body 300. Among adjacent two groups of magnet groups, the two magnets located on the same side and adjacent to each other have opposite magnetic poles.

[0240] The two magnets of the same magnet group are an N-type magnet 41 and an S-type magnet 42 respectively, and the magnetic poles of the N-type magnet 41 and the S-type magnet 42 are opposite.

[0241] Since the magnetic poles of the two magnets in the same magnet group are opposite, and in two adjacent magnet groups, the two magnets located on the same side and adjacent to each other have opposite magnetic poles. Therefore, during the process of electrons passing through the first electron channel 401, these electrons can undergo a wavy motion in the first electron channel 401 under the action of the undulator 400, and electromagnetic waves are radiated during this process. Compared with large-scale charged particle equipment, the undulator 400 of the present application has the characteristics of simple structure, low cost, and small occupied volume, and is particularly suitable for the miniaturized free electron laser 10.

[0242] The preparation method of the free electron laser 10 includes the following steps:

[0243] S20: Provide an electron source 100, a tube body 300, and an undulator 400.

[0244] S40: In a vacuum environment, load the electron source 100 into the tube body 300 through the first port 302 at one end of the tube body 300.

[0245] S60: In a vacuum environment, fix the undulator 400 on the inner side wall of the tube body 300 through the second port 303 at the other end of the tube body 300.

[0246] S80: Select a laser output window 500 made of glass and seal it at the second port 303 of the tube body 300.

[0247] Optionally, S80: Block the laser output window 500 at the second port 303 of the tube body 300, so that the electron source 100, the tube body 300, and the laser output window 500 define a vacuum chamber 301.

[0248] Optionally, before the step S30 of loading the electron source 100 into the tube body 300 through the first port 302 at one end of the tube body 300, the preparation method of the free electron laser 10 further includes:

[0249] S21: Load an insulating member 700 and an anode 200 into the tube body 300 through the first port 302 of the tube body 300.

[0250] Wherein, the outer diameters of the insulating member 700 and the anode 200 are equal to the outer diameter of the optical fiber 110 and are equal to the inner diameter of the tube body 300, which is convenient for the insulating member 700 and the anode 200 to be adaptively loaded into the tube body 300, and enables the second wire 21 on the electrode of the anode 200 to pass through the second wire passing hole out of the tube body 300 for external connection to the positive pole of the first power supply.

[0251] The step S40 of loading the electron source 100 into the tube body 300 through the first port 302 at one end of the tube body 300 specifically includes: loading the electron source 100 into the tube body 300 through the first port 302 of the tube body 300, so that in the extending direction of the optical fiber 110, the conductive connection layer 130 of the electron source 100 loaded into the tube body 300 abuts against the insulating member 700, and the first wire 1301 on the conductive connection layer 130 passes through the first wire passing hole and extends out of the tube body 300 for being externally connected to the negative electrode of the first power supply.

[0252] Specifically, the tube body 300 can be selected as an optical fiber capillary tube.

[0253] Taking the optical fiber 110 as a solid optical fiber and forming an electron excitation layer 121 covering the core 111 on the end face 11021 of the light-emitting end 1102 of the optical fiber 110 as an example to illustrate the preparation method of the electron source 100, the preparation method of the electron source 100 includes the following steps:

[0254] S210. Provide the optical fiber 110. Wherein, the optical fiber 110 includes a core 111 for transmitting laser and a cladding layer 112 wrapping the core 111.

[0255] Optionally, an appropriate length of the optical fiber 110 can be intercepted, the end coating layer of the optical fiber 110 can be removed, and one end of the cut optical fiber 110 can be processed to form the light-emitting end 1102. Specifically, a cutting mechanism can be used to cut one end of the cut optical fiber 110 to form the light-emitting end 1102. Forming the light-emitting end 1102 by cutting can make the cross section where the end face 11021 of the light-emitting end 1102 is located relatively flat, which is beneficial to forming a flat electron emission layer 120 on the end face 11021 of the light-emitting end 1102.

[0256] S220. Form an electron emission layer 120 on the end face 11021 of the light-emitting end 1102 of the optical fiber 110. The electron emission layer 120 at least includes an electron excitation layer 121, and the electron excitation layer 121 covers the core 111 of the optical fiber 110, so that the electron excitation layer 121 is located on the light-emitting path of the laser emitted from the core 111.

[0257] The electron excitation layer 121 can be formed by at least one of dry transfer, wet transfer and direct growth.

[0258] In some embodiments, the electron excitation layer 121 is prepared by dry transfer. The preparation method includes: transferring zero-dimensional materials, one-dimensional materials and / or two-dimensional materials to the tape by mechanical peeling, and transferring the zero-dimensional materials, one-dimensional materials and / or two-dimensional materials to the end face 11021 of the light-emitting end 1102 of the optical fiber 110.

[0259] Taking two-dimensional materials as an example for illustration, the preparation process of forming the electron excitation layer 121 by means of dry transfer is as follows:

[0260] (1) The two-dimensional material can be thinned by means of mechanical exfoliation until the electron excitation layer 121 with a preset thickness is formed. Specifically, the two-dimensional material is adhered to the highly viscous tape A, and the low-viscosity tape B can be used to mechanically exfoliate along the crystal cleavage plane of the two-dimensional material for multiple times until the electron excitation layer 121 with a preset thickness is formed.

[0261] (2) The electron excitation layer 121 with a preset thickness is transferred to the temporary substrate 20, and the tape B on the electron excitation layer 121 is removed. Specifically, the tape B can be melted by heating to peel the tape B from the electron excitation layer 121.

[0262] (3) The electron excitation layer 121 on the temporary substrate 20 is transferred to the end face 11021 of the light-emitting end 1102 of the optical fiber 110.

[0263] Optionally, the electron excitation layer 121 is made of two-dimensional materials, and the material of the temporary substrate 20 can be polycarbonate propylene ester film.

[0264] Of course, the present application is not limited thereto. The dry transfer method can also be combined with the direct growth method (such as chemical vapor deposition method). For example, the electron excitation layer 121 with a preset thickness is grown on the substrate to be peeled, and then the electron excitation layer 121 is transferred from the substrate to be peeled to the temporary substrate 20 by means of acid etching to remove the substrate to be peeled or tearing by hand. Among them, the substrate to be peeled can be a metal or other materials that can be etched by acid or torn by hand.

[0265] In some other embodiments, the electron excitation layer 121 is prepared by means of wet transfer. The preparation method includes: directly preparing zero-dimensional materials, one-dimensional materials or two-dimensional materials in a solution and floating them on the liquid surface, making the end face 11021 of the light-emitting end 1102 of the optical fiber 110 contact the zero-dimensional materials, one-dimensional materials or two-dimensional materials on the liquid surface, and drying the zero-dimensional materials, one-dimensional materials and / or two-dimensional materials on the end face 11021 of the light-emitting end 1102 of the optical fiber 110.

[0266] In still some other embodiments, the electron excitation layer 121 is prepared by means of direct growth. The preparation method includes: directly preparing the electron excitation layer 121 on the end face 11021 of the light-emitting end 1102 of the optical fiber 110 by at least one of chemical vapor deposition, physical vapor deposition, molecular beam epitaxy and liquid filling.

[0267] Optionally, before or after forming the electron emission layer 120 on the end face 11021 of the light output end 1102 of the optical fiber 110, the method for preparing the electron source 100 further includes:

[0268] S230. Form a conductive connection layer 130 on the end face 11021 of the light output end 1102 of the optical fiber 110, so that the conductive connection layer 130 overlaps with the electron excitation layer 121.

[0269] That is to say, the conductive connection layer 130 can be formed first and then the electron excitation layer 121; or the electron excitation layer 121 can be formed first and then the conductive connection layer 130; as long as the electron excitation layer 121 and the conductive connection layer 130 are electrically connected to each other, in this way, electrons can be supplied to the electron excitation layer 121 by means of the conductive connection layer 130, which is beneficial to the continuous electron emission of the electron excitation layer 121 under the excitation of laser.

[0270] Optionally, forming a conductive connection layer 130 on the end face 11021 of the light output end 1102 of the optical fiber 110, so that the conductive connection layer 130 overlaps with the electron excitation layer 121 specifically includes:

[0271] S231. Form a core protection layer on the end face 11021 of the light output end 1102 of the optical fiber 110, and the core protection layer covers the core 111 of the optical fiber 110.

[0272] It can be that the core protection layer directly covers the core 111 of the optical fiber 110, or it can be that the core protection layer indirectly covers the core 111 of the optical fiber 110, and no specific limitation is made here.

[0273] Optionally, the polymer microsphere solution can be coated on the end face 11021 of the light output end 1102 of the optical fiber 110 to form a core protection layer covering the core 111. Exemplarily, the polymer microsphere solution is a polymethyl methacrylate suspension.

[0274] S232. Form a conductive material layer covering the core protection layer on the optical fiber 110.

[0275] The conductive material layer can be formed by evaporation coating. Specifically, a metal evaporation coating device can be used to form the conductive material layer on the optical fiber 110.

[0276] S233. Remove the core protection layer and the part of the conductive material layer disposed on the core protection layer to form the conductive connection layer 130.

[0277] Optionally, a solvent capable of dissolving the core protective layer and having no interaction with the conductive material layer can be used to remove the core protective layer. Specifically, the light-emitting end 1102 of the optical fiber 110 can be immersed in acetone, so that the core protective layer (polymer beads) is dissolved, and a part of the conductive material layer disposed on the core protective layer (partial metal coating) is peeled off to obtain the conductive connection layer 130.

[0278] It can be understood that the core protective layer can be used to make the positive projection of the conductive connection layer 130 on the end face 11021 of the light-emitting end 1102 not coincide with the positive projection of the core 111 of the optical fiber 110 on the end face 11021 of the light-emitting end 1102, so that the laser transmitted in the core 111 of the optical fiber 110 can better interact with the electron excitation layer 121 covering the core 111 of the optical fiber 110.

[0279] In some embodiments, please refer to Figure 16 , the step S220 of forming the electron emission layer 120 on the end face 11021 of the light-emitting end 1102 of the optical fiber 110 specifically includes the following steps. Specifically, the specific steps of transferring the electron excitation layer 121 on the temporary substrate 20 to the end face 11021 of the light-emitting end 1102 of the optical fiber 110 are as follows:

[0280] S221. The electron excitation layer 121 and the end face 11021 of the light-emitting end 1102 of the optical fiber 110 are arranged opposite to each other and parallel to each other along the first direction F1.

[0281] Specifically, the end face 11021 of the light-emitting end 1102 of the optical fiber 110 and the electron excitation layer 121 are observed under a microscope, and the electron excitation layer 121 and the end face 11021 of the light-emitting end 1102 of the optical fiber 110 are arranged opposite to each other and parallel to each other along the first direction F1, and the center connection line of the two extends along the first direction F1.

[0282] S222. The optical fiber 110 is driven to move along the first direction F1 to contact the electron excitation layer 121.

[0283] S223. The electron excitation layer 121 is attached to the end face 11021 of the light-emitting end 1102 of the optical fiber 110 at a preset temperature.

[0284] In this way, the microscope can be used to align the center of the electron excitation layer 121 with the center of the end face 11021 of the light output end 1102 of the optical fiber 110, and the two are attached to each other at a certain temperature, so that the end face 11021 of the electron excitation layer 121 and the light output end 1102 of the optical fiber 110 can be closely attached under the action of van der Waals force, improving the bonding strength of the electron excitation layer 121 on the optical fiber 110, and also facilitating the electron excitation layer 121 to completely cover the fiber core 111 of the optical fiber 110, enabling the laser transmitted by the fiber core 111 to better interact with the electron excitation layer 121.

[0285] In some specific embodiments, the step S220 of forming the electron emission layer 120 on the end face 11021 of the light output end 1102 of the optical fiber 110 specifically includes the following steps. Specifically, the specific steps of transferring the electron excitation layer 121 on the temporary substrate 20 to the end face 11021 of the light output end 1102 of the optical fiber 110 are as follows:

[0286] S2201. Stick the annular heating sheet 40 on the back of the perforated glass slide 30 of the microscope, fix the temporary substrate 20 with the electron excitation layer 121 on the bottom side of the annular heating sheet 40 (the temporary substrate 20 can be fixed on the bottom side of the annular heating sheet 40 by an adhesive fixing method), and make the electron excitation layer 121 on the temporary substrate 20 face downward, and fix the optical fiber 110 below the electron excitation layer 121, so that the central axes of the objective lens of the microscope, the perforated glass slide 30, the annular heating sheet 40, the center of the electron excitation layer 121, and the center of the fiber core 111 coincide, and the objective lens of the microscope, the perforated glass slide 30, the annular heating sheet 40, the electron excitation layer 121, and the optical fiber 110 are arranged in sequence from top to bottom.

[0287] Optionally, the optical fiber 110 can be fixed on the moving platform by a fixture, and the end face 11021 of the light output end 1102 of the optical fiber 110 is set upward. The moving platform is used to adjust the position of the optical fiber 110 along the first direction F1, and to adjust the angle of the end face 11021 of the light output end 1102 of the optical fiber 110 relative to the horizontal plane to make it horizontal.

[0288] Optionally, the fixture can be a pneumatic gripper or an electric gripper.

[0289] Optionally, the moving platform can be a six-degree-of-freedom platform. The moving platform can also include a linear drive mechanism and a rotary drive mechanism connected to the linear drive mechanism. The output end of the rotary drive mechanism is connected to the fixture to drive the fixture and the optical fiber 110 clamped by the fixture to rotate around an axis parallel to the horizontal plane, so that the end face 11021 of the light output end 1102 is horizontal. The linear drive mechanism is used to drive the rotary drive mechanism, the fixture, and the optical fiber 110 to move along the first direction F1.

[0290] Among them, the linear driving mechanism can be a motor or a cylinder, and the rotary driving mechanism can be a motor or a rotary cylinder.

[0291] S2202. Observe the end face 11021 of the light-emitting end 1102 of the optical fiber 110 and the electron excitation layer 121 under a microscope, and arrange the electron excitation layer 121 and the end face 11021 of the light-emitting end 1102 of the optical fiber 110 opposite to each other and parallel to each other along the first direction F1, and make the center connection line of the two extend along the first direction F1.

[0292] The center alignment of the end face 11021 of the light-emitting end 1102 and the electron excitation layer 121 can be completed with the aid of a microscope.

[0293] S2203. Connect the annular heating sheet 40 to an external power supply to apply a first preset voltage to the annular heating sheet 40, and preheat the electron excitation layer 121 on the temporary substrate 20 (heat it to the preheating temperature), which is beneficial to make the electron excitation layer 121 flatter.

[0294] Optionally, the first preset voltage is 1V - 1.5V, and the preheating temperature is 50 - 60°C.

[0295] S2204. Drive the optical fiber 110 to move along the first direction F1 to contact the electron excitation layer 121. Newton's rings can appear when the end face 11021 of the light-emitting end 1102 contacts the electron excitation layer 121.

[0296] S2205. Make the electron excitation layer 121 closely adhere to the end face 11021 of the light-emitting end 1102 of the optical fiber 110 at a preset temperature, specifically including: applying a second preset voltage to the annular heating sheet 40, and heating the electron excitation layer 121 on the temporary substrate 20 to the preset temperature, which is beneficial to make the electron excitation layer 121 more closely arranged on the end face 11021 of the light-emitting end 1102.

[0297] Optionally, the second preset voltage is 2.5V - 4V, and the preset temperature is 90 - 100°C.

[0298] S2206. Remove the temporary substrate 20. The temporary substrate 20 can be removed by a method combining melting heating and solvent immersion. Specifically, apply a third preset voltage to the annular heating sheet 40, and heat the temporary substrate 20 to the melting temperature until it melts. It should be noted that the melting point of the electron excitation layer 121 is much higher than that of the temporary substrate 20.

[0299] Optionally, the third preset voltage is 5.5V - 6V, and the melting temperature is 130 - 150°C.

[0300] After the electron excitation layer 121 is closely disposed on the end face 11021 of the light output end 1102, the portion of the temporary substrate 20 in contact with the annular heating sheet 40 can be melted by means of melting and heating, and the electron excitation layer 121 can be separated from the annular heating sheet 40 and closely adhered to the end face 11021 of the light output end 1102 of the optical fiber 110, which is convenient for subsequent removal of the temporary substrate 20 remaining on the electron excitation layer 121. The portion of the temporary substrate 20 not in contact with the annular heating sheet 40 remains on the electron excitation layer 121. The optical fiber 110 can be removed from the fixture and the light output end 1102 of the optical fiber 110 can be immersed in acetone to dissolve the temporary substrate 20 remaining on the electron excitation layer 121 and completely remove the temporary substrate 20.

[0301] In some embodiments, in a vacuum environment, the step S60 of fixing the undulator 400 on the inner sidewall of the tube body 300 through the second port 303 at the other end of the tube body 300 specifically includes:

[0302] S610. Grow a magnetic material with a micron thickness by means of magnetron sputtering or direct growth (such as atomic cluster deposition method), and cut the magnetic material to obtain a plurality of magnets. In this way, a plurality of N-type magnets 41 and a plurality of S-type magnets 42 can be obtained.

[0303] S620. Form a plurality of N-type magnets 41 and a plurality of S-type magnets 42 arranged alternately on the first carrier 431.

[0304] S630. Form a plurality of S-type magnets 42 and a plurality of N-type magnets 41 arranged alternately on the second carrier.

[0305] S640. Oppositely arrange the first carrier 431 and the plurality of N-type magnets 41 and a plurality of S-type magnets 42 on the first carrier 431, and the second carrier and the plurality of S-type magnets 42 and a plurality of N-type magnets 41 on the second carrier, and respectively bond them to the inner sidewall of the tube body 300.

[0306] Optionally, before the step S80 of hermetically disposing the laser output window 500 made of glass material at the second port 303 of the tube body 300, the preparation method of the free electron laser further includes:

[0307] In a vacuum environment, the annular receiving electrode 600 is installed inside the tube body 300 and is located between the undulator 400 and the second port 303 of the tube body 300. Specifically, the annular receiving electrode 600 can be adhesively fixed inside the tube body 300, and a third wire passing hole and a fourth wire passing hole are formed in the tube body 300. The third wire on the conductive connection layer 130 can be externally connected to the negative electrode of the second power supply through the third wire passing hole, and the fourth wire on the annular receiving electrode 600 can be externally connected to the positive electrode of the second power supply through the fourth wire passing hole. A third sealant is provided between the part of the third wire passing through the third wire passing hole and the inner wall of the third wire passing hole, and a fourth sealant is provided between the part of the fourth wire passing through the fourth wire passing hole and the inner wall of the fourth wire passing hole. In this way, it is beneficial to improve the sealing performance of the vacuum chamber 301.

[0308] The embodiments of the present invention will be described in detail below in conjunction with the embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. For the experimental methods without specific conditions in the following embodiments, the guidance given in the present invention is preferably referred to, and it can also be carried out according to the experimental manuals or conventional conditions in the art, or according to the conditions recommended by the manufacturer, or referring to the experimental methods known in the art.

[0309] Example 1

[0310] The optical fiber 110 is a single-mode optical fiber. The diameter of the core 111 of the optical fiber 110 is 8.2 μm, the diameter of the optical fiber 110 is 125 μm, the angle ɑ is selected to be 30 degrees, that is, the bevel angle of the optical fiber 110 forms a 30-degree angle with the axis of the optical fiber 110, and the wavelength of the laser transmitted in the optical fiber 110 is 1550 nm. The conductive connection layer 130 includes 5 nm of titanium and 60 nm of gold laminated on the optical fiber 110. Among them, the core 111 at the end face 11021 of the light-emitting end 1102 is exposed (without being covered by the conductive connection layer 130). The electron excitation layer 121 is made of graphene two-dimensional material (the thickness of the graphene two-dimensional material is 1 nm). The shape of the graphene two-dimensional material is not limited and can be polygonal, circular, elliptical, etc. The electron excitation layer 121 is disposed on the end face 11021 of the light-emitting end 1102 of the optical fiber 110 and completely covers the core 111 of the optical fiber 110. Exemplarily, in the radial direction of the optical fiber 110, the size of the electron excitation layer 121 is 30 - 60 μm (much larger than the diameter of the core 111). In this embodiment, in the radial direction of the optical fiber 110, the size of the electron excitation layer 121 is 50 μm. The metal ring of the anode 200 is made of pure copper, the dielectric ring is made of a high-K dielectric material (such as boron nitride), the thickness of the anode 200 is 20 microns, the outer diameter of the anode 200 is 125 microns, and the inner diameter of the anode 200 is 62.5 microns. The outer diameter of the insulator 700 is 125 microns, and the inner diameter of the insulator 700 is 62.5 microns. The material of the magnet of the undulator 400 can be selected as ferrite magnetic material. The length, width, and height of the magnet are all 30 microns, and the magnet can be formed by magnetron sputtering.

[0311] Embodiment 2

[0312] The optical fiber 110 is a single-mode optical fiber. The diameter of the core 111 of the optical fiber 110 is 8.2 μm, the diameter of the optical fiber 110 is 125 μm, and the wavelength of the laser transmitted in the optical fiber 110 is 1550 nm. The conductive connection layer 130 includes 5 nm of titanium and 60 nm of gold laminated on the optical fiber 110. Among them, the core 111 at the light-emitting end 1102 is exposed (without being covered by the conductive connection layer 130). The electron excitation layer 121 is made of a two-dimensional graphene material (the thickness of the two-dimensional graphene material is 1 nm). The shape of the two-dimensional graphene material is not limited and can be polygonal, circular, elliptical, etc. The electron excitation layer 121 is disposed on the end face 11021 of the light-emitting end 1102 of the optical fiber 110 and completely covers the core 111 of the optical fiber 110. Exemplarily, along the radial direction of the optical fiber 110, the size of the electron excitation layer 121 is 30 - 60 μm (much larger than the diameter of the core 111). In this embodiment, along the radial direction of the optical fiber 110, the size of the electron excitation layer 121 is 40 μm. The metal ring of the anode 200 is made of pure copper, the dielectric ring is made of a high-K dielectric material (such as mica), the thickness of the anode 200 is 20 microns, the outer diameter of the anode 200 is 125 microns, and the inner diameter of the anode 200 is 62.5 microns. The outer diameter of the insulator 700 is 125 microns, and the inner diameter of the insulator 700 is 62.5 microns. The material of the magnet of the undulator 400 can be selected as a ferromagnetic material of magnetite. The length, width, and height of the magnet are all 30 microns, and the magnet can be formed by magnetron sputtering.

[0313] Embodiment 3

[0314] Please refer to Figure 14 , the optical fiber 110 is a single-mode optical fiber. The diameter of the core 111 of the optical fiber 110 is 8.2 μm, the diameter of the optical fiber 110 is 125 μm, and the wavelength of the laser transmitted in the optical fiber 110 is 1550 nm. The above-mentioned conductive connection layer 130 is formed on the outer surface of the optical fiber 110. The conductive connection layer 130 includes 5 nm of titanium and 50 nm of gold laminated on the light-emitting end 1102 of the optical fiber 110. Among them, the core 111 at the light-emitting end 1102 is exposed (without being covered by the conductive connection layer 130). By using the above operation steps of "transferring the electron excitation layer 121 on the temporary substrate 20 to the end face 11021 of the light-emitting end 1102 of the optical fiber 110", an auxiliary layer 122 with a thickness of 1 nm and a material of graphene is formed on the end face 11021 of the light-emitting end 1102 of the optical fiber 110; then, a plurality of nanotubes are deposited on the auxiliary layer 122, and the axial direction of the nanotubes is parallel to the extension direction of the core 111 to obtain the electron excitation layer 121, and then the electron source 100 is obtained. Among them, the first conductive part 131 of the conductive connection layer 130 is disposed on the end face 11021 of the light-emitting end 1102 of the optical fiber 110 and overlaps with the auxiliary layer 122, and the second conductive part 132 of the conductive connection layer 130 is disposed on the circumferential side surface of the optical fiber 110.

[0315] Comparative Example 1

[0316] An electron source was prepared according to the structure of Example 1, except that the electron excitation layer 121 in Example 1 was replaced with a gold layer having a thickness of 100 nm, and the gold layer was prepared by deposition.

[0317] Comparative Example 2

[0318] An electron source was prepared according to the structure of Comparative Example 1, except that the electron excitation layer 121 in Comparative Example 1 was replaced with a gold layer having a thickness of 1 nm.

[0319] The electron sources were prepared using the above-mentioned examples and comparative examples, and the performance of the prepared electron sources was tested. The test results are shown in the following table:

[0320] Table 1

[0321] Number Stability Lifetime Working vacuum degree Example 1 1％ 2000h 10 Pa Example 2 1％ 2000h 10 Pa Example 3 2％ 500h <![CDATA[10 -3 Pa]]> Comparative Example 1 10％ 100h <![CDATA[10 -5 Pa]]> Comparative Example 2 20％ 20h <![CDATA[10 -5 Pa]]>

[0322] Among them, stability refers to when the excitation power of the electron source is 50% or more of the damage power and the vacuum degree is 2×10 -5 Pa, the continuous emission current is for 1 hour. After removing the bad points, the ratio of the difference between the maximum current and the minimum current to the average current is the stability, and the stability can reflect the working stability of the electron source. Lifetime refers to when the excitation power of the electron source is 50% or more of the damage power and the vacuum degree is 2×10 -5 Pa, the continuous emission current until the current decays to less than 10% of the initial value, which is defined as the lifetime. The working vacuum degree refers to when the excitation power of the electron source is 50% or more of the damage power, the continuous emission current. The vacuum degree gradually increases until the current shows a rapid decay (the rapid decay is defined as the current decaying by more than 50% within 1 minute). The vacuum degree at this time is defined as the working vacuum degree. It can be seen from the above table that: the electron source of the present application has good stability, long lifetime, and good working vacuum degree.

[0323] It was found through testing that compared with the lifetime of the electron source prepared using the comparative examples, the lifetime of the electron source prepared using Examples 1-3 is higher; compared with the stability of the electron source prepared using the comparative examples, the stability of the electron source prepared using Examples 1-3 is better.

[0324] In this application, low-dimensional materials such as zero-dimensional materials, one-dimensional materials, and two-dimensional materials have atomic-level dimensions. Electrons incident from the back can be emitted into a vacuum without passing through in-body transmission, making them very suitable for ultrafast electron sources with narrow pulse widths. Moreover, low-dimensional materials can be directly integrated with different types of optical fibers, bringing ultra-high stability and integration. In addition, low-dimensional materials have no dangling bonds, are stable, have a high melting point, and are not easily damaged, making them suitable for high-power-excited large-beam electron sources. Integrating low-dimensional materials with a tip can result in a very sharp optical fiber tip, with large optical field and electric field enhancement factors, providing a large emission beam current. There are many combinations of low-dimensional materials, suitable for optoelectronic sources with various properties. Finally, the optical fiber integrated low-dimensional material electron source and low-dimensional material integration have significant advantages. The optical fiber can not only transmit laser light but also, as a carrier of low-dimensional materials, provide a stable excitation source with adjustable wavelength, polarization, and optical mode, which can be applied to different application scenarios, and there is no need to provide a complex optical path, with characteristics such as small volume and high integration. When integrated with other devices, it is possible to achieve stable integration without cracking and modifying vacuum electronic devices.

[0325] For the free electron laser 10 of this application, the anode 200 is selected as the electron acceleration structure, enabling the electrons emitted from the electron excitation layer 121 to pass through the second electron channel 201 of the anode 200 along the extension direction of the optical fiber 110 under the action of the first preset electric field and penetrate into the first electron channel 401. This allows these electrons to better undergo a wavy motion in the first electron channel 401 under the action of the undulator 400 to radiate uniform electromagnetic waves. In this way, the electron acceleration structure is simplified, the structure of the undulator 400 is simplified, and structures such as deflection magnets, wiggler magnets, and resonators are eliminated, greatly reducing the volume of the free electron laser 10. It can also reduce the manufacturing cost and energy consumption of the free electron laser 10, and the free electron laser 10 can be designed as an all-fiber integrated device to better achieve the integration and miniaturization of the free electron laser 10.

[0326] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0327] The above-described embodiments merely represent several implementation manners of this application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several modifications and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of this application patent should be subject to the appended claims.

Claims

1. A free electron laser, characterized in that, Comprising: A tube body having a vacuum chamber; An electron source including an optical fiber and an electron emission layer, the light-emitting end of the optical fiber being located in the vacuum chamber, the electron emission layer being disposed at the light-emitting end of the optical fiber, and the electron emission layer at least including an electron excitation layer, the electron excitation layer being disposed on the light path of the laser emitted by the optical fiber so that the electron excitation layer can emit electrons under the excitation of the laser; And A undulator disposed in the vacuum chamber and along the extending direction of the optical fiber, the light-emitting end of the optical fiber and the undulator being spaced apart; Wherein, the undulator has a first electron channel for electrons emitted from the electron excitation layer to pass through; The electron excitation layer includes at least one of a zero-dimensional material, a one-dimensional material, and a two-dimensional material.

2. The free electron laser according to claim 1, characterized in that, The free electron laser further includes an anode located between the electron source and the undulator; The anode has a second electron channel communicating with the first electron channel; There is a first preset electric field between the anode and the electron excitation layer so that the electrons emitted from the electron excitation layer can pass through the second electron channel and penetrate into the first electron channel under the action of the first preset electric field.

3. The free electron laser according to claim 2, wherein The electron source further includes a conductive connection layer disposed at least on the light-emitting end of the optical fiber and electrically connected to the electron excitation layer; The conductive connection layer and the anode are respectively used to externally connect the negative electrode and the positive electrode of a first power supply so that there is a first preset electric field between the anode and the electron excitation layer.

4. The free electron laser according to claim 3, characterized in that, The electron source further includes a first wire electrically connected to the conductive connection layer; The tube body is provided with a first wire passing hole for the first wire to pass through and communicating with the vacuum chamber, and a first sealant is provided between the side wall of the first wire passing hole and the part of the first wire passing through the first wire passing hole.

5. The free electron laser according to claim 2, characterized in that, The free electron laser further includes a second wire electrically connected to the anode, the tube body is provided with a second wire passing hole for the second wire to pass through and communicating with the vacuum chamber, and a second sealant is provided between the side wall of the second wire passing hole and the part of the second wire passing through the second wire passing hole.

6. The free electron laser according to claim 2, wherein The anode includes a plurality of spaced metal rings and dielectric rings located between two adjacent metal rings; All the metal rings and all the dielectric rings together define the second electron channel.

7. The free electron laser according to claim 6, characterized in that, The material of the dielectric ring includes a high-K dielectric material.

8. The free electron laser according to claim 2, characterized in that, The free electron laser further includes an insulator disposed between the electron source and the anode; The insulator has a third electron channel communicating with the second electron channel so that the electrons emitted from the electron excitation layer pass through the third electron channel and penetrate into the second electron channel.

9. The free electron laser according to claim 2, characterized in that, The radial cross-section of the second electron channel is circular, and the inner diameter of the second electron channel is D1; The outer diameter of the core of the optical fiber is D2; Wherein, D1 > 6D2.

10. The free electron laser according to any one of claims 1-9, characterized in that, The optical fiber includes a core for transmitting laser light and a cladding layer wrapped around the core. The end face of the light-emitting end of the optical fiber is arranged at an angle with the extending direction of the core. The electron emission layer is provided on the end face of the light-emitting end of the optical fiber, and the electron excitation layer covers the core of the optical fiber. The laser light emitted from the core can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the laser light emitted from the core and emits electrons.

11. The free electron laser according to any one of claims 1-9, characterized in that, The optical fiber includes a core for transmitting laser light and a cladding layer wrapped around the core; A light leakage notch is formed in the radial direction of the optical fiber at the light-emitting end of the optical fiber; The electron emission layer is provided on the bottom wall surface of the light leakage notch. The bottom wall surface of the light leakage notch is configured as a plane. The projection of the electron excitation layer on the bottom wall surface covers the projection of the core on the bottom wall surface; The electron excitation layer further extends to the light-emitting end of the optical fiber.

12. The free electron laser according to any one of claims 1-9, characterized in that, The optical fiber includes a perforated optical fiber which has a light guiding hole; The electron excitation layer is at least provided on the side wall of the light guiding hole and extends along the extending direction of the light guiding hole to the light-emitting end of the optical fiber.

13. The free electron laser according to any one of claims 1-9, characterized in that, The optical fiber includes a perforated optical fiber which has a light guiding hole; The electron emission layer is provided on the end face of the light-emitting end of the perforated optical fiber, and the electron excitation layer covers one end of the light guiding hole located at the end face of the light-emitting end; The laser light emitted from the perforated optical fiber can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the laser light emitted from the perforated optical fiber and emits electrons.

14. The free electron laser according to any one of claims 1-9, characterized in that, A pointed end portion is provided at the light-emitting end of the optical fiber; The electron excitation layer covers the surface of the pointed end portion of the optical fiber; The optical fiber includes a core for transmitting laser light. The laser light emitted from the core can directly irradiate on the electron emission layer, so that the electron excitation layer is excited by the laser light emitted from the core and emits electrons.

15. The free electron laser according to any one of claims 1-9, characterized in that, The tube body is sleeved on the optical fiber.

16. The free electron laser according to claim 15, characterized in that, The outer diameter of the tube body is 125 μm - 2000 μm, and the length of the tube body is 3 cm - 9 cm.

17. The free electron laser according to any one of claims 1-9, characterized in that, The thickness of the electron excitation layer is less than or equal to 50 nm.

18. The free electron laser according to any one of claims 1-9, characterized in that, A laser light emission window is provided on the tube body. Along the longitudinal extension direction of the tube body, the electron source, the undulator and the laser light emission window are arranged at intervals in sequence.

19. The free electron laser according to claim 18, characterized in that, The free electron laser further includes an annular receiving electrode located between the undulator and the laser light emission window. The annular receiving electrode has a laser channel for emitting the laser light; A second preset electric field is provided between the annular receiving electrode and the electron excitation layer, so that the annular receiving electrode can receive the electrons passing through the first electron channel.

20. The free electron laser according to claim 18, characterized in that, A first port is provided on the tube body and is arranged opposite to the laser light emission window; Along the longitudinal extension direction of the tube body, the light-emitting end of the optical fiber extends into the vacuum chamber through the first port, and the outer peripheral wall of the optical fiber is hermetically connected to the inner peripheral wall of the first port.

21. The free electron laser according to claim 20, characterized in that, The optical fiber has a light-incident end opposite to the light-emitting end. The end face of the light-incident end is flush with the plane where the first port is located.

22. The free electron laser according to any one of claims 1-9, characterized in that, The undulator includes multiple magnet groups arranged at intervals along the extending direction of the optical fiber, and the multiple magnet groups define the first electron channel; Each magnet group includes two magnets with opposite magnetic poles arranged on the inner peripheral wall of the tube body. Among two adjacent magnet groups, the two magnets located on the same side and adjacent to each other have opposite magnetic poles.

Images