Seed laser focusing and delaying device and method for free electron laser

Abstract

The application relates to a seed laser focusing and delaying device and method of a free electron laser, the free electron laser comprising an electron beam generating device, a first modulation section, a first dispersion section, a second modulation section, a second dispersion section and a radiation section, the seed laser focusing and delaying device being integrated in a vacuum chamber of the first dispersion section, the seed laser focusing and delaying device comprising a delay plate, a first lens and a second lens, the delay plate being used for time matching of an optical delay amount of the seed laser and an electron beam delay amount of the first dispersion section, and the first lens and the second lens being used for spatial matching of the seed laser and the electron beam in the second modulation section.

Description

Technical Field

[0001] This invention relates to the field of free-electron laser technology, and more specifically to a seed laser focusing and delay device and method for free-electron lasers. Background Technology

[0002] X-ray free-electron lasers, as "super cameras" capable of capturing dynamic processes at the atomic scale and femtosecond level, are revolutionary research tools in physics, chemistry, materials science, and life sciences. Their performance directly determines the research limits of related cutting-edge disciplines. In external seed operation mode, an external seed laser can apply coherent energy modulation to the electron beam, thereby generating highly stable, fully coherent free-electron laser pulses, which is one of the core technological pathways to achieve high-performance X-ray free-electron lasers.

[0003] Echo-Enabled Harmonic Generation (EEHG) is one of the most effective solutions for achieving high-order harmonic conversion. This solution employs an architecture combining two independent seed lasers with two dispersion sections, enabling harmonic conversions exceeding 100th order and providing crucial technical support for the generation of short-wavelength free-electron lasers. However, conventional EEHG schemes require injecting two independent seed lasers into two separate modulation sections. This structural design necessitates extremely high-precision control of the energy distribution, spatial shaping, and relative delay of the two lasers during laser transmission and injection, leading to numerous critical drawbacks in practical applications and severely hindering the development and implementation of high-repetition-rate, fully coherent short-wavelength free-electron lasers.

[0004] The specific shortcomings of the existing EEHG solution are as follows:

[0005] First, the synchronization accuracy requirements for dual-beam lasers are stringent. The two seed lasers need to achieve femtosecond-level precision synchronization control. Especially in high repetition frequency scenarios at the megahertz level, the heat accumulation generated by the laser optical components during long-term operation can cause optical path jitter, making it difficult to maintain a stable relative delay between the two lasers. This can easily lead to synchronization failure, directly affecting the stability and reliability of harmonic conversion.

[0006] Second, long-distance transmission makes spatial mode matching difficult. Due to the physical distance between the two modulation segments, the spatial characteristics of the seed laser, such as its wavefront and divergence angle, will inevitably be distorted after long-distance transmission. This makes it difficult for the second laser to simultaneously meet the dual requirements of high energy injection and good spatial mode matching, thereby reducing the efficiency and quality of the second energy modulation and affecting the final harmonic output performance.

[0007] Third, the system structure is complex, and debugging and maintenance are difficult. The two independent seed laser systems require precise energy distribution, spatial alignment and delay control, resulting in a cumbersome overall optical path structure, a complex and lengthy debugging process, and severely restricting the long-term stability and operational reliability of the system, increasing equipment maintenance costs and failure risks.

[0008] Therefore, how to achieve two-level modulation external seed mode under the premise of simplifying the system structure, while ensuring that the laser has stable and accurate time delay compensation and spatial mode matching capabilities, so that it can accurately act on the electron beam to achieve efficient high-order harmonic conversion, is of great practical significance and application value for promoting the technological breakthrough and practical application of high-repetition-rate, fully coherent short-wavelength free-electron lasers. Summary of the Invention

[0009] The purpose of this invention is to provide a seed laser focusing and delay device and method for free electron lasers, which is used to delay and spatially shape the seed laser to achieve spatiotemporal matching between the seed laser and the electron beam, so that two-way modulation can be achieved using only one seed laser, solving the problem of beam-electron beam failure and mismatch caused by the independent jitter of the two seed lasers, and simplifying the device structure.

[0010] To achieve the above objectives, the present invention provides a seed laser focusing and delay device for a free-electron laser. The free-electron laser includes an electron beam generating device for generating an electron beam and a first modulation section, a first dispersion section, a second modulation section, a second dispersion section, and a radiation section arranged sequentially along the electron beam transmission direction. The seed laser focusing and delay device constitutes a part of the first dispersion section, which includes a first magnetic compressor and the seed laser focusing and delay device.

[0011] The first modulation section receives the electron beam and an externally injected seed laser, both injected synchronously into the first modulation section, where the seed laser modulates the energy of the electron beam for the first time. The first magnetic compressor stretches the first energy modulation of the electron beam into a fine energy strip. The seed laser focusing and delay device introduces time delay and spatial shaping into the seed laser, so that the seed laser and the electron beam after passing through the first magnetic compressor are injected synchronously into the second modulation section and spatially matched. The second modulation section is configured to perform a second energy modulation of the electron beam by the seed laser; the second dispersion section converts the second energy modulation of the electron beam into density modulation and injects the density-modulated electron beam into the radiation section, while simultaneously extracting the seed laser output from the second modulation section; the radiation section generates and amplifies coherent radiation from the density-modulated electron beam to obtain a fully coherent high-harmonic X-ray free-electron laser pulse.

[0012] Optionally, the first modulation segment is further configured to cause the seed laser to receive an energy boost therein through coherent interaction with the electron beam.

[0013] Optionally, the first magnetic compressor includes a first diode, a second diode, a third diode, and a fourth diode arranged sequentially along the electron beam transmission direction, and the seed laser focusing and delay device is disposed between the first diode and the fourth diode.

[0014] Optionally, the seed laser focusing and delay device includes a delay plate and a focusing device. The delay plate is used to introduce a time delay for the seed laser, and the focusing device is located downstream of the delay plate and is used to spatially shape the seed laser so that the mode field distribution of the seed laser matches the transverse distribution of the electron beam in the second modulation segment.

[0015] Optionally, there are multiple delay plates with different thicknesses, each delay plate is fixed on a first push rod, the first push rod is mounted on a bracket, the first push rod is configured to slide relative to the bracket and move one of the delay plates into the optical path of the seed laser by sliding, so as to achieve coarse adjustment of the delay amount; the first push rod is also configured to rotate relative to the bracket and change the optical path of the seed laser through the delay plate in the optical path by rotating, so as to achieve fine adjustment of the delay amount.

[0016] Optionally, the focusing device includes a first lens and a second lens, both of which are mounted on the bracket, and the distance between the first lens and the second lens is adjustable.

[0017] Optionally, the first modulation segment is an undulator, the length of which is set to allow the seed laser to enter the high-gain amplification region, so that the energy of the seed laser is increased by at least one order of magnitude after coherently interacting with the electron beam;

[0018] The second modulation segment is an oscillator, and the length of the second modulation segment is shorter than that of the first modulation segment.

[0019] Another aspect of the present invention provides a method for a seed laser focusing and delay device for a free-electron laser, comprising:

[0020] A seed laser focusing and delay device for a free electron laser is provided. The free electron laser includes an electron beam generating device for generating an electron beam and a first modulation section, a first dispersion section, a second modulation section, a second dispersion section and a radiation section arranged sequentially along the electron beam transmission direction. The seed laser focusing and delay device constitutes a part of the first dispersion section. The first dispersion section includes a first magnetic compressor and the seed laser focusing and delay device.

[0021] The electron beam generating device generates an electron beam, and the electron beam and the external seed laser are synchronously injected into the first modulation segment;

[0022] The first modulation segment causes the seed laser to perform a first energy modulation on the electron beam therein;

[0023] The first dispersion section receives the seed laser and the electron beam after the first energy modulation. The first magnetic compressor stretches the electron beam into a fine energy strip after the first energy modulation. The seed laser focusing and delay device introduces time delay and spatial shaping to the seed laser so that the seed laser and the electron beam after passing through the first magnetic compressor are synchronously injected into the second modulation section and achieve spatial mode matching.

[0024] The second modulation segment modulates the energy of the electron beam after it has passed through the first magnetic compressor a second time using the seed laser; the second dispersion segment converts the second energy modulation of the electron beam into a second density modulation and injects the second density-modulated electron beam into the radiation segment; the radiation segment generates and amplifies coherent radiation from the second density-modulated electron beam to obtain a fully coherent high-harmonic X-ray free electron laser pulse. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a free-electron laser according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the structure of a modulation device for a free-electron laser according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the structure of the first dispersion segment of a free electron laser according to an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the seed laser focusing and delay device according to an embodiment of the present invention. Detailed Implementation

[0029] The preferred embodiments of the present invention are given below with reference to the accompanying drawings and described in detail.

[0030] like Figure 1 As shown, this embodiment of the invention provides a free electron laser, which includes an electron beam generating device 100 and a modulation device 200. The electron beam generating device 100 is used to generate an electron beam that meets preset requirements, and the modulation device 200 is used to receive the electron beam and perform two-stage modulation on the electron beam to generate a high repetition rate, fully coherent, and highly stable high-order harmonic X-ray free electron laser pulse.

[0031] The electron beam generating device 100 may include an electron gun and an accelerator. The electron gun is used to initially generate an electron beam (i.e., an electron source) and to perform preliminary focusing and extraction of the initial electron beam. The accelerator is used to accelerate, regulate the energy, and optimize the quality of the initial electron beam extracted by the electron gun, so that the electron beam reaches the preset indicators such as energy, flux, emittance, and energy dissipation required for free electron laser radiation, and finally outputs an electron beam that meets the requirements.

[0032] like Figure 2 As shown, the modulation device 200 includes a first modulation section 210, a first dispersion section 220, a second modulation section 230, a second dispersion section 240, and a radiation section 250 arranged sequentially along the electron beam transmission direction.

[0033] The first modulation section 210 is used to receive the electron beam output from the electron beam generating device 100 and the externally injected seed laser. The seed laser and the electron beam are synchronously injected into the first modulation section 210, maintaining sub-picosecond synchronization in time and coaxial transmission in space with matched spot sizes, to ensure that the seed laser field and the electron beam can undergo continuous and efficient coherent interaction, thereby achieving the first energy modulation of the electron beam.

[0034] After the first energy modulation, the electron beam and the seed laser enter the first dispersion section 220. The first dispersion section 220 is used to stretch the first energy modulation of the electron beam into a fine energy strip and to synchronously inject the electron beam and the seed laser into the second modulation section 230. In the second modulation section 230, the seed laser interacts coherently with the electron beam to achieve a second energy modulation of the electron beam.

[0035] The second dispersion section 240 is used to convert the second energy modulation of the electron beam into density modulation, and inject the density-modulated electron beam into the radiation section 250, while the seed laser is extracted by the second dispersion section 240. The radiation section 250 is used to generate and amplify coherent radiation from the density-modulated electron beam to output a high-repetition-rate, fully coherent, and highly stable high-harmonic X-ray free-electron laser pulse.

[0036] In some embodiments, the seed laser can also achieve energy enhancement through coherent interaction with the electron beam in the first modulation section 210. Specifically, the seed laser field resonates with the transverse oscillating motion of the electron beam, generating a mass force that causes the electrons to periodically accelerate and decelerate. The electrons decelerate at the peaks, transferring kinetic energy to the laser field; they accelerate at the troughs, absorbing a small amount of energy from the laser field. Overall, the net effect is that the kinetic energy of the electron beam is continuously transferred to the laser field. As the coherent interaction accumulates, the seed laser energy increases exponentially, with the enhancement magnitude positively correlated with the length of the first modulation section 210, the peak flux of the electron beam, and the initial energy of the seed laser. Simultaneously, the longitudinal phase space of the electron beam forms periodic energy fluctuations, completing the first energy modulation of the electron beam. The modulation amplitude is typically 2-6 times the initial energy dispersion of the electron beam, sufficient to meet the requirements of the subsequent dispersion section to convert energy modulation into density modulation (micro-beaming).

[0037] The first modulation segment 210 can be an undulator, configured to be long enough to allow the seed laser to enter the high-gain amplification region. The length of the first modulation segment 210 can be optimized based on the seed laser wavelength, electron beam energy, and beam quality. For example, the undulator length can be 8 m. The undulator period λ of the first modulation segment 210 is... u1 And magnetic field strength B1 and seed laser wavelength λ seed Resonance matching satisfies the resonance condition. After the seed laser coherently interacts with the electron beam in the first modulation section 210, its energy can be increased by one or more orders of magnitude, such as from microjoules to millijoules. Therefore, only microjoule-level seed laser injection is required to obtain strong energy modulation of the electron beam, fundamentally reducing the demand for seed laser power.

[0038] like Figure 3 As shown, the first dispersion section 220 includes a first magnetic compressor and a seed laser focusing and delay device 225. The first magnetic compressor is used to stretch the first energy modulation of the electron beam into a fine energy strip, and can adopt a four-magnet structure (e.g., the first to fourth dipole irons 221-224 arranged sequentially along the electron beam transmission direction).

[0039] The seed laser focusing and delay device 225 is located between the first diode 221 and the fourth diode 224. It is used to receive the seed laser emitted from the first modulation section 210 and introduce a time delay to it so that the seed laser is synchronized with the electron beam after passing through the first magnetic compressor, that is, synchronously injected into the second modulation section 230.

[0040] The first magnetic compressor is configured to have a large longitudinal dispersion coefficient. After passing through the first dipole iron 221, the electron beam is deflected by an angle of θ and an off-axis distance of A, providing installation space for the seed laser focusing and delay device 225.

[0041] Due to the dispersive effect of the first magnetic compressor, the longitudinal path length of the electron beam increases when it passes through the first magnetic compressor, resulting in a time delay Δt (the magnitude of which is determined by the design parameters of the magnetic compressor). To compensate for this time delay, the time delay introduced by the seed laser focusing and delay device 225 must be the same as Δt.

[0042] The seed laser focusing and delay device 225 may include a delay plate and a focusing device arranged sequentially along the optical path. The delay plate is used to introduce a time delay to the seed laser, and the magnitude of the time delay is related to the thickness of the delay plate. The focusing device is used to shape the seed laser, for example, by finely adjusting the laser beam waist size and focusing position to match its mode field with the transverse distribution of the electron beam in the second modulation section 230.

[0043] like Figure 4As shown, the seed laser focusing and delay device 225 may include multiple delay plates 2251 of different thicknesses. Each delay plate 2251 is fixed on a first push rod 2252, which is mounted on a bracket 2253. The first push rod 2252 is configured to slide relative to the bracket 2253. By sliding the first push rod 2252, any delay plate 2251 can be positioned in the optical path of the seed laser, that is, the seed laser can pass through a delay plate 2251 of any thickness, thereby achieving coarse adjustment of the delay amount. The first push rod 2252 is also configured to rotate relative to the bracket 2253 around its own axis. By rotating the first push rod 2252, the optical path of the seed laser through the delay plate in the optical path can be changed, thereby achieving continuous fine adjustment of the delay amount. Through coarse and fine adjustment of the delay amount, the seed laser and the electron beam can be synchronously injected into the second modulation section 230. The focusing device may include a first lens 2254 and a second lens 2255. Both the first lens 2254 and the second lens 2255 are mounted on a bracket 2253 and sequentially positioned downstream of a delay plate 2251. The first lens 2254 remains fixed, while the second lens 2255 is slidable relative to the bracket 2253 to move closer to or further away from the first lens 2254. After passing through the delay plate 2251, the seed laser passes sequentially through the first lens 2254 and the second lens 2255. The first lens 2254 and the second lens 2255 are used to shape the seed laser to precisely control its beam shape. By sliding the second lens 2255 relative to the bracket 2253, the distance between the second lens 2255 and the first lens 2254 can be adjusted, thereby finely adjusting the laser beam waist size and focusing position to focus the seed laser onto the second modulation segment 230. The second lens 2255 may be fixed to a second push rod 2256 so that the second push rod 2256 can drive the second lens 2255 to slide. The first push rod 2252 and the second push rod 2256 can be driven manually, by piezoelectric ceramics, by magnetic coupling, or by any other suitable method. The core function of the first lens 2254 and the second lens 2255 is to achieve spatial matching between the energy-enhanced seed laser and the electron beam. Their optical design follows Gaussian beam propagation theory. The input beam parameters of the two lenses include: beam waist position (usually located near the exit of the first modulation section 210), beam waist radius, and so on. The divergence angle θ, and its related formula is: ,in Where is the wavelength. For the beam waist, the size of the light spot transmitted over the z-distance can be calculated using the following formula: , It is the Rayleigh length.

[0044] The beam waist of the beam output from the two lenses should be located near the center of the second modulation section 230, and the beam waist radius should match the lateral dimension of the electron beam. For a single-lens system, the object-side beam waist... Like a square waistband The lens focal length f, object distance L1, and image distance L2 satisfy the Gaussian beam imaging formula:

[0045]

[0046]

[0047] In practical design, the object distance and image distance can be measured on-site, the divergence angle is calculated by the beam element, and the image-side beam waist depends on the specific physical design. Lens structures can be matched in different ways; for scenarios with high requirements for beam waist position and size, dual-lens or multi-lens systems can be used. Optical parameters for dual-lens or multi-lens systems can be calculated through successive transformations of the single-lens formula or matrix optics methods.

[0048] The seed laser output from the first modulation section 210 has significant divergence characteristics, with a divergence angle on the order of hundreds of microradians. The beam waist position is offset from the center of the second modulation section 230 by tens of meters. Through the precise design of the shaping mechanism, the divergent seed laser can be refocused into the second modulation section 230 to form a focused spot (typically a few tenths of a millimeter) that matches the lateral size of the electron beam. This spatial shaping enables the laser and electron beam, which were originally mismatched due to long-distance transmission, to achieve high-precision spatial overlap within the second modulation section 230.

[0049] When the electron beam passes through the first dispersion section 220, its longitudinal dispersion coefficient R 56 Under the influence of R, the electron beam undergoes longitudinal stretching and time shift (i.e., time delay), and the time delay Δt is determined by R. 56 It is determined by both the energy modulation amplitude and its calculation formula is as follows:

[0050]

[0051] in, denoted as the relative energy modulation amplitude applied to the first modulation segment 210, where c is the speed of light.

[0052] The time delay introduced by the retardation plate is determined by the thickness of the retardation plate and the refractive index of its material:

[0053]

[0054] in, Here, n is the time delay, n is the refractive index, and c is the speed of light.

[0055] To ensure that the electron beam and seed laser are injected synchronously into the second modulation segment 230, it is necessary to... .

[0056] The material for the delay film can be selected from materials such as calcium fluoride, magnesium fluoride, and fused silica, which have high transmittance at the seed laser wavelength, good refractive index stability, and can be used to prepare high-precision optical surfaces.

[0057] The second modulation segment 230 can be an undulator, shorter than the length of the first modulation segment 210. The seed laser, after energy enhancement, acts again on the electron beam within the second modulation segment 230, applying a second energy modulation. The undulator period λ of the second modulation segment 230 is... u2 The magnetic field strength B2 may be the same as or different from the first modulation segment 210, and needs to be resonantly matched with the seed laser wavelength.

[0058] The second dispersion section 240 includes a second magnetic compressor and a laser extraction element 245. The second magnetic compressor employs a four-magnet structure (fifth dipole 241 to eighth dipole 244) to convert the second energy modulation of the electron beam into density modulation. The laser extraction element 245 is located between the fifth dipole 241 and the eighth dipole 244 to receive and extract the seed laser emitted from the second modulation section 230, preventing it from entering the radiation section 250.

[0059] Radiation section 250 can be an oscillator with a period λ. u3 The magnetic field strength B3 is tuned to the target harmonic wavelength λ. n =λ seed / n, where n is the target harmonic order. The target harmonic order n can be selected according to experimental requirements, for example, n=8, 12, 16, 20, etc., and is achieved by adjusting the dispersion coefficient of the second dispersion section 240 and the resonant wavelength of the radiation section 250. In an exemplary embodiment, the harmonic order can reach 30th.

[0060] The free electron laser of this invention introduces a seed laser focusing and delay device 225 in the first dispersion section 220 to perform precise time delay compensation and spatial mode matching on the seed laser after passing through the first modulation section 210, so that it can accurately act on the electron beam again in the second modulation section 230, thereby realizing two-stage modulation under single-source seed laser conditions. Compared with the existing dual-laser-source EEHG scheme, it completely avoids the problem of multi-source synchronization, and changes the synchronization operation from the process of "dual-source active phase-locking" to the process of "single-source adaptive matching". The structure and device are simple and the debugging difficulty is reduced.

[0061] This invention also provides a method for a seed laser focusing and delay device for a free-electron laser, comprising:

[0062] A seed laser focusing and delay device 225 for a free electron laser is provided. The free electron laser includes an electron beam generating device 100 for generating an electron beam and a first modulation section 210, a first dispersion section 220, a second modulation section 230, a second dispersion section 240, and a radiation section 250 arranged sequentially along the electron beam transmission direction. The seed laser focusing and delay device 225 constitutes a part of the first dispersion section 220. The first dispersion section 220 includes a first magnetic compressor and the seed laser focusing and delay device 225.

[0063] The electron beam generating device 100 generates an electron beam, and the electron beam and the external seed laser are synchronously injected into the first modulation section 210;

[0064] The first modulation section 210 enables the seed laser to perform the first energy modulation on the electron beam therein;

[0065] The first dispersion section 220 receives the seed laser and the electron beam after the first energy modulation. The first magnetic compressor stretches the electron beam into a fine energy strip after the first energy modulation. The seed laser focusing and delay device 225 introduces time delay and spatial shaping to the seed laser so that the seed laser and the electron beam after the first magnetic compressor are synchronously injected into the second modulation section 230 and achieve spatial matching.

[0066] The second modulation section 230 modulates the energy of the electron beam after it has passed through the first magnetic compressor a second time using the seed laser; the second dispersion section 240 converts the second energy modulation of the electron beam into density modulation and injects the density-modulated electron beam into the radiation section; the radiation section 250 generates and amplifies coherent radiation from the density-modulated electron beam to obtain a fully coherent high-harmonic X-ray free electron laser pulse.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A seed laser focusing and delay device for a free-electron laser, characterized in that, The free electron laser includes an electron beam generating device for generating an electron beam and a first modulation section, a first dispersion section, a second modulation section, a second dispersion section, and a radiation section arranged sequentially along the electron beam transmission direction. The seed laser focusing and delay device constitutes a part of the first dispersion section, and the first dispersion section includes a first magnetic compressor and the seed laser focusing and delay device. The first modulation section receives the electron beam and an externally injected seed laser. The electron beam and the seed laser are synchronously injected into the first modulation section. The first modulation section is configured to allow the seed laser to perform a first energy modulation on the electron beam. The first magnetic compressor stretches the first energy modulation of the electron beam into a fine energy strip. The seed laser focusing and delay device introduces a time delay and spatial shaping into the seed laser so that the seed laser and the electron beam after passing through the first magnetic compressor are synchronously injected into the second modulation section and spatially matched. The second modulation section is configured to allow the seed laser to perform a second energy modulation on the electron beam after passing through the first magnetic compressor. The second dispersion section converts the second energy modulation of the electron beam into density modulation and injects the density-modulated electron beam into the radiation section. The seed laser output from the second modulation section is extracted by the second dispersion section. The radiation section generates and amplifies coherent radiation from the density-modulated electron beam to obtain a fully coherent high-harmonic X-ray free electron laser pulse.

2. The seed laser focusing and delay device for free-electron lasers according to claim 1, characterized in that, The first modulation segment is further configured to enable the seed laser to receive an energy boost through coherent interaction with the electron beam.

3. The seed laser focusing and delay device for free-electron lasers according to claim 1, characterized in that, The first magnetic compressor includes a first diode, a second diode, a third diode, and a fourth diode arranged sequentially along the electron beam transmission direction, and the seed laser focusing and delay device is located between the first diode and the fourth diode.

4. The seed laser focusing and delay device for free-electron lasers according to claim 1, characterized in that, The seed laser focusing and delay device includes a delay plate and a focusing device. The delay plate is used to introduce a time delay for the seed laser, and the focusing device is located downstream of the delay plate and is used to shape the seed laser so that the seed laser is focused at the center of the second modulation segment.

5. The seed laser focusing and delay device for a free-electron laser according to claim 4, characterized in that, The delay plates are multiple and have different thicknesses. Each delay plate is fixed on a first push rod, which is mounted on a bracket. The first push rod is configured to slide relative to the bracket and move one of the delay plates into the optical path of the seed laser by sliding. The first push rod is also configured to rotate relative to the bracket and change the optical path of the seed laser through the delay plates in the optical path by rotating.

6. The seed laser focusing and delay device for a free-electron laser according to claim 5, characterized in that, The focusing device includes a first lens and a second lens, both of which are mounted on the bracket, and the distance between the first lens and the second lens is adjustable.

7. The seed laser focusing and delay device for a free-electron laser according to claim 1, characterized in that, The first modulation segment is an undulator, and the length of the first modulation segment is set to enable the seed laser to enter the high-gain amplification region so that the energy of the seed laser is increased by at least one order of magnitude after coherent interaction with the electron beam. The second modulation segment is an oscillator, and the length of the second modulation segment is shorter than the length of the first modulation segment.

8. A method for seed laser focusing and delaying device for free-electron laser, characterized in that, include: A seed laser focusing and delay device for a free electron laser is provided. The free electron laser includes an electron beam generating device for generating an electron beam and a first modulation section, a first dispersion section, a second modulation section, a second dispersion section and a radiation section arranged sequentially along the electron beam transmission direction. The seed laser focusing and delay device constitutes a part of the first dispersion section. The first dispersion section includes a first magnetic compressor and the seed laser focusing and delay device. The electron beam generating device generates an electron beam, and the electron beam and the external seed laser are synchronously injected into the first modulation segment; The first modulation segment causes the seed laser to perform a first energy modulation on the electron beam therein; The first dispersion section receives the seed laser and the electron beam after the first energy modulation. The first magnetic compressor stretches the electron beam into a fine energy strip after the first energy modulation. The seed laser focusing and delay device introduces time delay and spatial shaping to the seed laser so that the seed laser and the electron beam after passing through the first magnetic compressor are synchronously injected into the second modulation section and achieve spatial matching. The second modulation section modulates the energy of the electron beam after it has passed through the first magnetic compressor a second time using the seed laser; the second dispersion section converts the second energy modulation of the electron beam into density modulation and injects the density-modulated electron beam into the radiation section; the radiation section generates and amplifies coherent radiation from the density-modulated electron beam to obtain a fully coherent high-harmonic X-ray free electron laser pulse.

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