Light source device, system and water window band full-coherent free electron laser generation method

Abstract

The application discloses a light source device, a system and a water window band full-coherent free electron laser generating method. The device comprises: a harmonic generation unit for connecting an electron beam and a seed laser and generating low-order harmonics; at least two cascaded amplifier units connected with the harmonic generation unit, for connecting the low-order harmonic radiation and generating coherent harmonic radiation, and for tuning the coherent harmonic laser to high-order harmonic radiation to obtain water window band full-coherent free electron laser pulses. The application constructs a multi-stage amplifier unit in the rear stage of the harmonic generation unit, and each subsequent amplifier unit is configured to resonate on a high-order harmonic of the radiation output by the previous amplifier unit, so that the harmonic radiation of the previous stage is used as the effective seed of the subsequent stage, the frequency is up-converted stage by stage, the frequency of the coherent radiation is converted to the target high-order harmonic stage by stage, and the water window band full-coherent free electron laser is obtained.

Description

Technical Field

[0001] This invention relates to the field of particle accelerators and laser technology, and more particularly to a light source device, system, and method for generating fully coherent free electron lasers in the water window band. Background Technology

[0002] The water window band is crucial for life sciences. If high-intensity, fully coherent X-ray pulses can be generated in this band, in-situ observation of living cells will be possible, providing a new way to analyze the process of cellular life activities in real time, while avoiding significant damage to biological structures.

[0003] Traditional single-stage high-gain harmonic generation (HGHG) free-electron lasers (FELs) suffer from a severe limitation in harmonic conversion efficiency due to the inherent contradiction between electron beam energy dissipation and FEL amplification. They typically struggle to stably generate radiation above the 25th harmonic, making it impossible to effectively cover the "water window" band (wavelength range of approximately 2.3 nm to 4.4 nm, corresponding to the K absorption edge of oxygen and carbon) crucial for in vivo biological imaging. While schemes such as echo-enabled harmonic generation (EEHG) and phase-merging enhanced harmonic generation (PEHG) can further shorten the wavelength, they usually require specific and complex modifications to the equipment, making implementation on existing facilities difficult and costly. Furthermore, while harmonic laser methods based on self-amplified spontaneous emission (SASE) can achieve short wavelengths, they suffer from poor temporal coherence and large pulse energy fluctuations, failing to meet the experimental requirements of many laser sources that demand high stability and high monochromaticity.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a light source device, system and water window band fully coherent free electron laser generation method to solve the problems of physical limitations of harmonic conversion efficiency, complexity and compatibility of high-order harmonic schemes, and coherence in the self-amplified spontaneous emission scheme in the generation of water window band coherent free electron laser pulses in existing free electron laser technology.

[0006] The technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a light source device comprising:

[0008] Harmonic generation unit for connecting electron beam and seed laser to generate low-order harmonic radiation;

[0009] At least two cascaded amplifier units are connected to the harmonic generation unit. The amplifier units are used to receive the low-order harmonic radiation and generate coherent harmonic radiation, and to tune the coherent harmonic laser into high-order harmonic radiation to obtain a fully coherent free electron laser pulse in the water window band.

[0010] In a further embodiment of the present invention, the harmonic generation unit includes: an electron accelerator, a first dispersion unit, a first modulation unit, and a second dispersion unit; wherein,

[0011] The electron accelerator is connected to the first dispersion unit and is used to receive the first electron beam and accelerate the first electron beam to form a second electron beam, which is then input to the first dispersion unit.

[0012] The first dispersion unit is connected to the first modulation unit and is used to compress the second electron beam and form a third electron beam that is input to the first modulation unit.

[0013] The first modulation unit is connected to the seed laser and the second dispersion unit to generate periodic energy modulation on the third electron beam and generate a fourth electron beam that is input to the second dispersion unit.

[0014] The second dispersion unit is connected to the amplifier unit and is used to convert periodic energy modulation into density modulation and generate a fifth electron beam that is input to the amplifier unit; the fifth electron beam is accompanied by the low-order harmonic radiation.

[0015] In a further embodiment of the present invention, the cascaded amplifier unit includes: a first amplifier unit, a second amplifier unit, and a third amplifier unit; the first amplifier unit, the second amplifier unit, and the third amplifier unit are cascaded sequentially.

[0016] The first amplifier unit is used to amplify the fifth electron beam to obtain the sixth electron beam;

[0017] The second amplifier unit is used to amplify the sixth electron beam to obtain the seventh electron beam;

[0018] The third amplifier unit is used to amplify the seventh electron beam to form a high-power water-window band fully coherent free electron laser pulse.

[0019] In a further embodiment of the present invention, the first amplifier unit includes a first oscillator; the second amplifier unit includes a second oscillator; and the third amplifier unit includes a third oscillator, a fourth oscillator, a fifth oscillator, and a sixth oscillator, wherein the third oscillator, the fourth oscillator, the fifth oscillator, and the sixth oscillator are cascaded.

[0020] A further embodiment of the invention includes a phase shifter connected between the two amplifier units.

[0021] In a further embodiment of the present invention, the first modulation unit is an oscillator;

[0022] The first dispersive unit includes a first diode, a second diode, a third diode, and a fourth diode; the first diode, the second diode, the third diode, and the fourth diode are symmetrically distributed.

[0023] Secondly, the present invention also provides a light source system, which includes an electronic source, a first seed laser generator and the light source device described above; the electronic source is connected to the harmonic generation unit and is used to generate an electron beam and input it into the harmonic generation unit; the first seed laser generator is connected to the harmonic generation unit and is used to generate a seed laser and input it into the harmonic generation unit.

[0024] Thirdly, the present invention also provides a method for generating a fully coherent free-electron laser in the water window band, comprising:

[0025] Low-order harmonic radiation is generated by modulating the incoming electron beam and seed laser through a harmonic generation unit.

[0026] The first amplifier unit resonates with the low-order harmonic radiation and generates coherent harmonic radiation. The next amplifier unit uses the harmonic radiation of the previous stage as an effective seed to tune the coherent harmonic radiation into higher-order harmonic radiation, so as to obtain a fully coherent free electron laser pulse in the water window band.

[0027] In a further embodiment of the present invention, the step of modulating the incoming electron beam and seed laser through the harmonic generation unit to generate low-order harmonic radiation includes:

[0028] The added electron beam is accelerated and compressed;

[0029] The accelerated and compressed electron beam is modulated with a seed laser and further compressed to convert the energy modulation of the electron beam into density modulation, thereby generating low-order harmonic radiation.

[0030] In a further embodiment of the present invention, the amplifier unit includes a first amplifier unit, a second amplifier unit, and a third amplifier unit; the first amplifier unit resonates with low-order harmonics and generates coherent harmonic radiation, and the next amplifier unit uses the harmonic radiation of the previous stage as an effective seed to tune the coherent harmonic radiation into higher-order harmonic radiation, thereby obtaining a fully coherent free electron laser pulse in the water window band, includes the following steps:

[0031] The fifth electron beam carrying micro-clusters is introduced into the first amplifier unit, causing the fifth electron beam to resonate at the frequency of the first harmonic radiation, so as to generate a sixth electron beam with micro-clusters and harmonic radiation having higher harmonics.

[0032] The first harmonic radiation is used as an effective seed to interact with the sixth electron beam in the second amplifier unit to obtain the amplified second harmonic radiation, and a seventh electron beam is generated.

[0033] The second harmonic radiation is used as an effective seed and interacts with the seventh electron beam in the third amplifier unit to obtain the amplified third harmonic radiation, so as to obtain a fully coherent free electron laser pulse in the water window band.

[0034] This invention provides a light source device, system, and method for generating a fully coherent free electron laser in the water window band. The method includes: a harmonic generation unit for receiving an electron beam and a seed laser to generate low-order harmonics; and at least two cascaded amplifier units connected to the harmonic generation unit. The amplifier units receive the low-order harmonic radiation to generate coherent harmonic radiation and tune the coherent harmonic laser to higher-order harmonic radiation to obtain a fully coherent free electron laser pulse in the water window band. This invention constructs multiple amplifier units after the harmonic generation unit, with each subsequent amplifier unit configured to resonate with a higher-order harmonic of the output radiation of its preceding amplifier unit. This allows the harmonic radiation of the preceding stage to serve as an effective seed for the subsequent stage, achieving a step-by-step upconversion of frequency. The frequency of the coherent radiation is gradually converted to the target higher-order harmonic, resulting in a fully coherent free electron laser in the water window band. Compared to existing technologies, the output water window band radiation has high pulse energy and peak power, while also possessing excellent longitudinal coherence. Furthermore, it does not require specific or complex modifications, making implementation easier and less costly. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the light source system in one embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the structure of the first dispersion unit in one embodiment of the present invention.

[0038] Figure 3 This is a schematic diagram of the structure of the second dispersion unit in one embodiment of the present invention.

[0039] Figure 4 This is an energy-time distribution diagram of the third electron beam in one embodiment of the present invention.

[0040] Figure 5 This is an energy-time distribution diagram of the fourth electron beam in one embodiment of the present invention.

[0041] Figure 6 This is an energy-time distribution diagram of the fifth electron beam in one embodiment of the present invention.

[0042] Figure 7 This is a schematic diagram of the light source system in another embodiment of the present invention.

[0043] Figure 8 This is a schematic diagram of the longitudinal phase space of the electron beam and the mass dynamic potential well during FEL radiation.

[0044] Figure 9 This is an example of the evolution of the weighted clustering factor and pulse energy along the amplifier for 27 nm (red), 9 nm (yellow), and 3 nm (blue) FEL radiation in one embodiment of the present invention.

[0045] Figure 10 The present invention describes the pulse shape and spectrum of FEL radiation with wavelengths of 27 nm, 9 nm and 3 nm.

[0046] Figure 11 This is a simulation result diagram from beginning to end of a multi-level harmonic cascade in one embodiment of the present invention.

[0047] Figure 12 This is a schematic flowchart of a water window band fully coherent free electron laser generation method in one embodiment of the present invention.

[0048] The following labels in the attached diagram represent the following: 100, electron source; 200, first seed laser generator; 300, harmonic generation unit; 310, electron accelerator; 320, first dispersion unit; 321, first diode; 322, second diode; 323, third diode; 324, fourth diode; 330, first modulation unit; 340, second dispersion unit; 350, second modulation unit; 360, third dispersion unit; 400, first amplifier unit; 410, first undulator; 500, second amplifier unit; 510, second undulator; 600, third amplifier unit; 610, third undulator; 620, fourth undulator; 630, fifth undulator; 640, sixth undulator; 710, first phase shifter; 720, second phase shifter; 800, second seed laser generator. Detailed Implementation

[0049] This invention provides a light source device, system, and method for generating fully coherent free-electron lasers in the water window band. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0050] In the implementation methods and claims, unless otherwise specified in the text, the terms "a," "an," "the," and "the" may also include plural forms. If the embodiments of the present invention involve descriptions of "first," "second," etc., such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0051] It should be further understood that the term "comprising" as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when an element is referred to as "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements present. Furthermore, "connected" or "coupled" as used herein can include wireless connections or wireless coupling. The term "and / or" as used herein includes all or any of the units and all combinations thereof of one or more associatedly listed items.

[0052] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0053] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0054] The inventors discovered through research that existing seed-type free-electron laser technology, especially the single-stage HGHG scheme, faces a series of key technical challenges in generating coherent X-ray radiation in the water window band:

[0055] (1) Physical limitations of harmonic conversion efficiency: In a single-stage HGHG, strong energy modulation is required to generate higher harmonics, but this introduces a large electron beam energy dissipation. The high-gain amplification process of FEL requires the electron beam to have very low energy dissipation. This contradiction between "harmonic multiplication" and "FEL amplification" in terms of electron beam energy dissipation fundamentally limits the highest harmonic order that a single-stage HGHG can achieve, usually making it difficult to break through 30th order and thus unable to effectively cover the water window band;

[0056] (2) Complexity and compatibility issues of existing high-order harmonic schemes: Although schemes such as EEHG can overcome the above limitations through two modulations, they usually require more precise magnet layouts (such as two modulator-dispersion pair), have more stringent requirements for electron beam quality, and are difficult to directly modify and implement on existing FEL devices based on single-stage HGHG.

[0057] (3) Coherence problem of SASE: Although the SASE mode can generate FEL radiation in the water window band, it originates from the spontaneous emission noise of the electron beam rather than a coherent seed laser. Therefore, the time coherence of its output pulse is poor, the spectral purity is low, and the pulse energy fluctuates greatly, which cannot meet the needs of many scientific experiments that require high stability, determinism and monochromaticity.

[0058] (4) Lack of high-throughput coherent light sources in the water window band: The water window band is crucial for life sciences. If high-intensity, fully coherent X-ray pulses can be generated in this band, in-situ observation of living cells can be achieved, providing a new approach for real-time analysis of cellular life processes, while avoiding significant damage to biological structures. However, there is currently a lack of practical solutions that can provide high-throughput, fully coherent, short-pulse X-ray sources in this band, which limits the development of revolutionary research such as real-time observation of living cells.

[0059] To address the aforementioned technical problems, this invention provides a light source device, system, and method for generating a fully coherent free-electron laser in the water-window band. By constructing a multi-stage amplifier unit after the harmonic generation unit, each subsequent amplifier unit is configured to resonate with a higher harmonic of the output radiation of its preceding amplifier unit. This allows the harmonic radiation of the preceding stage to serve as an effective seed for the subsequent stage, achieving a step-by-step upconversion of frequency. The frequency of the coherent radiation is progressively converted to the target higher harmonic, resulting in a fully coherent free-electron laser in the water-window band. Compared to existing technologies, the output water-window band radiation exhibits high pulse energy and peak power, while also possessing excellent longitudinal coherence. Furthermore, it requires no specific or complex modifications, making implementation easier and less costly.

[0060] Please also refer to Figures 1 to 8 The present invention provides a preferred embodiment of a light source device, system, and method for generating fully coherent free electron lasers in the water window band.

[0061] In some embodiments, such as Figure 1 As shown, the present invention provides a light source device, comprising: a harmonic generation unit 300 for receiving an electron beam and a seed laser and generating low-order harmonic radiation; and at least two cascaded amplifier units connected to the harmonic generation unit, wherein the amplifier units are used to receive the low-order harmonics and generate coherent harmonic radiation, and to tune the coherent harmonic laser to high-order harmonic radiation to obtain a fully coherent free electron laser pulse in the water window band.

[0062] Specifically, the electron beam refers to the initial electron beam generated by the electron source 100, which is typically a photocathode electron gun. Free electrons are generated by striking the cathode with laser pulses through the photoelectric effect, and then focused and pre-accelerated via a helical tube. The seed laser is generated by a first seed laser generator 200. This first seed laser generator 200 can use a ytterbium-doped (Yb) fiber laser or a titanium-doped sapphire laser based on optical parametric chirped pulse amplification (OPCPA) to generate infrared light, which is then frequency-doubled to generate an ultraviolet seed laser. This can produce ultraviolet light with high repetition rates, on the order of picoseconds or even shorter. For example, an infrared light of approximately 800 nm can be generated using a sapphire laser, and ultraviolet light of approximately 270 nm can be generated using a third-harmonic generation technique. In one implementation, the seed laser parameters can be: wavelength 270 nm, pulse half-width of approximately 100 fs, Rayleigh length of approximately 5 m, and peak power of approximately 100 MW.

[0063] The initial electron beam (which can be the first electron beam) interacts with the seed laser after being modulated by the harmonic generation unit 300. The resulting electron beam contains high-order harmonic components of the seed laser frequency, such as the 10th harmonic, thereby obtaining low-order harmonic radiation.

[0064] When there are only two amplification units, a 200nm deep ultraviolet laser is selected as the seed laser. The 15th harmonic is generated through the harmonic generation unit. The first-stage amplifier unit resonates at 13.3nm, and the second-stage amplifier unit resonates at 4.4nm. The third harmonic generated by the first stage is used as the seed for the second stage, which can generate 4.4nm radiation in the second stage amplification.

[0065] When a three-stage amplification unit is used, in the first stage of harmonic amplification, the magnetic field strength of the first amplifier unit 400 is designed to be such that the electron beam is at the [missing information]. Subharmonics (e.g.) Corresponding wavelength Resonance occurs at a certain frequency. The length and parameters of the first amplifier unit 400 are controlled to ensure that the... The power of the first harmonic radiation is much lower than the saturation power, but it simultaneously excites higher-order harmonic radiation. This prevents severe disruption of the phase space structure of the electron beam, creating conditions for subsequent cascading. During this process, the electron beam interacts with the radiation field, enhancing its longitudinal micro-clustering structure and generating higher-order harmonics (such as the first harmonic radiation). Subharmonics (corresponding to wavelengths of 9 nm) clustering and harmonic radiation.

[0066] In the second-stage harmonic amplification, the electron beam emitted from the first amplifier unit 400, carrying enhanced micro-groups and accompanying coherent first harmonics, is... The subharmonic radiation together enters the second amplifier unit 500. The second amplifier unit 500 is tuned to the third harmonic. The second harmonic, the first Subharmonics are relative to the wavelength of the first-order radiation (e.g., In other words, the resonant wavelength of the second amplifier unit 500 is... (For example, 27nm / 3=9nm). In the second-order harmonic amplification, the first... The second harmonic, acting as an effective seed, interacts with the electron beam input to the second amplifier unit 500, initiating the amplification of the third harmonic. The radiation of the second harmonic. Similarly, the amplification process is controlled so that the 9nm radiation is far from saturated, while simultaneously exciting higher harmonic radiation. After the second stage of amplification, the electron beam emits higher harmonic radiation in the next stage (such as the first harmonic). The clustering factor of the second harmonic (relative to the second stage) is further enhanced. In the second amplifier unit 500, the 9nm radiation is strongly amplified, ultimately achieving high power output.

[0067] In third-order harmonic amplification, the electron beam and the... The subharmonic radiation enters the third amplifier unit 600 and is tuned to the third harmonic in the third amplifier unit 600. Secondary harmonics (e.g.) (relative to the second level), i.e., the target wavelength At this point, the 3 nm radiation corresponds to the first photon of the initial seed laser. The 90th harmonic is 10 × 3 × 3 = 90th harmonic. In the third amplifier unit 600, the 3nm radiation is strongly amplified, ultimately achieving high power output.

[0068] In the above technical solution, this invention constructs a multi-stage amplifier unit after the harmonic generation unit. Each subsequent amplifier unit is configured to resonate with a higher harmonic of the output radiation of its preceding amplifier unit. This allows the harmonic radiation of the preceding stage to serve as an effective seed for the subsequent stage, achieving a step-by-step upconversion of frequency. The frequency of the coherent radiation is progressively converted to the target higher harmonic, resulting in a fully coherent free-electron laser in the water window band. Compared to existing technologies, this invention can generate fully coherent X-ray laser pulses with wavelengths less than 5 nm, particularly falling within the water window band (2.3-4.4 nm), without the need for an additional modulator-dispersion section. This provides an unprecedentedly powerful tool for cutting-edge scientific research in the water window band, such as high-contrast real-time biological imaging and in-situ observation of living cells. Furthermore, the output water window band radiation possesses high pulse energy and peak power, along with excellent longitudinal coherence, and requires no specific or complex modifications, making implementation easier and less costly.

[0069] In some embodiments, such as Figure 1 As shown, the harmonic generation unit 300 includes: an electron accelerator 310, a first dispersion unit 320, a first modulation unit 330, and a second dispersion unit 340; wherein, the electron accelerator 310 is connected to the first dispersion unit 320, and is used to receive a first electron beam and accelerate the first electron beam to form a second electron beam, which is then input to the first dispersion unit 320; the first dispersion unit 320 is connected to the first modulation unit 330, and is used to compress the second electron beam and form a third electron beam, which is then input to the first modulation unit 330; the first modulation unit 330 receives a seed laser and is connected to the second dispersion unit 340, and is used to generate periodic energy modulation on the third electron beam and generate a fourth electron beam, which is then input to the second dispersion unit 340; the second dispersion unit 340 is connected to the amplifier unit, and is used to convert the periodic energy modulation into density modulation and generate a fifth electron beam, which is then input to the amplifier unit; the fifth electron beam is accompanied by the low-order harmonic radiation.

[0070] In this embodiment, the electron accelerator accelerates the first electron beam generated by the electron source. The electron charge of the first electron beam generated by the electron source is approximately 100 pC, and the electron beam energy is approximately 20 MeV. The first electron beam enters a linear accelerator, which typically employs superconducting radio frequency technology. In continuous wave operation mode, a high-gradient electric field further accelerates the first electron beam, and through magnetic compression and other means, changes are made to the electron beam's energy, energy dissipation, emittance, and flux intensity, ultimately obtaining a high-quality electron beam (i.e., the second electron beam) that meets the subsequent light emission requirements. Generally, the parameters of the second electron beam are approximately as follows: electron beam energy 2.5 GeV, relative energy dissipation... Normalized emissivity 0.4 mm mrad, peak current 800A, bundle length 170fs.

[0071] It's important to understand that linear accelerators typically consist of several acceleration modules connected in series. The core component of each module is the accelerating tube, and each accelerating tube is composed of accelerating cavities. A typical linear accelerator may have 15-20 modules, each module has 8 accelerating tubes, and each accelerating tube has 9 cells. By feeding power into these accelerating cavities through a solid-state power source, a high-gradient electric field can be generated, which is used to accelerate the electron beam. In addition, the acceleration module also includes a support system, a cooling system, a beam diagnostic system, a vacuum system, etc., making it a complex component integrating multiple systems.

[0072] The third electron beam, after passing through the first dispersive unit 320, such as Figure 4As shown, the peak current is only increased to approximately 804A, which is negligible. The main function of the first dispersive unit 320 is to deflect the electron beam to provide space for the plane mirror where the seed laser is injected. Figure 2 As shown, the first dispersion unit 320 includes a first diode 321, a second diode 322, a third diode 323, and a fourth diode 324. The first diode 321, the second diode 322, the third diode 323, and the fourth diode 324 are symmetrically distributed. The strength of the four magnets needs to be exactly the same, which can usually be achieved by connecting the four magnets in series with a solid-state power supply. The first dispersion unit 320 has two main functions: 1. It can selectively further compress the second electron beam, generating a higher current intensity; 2. It deflects the second electron beam, providing space for the mirror used for seed laser injection (during seed laser injection, a mirror is placed between the second diode 322 and the third diode 323 to guide the laser into the vacuum tube). In one implementation, the parameters of the first dispersive unit 320 can be set as follows: the length of each of the four B iron blocks is approximately 0.2 meters; the distance between the first diode 321, the second diode 322, the third diode 323, and the fourth diode 324 is approximately 0.8 meters; the distance between the second diode 322 and the third diode 323 is approximately 0.6 meters; and the deflection angle is... Approximately 20 mrad, the distance between the centers of the first diode 321 and the second diode 322 is d.

[0073] The first modulation unit 330 can be a relatively short undulator, which refers to a periodically arranged array of magnets. The third electron beam and the seed laser interact in the modulation section, satisfying a resonance relationship:

[0074] ;

[0075] in It refers to the radiation wavelength (also called the resonance wavelength, which is equal to the seed laser wavelength in the modulation segment), and γ refers to the relativistic Lorentz factor. The period is the undulator period, usually determined by the magnet structure that makes up the undulator. K is the undulator parameter, which is proportional to the undulator's magnetic field strength. During the modulation phase, the third electron beam undergoes energy modulation under the influence of the seed laser, with the modulation wavelength being the seed laser wavelength. After the modulation phase, the third electron beam becomes the fourth electron beam, such as... Figure 5As shown, the fourth electron beam is drawn from the modulation section and enters the second dispersion unit. The energy-time distribution of the fourth electron beam is sinusoidal, with the period of the sinusoid being the seed laser wavelength. The height of the sinusoid (energy modulation amplitude) is related to the seed laser power, beam waist radius, modulation section length, modulation section undulator strength, electron beam energy, and electron beam energy dispersion, typically requiring more than 1 times the initial energy dispersion of the third electron beam. After passing through the first modulation unit, the fourth electron beam will form a sinusoidal modulation in the energy-time distribution. The electron beam energy remains essentially unchanged, but the energy dispersion increases to several times that of the third electron beam (e.g., 5 times in this example). In one implementation, the undulator length in the first modulation unit is approximately 2 meters, the period is approximately 0.09 meters, and the introduced energy modulation amplitude is 5 times the initial energy dispersion of the third electron beam.

[0076] like Figure 2 and Figure 3 As shown, the basic structure of the second dispersion unit 340 is the same as that of the first dispersion unit 320, except that its magnet strength may be lower. The function of the second dispersion unit is to convert the energy modulation in the fourth electron beam into density modulation, forming a fifth electron beam with micro-clusters, such as... Figure 6 As shown. The basic principle is as follows: The fourth electron beam is modulated by a seed laser, exhibiting a sinusoidal energy-time distribution. Electrons with different energies are deflected at different angles when passing through the diodes. The paths taken by the first and second diodes and the third and fourth diodes in the second dispersive unit 340 are different; higher-energy electrons travel shorter distances, while lower-energy electrons travel longer distances. This causes the tail electrons to catch up with the head electrons during beam compression, thus achieving longitudinal / temporal compression of the beam and ultimately generating micro-clusters at the target wavelength. After passing through the second dispersive unit 340, the energy of the fourth electron beam is modulated to density modulation, forming a fifth electron beam with a micro-cluster structure. The fifth electron beam then enters the amplifier unit.

[0077] To achieve good clustering, the dispersion intensity of the second dispersive unit 340 needs to be carefully tuned. The dispersion intensity is mainly determined by the dispersion diode's ground strength and layout. The calculation can be simplified to:

[0078] ;

[0079] in, It is the horizontal distance between the first and second dipoles. It is the length of iron B ( ), The angle representing the deflection of the fourth electron beam through iron B (i.e., the angle of deviation from the horizontal direction) is related to the magnetic field strength of iron B and the energy of the electron beam. The angle can be adjusted by regulating the current in the iron B coil, thereby regulating the dispersion intensity in the dispersion section. .

[0080] In one implementation, the length of the B-type iron in the second dispersive unit 340 is approximately 0.2 meters, the distance between the first and second, and third and fourth iron plates is approximately 1 meter, the distance between the second and third iron plates is 0.5 meters, the deflection angle is approximately 7 mrad, and the dispersion intensity is approximately 0.11 m. Under this configuration, the fourth electron beam entering the second dispersive unit 340 can generate strong micro-clusters at the 10th harmonic, resulting in a fifth electron beam, which is accompanied by the low-order harmonic radiation.

[0081] In some embodiments, such as Figure 7 As shown, the laser source also includes a second modulation unit 350 and a third dispersion unit 360. The second modulation unit is connected between the second dispersion unit and the third dispersion unit 360, and the third dispersion unit is connected to the first amplifier unit. In this way, the 20th harmonic can be directly generated by the harmonic generation unit, using a 240nm seed laser. The first-stage amplifier unit can resonate at 12nm, and the second-stage amplifier unit can resonate at 4nm, thus obtaining a fully coherent free electron laser pulse in the water window band. The seed laser used by the second modulation unit, provided by the second seed laser generator, can be identical to the seed laser provided by the first seed laser of the first modulation unit, or it can be non-identical, differing only in the power / full width at half maximum (FWHM) and other characteristics of the seed laser.

[0082] In some embodiments, the cascaded amplifier units include: a first amplifier unit 400, a second amplifier unit 500, and a third amplifier unit 600; the first amplifier unit 400, the second amplifier unit 500, and the third amplifier unit 600 are cascaded sequentially; the first amplifier unit 400 is used to amplify the fifth electron beam to obtain a sixth electron beam; the second amplifier unit 500 is used to amplify the sixth electron beam to obtain a seventh electron beam; and the third amplifier unit 600 is used to amplify the seventh electron beam to form a high-power water-window band fully coherent free electron laser pulse.

[0083] In this embodiment, the cascaded amplifier unit consists of a first amplifier unit 400, a second amplifier unit 500, and a third amplifier unit 600.

[0084] In this embodiment, the first harmonic order The value was chosen as 10 because this is the highest harmonic order that the HGHG mode can achieve under normal conditions. Additionally, the harmonic orders of the second and third orders... The choice of 3 is based on the fact that both theory and simulations demonstrate that, under suitable parameters, the gain length of the third harmonic can be shorter than that of the fundamental frequency, which is beneficial for achieving efficient harmonic amplification before the fundamental frequency saturates. In amplifier length control, the length of each amplifier stage is a key optimization parameter, requiring a balance between increasing the higher harmonic clustering factor and controlling electron beam energy dissipation growth. Generally, the preamplifier length is shorter to avoid excessively compromising electron beam quality.

[0085] When three harmonic amplifier units are cascaded, the overall workflow is divided into initial modulation and micro-group formation, first-stage harmonic amplification, second-stage harmonic amplification and third-stage harmonic amplification.

[0086] In this process, initial modulation and micro-cluster formation occur as follows: A high-quality relativistic electron beam interacts with an external seed laser (e.g., a 270 nm ultraviolet laser) in the first modulation unit. This interaction imprints a sinusoidal energy modulation in the longitudinal phase space of the electron beam. The modulated electron beam then enters the second dispersion unit. The second dispersion unit has a specific momentum compressibility factor (…). This allows the energy modulation of the electron beam to be converted into density modulation, forming "micro-clustering." At this point, the electron beam current contains high-order harmonic components of the seed laser frequency (e.g., the 10th harmonic). Through optimization... The value can maximize the clustering factor at the target harmonic (such as the 10th harmonic).

[0087] First-stage harmonic amplification: An electron beam carrying micro-groups enters the first amplifier unit. The magnetic field strength of this amplifier unit is set to cause the electron beam to interact with the first harmonic amplification stage. Subharmonics (e.g.) Corresponding wavelength Resonance occurs at a certain frequency. By controlling the length and parameters of the first amplifier unit, this... The power of the second harmonic radiation is much lower than the saturation power, but it simultaneously excites higher-order harmonic radiation. This prevents the phase space structure of the electron beam from being severely disrupted, creating conditions for subsequent cascading. In this process, the fifth electron beam interacts with the radiation field, its longitudinal micro-clustering structure is enhanced, and higher-order harmonics (such as the first harmonic radiation) are generated. The sixth electron beam and harmonic radiation, which are clustered together (corresponding to a wavelength of 9 nm).

[0088] Second-stage harmonic amplification: The sixth electron beam, carrying enhanced micro-groups, emitted from the first amplifier unit, and the accompanying... The coherent radiation of the second harmonic enters the second amplifier unit together. The second amplifier unit is tuned to the third harmonic. Second harmonics, this unit Subharmonics are relative to the wavelength of the first-order radiation (e.g., In other words, the resonant wavelength of the second amplifier unit is... (For example, 27nm / 3=9nm). From the first amplifier unit. The subharmonic radiation, acting as an effective "seed," interacts with the sixth electron beam in the second amplifier unit, initiating the amplification of the... The radiation of the second harmonic (i.e., 9 nm). Similarly, the amplification process is controlled so that the 9 nm radiation is far from saturated, but at the same time, it excites higher harmonic radiation. After being amplified by the second amplifier unit, the resulting seventh electron beam is emitted at the next higher harmonic level (such as the first harmonic). The clustering factor of the second harmonic (relative to the second level) is further enhanced.

[0089] Third-order and subsequent harmonic amplification: the seventh electron beam and the preceding... The second harmonic radiation enters the third amplifier unit, which is then tuned to the third harmonic. Subharmonics (e.g.) (relative to the second level), i.e., the target wavelength At this point, the 3 nm radiation corresponds to the first photon of the initial seed laser. The 90th harmonic is 10 × 3 × 3 = 90th harmonic. In the third amplifier unit, the 3nm radiation is strongly amplified, ultimately achieving high power output.

[0090] In some embodiments, the first amplifier unit 400 includes a first oscillator 410; the second amplifier unit 500 includes a second oscillator 510; and the third amplifier unit 600 includes a third oscillator 610, a fourth oscillator 620, a fifth oscillator 630, and a sixth oscillator 640, wherein the third oscillator 610, the fourth oscillator 620, the fifth oscillator 630, and the sixth oscillator 640 are cascaded.

[0091] In this embodiment, the amplifier unit is composed of undulators. Taking a three-stage cascaded amplifier unit as an example, the first two stages typically have a smaller number of undulators, and the first amplifier unit 400 and the second amplifier unit 500 have a smaller number of undulators. It should be understood that if the first amplifier unit 400 and the second amplifier unit 500 have too few undulators, they may not be able to generate a sufficiently strong third harmonic. Without a sufficiently strong third harmonic, the subsequent stages cannot generate fully coherent short-wavelength radiation. On the other hand, if the number of undulators is too large, it may lead to excessive degradation of the electron beam quality, making it impossible to generate water window band radiation in the subsequent stages, while the generated long-wavelength radiation will dominate.

[0092] In the three stages described above, the first amplifier unit 400 and the second amplifier unit 500 have relatively few undulators, typically one or two are sufficient. In principle, the gain length of the third harmonic is shorter than that of the fundamental radiation. Therefore, by using an appropriate number / length of undulators, the fundamental radiation can be suppressed while generating the third harmonic. This ensures that the quality of the electron beam is not severely compromised while obtaining the third harmonic; this applies to both the first amplifier unit 400 and the second amplifier unit 500. The third amplifier unit 600 represents the normal high-gain process of free-electron laser. Furthermore, by employing a gradient undulator technique (adjusting the gap between the undulator inlet and outlet to be different, i.e., the undulator gap gradually changes along the undulator), even higher pulse energy (3nm FEL radiation) can be obtained.

[0093] To ensure the electron beam is not severely damaged, based on the available electron beam and undulator parameters, the number of undulators in the first and second amplifier units should not exceed two; for example, it could be two or one. The number of undulators in the final stage is related to the final radiation intensity; typically, three to five undulators are needed to reach saturation. The specific number depends on the specific parameters of the electron beam and the impact of the first two stages on electron beam energy dispersion and emittance. In one implementation, the number of undulators in the three stages is one, one, and four, respectively. By optimizing the parameters of each undulator (e.g., using gradient undulator technology), the output performance can be further improved. Furthermore, by controlling the number / length of undulators in the first two stages, the gain length of harmonic radiation can be ensured to be significantly shorter than that of fundamental radiation, ensuring that the fundamental radiation is far from saturation. This allows the electron beam quality to be maintained even with a certain intensity of harmonic radiation, providing a foundation for realizing multi-stage cascaded harmonic radiation.

[0094] Each amplifier unit uses a uniformly sized, adjustable-gap permanent magnet vacuum external plane undulator. This undulator consists of two symmetrical rows of Halbach-type magnets, generating a near-sinusoidal vertical magnetic field in the mid-plane. When the electron beam passes through, it undergoes a gyratory motion on the horizontal plane, producing horizontally polarized radiation. The gap between the upper and lower magnets is adjustable to obtain magnetic fields with different peak values. The peak magnetic field strength can be estimated using the following formula:

[0095] ;

[0096] Where a, b, and c depend on the remanence of the permanent magnet, and a, b, and c are constants. For example, for samarium cobalt (SmCo) materials, For NdFeB materials, The gap is the magnetic gap of the oscillator. The oscillator period. The oscillator parameters in the resonance condition. A complete conventional undulator includes a magnet array, a fixed structure for the magnet array, a main beam and its support, a transmission system, and a motion control system. The motion control system, in addition to functions such as gap transmission control and interlocking protection of the undulator, also needs Ethernet networking capabilities to connect to a remote computer for remote operation and control. The control system needs to synchronously control four drive motors to ensure that the upper and lower main beams of the undulator move in parallel up and down. The position of the main beam is monitored using an absolute value grating ruler, and its reading is also used for closed-loop control. The main beam position is generally monitored and protected by a triple drive system of software limit switches, photoelectric positioning switches, and mechanical positioning switches. In this embodiment, the undulators in the three amplifier stages use the same specifications, with a length of 4 meters and a period of 0.05 meters. The difference lies in the gaps of the undulators in the three stages, which are 9.35 mm, 16.24 mm, and 25.47 mm, respectively. Based on the resonance relationship (the same formula as in the modulation section, and this relationship applies to all undulators), the undulators in the three amplifier stages will resonate at 27nm, 9nm, and 3nm, respectively. The undulator gap can be controlled remotely via a computer. A high-gain process of free-electron laser light occurs within the amplifier, namely a positive feedback process of energy modulation-density modulation-optical field enhancement. In the first amplifier stage, the fifth electron beam, with its 10th harmonic cluster, generates fundamental radiation at 27nm (relative to the resonant wavelength of this stage) and third harmonic radiation at 9nm. The electron beam quality is not severely compromised, forming the sixth electron beam.

[0097] In some embodiments, the light source device further includes a phase shifter connected between the two amplifier units.

[0098] In this embodiment, the phase shifter is a very small undulator, typically containing only one cycle. The electron beam oscillates within the phase shifter due to the magnetic field, causing it to travel a greater distance than the radiated light. By controlling the undulator's magnetic field, the electron beam's travel distance is adjusted, thus matching the phase of the electron beam with the phase of the radiated light. In one implementation, the phase shifter parameters are as follows: the phase shifter has one cycle, a total length of 10 cm, and the introduced phase integral is approximately... .

[0099] A phase shifter is installed between amplifier units to ensure that the radiation field generated by the previous amplifier unit and the electron beam micro-group are in the optimal phase when entering the next amplifier unit.

[0100] First, it's important to understand that during radiation, the phase space (phase-energy space) of the electron beam is constantly changing (which can be simply viewed as the electron beam continuously rotating and stretching). The undulator, the electron beam, and the radiated light (specifically, factors such as undulator intensity, electron beam resonant energy, and light field resonant phase; the resonant energy / resonant phase can be understood as a physical quantity closely related to the ideal energy (2.5 GeV) and the radiation wavelength (9nm / 3nm)) determine an ideal, kinetic potential well (e.g., ...). Figure 8 (The red solid line in the diagram) Only electrons trapped in this potential well are useful for the luminescence gain process.

[0101] During radiation, due to the continuous transformation of the electron beam (energy loss, phase rotation, etc.), more and more electrons are no longer captured by the kinetic potential well, causing radiation to stop increasing. On the other hand, since electrons are constantly oscillating in the undulator, their forward speed will inevitably lag behind the speed of light. This causes the electron beam to gradually lag behind the radiated light field, and the phases of the electron beam and the light field gradually become misaligned. The phase of the light generated by the electron beam is the same as that of the electron beam. As the electron beam gradually lags behind, the phases of the two gradually become misaligned. This phenomenon is called detuning between the phase of the electron beam and the phase of the light field, which exists in all undulator radiation. In this embodiment, the third harmonic is used, and this detuning between the phase of the electron beam and the phase of the light field will only be more severe. Therefore, a phase shifter is needed to adjust the phase of the electron beam to ensure that the phase of the third harmonic generated by the previous amplifier unit matches the phase of the micro-clusters in the electron beam (falling in a better position in the kinetic potential well). This allows for better luminescence, enabling more electrons to participate in the radiation luminescence process of the next stage amplifier, thereby increasing the energy of the overall radiation pulse. In practice, this goal is typically achieved by scanning the gap of the phase shifter (which alters the magnetic field strength of the phase shifter to adjust the swaying of the electron beam during its movement, thereby tuning the phase difference between the electron beam and the light field), and observing the intensity of the radiated light to ensure the electron beam lands at a favorable position within the dynamic potential well. The optimal phase refers to a specific phase within the dynamic potential well where the electron beam can be continuously captured (staying within this range longer) and thus generate more radiated light. Being in the optimal phase allows more electrons to participate in the next stage of radiation, improving the radiation efficiency of the next stage and generating higher-energy radiation pulses.

[0102] Taking a three-amplifier unit as an example, the undulators in the three amplifier stages will resonate at 27nm, 9nm, and 3nm respectively. Figure 1As shown, a first phase shifter 710 is disposed between the first amplifier unit 400 and the second amplifier unit 500, and a second phase shifter 720 is disposed between the second amplifier unit 500 and the third amplifier unit 600. After passing through the first phase shifter 710, the fifth electron beam is phase-matched with the 9nm radiation and enters the second amplifier unit 500. In the second amplifier unit 500, the 9nm radiation serves as the seed for the sixth electron beam, generating 9nm fundamental radiation (relative to the resonant wavelength of this stage) and 3nm third harmonic radiation. The electron beam quality is still not severely degraded, forming the seventh electron beam. In the second phase shifter 720, the seventh electron beam is phase-matched with the 3nm radiation and enters the third amplifier unit 600. In the third amplifier stage, the 3nm radiation is further amplified, forming a high-power FEL radiation pulse.

[0103] In some embodiments, such as Figure 1 As shown, the present invention also provides a light source system, which includes an electron source 100, a first seed laser generator 200 and the light source device described above; the electron source 100 is connected to the harmonic generation unit 300 and is used to generate an electron beam and input it into the harmonic generation unit; the first seed laser generator 200 is connected to the harmonic generation unit 300 and is used to generate a seed laser and input it into the harmonic generation unit 300.

[0104] Specifically, before entering the linear accelerator, an electron source (electron gun) generates the initial electron beam. This source is typically a photocathode electron gun, where laser pulses strike the cathode to generate free electrons through the photoelectric effect. These free electrons are then focused and pre-accelerated via a helical tube. The first seed laser generator is used to produce the seed laser. It can employ a ytterbium-doped fiber laser or a titanium-doped sapphire laser based on optical parametric chirped pulse amplification (OPCPA) to generate infrared light, which is then frequency-doubled to produce an ultraviolet seed laser. This first seed laser generator can produce high repetition rates, on the order of picoseconds or even shorter ultraviolet light. For example, an infrared beam of approximately 800 nm can be generated using a sapphire laser, and ultraviolet light of approximately 270 nm can be generated using a third-harmonic generation technique. The seed laser is used to modulate the energy of the second electron beam in the first modulation unit and is exited from the first modulation unit; it is used only once. The repetition frequency of the seed laser is the same as that of the second electron beam, and the two interact spatially and temporally in the first modulation unit. In one implementation, the seed laser parameters are: wavelength 270 nm, pulse half-width at half-maximum of approximately 100 fs, Rayleigh length approximately 5 m, and peak power approximately 100 MW.

[0105] Through simulation and preliminary experimental verification, the method of this invention can generate fully coherent X-ray FEL pulses with pulse energy exceeding 70 μJ, peak power approaching the GW level, and wavelength stable at around 3 nm using electron beams and seed lasers with conventional parameters. This provides an unprecedentedly powerful tool for cutting-edge scientific research such as high-contrast real-time biological imaging and in-situ observation of living cells in the water window band.

[0106] To fully illustrate the specific embodiments of the present invention, verify its feasibility, and demonstrate its excellent effects, such as Figure 9 and Figure 10 As shown, where, Figure 9 In this context, 'a' represents the weighted clustering factor for 27 nm (red), 9 nm (yellow), and 3 nm (blue) FEL radiation. Figure 9 In the diagram, 'b' represents the evolution of the pulse energy along the amplifier path, and the shaded area represents the root mean square (RMS) undulator strength. Figure 10 In this context, 'a' represents the pulse shape and spectrum of FEL radiation at a wavelength of 27 nm. Figure 10 In this context, 'b' represents the pulse shape and spectrum of FEL radiation at a wavelength of 9 nm. Figure 10 In this context, 'c' represents the pulse shape and spectrum of FEL radiation with a wavelength of 3 nm. The following will elaborate on this in detail with simulation examples.

[0107] Example 1: Simulation Verification Based on an Ideal Electron Beam

[0108] 1. Simulation parameters: The particle simulation software GENESIS was used. Electron beam energy 2.5 GeV, normalized emittance 0.4 mm·mrad, peak current 800 A, relative energy dispersion... The seed laser wavelength is 270nm, and the peak power is 100MW. The modulator length is 2m. Dispersion section... The amplifier consists of six 4-meter-long variable gap undulators, divided into three stages.

[0109] 2. Cascaded Configuration: First-stage amplifier: Contains a 4-meter-long oscillator resonating at the 10th harmonic, wavelength... The second-stage amplifier contains a 4-meter-long undulator that resonates at the third harmonic (relative to the first stage), with a wavelength of... The third-stage amplifier contains four 4-meter-long undulators, resonating at the third harmonic (relative to the second stage), with a wavelength of... .

[0110] 3. Simulation Results: Clustering Evolution: Upon entering the amplifier, the 10th harmonic clustering factor is 2.5%. After the first stage, the 30th harmonic (9nm) clustering factor rises to 7.5%. After the second stage, the 90th harmonic (3nm) clustering factor reaches 2.6%. These sufficiently high clustering factors effectively suppress shot noise and ensure the coherence of the radiation pulse. Energy Dissipation Evolution: The relative weighted energy dissipation of the electron beam upon entering the first, second, and third stages are as follows: , , It is always less than the Pierce parameter. This satisfies the FEL amplification condition. Output performance: The final FEL pulse energy obtained at 3nm is... Peak power is approximately 1.5GW. Relative bandwidth is... This demonstrates extremely high spectral purity. In comparison, the pulse energies at 27 nm and 9 nm are respectively... and This indicates that energy is effectively transferred and concentrated onto the final target harmonic.

[0111] 4. Consider the robustness of actual effects:

[0112] Space Charge and Intrabeam Scattering Effects: The effects of longitudinal space charge (LSC) and intrabeam scattering (IBS) were simulated and analyzed. Calculations show that the maximum energy loss caused by LSC is approximately... The total energy dissipation increase caused by IBS is approximately 28.57 keV, which is much smaller than the energy dissipation change caused by FEL interaction, and therefore its effect is negligible. Parameter sensitivity analysis: When the normalized emittance increases by 50%, the 3nm pulse energy decreases to... When the initial energy dissipation increases to At that time, the pulse energy dropped to This indicates that the scheme has a certain degree of robustness to beam parameter degradation. Energy jitter stability: 100 random simulations were conducted, assuming an RMS jitter of 0.01% in the electron beam energy. The results show that the average value of the 3 nm pulse energy is... The RMS jitter is 7.17%; the average bandwidth of the center wavelength is... RMS jitter is 9.40×10 -5 The output performance is stable, with fluctuations within an acceptable range according to user experiments.

[0113] Example 2: Start-to-End Simulation Based on S3FEL Device

[0114] A full-scale simulation, starting from the electron gun, was conducted using specific beam parameters from the planned Shenzhen Zhongneng High Repetition Rate X-ray Free Electron Laser (S3FEL). The simulation focused on optimizing the dispersion intensity (R... 56 After adjusting the radiator parameters (≈ 0.12 mm) and setting the radiator parameters, a pulse with energy of 3 nm was successfully generated at a wavelength of 3 nm. Relative bandwidth narrow to The FEL pulse. For example... Figure 11 As shown, Figure 11 Figure 'a' illustrates the evolution of the pulse energy of the FEL radiation at various wavelengths along the amplifier. Figure 11 b in the figure shows the pulse shape and spectral characteristics of 3nm FEL radiation, which fully demonstrates the application potential of the present invention in future practical devices.

[0115] In some embodiments, such as Figure 12 As shown, the present invention also provides a method for generating a fully coherent free electron laser in the water window band, comprising:

[0116] S100. The incoming electron beam and seed laser are modulated by the harmonic generation unit to generate low-order harmonic radiation; wherein the low-order harmonic radiation contains high-order harmonic components in the seed laser frequency; as described in an embodiment of a light source device, it will not be repeated here.

[0117] S200: The first amplifier unit resonates with low-order harmonics and generates coherent harmonic radiation. The next amplifier unit uses the harmonic radiation from the previous stage as an effective seed to tune the coherent harmonic radiation into higher-order harmonic radiation, thereby obtaining a fully coherent free electron laser pulse in the water window band. Specific details are as described in an embodiment of a light source device and will not be repeated here.

[0118] In some embodiments, the step of modulating the incoming electron beam and seed laser through the harmonic generation unit to generate low-order harmonic radiation includes:

[0119] S110. The added electron beam is accelerated and compressed; as described in an embodiment of a light source device, it will not be repeated here.

[0120] S120. The accelerated and compressed electron beam and seed laser are modulated and further compressed to convert the energy modulation of the electron beam into density modulation, generating low-order harmonic radiation. Specific details are as described in an embodiment of a light source device, and will not be repeated here.

[0121] In some embodiments, the amplifier unit includes a first amplifier unit, a second amplifier unit, and a third amplifier unit; the first amplifier unit resonates with low-order harmonics and generates coherent harmonic radiation, and the next amplifier unit uses the harmonic radiation of the previous stage as an effective seed to tune the coherent harmonic radiation to higher-order harmonic radiation, in order to obtain a fully coherent free electron laser pulse in the water window band, includes the following steps:

[0122] S210. The fifth electron beam carrying micro-clusters is introduced into the first amplifier unit, so that the fifth electron beam resonates with the frequency of the first harmonic radiation to generate a sixth electron beam with micro-clusters and harmonic radiation having higher harmonics; as described in an embodiment of a light source device, it will not be repeated here.

[0123] S220. The first harmonic radiation is used as an effective seed to interact with the sixth electron beam in the second amplifier unit to obtain the amplified second harmonic radiation, and a seventh electron beam is generated; as described in an embodiment of a light source device, it will not be repeated here.

[0124] S230. The second harmonic radiation is used as an effective seed to interact with the seventh electron beam in the third amplifier unit to obtain the amplified third harmonic radiation, thereby obtaining a fully coherent free electron laser pulse in the water window band. Specific details are as described in an embodiment of a light source device, and will not be repeated here.

[0125] In summary, the light source device, system, and water-window band fully coherent free electron laser generation method provided by the present invention have the following beneficial effects:

[0126] Ultra-high harmonic conversion has been achieved: the harmonic conversion capability of a single-stage HGHG has been successfully increased from the usual -25th to -90th, directly covering the water window band, which is something that a single-stage HGHG simply cannot achieve.

[0127] Excellent output performance: The output water window band radiation has high impulse energy and peak power, while also having excellent longitudinal coherence;

[0128] The device boasts strong compatibility and ease of implementation: The core of this invention lies in the structural innovation of the radiator section, while the front end (electron gun, accelerator, modulator, and dispersive band) is completely identical to that of a standard single-stage HGHG. This means that existing or planned HGHG-type FEL devices can be upgraded to achieve water window band radiation capability without any disruptive modifications, greatly saving costs and construction time.

[0129] High robustness and stability: This scheme exhibits a certain degree of tolerance to fluctuations in electron beam parameters (such as emittance and energy dispersion). Simulations show that even with a 50% increase in emittance, the 3 nm pulse energy can still be maintained. The level of multi-beam cluster simulation shows that, under the condition of 0.01% jitter in electron beam energy, the relative standard deviation (RMSjitter) of the output pulse energy is less than 10%, and the center wavelength jitter is negligible, meeting the stability requirements of user experiments;

[0130] The adverse effects were effectively suppressed: by optimizing the electron beam current intensity and radiator length, the effects of longitudinal space charge effect and beam scattering effect were controlled at a very low level, and would not cause substantial interference to the generation and amplification process of harmonic clustering.

[0131] This method expands experimental capabilities: it can not only generate single water window band pulses, but also has the potential to achieve the synchronous generation of multicolor FEL pulses (e.g., simultaneously generating 27nm, 9nm, and 3nm pulses) by adjusting the intensity of the dispersion band and using a gradient undulator scheme. Furthermore, the intensity of each pulse is adjustable, providing new possibilities for complex experiments such as pump-probe.

[0132] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A light source apparatus, characterized by comprising: include: Harmonic generation unit for connecting electron beam and seed laser to generate low-order harmonic radiation; At least two cascaded amplifier units are connected to the harmonic generation unit. The amplifier units are used to receive the low-order harmonic radiation and generate coherent harmonic radiation, and to tune the coherent harmonic laser into high-order harmonic radiation to obtain a fully coherent free electron laser pulse in the water window band. The amplifier units include a first amplifier unit and a second amplifier unit. The harmonic generation unit includes: an electron accelerator, a first dispersion unit, a first modulation unit, and a second dispersion unit; wherein... The electron accelerator is connected to the first dispersion unit and is used to receive the first electron beam and accelerate the first electron beam to form a second electron beam, which is then input to the first dispersion unit. The first dispersion unit is connected to the first modulation unit and is used to compress the second electron beam and form a third electron beam that is input to the first modulation unit to generate a higher flux intensity and to deflect the second electron beam to provide space for seed laser injection. The first modulation unit is connected to the seed laser and the second dispersion unit to generate periodic energy modulation on the third electron beam and generate a fourth electron beam that is input to the second dispersion unit. The second dispersive unit is connected to the first amplifier unit and is used to convert periodic energy modulation into density modulation and generate a fifth electron beam that is input to the first amplifier unit; the fourth electron beam can generate micro-clusters at the 10th harmonic to obtain the fifth electron beam, which is accompanied by the low-order harmonic radiation. The first dispersive unit includes a first diode, a second diode, a third diode, and a fourth diode; the first diode, the second diode, the third diode, and the fourth diode are symmetrically distributed; the second dispersive unit has the same structure as the first dispersive unit; electron beams with different energies are deflected at different angles when they pass through the diodes, so as to generate micro-clusters at the target wavelength; after the fourth electron beam passes through the second dispersive unit, the energy modulation is converted into density modulation, forming a fifth electron beam with a micro-cluster structure; It also includes a phase shifter connected between the first amplifier unit and the second amplifier unit to adjust the phase of the electron beam to ensure that the phase of the third harmonic generated by the first amplifier unit matches the phase of the micro-groups in the electron beam, so that the electron beam falls in a better position in the mass-driven potential well; wherein, the phase shifter is an undulator with one period. It also includes: a second modulation unit and a third dispersion unit. The second modulation unit is connected between the second dispersion unit and the third dispersion unit. The third dispersion unit is connected to the first amplifier unit. It can directly generate the 20th harmonic through the harmonic generation unit. Using a 240nm seed laser, it can resonate at 12nm in the first amplifier unit and at 4nm in the second amplifier unit, thereby obtaining a fully coherent free electron laser pulse in the water window band.

2. The light source apparatus according to claim 1, wherein The cascaded amplifier unit also includes a third amplifier unit; the first amplifier unit, the second amplifier unit, and the third amplifier unit are cascaded in sequence. The first amplifier unit is used to amplify the fifth electron beam to obtain the sixth electron beam; The second amplifier unit is used to amplify the sixth electron beam to obtain the seventh electron beam; The third amplifier unit is used to amplify the seventh electron beam to form a high-power water-window band fully coherent free electron laser pulse.

3. The light source apparatus according to claim 2, wherein The first amplifier unit includes a first oscillator; the second amplifier unit includes a second oscillator; the third amplifier unit includes a third oscillator, a fourth oscillator, a fifth oscillator, and a sixth oscillator, which are cascaded together.

4. The light source device according to claim 1, characterized in that, The first modulation unit is an oscillator.

5. A light source system, characterized in that, The device includes an electron source, a first seed laser generator, and a light source device as described in any one of claims 1-4; the electron source is connected to the harmonic generation unit and is used to generate an electron beam and input it into the harmonic generation unit; the first seed laser generator is connected to the harmonic generation unit and is used to generate a seed laser and input it into the harmonic generation unit.

6. A method for generating a fully coherent free-electron laser in the water window band based on the light source device according to any one of claims 1-4, characterized in that, include: Low-order harmonic radiation is generated by modulating the incoming electron beam and seed laser through a harmonic generation unit. The first amplifier unit resonates with the low-order harmonics and generates coherent harmonic radiation. The next amplifier unit uses the harmonic radiation of the previous stage as an effective seed to tune the coherent harmonic radiation into higher-order harmonic radiation, so as to obtain a fully coherent free electron laser pulse in the water window band.

7. The method for generating a fully coherent free-electron laser in the water window band according to claim 6, characterized in that, The step of modulating the incoming electron beam and seed laser through the harmonic generation unit to generate low-order harmonic radiation includes: The added electron beam is accelerated and compressed; The accelerated and compressed electron beam is modulated with a seed laser and further compressed to convert the energy modulation of the electron beam into density modulation, thereby generating low-order harmonic radiation.

8. The method for generating a fully coherent free-electron laser in the water window band according to claim 6, characterized in that, The amplifier unit further includes a third amplifier unit; the first amplifier unit resonates with low-order harmonic radiation and generates coherent harmonic radiation, and the next amplifier unit uses the harmonic radiation of the previous stage as an effective seed to tune the coherent harmonic radiation into higher-order harmonic radiation, in order to obtain a fully coherent free electron laser pulse in the water window band, includes the following steps: The fifth electron beam carrying micro-clusters is introduced into the first amplifier unit, causing the fifth electron beam to resonate at the frequency of the first harmonic radiation, so as to generate a sixth electron beam with micro-clusters and harmonic radiation having higher harmonics. The first harmonic radiation is used as an effective seed to interact with the sixth electron beam in the second amplifier unit to obtain the amplified second harmonic radiation, and a seventh electron beam is generated. The second harmonic radiation is used as an effective seed and interacts with the seventh electron beam in the third amplifier unit to obtain the amplified third harmonic radiation, so as to obtain a fully coherent free electron laser pulse in the water window band.

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