A method and device for generating attosecond mode-locked X-ray pulses modulated by temporal transverse coupling

Abstract

The present invention relates to the field of data processing technology, and discloses a method and device for generating attosecond mode-locked X-ray pulses using time-transverse coupling modulation. The method comprises: a linear accelerator acquires a first electron beam, performs acceleration processing on the beam, obtains a second electron beam, and sends the beam to a first dispersion section; the first dispersion section processes the second electron beam to obtain a third electron beam, which is sent to a laser modulation section; the laser modulation section performs energy modulation processing on the third electron beam to obtain a fourth electron beam, which is sent to a second dispersion section; the second dispersion section performs spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, which is sent to a mode-locked amplifier; the mode-locked amplifier processes the fifth electron beam and outputs an attosecond mode-locked X-ray pulse train. By performing energy modulation and spatial distribution modulation on the electron beam, the present invention can effectively avoid mutual interference between pulse signals and significantly improve the signal-to-noise ratio of the pulse train.

Description

Technical Field

[0001] The present invention relates to the field of data processing technology, and in particular to a method and device for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation. Background Art

[0002] Existing free-electron laser technology typically uses an external laser to modulate the electron beam energy distribution, creating a periodic energy chirp to synthesize a pulse train. However, high-energy and low-energy electrons that are not effectively separated will still radiate synchronously in the undulator, resulting in significant background noise. Alternatively, methods such as nonlinear compression, plasma, or metal sheets are commonly used to modulate the electron bunch energy, but this limits the pulse duration.

[0003] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method and device for generating attosecond mode-locked X-ray pulses with temporal transverse coupling modulation, aiming to solve the problem in the prior art that the pulse signals generated by free electron laser technology have significant background noise and limited pulse duration.

[0005] To achieve the above objectives, the present invention provides a method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation. The method is applied to an attosecond mode-locked X-ray pulse generating device using temporal transverse coupling modulation. The attosecond mode-locked X-ray pulse generating device using temporal transverse coupling modulation includes a linear accelerator, a first dispersion section, a laser modulation section, a second dispersion section, and a mode-locked amplifier. The method comprises the following steps:

[0006] The linear accelerator acquires a first electron beam, accelerates the first electron beam to obtain a second electron beam, and sends the second electron beam to the first dispersion section;

[0007] The first dispersion section processes the second electron beam to obtain a third electron beam, and sends the third electron beam to the laser modulation section;

[0008] The laser modulation section performs energy modulation processing on the third electron beam to obtain a fourth electron beam, and sends the fourth electron beam to the second dispersion section;

[0009] The second dispersion section performs spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, and sends the fifth electron beam to the mode-locked amplifier;

[0010] The mode-locked amplifier processes the fifth electron beam and outputs an attosecond mode-locked X-ray pulse sequence.

[0011] Optionally, in the method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation, the phase space expression of the second electron beam is:

[0012] ;

[0013] in, is the phase space expression of the second electron beam, is the horizontal coordinate, is the horizontal divergence, is the vertical coordinate, is the vertical divergence, is the vertical coordinate, is the relative energy deviation.

[0014] Optionally, the method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation, wherein the first dispersion section processes the second electron beam to obtain a third electron beam, and sends the third electron beam to the laser modulation section, specifically comprises:

[0015] The first dispersion section receives the second electron beam sent by the linear accelerator and obtains a first transmission matrix, wherein the expression of the first transmission matrix is:

[0016] ;

[0017] in, is the first transmission matrix, is the length of the first dispersion segment, is the dispersion generated in the first dispersion segment, is the momentum compression generated in the first dispersion segment;

[0018] The first dispersion segment processes the second electron beam using the first transmission matrix to obtain a third electron beam, wherein the phase space expression of the third electron beam is: ;

[0019] The first dispersion section sends the third electron beam to the laser modulation section.

[0020] Optionally, the method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation, wherein the laser modulation section performs energy modulation processing on the third electron beam to obtain a fourth electron beam, and sends the fourth electron beam to the second dispersion section, specifically includes:

[0021] The laser modulation section receives the seed laser sent by the seed laser generator, and receives the third electron beam sent by the first dispersion section;

[0022] The laser modulation section calculates an undulator parameter of the laser modulation section according to an average Lorentz factor of the third electron beam, a laser wavelength of the seed laser, and a modulation section undulator period of the laser modulation section, and calculates an energy change of the third electron beam according to the undulator parameter and laser power;

[0023] The laser modulation section obtains a second transmission matrix, and processes the second transmission matrix and the third electron beam according to the energy change to obtain a fourth electron beam;

[0024] The laser modulation section sends the fourth electron beam to the second dispersion section.

[0025] Optionally, in the method for generating attosecond mode-locked X-ray pulses modulated by time transverse coupling, the resonance relationship between the average Lorentz factor of the third electron beam, the laser wavelength of the seed laser, the modulation segment undulator period of the laser modulation segment, and the undulator parameters of the laser modulation segment is expressed as follows:

[0026] ;

[0027] in, is the laser wavelength of the seed laser, is the modulation segment undulator period, are the undulator parameters, is the average Lorentz factor;

[0028] The expression for the energy change of the third electron beam is:

[0029] ;

[0030] in, is the energy change, is the maximum value of the Lorentz factor variation.

[0031] Optionally, the method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation, wherein the second dispersion segment performs spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, and sends the fifth electron beam to the mode-locked amplifier, specifically includes:

[0032] The second dispersion section receives the fourth electron beam sent by the laser modulation section and obtains a third transmission matrix;

[0033] The second dispersion section processes the fourth electron beam according to the third transmission matrix to obtain an initial transmission matrix;

[0034] The second dispersion segment simplifies the initial transmission matrix to obtain a target transmission matrix;

[0035] The second dispersion section outputs the fifth electron beam according to the target transmission matrix and sends the fifth electron beam to the mode-locked amplifier.

[0036] Optionally, in the method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation, the target transmission matrix is expressed as follows:

[0037] ;

[0038] in, is the target transmission matrix, is the sum of the lengths of the first dispersion segment, the laser modulation segment, and the second dispersion segment, Chirp for energy, is the length of the dispersion segment, is the bending angle value.

[0039] In addition, to achieve the above-mentioned object, the present invention further provides an attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation, wherein the attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation comprises:

[0040] a linear accelerator, configured to obtain a first electron beam, accelerate the first electron beam to obtain a second electron beam, and send the second electron beam to a first dispersion section;

[0041] a first dispersion section, configured to process the second electron beam to obtain a third electron beam, and send the third electron beam to the laser modulation section;

[0042] a laser modulation section, configured to perform energy modulation processing on the third electron beam to obtain a fourth electron beam, and send the fourth electron beam to the second dispersion section;

[0043] a second dispersion section, configured to perform spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, and send the fifth electron beam to a mode-locked amplifier;

[0044] A mode-locked amplifier is used to process the fifth electron beam and output an attosecond mode-locked X-ray pulse sequence.

[0045] Optionally, the attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation further comprises:

[0046] The electron source is used to generate a first electron beam and send the first electron beam to the linear accelerator.

[0047] Optionally, the attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation further comprises:

[0048] The seed laser generator is used to generate seed laser and send the seed laser to the laser modulation section.

[0049] In the present invention, the linear accelerator obtains a first electron beam, accelerates the first electron beam to obtain a second electron beam, and sends the second electron beam to the first dispersion section; the first dispersion section processes the second electron beam to obtain a third electron beam, and sends the third electron beam to the laser modulation section; the laser modulation section performs energy modulation on the third electron beam to obtain a fourth electron beam, and sends the fourth electron beam to the second dispersion section; the second dispersion section performs spatial distribution modulation on the fourth electron beam to obtain a fifth electron beam, and sends the fifth electron beam to the mode-locked amplifier; the mode-locked amplifier processes the fifth electron beam and outputs an attosecond mode-locked X-ray pulse train. By performing energy modulation and spatial distribution modulation on the electron beam, the present invention can effectively avoid mutual interference between pulses and significantly improve the signal-to-noise ratio of the pulse train, ultimately obtaining a high-purity, short-pulse attosecond mode-locked X-ray pulse train. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a flow chart of a preferred embodiment of the method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation according to the present invention;

[0051] Figure 2 Schematic diagram of the overall structure of a preferred embodiment of the attosecond mode-locked X-ray pulse generation method using temporal transverse coupling modulation according to the present invention;

[0052] Figure 3 Schematic diagram of the principle of a preferred embodiment of the method for generating attosecond mode-locked X-ray pulses modulated by temporal transverse coupling of the present invention;

[0053] Figure 4 Schematic diagram of the energy distribution, lateral distribution, and current intensity distribution of an electron bunch in a preferred embodiment of the attosecond mode-locked X-ray pulse generation method using temporal lateral coupling modulation according to the present invention;

[0054] Figure 5 This is a schematic diagram of FEL simulation results of a preferred embodiment of the attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation of the present invention. DETAILED DESCRIPTION

[0055] Existing free electron laser (FEL) technology faces two key technical challenges in attosecond pulse generation: 1. Inadequate background noise suppression in mode-locked FEL pulse trains: Conventional mode-locked FEL schemes use an external laser to modulate the electron beam energy distribution, creating a periodic energy chirp to synthesize the pulse train. However, high-energy and low-energy electrons that are not effectively separated will still radiate synchronously in the undulator, resulting in significant background noise. In conventional schemes, the noise power in the time domain typically reaches over 10% of the FEL pulse train power. This temporal noise also causes spectral broadening and random noise in the frequency domain. 2. Pulse duration limitations of fresh bunching techniques: Existing fresh slicing schemes typically use methods such as nonlinear compression, plasma, and metal slicing to modulate the electron bunch energy. The modulation range is comparable to the beam length, resulting in the subsequent temporal-lateral modulation accuracy being limited to the beam length, limiting the achievable shortest pulse duration to just over 1 fs.

[0056] To address the above issues, the present invention discloses a method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation. Through the coordinated design of electron beam energy modulation and orbital control technology, this method specifically addresses the technical challenges of insufficient noise suppression of mode-locked FEL pulse trains and excessively long fresh bunch pulse duration. The specific implementation method is as follows:

[0057] 1. Introducing a wiggler for laser modulation within the magnetic bend system, the team converted more refined energy modulation into temporal-transverse modulation (including energy modulation generated by the laser modulation phase, and spatial distribution modulation converted by energy modulation in the second dispersion phase). As the bunch advances through the undulator, the effective on-axis interaction length is shortened to 150 nm within a single laser wavelength. By independently controlling the orbits of high-energy and low-energy electrons, the mutual interference of multi-color pulses in traditional fresh slices is avoided, further improving the purity of monochromatic pulses. Furthermore, the magnetic bend system separates high-energy and low-energy electrons laterally by 240 μm, and orbital switching within the undulator phase allows only electrons of specific energies to participate in the lasing process. This suppresses the FEL gain of off-axis electrons to below 0.01 GW, optimizes the spectral bandwidth to 2.1%, and precisely controls the mode spacing to 1.55 eV, significantly improving the signal-to-noise ratio of the pulse train.

[0058] 2. To address the issue of excessively long fresh bunch pulse duration, this invention achieves ultrashort pulse generation through optimized momentum compression factors and mode-locked amplifier design. A second dispersion stage (e.g., setting the momentum compression factor ξ = 90 μm) is implemented downstream of the modulator to convert the electron beam energy modulation into finer temporal-transverse modulation, shortening the effective on-axis interaction length to 150 nm. Combined with the slip design of the mode-locked amplifier (e.g., setting the first-stage slip to 40 nm), the interaction period between the electron beam and the radiation field is compressed to sub-femtoseconds. Simulation results show that single pulse duration can be reduced to 250 attoseconds, with a maximum power of 2 GW and an average power of 0.5 GW.

[0059] Through precise electron beam manipulation and undulator parameter optimization, the present invention breaks through the performance bottleneck of existing attosecond FEL technology, providing a high-purity, ultrashort pulse two-color attosecond mode-locked FEL light source for ultrafast scientific research, which is particularly suitable for precision detection in the fields of electron dynamics and quantum control.

[0060] The method for generating attosecond mode-locked X-ray pulses by temporal transverse coupling modulation according to a preferred embodiment of the present invention is as follows: Figure 1 As shown, the method for generating attosecond mode-locked X-ray pulses modulated by temporal transverse coupling includes the following steps:

[0061] Step S10: The linear accelerator obtains a first electron beam, accelerates the first electron beam to obtain a second electron beam, and sends the second electron beam to the first dispersion section.

[0062] like Figure 2The present invention relates to an attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation, comprising an electron linear accelerator, a first dispersion section, a first modulation section, a second dispersion section, and a mode-locked amplifier. The specific generation process of an attosecond mode-locked X-ray pulse sequence is as follows: 1. A first electron beam generated by an electron source is accelerated by the electron linear accelerator to form a second electron beam; 2. The second electron beam passes through the first dispersion section to form a third electron beam; 3. A seed laser generator is used to generate a seed laser, which is injected into the first modulation section along with the third electron beam to produce a periodic energy modulation in the third electron beam, thereby producing a fourth electron beam; 4. After the fourth electron beam passes through the second dispersion section, its periodic energy modulation is converted into a periodic temporal transverse modulation, thereby producing a fifth electron beam; 5. The fifth electron beam enters the mode-locked amplifier, thereby generating an attosecond free electron laser pulse sequence. The mode-locked amplifier consists of multiple units, each of which consists of an undulator and a delay structure. Such a structure can generate a sequence of attosecond pulses with adjustable wavelengths of soft X-rays ranging from 1 nm to 10 nm. The shortest pulse width of each attosecond pulse is between 250 attoseconds and several femtoseconds. The generated attosecond pulse sequence can provide a new tool for ultrafast scientific research, especially for two-color synchronous pump-probe experiments, and has important application potential in the fields of electron dynamics and quantum control.

[0063] The particle accelerator of the present invention is used to generate a relativistic electron beam, achieving continuously adjustable bunch length (i.e., beam length) between 200 femtoseconds and 3 picoseconds. The particle accelerator can be either an accelerator with a beam energy between 50 and 150 MeV or one with a beam energy above 1 GeV. The particle accelerator is a photocathode electron gun comprising a photocathode, a band accelerator tube, a band accelerator tube, and a magnetic compression section. Laser light strikes the photocathode to generate photoemission, while the band accelerator tube and band accelerator accelerate the electron beam. The band accelerator tube and magnetic compression section control the beam length of the electron beam. The specific beam length is determined by adding an energy chirp to the electron beam longitudinally through the phase of the band accelerator tube. After passing through the magnetic compression section, the electron beam with the energy chirp is compressed. The bunch length of the compressed electron beam is related to the energy chirp and the length of the magnetic compression section. If the beam length needs to be adjusted, this can be achieved by adjusting the energy chirp of the electron beam by adjusting the phase of the band accelerator tube.

[0064] Specifically, the phase space expression of the second electron beam is:

[0065] ;

[0066] in, is the phase space expression of the second electron beam, is the horizontal coordinate, is the horizontal divergence, is the vertical coordinate, is the vertical divergence, is the vertical coordinate, is the relative energy deviation.

[0067] In order to perform linear optical analysis on the proposed solution, the present invention uses a beam transfer matrix to process the six-dimensional phase space of the electron bunch. The electron bunch phase space is composed of six-dimensional vectors Definition (the dimension of the transfer matrix is 6×6, and the number of rows in the electron bunch phase space is the number of electrons), where 、 and are the horizontal, vertical and longitudinal coordinates respectively, and are the horizontal and vertical divergences, is the relative energy deviation relative to the reference particle. The transverse structure generated by laser modulation can be in the horizontal or vertical direction. The main difference is that in the plane undulator Direction magnetic field ratio The magnetic field in the direction of decays much faster. The center of the oscillator and the undulator are located on the same horizontal plane, so this adjustment can be easily applied to existing seed free electron lasers. The following changes, that is, use represents the phase space of the electron bunch, and assuming that the first electron bunch 、 、 is a Gaussian distribution.

[0068] Step S20: The first dispersion section processes the second electron beam to obtain a third electron beam, and sends the third electron beam to the laser modulation section.

[0069] like Figure 3 As shown ( Figure 3 Where L is the length of the dispersion segment, (where λ is the angle between the center line of the dispersion segments and the direction of electron beam travel, i.e., the bending angle of the dispersion segments, and LM is the length of the laser modulation segment.) The present invention employs a first dispersion segment-laser modulation segment-second dispersion segment structure. This structure is equivalent to splitting a bending magnet into two dispersion segments, with the laser modulation segment placed between them. This structure allows for temporal-transverse modulation of the electron beam at the exit of the linear accelerator on the scale of the laser wavelength. Furthermore, the modulated electron bunch with this temporal-transverse structure enters a mode-locked amplifier, generating a train of attosecond mode-locked free electron laser pulses. The mode-locked amplifier is composed of several repeating units, each of which includes an undulator and an inter-segment delay structure, typically composed of a bending magnet.

[0070] Specifically, the first dispersion section receives the second electron beam sent by the linear accelerator and obtains a first transmission matrix, wherein the expression of the first transmission matrix is:

[0071] ;

[0072] in, is the first transmission matrix, is the length of the first dispersion segment, is the dispersion generated in the first dispersion segment, is the momentum compression produced in the first dispersion segment.

[0073] The first dispersion segment processes the second electron beam using the first transmission matrix to obtain a third electron beam, wherein the phase space expression of the third electron beam is: ; The first dispersion section sends the third electron beam to the laser modulation section.

[0074] After obtaining the second electron beam, the present invention first passes through a dispersion section composed of two bent irons (i.e., the first dispersion section in the present invention). The transmission matrix of the first dispersion section is: ,in is the length of the first dispersion segment, is the dispersion generated in the first dispersion segment, is the momentum compression generated in the first dispersion segment (wherein, the first dispersion segment and the second dispersion segment have opposite polarities and are both composed of two dipole irons. Assume that the length of the dispersion segment is L The angle between the center line and the electron beam direction is , then the dispersion and momentum compression factor It can be expressed as and ).

[0075] Second electron beam phase space After the transmission matrix , and the third electron beam is obtained. The phase space of the third electron beam is .

[0076] Step S30: The laser modulation section performs energy modulation processing on the third electron beam to obtain a fourth electron beam, and sends the fourth electron beam to the second dispersion section.

[0077] After the energy of the third electron beam is modulated, the fourth electron beam is obtained. The phase space of the fourth electron beam is ,in, is the transmission matrix corresponding to the laser modulation part.

[0078] Specifically, the laser modulation segment receives the seed laser sent by the seed laser generator, and receives the third electron beam sent by the first dispersion segment; the laser modulation segment calculates the undulator parameters of the laser modulation segment based on the average Lorentz factor of the third electron beam, the laser wavelength of the seed laser, and the modulation segment undulator period of the laser modulation segment, and calculates the energy change of the third electron beam based on the undulator parameters and the laser power.

[0079] The resonance relationship between the average Lorentz factor of the third electron beam, the laser wavelength of the seed laser, the modulation segment undulator period of the laser modulation segment, and the undulator parameters of the laser modulation segment is expressed as follows:

[0080] ;

[0081] in, is the laser wavelength of the seed laser, is the modulation segment undulator period, are the undulator parameters, is the average Lorentz factor.

[0082] An example of seed laser generation is shown below: a traveling-wave femtosecond optical parametric amplifier, pumped at approximately 800 nanometers by a Ti:Sapphire laser amplifier with a repetition rate of 1 kHz. Using a monoclinic BiB3O6 crystal and a two-stage continuous spectrum seed injection scheme, the amplifier achieves a total energy output exceeding 1 millijoule, corresponding to an intrinsic conversion efficiency of approximately 32% in the second stage. The tuning range extends from 1.1 to 2.9 microns. The high parametric gain and wide amplification bandwidth of the crystal enable the pump pulse width to be maintained. Even at this high output level, the pulse widths of the signal and idler light pulses remain less than 140 femtoseconds.

[0083] Regarding the interaction between the seed laser and the electron bunch in the laser modulation section: In the laser modulation section, the seed laser and the electron bunch oscillate in the same direction. In a specific embodiment, the first modulation section can be an undulator (an undulator is a magnet array that generates a periodic magnetic field). The third electron beam satisfies the following resonance relationship in the first modulation section:

[0084] ;

[0085] in, is the laser wavelength of the seed laser, is the modulation segment undulator period, In the present invention, the modulation section undulator preferably used is a planar undulator with a period of 15 cm and a total length of 0.9 m. The length of the modulation section undulator is usually in the range of 0.3 m to 2 m.

[0086] The laser modulation section calculates the energy change of the third electron beam according to the average Lorentz factor.

[0087] The expression for the energy change of the third electron beam is:

[0088] ;

[0089] in, is the energy change, is the maximum value of the Lorentz factor variation.

[0090] The laser modulation section obtains a second transmission matrix, and processes the second transmission matrix and the third electron beam according to the energy change to obtain a fourth electron beam; the laser modulation section sends the fourth electron beam to the second dispersion section.

[0091] When the average Lorentz factor of the electron bunch is , the maximum value of the Lorentz factor change is The energy of the electron bunch is given by Changes to .

[0092] The third electron beam is mixed with the wavelength of The seed laser interacts and obtains energy changes For electrons within a seed wavelength range, only electrons near the maximum energy modulation position will generate laser light in the undulator. These electrons are compared with reference electrons that are not energy modulated. The present invention assumes that the energy modulation is still linear, and the energy chirp is:

[0093] ;

[0094] Therefore, the energy change of these electrons can be written as: ,in, , the transmission matrix corresponding to the electron beam in the laser modulation part It can be described as:

[0095] ;

[0096] in, is the length of the modulator, is the momentum compression generated in the undulator.

[0097] Step S40: The second dispersion section performs spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, and sends the fifth electron beam to the mode-locked amplifier.

[0098] After the fourth electron beam passes through the second dispersion section, the fifth electron beam is obtained. The phase space of the fifth electron beam is ,in, is the transmission matrix of the second dispersion segment.

[0099] Specifically, the second dispersion segment receives the fourth electron beam sent by the laser modulation segment and obtains a third transmission matrix; the second dispersion segment processes the fourth electron beam according to the third transmission matrix to obtain an initial transmission matrix; the second dispersion segment simplifies the initial transmission matrix to obtain a target transmission matrix.

[0100] The target transmission matrix is expressed as follows:

[0101] ;

[0102] in, is the target transmission matrix, is the sum of the lengths of the first dispersion segment, the laser modulation segment, and the second dispersion segment, Chirp for energy, is the length of the dispersion segment, is the bending angle value of the dispersion segment.

[0103] The second dispersion section outputs the fifth electron beam according to the target transmission matrix and sends the fifth electron beam to the mode-locked amplifier.

[0104] Since the momentum compression of the modulator is usually much smaller than the momentum compression of the subsequent dispersion segment (i.e., the second dispersion segment), it is ignored in the following calculations. (i.e., the momentum compression produced in the undulator), The expression is:

[0105] ;

[0106] in, L 2 is the length of the downstream dispersion section, and are the compression of the diffusivity and momentum in the downstream dispersion section, respectively. Then the transmission matrix of the entire beam line before the inserter is:

[0107] ;

[0108] in, , since the first dispersion segment and the second dispersion segment can be considered to constitute a bending magnet together, and the polarities of the first dispersion segment and the second dispersion segment are opposite, we can get and Considering the structure of the actual device, and The relationship between can be expressed as and ,in, , the simplified transmission matrix can be expressed as:

[0109] .

[0110] Subsequently, the lateral position of the electron after the downstream bend It can be expressed as:

[0111] ;

[0112] exist In the equation, This indicates that transverse modulation is closely related to longitudinal energy modulation. The dispersion segment-laser modulation segment-dispersion segment structure proposed in this invention achieves time-transverse coupling modulation on the laser wavelength scale through energy modulation on the laser wavelength scale. When such a bunch is combined with a subsequent mode-locked amplifier, it can generate attosecond mode-locked free electron lasers.

[0113] Step S50: The mode-locked amplifier processes the fifth electron beam and outputs an attosecond mode-locked X-ray pulse sequence.

[0114] In a mode-locked amplifier, assuming The undulator and the subsequent delay structure, the final spectral shape Approximately:

[0115] ;

[0116] in, is the normalized frequency, is the initial noise, is the slip length between the FEL and the bunch in an undulator, is the total slip length in an undulator and a delay structure.

[0117] Example display:

[0118] The electron beam extracted from the linear accelerator has the following parameters: energy of 2.53 GeV, average current of 3 kA, rms normalized emittance of 0.4 mm-rad, and an uncorrelated energy spread of 180 keV. =800 nm, a peak power of 50 GW, a beam waist size of 0.5 mm, and an RMS pulse duration of 100 femtoseconds. The electron beam interacts with the external laser in the undulator and achieves an energy modulation amplitude of 10 MeV. The total length of the wiggler is 0.9 m and contains 6 cycles. The wavelength of the mode-locked amplifier emission The undulator period is chosen to be 2 nm. When the modulation amplitude is 10 MeV, No need to be big, here = 0.03 m, the separation between the high-energy electron and the reference particle can be calculated as ≈ 120 μm, indicating that the separation between high-energy electrons and low-energy electrons is about 240 μm.

[0119] Initial waist radius and divergence angle The length of each dispersion segment is 60 microns and 1.3 microradians respectively. The angle of deflection of each dipole iron is 5 meters, and the deflection angle of each dipole iron is 6 milliradians. The transmission of the electron beam in the modulator and dispersion section is tracked using the ELEGANT code, and the simulation takes into account the second-order transmission effect. The FEL laser process is simulated using the time-varying mode of GENESIS. These simulations take into account the actual transfer matrix of each component. Various nonlinear effects, such as coherent synchrotron radiation, incoherent synchrotron radiation and longitudinal space charge effects, are also included in these simulations. After setting the structure of dispersion section-laser modulation section-dispersion section, the energy distribution (i.e. Figure 4 (a) in the figure), the lateral distribution of the electron bunch (i.e. Figure 4 (b) in the figure), current intensity distribution (i.e. Figure 4 (c) in the above example Figure 4 shown.

[0120] like Figure 4 As shown in (a), the sinusoidal energy modulation is over-compressed, with the highest density located in the regions with the highest and lowest beam energies. Figure 4 In (b), after passing the downstream bend, the centers of the highest and lowest energy electrons are 200 μm apart, which is sufficient for a two-stage fresh-sheet lasing scheme. The length of the on-axis region within a single cycle of the undulator segment is approximately 150 nm. Figure 4 (c) shows that the peak current is enhanced to 5 kA, and the peak current of the on-axis beam is about 4.2 kA.

[0121] Taking the peak current as 4200 amperes, the Planck constant as H, and the speed of light as c, we can estimate that the energy difference between adjacent modes in the obtained spectrum is: ; The Pierce parameter of FEL is estimated to be , the gain length is meters, of which is the undulator period of the mode-locked undulator, and the coherence time is calculated as Attoseconds, where It is the central wavelength of the X-ray free electron laser obtained in the mode-locked undulator (also called amplifier).

[0122] The simulation results of FEL are as follows Figure 5 As shown in the figure, in the mode-locked amplifier, the performance of the 13 undulator end FELs are Figure 5 (a) and Figure 5 (b) is given in . Figure 5 The pulse interval of a train of pulses in (a) is Ts = 1.33 femtoseconds, the total pulse energy is 4.23 microjoules, the average peak power is 0.517 gigawatts, and the average pulse duration is = 248 attoseconds. The slip caused by the delay magnets results in the total number of pulses being slightly greater than the number of electron cycles, which is also the reason why the peak power of the pulses near the beam tail is lower than the average.

[0123] In addition, the peak power of the free electron laser from the off-axis beam was suppressed to below 0.01 GW. Figure 5 In (b), the spectrum width (full width at half maximum) is 2.10%, consisting of about 40 modes with a mode spacing of 0.25% (1.55 eV), and the average bandwidth of each individual mode is 0.41 eV.

[0124] Beneficial effects of the present invention:

[0125] 1. High-purity and low-noise output: A magnetic bend system achieves a transverse separation of high-energy and low-energy electrons (this process is accomplished jointly by the first dispersion stage, the modulation stage, and the second dispersion stage. The relationship between the transverse separation and the corresponding parameters can be derived from the transfer matrix. Under the given parameters, the calculated transverse separation reaches 240 μm). In the undulator stage, only electrons of a specific energy are allowed to participate in the lasing process, effectively suppressing the spontaneous emission (SASE) noise of off-axis electrons. Experiments show that the FEL peak power of off-axis electrons is suppressed to below 0.01 GW, the spectral full width at half maximum is optimized to 2.1%, and the mode spacing is precisely matched to the external laser wavelength (1.55 electron volts), significantly improving the coherence and signal-to-noise ratio of the pulse train.

[0126] 2. Ultrashort pulse duration breakthrough: through momentum compression factor optimization ( =90 μm) and a mode-locked amplifier design shorten the effective interaction length of the electron beam and the radiation field to 150 nanometers, and compress the single pulse duration to 250 attoseconds, which is nearly an order of magnitude higher than the traditional fresh slicing scheme (about 2 femtoseconds), providing finer time resolution for detecting ultrafast processes such as electron dynamics.

[0127] 3. High Compatibility and Scalability: Horizontal modulation facilitates direct integration into existing seed FEL devices. Vertical modulation can further reduce external laser power requirements (e.g., by achieving sufficient lateral separation through smaller energy modulation amplitudes). Furthermore, this invention can be expanded to generate multicolor pulses or output isolated attosecond pulses, providing a technical foundation for the development of novel light sources.

[0128] Further, if Figure 2 As shown, based on the above-mentioned attosecond mode-locked X-ray pulse generation method using temporal transverse coupling modulation, the present invention also provides an attosecond mode-locked X-ray pulse generation device using temporal transverse coupling modulation, wherein the attosecond mode-locked X-ray pulse generation device using temporal transverse coupling modulation includes:

[0129] a linear accelerator, configured to obtain a first electron beam, accelerate the first electron beam to obtain a second electron beam, and send the second electron beam to a first dispersion section;

[0130] a first dispersion section, configured to process the second electron beam to obtain a third electron beam, and send the third electron beam to the laser modulation section;

[0131] a laser modulation section, configured to perform energy modulation processing on the third electron beam to obtain a fourth electron beam, and send the fourth electron beam to the second dispersion section;

[0132] a second dispersion section, configured to perform spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, and send the fifth electron beam to a mode-locked amplifier;

[0133] A mode-locked amplifier is used to process the fifth electron beam and output an attosecond mode-locked X-ray pulse sequence.

[0134] The attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation further comprises:

[0135] The electron source is used to generate a first electron beam and send the first electron beam to the linear accelerator.

[0136] The attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation further comprises:

[0137] The seed laser generator is used to generate seed laser and send the seed laser to the laser modulation section.

[0138] In summary, the present invention provides a method and device for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation. The method comprises: the linear accelerator acquires a first electron beam, accelerates the first electron beam to obtain a second electron beam, and sends the second electron beam to the first dispersion section; the first dispersion section processes the second electron beam to obtain a third electron beam, and sends the third electron beam to the laser modulation section; the laser modulation section performs energy modulation on the third electron beam to obtain a fourth electron beam, and sends the fourth electron beam to the second dispersion section; the second dispersion section performs spatial distribution modulation on the fourth electron beam to obtain a fifth electron beam, and sends the fifth electron beam to the mode-locked amplifier; the mode-locked amplifier processes the fifth electron beam and outputs an attosecond mode-locked X-ray pulse train. By performing energy modulation and spatial distribution modulation on the electron beam, the present invention can effectively avoid mutual interference between pulses and significantly improve the signal-to-noise ratio of the pulse train, ultimately obtaining a high-purity, short-pulse attosecond mode-locked X-ray pulse train.

[0139] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or terminal comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or terminal. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or terminal comprising the element.

[0140] Of course, those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing related hardware (such as a processor, controller, etc.) through a computer program. The program can be stored in a computer-readable storage medium that can be read by a computer. When executed, the program can include the processes in the above-described method embodiments. The computer-readable storage medium can be a memory, a magnetic disk, an optical disk, etc.

[0141] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for generating attosecond mode-locked X-ray pulses modulated by temporal transverse coupling, characterized in that: The method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation is applied to an attosecond mode-locked X-ray pulse generating device using temporal transverse coupling modulation, wherein the attosecond mode-locked X-ray pulse generating device using temporal transverse coupling modulation includes a linear accelerator, a first dispersion section, a laser modulation section, a second dispersion section, and a mode-locked amplifier. The method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation includes: The linear accelerator acquires a first electron beam, accelerates the first electron beam to obtain a second electron beam, and sends the second electron beam to the first dispersion section; The first dispersion section processes the second electron beam to obtain a third electron beam, and sends the third electron beam to the laser modulation section; The laser modulation section performs energy modulation processing on the third electron beam to obtain a fourth electron beam, and sends the fourth electron beam to the second dispersion section; A bending magnet is split into two dispersion segments, and a laser modulation segment is placed in between, resulting in a first dispersion segment-laser modulation segment-second dispersion segment structure, which is used to perform temporal-lateral modulation of the electron beam at the exit of the linear accelerator on the scale of the laser wavelength. The first dispersion segment and the second dispersion segment have opposite polarities and are both composed of two dipole irons. The first dispersion segment-laser modulation segment-second dispersion segment structure achieves time-transverse coupling modulation on the laser wavelength scale through energy modulation on the laser wavelength scale. When combined with a subsequent mode-locked amplifier, it generates attosecond mode-locked free electron laser. The second dispersion section performs spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, and sends the fifth electron beam to the mode-locked amplifier; The second dispersion section performs spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, and sends the fifth electron beam to the mode-locked amplifier, specifically including: The second dispersion section receives the fourth electron beam sent by the laser modulation section and obtains a third transmission matrix; The second dispersion section processes the fourth electron beam according to the third transmission matrix to obtain an initial transmission matrix; The second dispersion segment simplifies the initial transmission matrix to obtain a target transmission matrix; The second dispersion section outputs the fifth electron beam according to the target transmission matrix, and sends the fifth electron beam to the mode-locked amplifier; The expression of the target transmission matrix is: ； in, is the target transmission matrix, is the sum of the lengths of the first dispersion segment, the laser modulation segment, and the second dispersion segment, Chirp for energy, is the length of the dispersion segment, is the bending angle value; A second dispersion section is provided downstream of the laser modulation section to convert the electron beam energy modulation into time-transverse modulation; The modulated electron bunch with a temporal-transverse structure enters a mode-locked amplifier, generating an attosecond mode-locked free electron laser pulse train. The mode-locked amplifier processes the fifth electron beam and outputs an attosecond mode-locked X-ray pulse sequence.

2. The method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation according to claim 1, characterized in that: The phase space expression of the second electron beam is: ； in, is the phase space expression of the second electron beam, is the horizontal coordinate, is the horizontal divergence, is the vertical coordinate, is the vertical divergence, is the vertical coordinate, is the relative energy deviation.

3. The method for generating attosecond mode-locked X-ray pulses with temporal transverse coupling modulation according to claim 2, characterized in that: The first dispersion section processes the second electron beam to obtain a third electron beam, and sends the third electron beam to the laser modulation section, specifically including: The first dispersion section receives the second electron beam sent by the linear accelerator and obtains a first transmission matrix, wherein the expression of the first transmission matrix is: ； in, is the first transmission matrix, is the length of the first dispersion segment, is the dispersion generated in the first dispersion segment, is the momentum compression generated in the first dispersion segment; The first dispersion segment processes the second electron beam using the first transmission matrix to obtain a third electron beam, wherein the phase space expression of the third electron beam is: ; The first dispersion section sends the third electron beam to the laser modulation section.

4. The method for generating attosecond mode-locked X-ray pulses using temporal transverse coupling modulation according to claim 2, wherein: The laser modulation section performs energy modulation processing on the third electron beam to obtain a fourth electron beam, and sends the fourth electron beam to the second dispersion section, specifically including: The laser modulation section receives the seed laser sent by the seed laser generator, and receives the third electron beam sent by the first dispersion section; The laser modulation section calculates an undulator parameter of the laser modulation section according to the average Lorentz factor of the third electron beam, the laser wavelength of the seed laser, and the modulation section undulator period of the laser modulation section, and calculates an energy change of the third electron beam according to the undulator parameter and the laser power of the seed laser; The laser modulation section obtains a second transmission matrix, and processes the second transmission matrix and the third electron beam according to the energy change to obtain a fourth electron beam; The laser modulation section sends the fourth electron beam to the second dispersion section.

5. The method for generating attosecond mode-locked X-ray pulses with temporal transverse coupling modulation according to claim 4, characterized in that: The resonance relationship between the average Lorentz factor of the third electron beam, the laser wavelength of the seed laser, the modulation section undulator period of the laser modulation section, and the undulator parameters of the laser modulation section is expressed as follows: ； in, is the laser wavelength of the seed laser, is the modulation segment undulator period, are the undulator parameters, is the average Lorentz factor; The expression for the energy change of the third electron beam is: ； in, is the energy change, is the maximum value of the Lorentz factor variation.

6. A temporal transverse coupling modulated attosecond mode-locked X-ray pulse generation device, characterized in that: The attosecond mode-locked X-ray pulse generation device modulated by time transverse coupling is used to implement the attosecond mode-locked X-ray pulse generation method modulated by time transverse coupling according to any one of claims 1 to 5, and the attosecond mode-locked X-ray pulse generation device modulated by time transverse coupling comprises: a linear accelerator, configured to obtain a first electron beam, accelerate the first electron beam to obtain a second electron beam, and send the second electron beam to a first dispersion section; a first dispersion section, configured to process the second electron beam to obtain a third electron beam, and send the third electron beam to the laser modulation section; a laser modulation section, configured to perform energy modulation processing on the third electron beam to obtain a fourth electron beam, and send the fourth electron beam to the second dispersion section; a second dispersion section, configured to perform spatial distribution modulation processing on the fourth electron beam to obtain a fifth electron beam, and send the fifth electron beam to a mode-locked amplifier; A mode-locked amplifier is used to process the fifth electron beam and output an attosecond mode-locked X-ray pulse sequence.

7. The attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation according to claim 6, characterized in that: The temporal transverse coupling modulated attosecond mode-locked X-ray pulse generation device further comprises: The electron source is used to generate a first electron beam and send the first electron beam to the linear accelerator.

8. The attosecond mode-locked X-ray pulse generation device with temporal transverse coupling modulation according to claim 6, characterized in that: The temporal transverse coupling modulated attosecond mode-locked X-ray pulse generation device further comprises: The seed laser generator is used to generate seed laser and send the seed laser to the laser modulation section.

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