A method for generating attosecond electron bunches driven by laser

Abstract

The application relates to a method for generating laser-driven attosecond electron bunches. The method comprises the following steps: constructing a laser-driven attosecond electron bunch generation system; in the system, a left-handed circularly polarized Laguerre-Gaussian laser light source is vertically incident on the surface of a low-density plasma target; the left-handed circularly polarized Laguerre-Gaussian laser light source is turned on; through interaction between the left-handed circularly polarized Laguerre-Gaussian laser and the low-density plasma target, a bubble structure is obtained; the bubble structure is used for confining electrons, the left-handed circularly polarized Laguerre-Gaussian laser is used for pushing the electrons located at the front end of the bubble structure away from the low-density plasma target, and high-density and low-divergence-angle attosecond electron bunches are obtained.

Description

Technical Field

[0001] This application relates to the field of high-power laser technology, and in particular to a method for generating attosecond electron strings driven by laser. Background Technology

[0002] With the advancement and development of laser technology, the quality of lasers has been continuously improved, leading to significant progress in the theoretical and experimental research on laser-driven attosecond electron strings. High-quality attosecond electron strings generated through the interaction of relativistic lasers and plasma have extremely high application value and broad prospects in fields such as free electron laser injection, relativistic electron mirrors, attosecond X / γ-ray generation, and ultrafast physics. To stably generate high-quality attosecond electron strings, extensive research has been conducted, and various laser-plasma interaction schemes have been proposed.

[0003] Currently, there are three main methods for generating attosecond electron strings using lasers.

[0004] The first method is the laser wakefield acceleration mechanism. This scheme utilizes the interaction between an ultra-intense laser pulse and a rarefied plasma to excite a large-amplitude plasma wave at the tail of the laser field. This plasma wave is called the wakefield, and the electromagnetic field obtained from the laser wakefield is also called the laser wakefield field. This laser wakefield field structure can effectively accelerate electrons, thereby achieving the acquisition of high-quality electron strings. In 2010, Luttikhof et al. successfully separated a single electron beam into several attosecond electron strings by injecting a single electron beam into a specific location in the wakefield in a simulation. The pulse width was approximately 630 as, the spacing was 800 nm, the peak energy was 655 MeV, and the energy divergence was approximately 10%. The advantage of this scheme is that it has very low requirements for the laser, and the attosecond electron beam obtained by this scheme has high energy and low energy divergence. However, this scheme has high requirements for the electron injection location, and it is relatively difficult to obtain isolated attosecond electron pulses. In addition, the density of attosecond electron strings obtained by this scheme is relatively low.

[0005] Besides laser wakefield acceleration, another mechanism involves using ultra-intense laser irradiation of a high-density nanotarget to obtain attosecond electron beams. This approach utilizes relativistically strong laser irradiation of a high-density thin nanotarget, using high-intensity laser pressure to eject the electron layer within the nanotarget as a whole, thus obtaining high-density isolated attosecond electron pulses. In 2007, Kulagin et al. conducted two-dimensional numerical simulations, using a high-intensity laser pulse with a steeply rising laser tip interacting with a solid-density plasma thin-film target to obtain isolated attosecond electron pulses with a large charge exceeding 10 nC. Obtaining high-quality attosecond electron pulses using this method requires the laser intensity to meet certain conditions, ensuring the laser pressure is much greater than the charge separation field between electrons and ions, thus enabling synchronous acceleration of electrons within the nanotarget in the longitudinal direction. The advantage of this approach is its ability to obtain isolated, high-charge attosecond electron pulses, and some of its quality is easily adjustable. However, attosecond electron pulses obtained through this method generally exhibit significant divergence. In addition, this scheme also has very high requirements for laser quality. It not only requires high laser intensity, but also a steep rise edge; otherwise, isolated electron pulses will be difficult to generate.

[0006] Furthermore, high-quality attosecond electron pulses can also be obtained using a vacuum heating mechanism. When a relativistic p-polarized short-pulse laser is incident obliquely at a certain angle onto a solid target with a very steep density gradient, a large number of electrons will oscillate on the surface of the solid target. When the plasma wave breaks, some electrons will be injected into the vacuum and accelerated under the action of the laser field, eventually forming attosecond electron strings.

[0007] Currently, various schemes have been proposed to interact lasers with solid targets of various shapes, such as conical targets and channel targets, to generate attosecond electron strings that meet the requirements and can be stably transmitted. The advantage of this type of scheme is that it does not impose too many constraints and restrictions on the parameters of the laser and the target. However, since this mechanism requires a high density gradient at the boundary of the solid target, and the prepulse of the relativistic laser can damage it, this type of scheme places high demands on the quality of the laser itself.

[0008] Currently, most research on laser-driven attosecond electron generation focuses on the interaction between Gaussian lasers and plasma targets. However, many researchers are also using other types of lasers for related studies. Among these, the Laguerre-Gaussian laser has attracted attention and research due to its significant differences from Gaussian lasers, such as its helical equiphase surface, hollow laser intensity distribution, and orbital angular momentum. In 2018, Hu et al. proposed a scheme to generate high-quality attosecond electron strings using the interaction of a Laguerre-Gaussian laser with a solid wire target. The attosecond electron strings obtained by this scheme exhibit excellent collimation, and the performance of related parameters such as energy dispersion, charge, and pulse width is also very good. However, because this scheme requires the laser and the wire target to be collimated, the experimental conditions are quite demanding, making it difficult to realize under experimental conditions.

[0009] In summary, various schemes for generating attosecond electron strings using laser-driven methods have been proposed. However, these schemes place high demands on experimental conditions, and some of the electron strings obtained using these methods suffer from problems such as low density and large divergence angle. More importantly, research on pulse width tuning of attosecond electron strings is relatively limited, and there is an urgent need to propose tunable attosecond electron pulse width schemes. Summary of the Invention

[0010] Therefore, it is necessary to provide a laser-driven attosecond electron string generation method to address the above-mentioned technical problems, so as to generate high-density attosecond electron strings with low divergence angles.

[0011] A method for generating attosecond electron strings driven by a laser, the method comprising:

[0012] A laser-driven attosecond electron string generation system is constructed. In the system, the positional relationship between the left-hand circularly polarized Laguerre-Gaussian laser source and the low-density plasma target is that the left-hand circularly polarized Laguerre-Gaussian laser source is perpendicularly incident on the surface of the low-density plasma target.

[0013] Turn on the left-hand circularly polarized Laguerre-Gaussian laser source; wherein the dimensionless parameters of the laser are a0 = 10 ~ 30, the beam waist radius is σ0 = 2 ~ 4λ0, the laser wavelength is λ0 = 0.8 ~ 1.06 μm, and the laser pulse width is τ = 2 ~ 4T0, where T0 is the laser period;

[0014] A cavitation structure was obtained by interacting a left-handed circularly polarized Laguerre-Gaussian laser with a low-density plasma target; where "low density" refers to a density below 0.5n. c , where n c The critical density of plasma;

[0015] Electrons are confined by a cavitation structure, and then propelled away from a low-density plasma target by a left-handed circularly polarized Laguerre-Gaussian laser, resulting in a high-density attosecond electron string with a low divergence angle; where high density refers to a density greater than 10n. c A low divergence angle refers to a divergence angle less than 5°. Attached Figure Description

[0016] Figure 1 A schematic diagram of a laser-driven attosecond electron string generation method;

[0017] Figure 2 A schematic diagram of the interaction between a left-handed circularly polarized Laguerre-Gaussian laser and a near-critical density plasma hydrogen target;

[0018] Figure 3 A schematic diagram illustrating the process by which a left-handed circularly polarized Laguerre-Gaussian laser interacts with a low-density plasma target to generate a cavitation structure.

[0019] Figure 4 This is a schematic diagram of particle simulation results for attosecond electron strings obtained by the interaction of a left-handed circularly polarized Laguerre-Gaussian laser with a low-density hydrogen target; where (a) is the electron density distribution at t=40T0, (b) is the electron density distribution at t=60T0, (c) is the electron density distribution at t=80T0, (d) is the electron divergence angle distribution at t=40T0, (e) is the electron divergence angle distribution at t=60T0, (f) is the electron divergence angle distribution at t=80T0, (g) is the evolution curve of electron density over time, (h) is the evolution curve of full width at half maximum (FWHM) of electron divergence angle over time, and (i) is the energy spectrum distribution of electrons at 40T0, 60T0, and 80T0.

[0020] Figure 5 The diagram shows the trajectory and forces acting on a portion of the electrons; (a) shows the trajectory of a portion of the electrons before x = 40λ0, where the color scale represents the electron energy; (b) shows a cross-sectional view of the trajectory of a portion of the electrons in the yOz plane, where the color scale represents the electron energy; and (c) shows the motion and forces acting on the electrons.

[0021] Figure 6 The curves showing the position, velocity, and force changes of one electron obtained through simulation analysis using the VLPL program;

[0022] Figure 7This is a schematic diagram of the effect of laser intensity on the quality of attosecond electron trains; where (a) is the distribution of electron density at positions r = 0 and x = 57~58λ0 when the laser intensity a0 takes different values ​​at time t = 60T0; and (b) is the curve of electron density, peak divergence angle and electron cutoff energy as a function of laser intensity a0 at time t = 60T0.

[0023] Figure 8 This diagram illustrates the effect of the laser carrier envelope phase on the quality of the attosecond electron string; where (a) represents the laser carrier envelope phase at time t = 60T0. (a) The distribution of electron density at positions r = 0 and x = 57–58λ0 for different values. (b) The electron density, peak divergence angle, and electron cutoff energy at time t = 60T0 are shown as a function of the laser carrier envelope phase. The curve showing the change. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0025] In one embodiment, such as Figure 1 As shown, a method for generating attosecond electron strings driven by a laser is provided, comprising:

[0026] Step 102: Construct a laser-driven attosecond electron string generation system.

[0027] In this system, the positional relationship between the left-hand circularly polarized Laguerre-Gaussian laser source and the low-density plasma target is as follows: the left-hand circularly polarized Laguerre-Gaussian laser source is incident perpendicularly on the surface of the low-density plasma target.

[0028] The Laguerre-Gaussian laser is a laser with a special structure and a hollow optical field distribution. Its electromagnetic field distribution can effectively confine charged particles.

[0029] Step 104: Turn on the left-hand circularly polarized Laguerre-Gaussian laser source.

[0030] The dimensionless parameters of the laser are a0 = 10 to 30, the beam waist radius is σ0 = 2 to 4λ0, the laser wavelength is λ0 = 0.8 to 1.06 μm, and the laser pulse width is τ = 2 to 4T0, where T0 is the laser period.

[0031] Step 106: A cavitation structure is obtained by interacting a left-handed circularly polarized Laguerre-Gaussian laser with a low-density plasma target.

[0032] Low density refers to a density below 0.5n.c , where n c This is the critical density of the plasma. Figure 2 This is a schematic diagram of the interaction between a left-handed circularly polarized Laguerre-Gaussian laser and a near-critical density plasma hydrogen target.

[0033] Step 108: Confine electrons by a cavitation structure, and use a left-handed circularly polarized Laguerre-Gaussian laser to push the electrons located at the front end of the cavitation structure away from the low-density plasma target, resulting in a high-density attosecond electron string with a low divergence angle.

[0034] High density refers to a density greater than 10n. c A low divergence angle refers to a divergence angle less than 5°.

[0035] It is worth noting that the laser wakefield acceleration mechanism mentioned in the background of this application differs from that of this application in the following ways: 1) In the prior art, the electrons acquired are located at the tail end of the cavitation bubble, while in this application, the accelerated electrons are located at the front end of the cavitation bubble; 2) In the prior art, the cavitation bubble plays a role in accelerating and confining the electrons at the tail end; in this application, the cavitation bubble is not crucial, and its role is relatively limited, only serving to confine the electrons at the front end in the early stage. In this application, the acceleration of electrons is mainly achieved through laser. Based on these differences, it can be understood that this application and the laser wakefield acceleration mechanism are two completely different acceleration mechanisms. Specifically, this is achieved by adjusting the laser parameters.

[0036] like Figure 3 The diagram illustrates the process of generating a cavitation structure through the interaction of a left-handed circularly polarized Laguerre-Gaussian laser with a low-density plasma target. The structure shown is a cavitation structure generated by the interaction of a relativistic laser pulse with a rarefied plasma. The xOy plane represents the electron density distribution along the laser axis, and the yOz plane represents the electron density distribution cross-section at the location of the white circle in the diagram. The relativistic laser pulse used is left-handed circularly polarized. The Laguerreotype laser, after interacting with a rarefied plasma target, produces electrons at the front of the cavitation bubble, i.e. Figure 3 The electrons, marked by the white dashed circles, were well accelerated and confined. Subsequently, the laser pulse propelled the electrons at the front end of the bubble away from the plasma target, eventually forming a high-density attosecond electron string structure.

[0037] In one embodiment, the plasma target is one of a hydrogen target, a carbon target, or a hydrocarbon target.

[0038] In one embodiment, the laser-driven attosecond electron string generation system further includes: a planar reflector and a concave reflector;

[0039] Plane mirrors are used to change the propagation path of laser light;

[0040] Concave mirrors are used to focus laser light.

[0041] In one embodiment, the dimensionless parameter of the laser is a0 = 20.

[0042] In one embodiment, the beam waist radius of the laser is σ0 = 3λ0.

[0043] In one embodiment, the laser wavelength is λ0 = 1 μm.

[0044] In one embodiment, the laser pulse width is τ = 3T0.

[0045] In one embodiment, during the process of using a left-handed circularly polarized Laguerre-Gaussian laser to propel electrons located at the front end of the cavitation structure away from the low-density plasma target, the electrons all move outward after acceleration and then focus inward.

[0046] In one embodiment, electrons are focused at a position near x = 15λ0, and then remain collimated and move forward.

[0047] In one embodiment, after acceleration, the electrons all move counterclockwise, and the distance between the electrons and the axis first increases and then decreases as the electrons move counterclockwise; the axis refers to the center position of the cross-sectional view of the trajectory in the yOz plane.

[0048] After the electrons move counterclockwise to a position relatively close to the axis, they do not continue to move counterclockwise. Instead, they focus directly towards the axis and then move clockwise near the axis, completing the focusing process. For example... Figure 4 As shown, a schematic diagram of particle simulation results for attosecond electron strings obtained by the interaction of a left-hand circularly polarized Laguerre-Gaussian laser with a low-density hydrogen target is provided. Among them, (a)-(c) show the electron density distribution at t=40T0, 60T0 and 80T0, respectively; (d)-(f) show the electron divergence angle distribution at t=40T0, 60T0 and 80T0, respectively; (g) is the evolution curve of electron density over time; (h) is the evolution curve of full width at half maximum (FWHM) of electron divergence angle over time; and (i) shows the energy spectrum distribution of electrons at 40T0, 60T0 and 80T0.

[0049] As can be seen, after the Laguerre-Gaussian laser pulse leaves the plasma target, the electrons at the front of the bubble it propelled evolve into attosecond electron strings, maintaining their stable shape and structure and continuing to move forward at near-vacuum light speeds for hundreds of fs. It can also be noted that at t = 40T0, the electron sheet density reaches a maximum of 240n0, which is 240 times the original hydrogen target density, or 24n. cThe electron density further increases to about 300n0 at t=60T0, and then the electron plate density decreases, but it can still reach 100n0 at t=80T0. Figure 4 (g) shows the evolution of the electron density over simulation time in more detail. It can be seen that between t = 40T0 and t = 60T0, the electron density remains at around 300n0, which is an extremely high density level. In addition, at these times, the pulse width of the electron train is always within 100 attoseconds.

[0050] The formula for calculating the electron divergence angle θ is θ = arctan(p ⊥ / p x ),and This refers to the transverse momentum of the electron. These figures show that throughout the forward propagation of the attosecond electron string, the electron divergence angle is very small, especially as the electrons propagate forward, their collimation improves. More precise calculations show that at t = 40T0, 60T0, and 80T0, the peak value and full width at half maximum (FWHM) of the electron divergence angle distribution are 0.7°, 0.5°, and 0.4°, and 2.0°, 0.9°, and 0.6°, respectively.

[0051] pass Figure 4 (i) It becomes more apparent that after t = 20T0, the divergence angle of the attosecond electron string remains at a very low level, and continues to decrease as the simulation time progresses. These results are consistent with... Figure 4 The information in (d)-(f) remains consistent, demonstrating the good collimation of the attosecond electron string. Figure 4 (i) shows the energy spectrum distribution of electrons at t = 40T0, 60T0, and 80T0. It can be seen that at t = 40T0, electrons have good quasi-monoenergetic properties, with a relative energy dissipation of about 27%. However, as time progresses, these electrons are not in the accelerating phase of the laser field, and considering the dissipation of electrons, the electron energy decreases to some extent.

[0052] In this scheme, the main principle of using a left-handed circularly polarized Laguerre-Gaussian laser to drive rarefied plasma to generate attosecond electron strings with excellent qualities such as high density and low divergence angle is as follows:

[0053] from Figure 4 In (c), a portion of the electrons in the electron string at time t = 80T0 were selected, and their trajectories before reaching position x = 40λ0 were plotted, as shown below. Figure 5As shown, the motion trajectory and force diagram of some electrons are provided, where (a) is the motion trajectory of some electrons before x = 40λ0, where the color scale represents the electron energy, (b) is a cross-sectional view of the motion trajectory of some electrons in the yOz plane, where the color scale represents the electron energy, and (c) shows the motion and force conditions of the electrons.

[0054] like Figure 5 As shown in (a), most electrons initially appear to be around x = 10λ0. After acceleration, they move outwards, then focus inwards, completing their focusing near x = 15λ0. They then remain collimated and continue moving forward. The electron trajectories depicted in the figure represent the period up to x = 40λ0. In reality, however, these electrons maintain good collimation until t = 80T0, consistent with the low divergence of the electron sheet.

[0055] Figure 5 (b) It can show more details of the electron's trajectory. It can be clearly seen that these electrons move counterclockwise after acceleration, and their distance from the axis, i.e., the center of the cross-section, first increases and then decreases with counterclockwise motion. This corresponds to... Figure 5 (a) shows the process of electrons accelerating, moving outwards, and then focusing inwards. After moving counterclockwise to a position relatively close to the axis, the electrons do not continue to move counterclockwise, but instead focus directly towards the axis and move clockwise near the axis, completing the focusing process.

[0056] Figure 5 (c) shows the electron velocity and forces that require detailed analysis, where r is the distance between the electron and the axis, and v is the electron velocity. r It is the radial velocity of the electron (taking the direction outward from the axis as positive). It is the electron angular velocity (taking counterclockwise as positive), F r The radial force on the electron is assumed to be outward from the axis (positive direction). In addition, a virtual radial force F on the electron is introduced. r ′ (Taking the outward direction of the axis as positive), this is used to analyze the reason for electron focusing. F r ′ The calculation formula is:

[0057]

[0058] Where m e Let F be the electron mass. Therefore, we can know that when F... r =F r ′ At that time, the movement of electrons is uniform circular motion around the axis.

[0059] Figure 6 This is a curve showing the position, velocity, and force changes of one of the electrons obtained through simulation analysis using the VLPL program. The focusing position of this electron is slightly different from the electrons obtained in the previous program, but the shape of the electron trajectory and the focusing process are almost identical to those of the other electrons. Therefore, we can assume that their focusing mechanisms are consistent. Figure 6 (a) represents the distance x between the electron and the axis, and the angular velocity. The curve showing the change in electron's longitudinal position x. Figure 6 (b) is the radial force F on the electron. r and virtual radial force F r ′ The curve showing how the electron's longitudinal position x changes.

[0060] From the moment the electron begins to move, until Figure 6 Before the position indicated by the dashed line, F r and F r ′ The differences are not significant and remain near 0, so this segment can be approximated as circular motion, and the change in the distance x between the electron and the axis is not particularly drastic. However, starting from the position indicated by the dashed line, the electron undergoes a phase shift, which leads to a greater radial force F acting on it. r Suddenly increased, and at the same time, the electron angular velocity It started to decrease suddenly, which also led to F r ′ The decrease of F at this time r Significantly greater than F r ′ This is precisely why electrons begin to move rapidly toward the axis, i.e., electron focusing.

[0061] The electron focusing process continues until approximately x = 45λ0, at which point the electron angular velocity... The value is relatively large (clockwise), and the electrons are also very close to the axis, therefore F r ′ It increases rapidly and exceeds the actual radial force F. r At this point, the electrons begin to tend to move outwards, increasing their distance from the axis. However, after the position x = 45λ0, due to... It then rapidly decreases until it approaches 0, therefore F r ′ The value also decreases accordingly, and also approaches 0, at which point F r Greater than F r ′This effectively curbs the tendency of electrons to move further outwards and achieves confinement of the electrons. This explains why the electrons maintain excellent collimation after focusing, and why the divergence angle decreases over time in the simulation.

[0062] like Figure 8 As shown, a schematic diagram illustrates the effect of laser intensity on the quality of the attosecond electron string, where... Figure 8 (a) The distribution of electron density at positions r = 0 and x = 57-58λ0 when the laser intensity a0 takes different values ​​at time t = 60T0. Figure 8 (b) shows the curves of electron density, peak divergence angle and electron cutoff energy as a function of laser intensity a0 at time t = 60T0.

[0063] like Figure 8 As shown, a schematic diagram illustrates the effect of the laser carrier envelope phase on the quality of the attosecond electron string. Figure 8 (a) is the laser carrier envelope phase at time t = 60T0. The distribution of electron density at positions r = 0 and x = 57–58λ0 for different values. Figure 8 (b) shows the electron density, peak divergence angle, and electron cutoff energy at time t = 60T0 as a function of the laser carrier envelope phase. The curve showing the change.

[0064] This solution can not only generate high-quality attosecond electron strings, but also adjust the quality of the attosecond electron strings, such as pulse width, by changing laser parameters, such as laser intensity and carrier envelope phase. Figure 7 and Figure 8 The effects of laser intensity and laser carrier envelope phase on various qualities of the attosecond electron train were demonstrated. Figure 6 (a) It can be seen that when the laser intensity is low, an isolated attosecond electron sheet structure can be obtained, while when the laser intensity is high, the attosecond electron string exhibits a complex structure of two or even multiple sheets, and the pulse width of the electron string also varies significantly with different laser intensities. Similarly, Figure 8 Similar changes were also observed in (a), where the structure and pulse width of the electron string changed significantly with the change of the laser carrier envelope phase, and the position of the electron string shifted at the same moment as the carrier envelope phase changed. Figure 7 (b) Figure 8 (b) shows in more detail the effects of laser intensity and carrier envelope phase on electron string density, divergence angle and cutoff energy.

[0065] In summary, this application utilizes the interaction between a laser with a special structure and a rarefied plasma to generate high-quality attosecond electron strings, and then optimizes their quality. Most previous laser-driven attosecond electron string generation schemes used Gaussian lasers interacting with plasma. Compared to these schemes, this approach offers several advantages, such as relatively lower experimental requirements, a degree of reproducibility, extremely high electron string density, and excellent control over divergence angle and pulse width. Furthermore, by adjusting certain laser parameters, the structure and pulse width of the generated attosecond electron strings can be effectively controlled.

[0066] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0067] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method of laser-driven attosecond electron streak generation, characterized by, The method comprises: A laser-driven attosecond electron string generation system is constructed; in the system, the positional relationship between the left-handed circularly polarized Laguerre-Gaussian laser light source and the low-density plasma target is that the left-handed circularly polarized Laguerre-Gaussian laser light source is vertically incident on the surface of the low-density plasma target; The left-handed circularly polarized Laguerre-Gaussian laser light source is turned on; wherein the dimensionless parameter of the laser is a0=10-30, the beam waist radius is σ0=2-4λ0, the laser wavelength is λ0=0.8-1.06 μm, and the laser pulse width is τ=2-4T0, wherein T0 is the laser period; The left-handed circularly polarized Laguerre-Gaussian laser interacts with a low-density plasma target to obtain a bubble structure; wherein the low density refers to a density lower than 0.5n c , wherein n c is a plasma critical density; By the hollow structure to constrain the electron, by the left-handed circularly polarized Laguerre-Gaussian laser to push the electron located in the front end of the hollow structure away from the low-density plasma target, and to obtain the high-density and low-divergence angle attosecond electron string; wherein, high-density refers to the density greater than 10n c ; low-divergence angle refers to the divergence angle less than 5°.

2. The method of claim 1, wherein, The plasma target is one of a hydrogen target, a carbon target, or a carbon-hydrogen target.

3. The method of claim 1, wherein, The laser-driven attosecond electron string generation system further comprises a plane mirror and a concave mirror; The plane mirror is used to change the laser light path propagation; The concave mirror is used to focus the laser.

4. The method of claim 1, wherein, The dimensionless parameter of the laser is a0=20.

5. The method of claim 1, wherein, The beam waist radius of the laser is σ0=3λ0.

6. The method of claim 1, wherein, The laser wavelength is λ0=1 μm.

7. The method of claim 1, wherein, The laser pulse width is τ=3T0.

8. The method of claim 1, wherein, In the process of pushing the electrons located at the front end of the cavity structure away from the low-density plasma target by the left-handed circularly polarized Laguerre-Gaussian laser, the electrons all move outward after acceleration, and then focus inward.

9. The method of claim 8, wherein, The electrons all complete focusing at the position near x=15λ0, and then keep collimating and moving forward.

10. The method of claim 9, wherein, After acceleration, the electrons all move counterclockwise, and the distance between the electron and the axis increases first and then decreases with the counterclockwise movement; the axis refers to the center position of the motion trajectory cross-sectional view in the yOz plane; After the electron moves counterclockwise to a position relatively close to the axis, the electron does not continue to move counterclockwise, but directly focuses on the axis, and moves clockwise near the axis to complete the focusing process of the electron.

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