Method and device for realizing relativistic laser focusing

Abstract

The present invention belongs to the field of laser and plasma technology, and provides a method and device for realizing relativistic laser focusing. A beam of light is used to irradiate a plasma lens, and the density distribution of the plasma lens is set so that the phase velocity of the laser propagating in the plasma changes, thereby realizing the focusing of the laser and realizing arbitrary regulation of the focusing position.

Description

Technical Field

[0001] The invention belongs to the technical field of laser and plasma, and particularly relates to a method and a device for realizing relativistic laser focusing. Background Art

[0002] The field of laser technology has achieved remarkable progress in recent decades. However, the generation and manipulation of high-intensity laser pulses have become increasingly difficult as the laser peak intensity increases due to the damage threshold of conventional solid-state optical components. To address this challenge, plasma-based optical components have been extensively studied, with damage thresholds several orders of magnitude higher than those of solid-state optical components. Various advanced plasma optical components have been demonstrated to effectively modulate the temporal contrast, phase, polarization, pulse width, and intensity of relativistic laser pulses. In addition, the use of plasmas to focus laser pulses as a means of modulation to increase laser intensity has recently gained considerable attention in the academic community.

[0003] Due to the small focal spot and high intensity of plasma, tightly focused lasers have a wide range of applications in different fields such as particle acceleration, high harmonic and X-ray generation, and inertial confinement fusion. However, the generation of such relativistic laser pulses still faces great challenges. A series of technologies for increasing the intensity of relativistic laser pulses have been previously studied. They include stimulated Raman scattering amplification, self-focusing laser amplification, conical target laser amplification, plasma-based optical device laser amplification, and plasma-based multi-beam combination amplification. It leads to a reduction of the laser focus spot size by several times and an increase of the incident relativistic laser intensity by an order of magnitude. However, the energy conversion efficiency of these methods is low, and the focused laser diverges rapidly after passing through the focus. Therefore, it is particularly important to design a scheme with high laser energy conversion efficiency and that can maintain the intensity of the focused laser. Summary of the invention

[0004] In view of the defects and shortcomings in the prior art, a method and device for realizing relativistic laser focusing are provided, in which a beam of light is used to irradiate a plasma lens, and the axial density distribution of the plasma lens is adjusted to change the phase velocity of the laser propagating in the plasma, thereby realizing laser focusing.

[0005] In order to solve the technical problems existing in the above-mentioned prior art, the technical solution adopted by the present invention is:

[0006] On the one hand, a method for realizing relativistic laser focusing is proposed, comprising:

[0007] Setting the incident laser and the focusing position of the incident laser after passing through the plasma lens, i.e., the focal position, wherein the focusing position is any position in the direction of the central axis of the plasma lens, and the incident laser is a relativistic intensity laser;

[0008] determining a density distribution of the plasma lens according to the focusing position;

[0009] The incident laser is incident on the plasma lens having the density distribution, and the phase velocity of the incident laser propagating in the plasma lens changes, thereby achieving focusing of the incident laser at a set focusing position.

[0010] Preferably, the incident laser is a linearly polarized Gaussian laser pulse of relativistic intensity.

[0011] Further, determining the density distribution of the plasma lens according to the focus position includes:

[0012] For any point on the plasma lens i , its plasma density Determined by the following formula:

[0013] ;

[0014] in Corresponding to wavelength is 1 μm The critical density of the laser, , are the unit charge and the mass of the electron, is the vacuum dielectric constant, is the object light frequency; is the relativistic factor of linearly polarized light, is the normalized amplitude of the laser, represents the density at the center of the plasma lens, h Indicates that the plasma lens i The difference between the distance to the focal point and the distance from the center point of the plasma lens to the focal point, d is the thickness of the plasma lens, the minimum value of the plasma lens density ;

[0015] The above formula is used to determine the plasma density at different positions on the plasma lens, and then the density distribution of the plasma lens is determined.

[0016] Furthermore, the phase velocity of the incident laser at any point in the plasma lens is Will be based on Modulate to achieve the focusing of the incident laser at the set focusing position, where c It's the speed of light.

[0017] On the other hand, a device for realizing relativistic laser focusing is provided, comprising an incident laser generating device and a plasma lens, wherein the incident laser generating device outputs an incident laser of relativistic intensity and irradiates the incident laser onto a plasma lens having a set density distribution, and the phase velocity of the incident laser propagating in the plasma lens changes, thereby realizing focusing of the incident laser at a set focusing position, wherein the focusing position is any position in the direction of the central axis of the plasma lens.

[0018] The present invention utilizes a beam of light to irradiate a plasma lens, and by setting the axial density distribution of the plasma lens, the phase velocity of the laser propagating in the plasma changes, thereby generating high-intensity tightly focused laser, thereby achieving laser focusing at a set focus position. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0020] Figure 1 A schematic diagram of a method for realizing relativistic laser focusing in an embodiment;

[0021] Figure 2 is a phase distribution diagram of a plasma lens in one embodiment;

[0022] Figure 3 A schematic diagram of performing 3D-PIC simulation for achieving relativistic laser focusing in one embodiment;

[0023] Figure 4 is a density distribution diagram of a plasma lens in one embodiment;

[0024] Figure 5 : is a diagram of the intensity distribution of the focused laser at different times in an embodiment and a comparison diagram between theory and simulation, wherein Figure 5 (a) is the intensity distribution diagram of the focused laser at different times. Figure 5 (b) Figure 5 (c) Figure 5 (d) respectively represent the , , The laser electric field E is focused on the (y, z) plane at y Distribution plot where circles represent contours of laser intensity. Figure 5 (e) Figure 5 (f) Figure 5(g) respectively represent the Fresnel-Kirchhoff diffraction formula , , The laser electric field E is focused on the (y, z) plane at y Distribution map;

[0025] Figure 6 The effect diagram of different laser parameters and target parameters on the plasma lens density, the output laser Intensity distribution diagram of cross section, output laser along x The intensity distribution of the axis and the evolution of the laser energy conversion efficiency, where Figure 6 (a) is the incident laser intensity a = 1, the thickness of the plasma lens, the incident Gaussian laser spot size and the preset focal length Effect diagram of plasma lens density. Figure 6 (b) and Figure 6 (c) The output laser in the cross section and along the x The strength distribution of the axis, Figure 6 (d) is the evolution diagram of laser energy conversion efficiency;

[0026] Figure 7 is the laser energy conversion efficiency, the ratio of the output laser intensity to the incident laser intensity, the output laser focal spot size and the normalized amplitude of the laser electric field and plasma lens thickness d The change relationship diagram of Figure 7 (a) is the incident laser intensity Energy conversion efficiency of focused laser , laser intensity magnification and focal spot radius The impact effect diagram, Figure 7 (b) is the thickness of the plasma lens Effect diagram of the effect on the energy conversion efficiency, laser intensity magnification and focal spot radius of the focused laser. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In one embodiment, a method for achieving relativistic laser focusing is provided, comprising:

[0029] Setting the incident laser and the focusing position of the incident laser after passing through the plasma lens, i.e., the focal position, wherein the focusing position is any position in the direction of the central axis of the plasma lens, and the incident laser is a relativistic intensity laser;

[0030] determining a density distribution of the plasma lens according to the focusing position;

[0031] The incident laser is incident on the plasma lens having the density distribution, and the phase velocity of the incident laser propagating in the plasma lens changes, thereby achieving focusing of the incident laser at a set focusing position.

[0032] Reference Figure 1 , is a schematic diagram of realizing relativistic laser focusing in an embodiment, which utilizes the method for realizing relativistic laser focusing proposed in the present invention to focus at a set focus position in the central axis direction of the plasma lens 1. In this embodiment, the density distribution of the plasma lens is determined according to the focus position, including:

[0033] For any point on the plasma lens, the plasma density Determined by the following formula:

[0034] ;

[0035] in Corresponding to wavelength is 1 μm The critical density of the laser, , are the unit charge and the mass of the electron, is the vacuum dielectric constant, is the object light frequency. is the relativistic factor of linearly polarized light, is the normalized amplitude of the laser, represents the minimum value of plasma lens density, h It represents the difference between the distance from any point on the plasma lens to the focus and the distance from the minimum value of the plasma lens density to the focus. d is the thickness of the plasma lens, the minimum value of the plasma off-axis lens density ;

[0036] The above formula is used to determine the plasma density at different positions on the plasma lens, and then the density distribution of the plasma lens is determined. Due to the different density distributions of the plasma lens, the phase velocity of the laser propagating in the plasma lens changes, and the laser is focused at the set focus position.

[0037] When a relativistic Gaussian laser pulse irradiates a plasma with an axial density gradient, the laser phase velocity Will be based on Modulation is performed, where is the plasma density, Corresponding to a wavelength of 1 μm The critical density of the laser, It is the relativistic factor of linearly polarized light. The process of Gaussian laser pulse passing through the plasma lens (ADGPL) follows the principle of equal optical path:

[0038] ;

[0039] Here d is the thickness of the plasma lens, and Represent the refractive index at any two positions A and B on the plasma lens, and Respectively represent the distances from points A and B to the focus. Figure 2 FIG. 4 is a phase distribution diagram of a plasma lens in one embodiment.

[0040] Figure 3 FIG. 1 is a schematic diagram of a 3D-PIC simulation for realizing relativistic laser focusing in an embodiment. In this embodiment, the relativistic electromagnetic code EPOCH is used to perform the 3D-PIC simulation. In the simulation, the incident laser is a linearly polarized Gaussian laser pulse with a wavelength of 1 , the focal spot size is . Laser in x = 0, starting from the left boundary along the positive x The normalized amplitude of the electric field of the incident laser is .here, is the unit charge, is the electric field amplitude, is the mass of the electron, is the speed of light in a vacuum, is the laser frequency. The total duration of the incident laser pulse is 6 . Figure 4 FIG4 is a density distribution diagram of a plasma lens in an embodiment, wherein the plasma lens is composed of fully ionized carbon ions, hydrogen ions and electrons. As shown in FIG4, the plasma density distribution is within the radius R= 10 of the plasma lens (ADGPL). μm The density gradient distribution is presented along the axial direction. The minimum value of plasma density is 0.1 , with a maximum value of 0.92 In the simulation, the plasma lens can focus the laser into the designed focal volume. The focal volume can be obtained from Adjust to , which is set to = 20 and = 30 The plasma lens is located at x = 3 and x = 5.5 Between, the thickness is d =2.5 The simulation box is set to , the grid is set to , each grid is set with 6 macro particles. The density of the lightest known solid material can reach 0.16 kg / m 3 , corresponding to a fully ionized plasma density of 0.028 In contrast, the minimum density of a plasma lens is 0.1 The unique density gradient structure of the plasma lens can be efficiently manufactured using 3D printing technology.

[0041] Figure 5 : is the intensity distribution diagram of the focused laser at different times in an embodiment (i.e. the above-mentioned simulation embodiment) and the comparison diagram between theory and simulation, wherein Figure 5 (a) is the intensity distribution diagram of the focused laser at different times. Figure 5 (b) Figure 5 (c) Figure 5 (d) respectively represent the , , The laser electric field E is focused on the (y, z) plane at y Distribution plot where circles represent contours of laser intensity. Figure 5 (e) Figure 5 (f) Figure 5 (g) respectively represent the Fresnel-Kirchhoff diffraction formula , , The laser electric field E is focused on the (y, z) plane at y Distribution map. Figure 5 (a) shows the simulation box from At different times, the output laser is ( x , y ) plane. The incident laser pulse is gradually focused after passing through the plasma lens, resulting in a gradual increase in laser intensity. The peak intensity of the output laser reaches 2.34 × 10 19 W / cm 2 , which is one order of magnitude higher than the incident laser pulse. To evaluate the plasma lens, the Fresnel-Kirchhoff diffraction formula is used to analytically predict the electric field components of the output laser. Here, the diffracted electric field can be expressed as:

[0042] ;

[0043] here represents the incident Gaussian laser, is the tilt factor. The transmission function of ADGPL can be expressed as:

[0044] ;

[0045] here, l represents the distance from the center of the plasma lens to the focal position. x Axis from The diffracted electric field of the output reading light is calculated at three positions within the range of . Figure 5 (b)- Figure 5 (d) and Figure 5 (e)- Figure 5 (g) shows the analytical results, and the theoretical calculations are basically consistent with the simulation results.

[0046] like Figure 6 As shown in the figure, the effect of different laser parameters and target parameters on the plasma lens density is shown, and the output laser Intensity distribution diagram of cross section, output laser along x The intensity distribution of the axis and the evolution of the laser energy conversion efficiency. The density of the plasma lens is affected by the laser parameters and the target parameters. Figure 6 (a) is the incident laser intensity a = 1, the thickness of the plasma lens, the incident Gaussian laser spot size and the preset focal length The effect of plasma lens density. =20 to 50 , , Select six points each. As for the influence of plasma lens density, it can be seen from the figure that , Impact on ADGPL, when fixed or , the change of plasma lens density is affected by the parameter The impact is small, for As for the influence of plasma lens density, the density of plasma lens increases with This shows that the density of the plasma lens is mainly controlled by the thickness of the plasma lens and the preset focal length, which has a great influence on the laser focal spot. The sensitivity is smaller. Figure 6 (b) and Figure 6 (c) The output laser in the cross section and along thex The results show that when x = 23 When the laser beam is focused, the intensity of the output laser is significantly enhanced in the focal volume. This indicates that the generated output laser pulse has a long focal volume, which is a unique feature of the plasma lens. Due to the focusing ability of the plasma lens, the intensity of the obtained focused laser can reach 10 19 W / cm 2 , with about 2.3 μm The focus radius. Figure 6 (d) is the evolution diagram of laser energy conversion efficiency. The total electromagnetic energy of the output laser can be expressed as: , the output laser maintains high energy conversion efficiency within the focal volume. x = 30 μm The maximum value is 29%.

[0047] Tables 1 and 2 present the corresponding and The maximum plasma density of the plasma lens . Figure 7 Demonstrates laser energy conversion efficiency, the ratio of output laser intensity to incident laser intensity, and the output laser focal spot size and normalized amplitude of the laser electric field and plasma lens thickness d The change relationship diagram of Figure 7 (a) is the incident laser intensity Energy conversion efficiency of focused laser , laser intensity magnification and focal spot radius It can be seen that when the incident laser intensity = 1, the energy conversion efficiency reaches 29%, the magnification is up to 18 times, and the focal spot radius can be reduced to 2.3 However, as the incident laser intensity increases, the focusing efficiency of the plasma lens gradually decreases, which indicates that the scheme proposed in the present invention has a strong focusing ability at relatively low incident laser intensity, but has poor focusing performance at high incident laser intensity. Figure 7 (b) shows the thickness of the plasma lens The effect diagram of the energy conversion efficiency, laser intensity magnification and focal spot radius of the focused laser. Figure 7 As shown in (b), at lower incident laser intensity, the change in thickness only leads to a slight change in the parameters of the focused laser. This shows that the focusing efficiency of the plasma lens is insensitive to the change in the thickness of the plasma lens. This verifies the robustness of the plasma lens.

[0048] Table 1

[0049]

[0050] Table 2

[0051]

[0052] The present invention proposes a method for realizing relativistic laser focusing based on plasma lens. According to the set focusing position, which is any position in the central axis direction of the plasma lens, the axial density gradient of the plasma is modulated according to the focusing position to manipulate the phase velocity of the laser pulse transmitted in the plasma, thereby generating a high-intensity tightly focused laser. The focal spot radius of the output laser can reach , which is three times smaller than the focal radius of the incident Gaussian laser, and the laser intensity reaches 10 19 W / cm 2 , the energy conversion efficiency is 29%. The scheme proposed by the present invention has potential applications in the interaction between strong laser and plasma in high energy density physics, laboratory astrophysics and nonlinear optics.

[0053] In one embodiment, a device for realizing relativistic laser focusing is provided, comprising an incident laser generating device and a plasma lens 1;

[0054] The incident laser generating device outputs an incident laser of relativistic intensity and irradiates the incident laser onto a plasma lens 1 having a set density distribution. The phase velocity of the incident laser propagating in the plasma lens changes, so that the incident laser is focused at a set focusing position, and the focusing position is any position in the direction of the central axis of the plasma lens. The density distribution of the plasma lens 1 is determined according to the set focusing position, including: for any point on the plasma lens 1 i , its plasma density Determined by the following formula:

[0055] ;

[0056] in Corresponding to wavelength is 1 μm The critical density of the laser, , are the unit charge and the mass of the electron, is the vacuum dielectric constant, is the object light frequency; is the relativistic factor of linearly polarized light, is the normalized amplitude of the laser, represents the density at the center of the plasma lens, h Indicates that the plasma lens iThe difference between the distance to the focal point and the distance from the center point of the plasma lens to the focal point, d is the thickness of the plasma lens, the minimum value of the plasma lens density ;

[0057] The above formula is used to determine the plasma density at different positions on the plasma lens, and then the density distribution of the plasma lens is determined.

[0058] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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.

[0059] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for realizing relativistic laser focusing, characterized in that: include: Setting the incident laser and the focusing position of the incident laser after passing through the plasma lens, i.e., the focal position, wherein the focusing position is any position in the direction of the central axis of the plasma lens, and the incident laser is a relativistic intensity laser; determining a density distribution of the plasma lens according to the focusing position; The incident laser is incident on the plasma lens having the density distribution, and the phase velocity of the incident laser propagating in the plasma lens changes, thereby achieving focusing of the incident laser at a set focusing position.

2. The method for realizing relativistic laser focusing according to claim 1, characterized in that: The incident laser is a Gaussian laser pulse with linear polarization and relativistic intensity.

3. The method for realizing relativistic laser focusing according to claim 1 or 2, characterized in that: Determining the density distribution of the plasma lens according to the focusing position includes: For any point on the plasma lens , its plasma density Determined by the following formula: in Corresponding to wavelength is 1 μm The critical density of the laser, , are the unit charge and the mass of the electron, is the vacuum dielectric constant, is the object light frequency; is the relativistic factor of linearly polarized light, is the normalized amplitude of the laser, represents the density at the center of the plasma lens, h Indicates that the plasma lens i The difference between the distance to the focal point and the distance from the center point of the plasma lens to the focal point, d is the thickness of the plasma lens, the minimum value of the plasma lens density ; The above formula is used to determine the plasma density at different positions on the plasma lens, and then the density distribution of the plasma lens is determined.

4. The method for realizing relativistic laser focusing according to claim 3, characterized in that: The phase velocity of the incident laser at any point in the plasma lens Will be based on Modulation is performed to achieve the focusing of the incident laser at the set focusing position, where It's the speed of light.

5. A device for implementing the method according to claim 1, characterized in that: It includes an incident laser generating device and a plasma lens, The incident laser generating device outputs an incident laser of relativistic intensity and irradiates the incident laser onto a plasma lens with a set density distribution. The phase velocity of the incident laser propagating in the plasma lens changes, so that the incident laser is focused at a set focusing position, which is any position in the direction of the central axis of the plasma lens.

6. The device according to claim 5, characterized in that Determine the density distribution of the plasma lens according to the set focus position, including: for any point on the plasma lens , its plasma density Determined by the following formula: in Corresponding to wavelength is 1 μm The critical density of the laser, , are the unit charge and the mass of the electron, is the vacuum dielectric constant, is the object light frequency; is the relativistic factor of linearly polarized light, is the normalized amplitude of the laser, represents the density at the center of the plasma lens, h Indicates that the plasma lens The difference between the distance to the focal point and the distance from the center point of the plasma lens to the focal point, d is the thickness of the plasma lens, the minimum value of the plasma lens density ; The above formula is used to determine the plasma density at different positions on the plasma lens, and then the density distribution of the plasma lens is determined.

7. The device according to claim 5, characterized in that The incident laser is a Gaussian laser pulse with linear polarization and relativistic intensity.

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