Method for generating high energy femtosecond laser with four femtosecond lasers

Abstract

The present invention provides a method for generating high-energy femtosecond lasers by using four femtosecond lasers, wherein four femtosecond laser pulses with initial phase differences are simultaneously hit on the front surface of a plasma target according to a certain spatial position, and the nonlinear effect causes the four femtosecond lasers to interact with each other when transmitted in the plasma target, so that the lasers are rapidly coupled to synthesize high-energy femtosecond lasers. The light intensity of the high-energy femtosecond laser synthesized by the present invention can be amplified by 6 times compared to that of a single incident femtosecond laser, and a high-intensity light source can be generated.

Description

Technical Field

[0001] The invention mainly relates to the technical field of high-energy laser synthesis, in particular to a method for generating high-energy femtosecond lasers using four femtosecond lasers. Background Art

[0002] With the development of femtosecond laser technology, it has been widely used in cutting-edge fields, such as biomedicine, industrial manufacturing, information mapping, etc. The design of single-beam laser-plasma interaction schemes is the most common in applications such as laser wakefield acceleration (LWFA), target back sheath acceleration (TNSA), and Betatron radiation. In recent years, as the excellent output effect brought by the interaction of multiple laser beams with plasma has been continuously verified in simulations and experiments, more and more related schemes have been proposed. Therefore, the nonlinear evolution process of laser in plasma has always been a focus of attention in the application of strong laser pulses.

[0003] When multiple laser beams are transmitted in a vacuum, they will be transmitted independently in their own way without interfering with each other. This limits the purpose of enhancing the laser intensity at a point to simply coherently superimposing multiple laser beams at that point, which cannot be stably superimposed and transmitted. However, when the laser is transmitted in a nonlinear medium, there will be self-interaction and interaction between multiple beams. Especially when the incident laser is a laser of relativistic intensity, it will cause more significant nonlinear effects in the plasma. During the propagation of a single beam of relativistic intensity laser in the plasma, the laser's ponderomotive force causes local plasma density disturbances and relativistic electron mass corrections, which will cause the refractive index of the nonlinear medium to change. Nonlinear effects will also cause interactions between the laser and other adjacent lasers, such as: merging, spiraling, repulsion, attraction, etc.

[0004] However, how to design the initial laser parameters so that multiple light beams can be coupled to produce higher intensity lasers is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a method for generating high-energy femtosecond lasers by using four femtosecond lasers.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides a method for generating high-energy femtosecond lasers using four femtosecond lasers, wherein four femtosecond laser pulses with initial phase differences are simultaneously projected onto the front surface of a plasma target according to a certain spatial position, and nonlinear effects cause the four femtosecond lasers to interact with each other when transmitted in the plasma target, so that the lasers are rapidly coupled to synthesize high-energy femtosecond lasers, wherein the plasma target is a plasma target with an electron density value range of 2.2 × 10 19 / cm 3 to 2.2 × 10 20 / cm 3 The adjustable range of the incident intensity of each femtosecond laser pulse is 1.1× 10 17 W / cm 2 to 1.1× 10 21 W / cm 2 The adjustable range of the optical center distance when hitting the front surface of the plasma target is 2 µ m to 6 µ m.

[0008] Preferably, the spatial size of the plasma target is not limited, such as the spatial size of the plasma target is x = 60 µ m and y = 60 µ m.

[0009] Preferably, the four femtosecond laser pulses may be circularly polarized femtosecond laser pulses, s -Polarized femtosecond laser pulses or p -Polarized femtosecond laser pulses.

[0010] Preferably, when four femtosecond laser pulses are transmitted in the plasma target, the interactions caused by the phase difference include: repulsion, attraction, energy transfer, and coupling.

[0011] Preferably, the four femtosecond laser pulses are circularly polarized femtosecond laser pulses, and the light intensity of each circularly polarized femtosecond laser is 9.89 × 10 18 W / cm 2 , pulse width is 100fs, wavelength is 1 µ m, the focal spot radius is 2 µ m, the optical center spacing when hitting the front surface of the plasma target is 4 µ m.

[0012] Preferably, four femtosecond laser pulses with initial phase differences are simultaneously hit on the front surface of the plasma target according to a certain spatial position, wherein the two femtosecond laser pulses located on the two outer sides serve as guide lights, and the two femtosecond laser pulses on the inner side of the guide lights serve as intermediate light beams. The guide light and the two intermediate light beams on the inner side of the guide light have an initial phase difference when hitting the front surface of the plasma target, and the transmission axes of the outer guide light and the intermediate light beams adjacent to the inner side thereof are symmetrically distributed along the central axis of the plasma target.

[0013] Preferably, the transmission axis of the outer guiding light and the inner adjacent intermediate light beam have a certain angle, and the angle ranges from 0° to 10°.

[0014] Preferably, when four femtosecond lasers are transmitted in the plasma target, the two outer laser guide beams are designed to have an adjustable dynamic phase difference with the two inner intermediate beams due to the combined effects of the optical path difference, the initial phase difference, and the phase velocity change caused by the energy transfer between beams.

[0015] Preferably, by generating an adjustable dynamic phase difference, the two outer laser beams can guide the synthesis of the two middle laser beams to guide the synthesis of high-energy femtosecond lasers, and the two outer laser beams are referred to as guiding light hereinafter. Moreover, when the phase difference is adjusted to a certain condition, the guiding light will also participate in the coupling process.

[0016] Compared with the prior art, the technical effects of the present invention are:

[0017] The light intensity of the high-energy femtosecond laser synthesized by the present invention can be amplified by 6 times compared with that of a single incident femtosecond laser, and is expected to be used in many fields to provide high-intensity light sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] Figure 1 A schematic diagram of the principle of a method for generating high-energy femtosecond lasers using four femtosecond lasers provided in an embodiment;

[0020] Figure 2Schematic diagrams of the principles of three femtosecond lasers generating high-energy femtosecond lasers, wherein (a) is a schematic diagram of the principles of dual-beam femtosecond lasers generating high-energy femtosecond lasers; (b) is a schematic diagram of the principles of four femtosecond laser pulses with initial phase differences that simultaneously and equidistantly and in parallel hit the front surface of a plasma target to generate high-energy femtosecond lasers; (c) is a schematic diagram of the principles of four femtosecond laser pulses with initial phase differences that simultaneously and equidistantly and with a certain incident angle between their transmission axes hit the front surface of a plasma target to generate high-energy femtosecond lasers;

[0021] Figure 3 is the normalized light field of the dual-beam femtosecond laser when the initial phase difference is π, π / 2, and 0 ( I / I 0) Distribution map, I 0=2.74×10 18 W / cm 2 , where (a)-(c) are the initial phase difference of the dual-beam femtosecond laser at 0 at time t =44T0, t =60T0, t =76T0, (d)-(f) are the normalized light field distribution diagrams of the dual-beam femtosecond laser with an initial phase difference of π / 2 at time t =44T0, t =60T0, t =76T0, (g)-(i) are the normalized light field distribution diagrams of the dual-beam femtosecond laser with an initial phase difference of π at time t =44T0, t =60T0, t = Normalized light field distribution diagram at 76T0;

[0022] Figure 4 is the normalized light field of the dual-beam femtosecond laser when the initial phase difference is π, π / 2, and 0 ( I / I 0) distribution diagram, normalized current density ( J / J 0) distribution map, normalized electron density ( n / n c ) distribution map, I 0=2.74×10 18 W / cm 2 , J 0=1×10 16 A / cm 2 , n c =1.1 × 10 21 / cm 3 . (a) is the time when the initial phase difference of the two femtosecond laser beams is 0t =40T0 normalized light field distribution diagram, (b) the initial phase difference of the dual-beam femtosecond laser is 0 at time t =40T0, (c) the normalized current density distribution diagram of the dual-beam femtosecond laser with an initial phase difference of 0 at time t =42T0 normalized electron density distribution diagram, (d) is the initial phase difference of the double-beam femtosecond laser is π / 2 at time t =50T0 normalized light field distribution diagram, (e) is the initial phase difference of the double-beam femtosecond laser is π / 2 at time t =50T0 normalized current density distribution diagram, (f) is the initial phase difference of the double-beam femtosecond laser is π / 2 at time t =52T0 normalized electron density distribution diagram, (g) is the initial phase difference of the double-beam femtosecond laser is π at time t =40T0 normalized light field distribution diagram, (h) is the initial phase difference of the double-beam femtosecond laser is π at time t =40T0 normalized current density distribution diagram, (i) is the initial phase difference of the double-beam femtosecond laser at time π t = Normalized electron density distribution map of 42T0;

[0023] Figure 5 is the normalized light field of case 2 and case 3 ( I / I 0) Distribution map, I 0=2.74×10 18 W / cm 2 , where (a)-(c) are respectively the time t =44T0, t =56T0, t =76T0 normalized light field distribution diagram, (d)-(f) are respectively the case 3 (case 3) at time t =44T0, t =58T0, t = Normalized light field distribution diagram at 76T0;

[0024] Figure 6 is the normalized light field of case 4 and case 5 ( I / I 0) Distribution map, I 0=2.74×10 18 W / cm 2 , where (a)-(c) are respectively the time t =44T0, t =56T0, t=76T0 normalized light field distribution diagram, (d)-(f) are respectively the normalized light field distribution diagram of case 5 at time t =44T0, t =60T0, t = Normalized light field distribution diagram at 76T0;

[0025] Figure 7 is the normalized electron density of scheme 1 (case1), scheme 2 (case2), and scheme 3 (case3) at different times ( n / n c ) distribution map, n c =1.1 × 10 21 / cm 3 , where (a)-(d) are respectively the time t =38T0, t =42T0, t =46T0, t =60T0 normalized electron density distribution diagram, (e)-(h) are respectively case 2 (case 2) at time t =34T0, t =36T0, t =40T0、 t =60T0 normalized electron density distribution diagram, (i)-(l) are respectively case 3 at time t =36T0, t =40T0、 t =44T0, t = Normalized electron density distribution map of 60T0;

[0026] Figure 8 is the normalized electron density of scheme 1 (case1), scheme 4 (case4), and scheme 5 (case5) at different times ( n / n c ) distribution map, n c =1.1 × 10 21 / cm 3 , where (a)-(d) are respectively the time t =38T0, t =42T0, t =46T0, t =60T0 normalized electron density distribution diagram, (e)-(h) are respectively case 4 at time t =36T0, t=40T0、 t =44T0, t =60T0 normalized electron density distribution diagram, (i)-(l) are respectively case 5 at time t =36T0, t =44T0, t =56T0, t = Normalized electron density distribution map of 76T0;

[0027] Fig. 9 are the light intensity distribution diagrams of incident seed light, scheme 1 (case1), scheme 2 (case2), scheme 3 (case3), scheme 4 (case4), and scheme 5 (case5), where (a) is the longitudinal light intensity distribution diagram of incident seed light, scheme 1 (case1), scheme 2 (case2), scheme 3 (case3), scheme 4 (case4), and scheme 5 (case5), and (b) is the transverse light intensity distribution diagram of incident seed light, scheme 1 (case1), scheme 2 (case2), scheme 3 (case3), scheme 4 (case4), and scheme 5 (case5);

[0028] Fig.10 Energy conversion efficiency diagrams of Scheme 1 (case1), Scheme 2 (case2), Scheme 3 (case3), Scheme 4 (case4), and Scheme 5 (case5), where (a) is the efficiency diagram of total input laser energy converted into electron energy of Scheme 1 (case1), Scheme 2 (case2), Scheme 3 (case3), Scheme 4 (case4), and Scheme 5 (case5), and (b) is the conversion efficiency (color bar) of total input laser energy converted into synthetic laser energy of Scheme 1 (case1), Scheme 2 (case2), Scheme 3 (case3), Scheme 4 (case4), and Scheme 5 (case5), the normalized ratio of synthetic laser to the laser with the highest synthesizable energy (black frame), and the optimal output time (point) diagram of synthetic laser;

[0029] Fig.11 is the normalized optical center distance ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) for the intensity of high-energy femtosecond laser synthesized by Scheme 3 (case 3) and Scheme 5 (case 5) ( I ), λ 0=1 μm. n c =1.1 × 10 21 / cm 3 , where (a) is the normalized optical center distance ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) The relationship between the intensity of the high-energy femtosecond laser synthesized by Scheme 3 (case3) and Scheme 5 (case5) and the normalized optical center distance. (b) is the normalized optical center distance ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) is the relationship between the intensity of the high-energy femtosecond laser synthesized by Scheme 3 (case3) and Scheme 5 (case5) and the angle between the guide light and the intermediate laser transmission axis. (c) is the normalized optical center spacing ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) The relationship between the intensity of the high-energy femtosecond laser synthesized by Scheme 3 (case3) and Scheme 5 (case5) and the angle between the guide light and the intermediate laser transmission axis. (d) is the normalized optical center spacing ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) is the relationship between the light intensity of the high-energy femtosecond laser synthesized by Scheme 3 (case 3) and Scheme 5 (case 5) and the normalized background electron density. DETAILED DESCRIPTION

[0030] 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.

[0031] Reference Figure 1 In one embodiment, a method for generating high-energy femtosecond lasers by using four femtosecond lasers is provided, including four femtosecond laser pulses, namely, a first femtosecond laser pulse 1, a second femtosecond laser pulse 2, a third femtosecond laser pulse 3, and a fourth femtosecond laser pulse 4. By simultaneously hitting the front surface of a plasma target 5 with four femtosecond laser pulses having an initial phase difference according to a certain spatial position, the nonlinear effect causes the four femtosecond lasers to interact with each other when transmitting in the plasma target, so that the lasers are rapidly coupled to synthesize high-energy femtosecond lasers.

[0032] The adjustable density range of the plasma target used in the present invention is 2.2 × 10 19 / cm 3 to 2.2 × 10 20 / cm 3 , the distance between the optical center of the femtosecond laser pulse used and the adjacent femtosecond laser pulse when it hits the target d The adjustable range of 0 is 2 µ m to 6 µ m, the adjustable range of laser intensity using femtosecond laser pulses is 1.1× 10 17 W / cm 2 to 1.1× 10 21 W / cm 2 .

[0033] The femtosecond laser pulses used can be circularly polarized femtosecond laser pulses, s -Polarized femtosecond laser pulses, p -Polarized femtosecond laser pulses, all of the above can achieve the purpose of synthesizing high-energy lasers with four femtosecond lasers.

[0034] In one embodiment, the low-density plasma target used is an electron density of 1.1 × 10 20 / cm 3 The hydrogen target is constructed by x Direction) 60 μ m, width( y Direction) 60 μ The electron density of m is 1.1 × 10 20 / cm 3The plasma target 5 is formed by the first femtosecond laser pulse 1, the second femtosecond laser pulse 2, the third femtosecond laser pulse 3 and the fourth femtosecond laser pulse 4 with initial phase difference, which are all circularly polarized femtosecond laser pulses. The four femtosecond laser pulses are simultaneously hit on the front surface of the plasma target 5 according to a certain spatial position. During the transmission in the target, the transmission behavior of the laser is regulated due to the nonlinear effect, so that the light beams can interact with each other until coupling occurs. The light intensity of each incident circularly polarized femtosecond laser is 9.89× 10 18 W / cm 2 , pulse width is 100fs, wavelength is 1 µ m, the focal spot radius is 2 µ m, the optical center spacing when hitting the front surface of the target is 4 µ m.

[0035] In the present invention, four femtosecond laser pulses with initial phase differences are simultaneously hit on the front surface of the plasma target according to a certain spatial position, wherein the two femtosecond laser pulses located on the two outer sides are used as guide lights, the two femtosecond laser pulses inside the guide lights are intermediate light beams, the guide lights and the two intermediate light beams inside the guide lights have an initial phase difference when hitting the front surface of the plasma target, and the transmission axes of the outer guide lights and the intermediate light beams adjacent to the inner side thereof are symmetrically distributed along the central axis of the plasma target. The transmission axes of the outer guide lights and the intermediate light beams adjacent to the inner side thereof have a certain angle, and the angle ranges from 0° to 10°.

[0036] When four femtosecond laser beams are transmitted in the plasma target, the two outer laser guide beams are designed to have an adjustable dynamic phase difference with the two inner intermediate beams due to the combined effect of the optical path difference, the initial phase difference, and the phase velocity change caused by the energy transfer between beams.

[0037] By generating an adjustable dynamic phase difference, the two outer laser beams can guide the synthesis of the two middle laser beams to guide the synthesis of high-energy femtosecond lasers. The two outer laser beams are referred to as guiding light. Moreover, when the phase difference is adjusted to a certain condition, the guiding light will also participate in the coupling process. When four femtosecond laser beams are transmitted in the target, the interactions caused by the phase difference include repulsion, attraction, energy transfer, and coupling.

[0038] At present, multiple laser beams can be precisely controlled in terms of time delay at the femtosecond scale, and can also be controlled at the micrometer level in terms of transmission space. This shows that the interaction between femtosecond lasers and matter is already a mature technology. Therefore, it is realistically controllable within the controllable range provided by the present invention, and the method provided by the present invention to synthesize high-energy lasers by controlling the parameters of multiple laser beams in time and space is feasible.

[0039] Figure 2The schematic diagrams are schematic diagrams of the principles of three femtosecond lasers generating high-energy femtosecond lasers, where (a) is a schematic diagram of the principles of dual-beam femtosecond lasers generating high-energy femtosecond lasers; (b) is a schematic diagram of the principles of four femtosecond laser pulses with initial phase differences that simultaneously and equidistantly and parallelly hit the front surface of the plasma target to generate high-energy femtosecond lasers; (c) is a schematic diagram of the principles of four femtosecond laser pulses with initial phase differences that simultaneously and equidistantly and with a certain incident angle between the transmission axes hit the front surface of the plasma target to generate high-energy femtosecond lasers. To demonstrate the effectiveness of the method of the present invention, the following five schemes are provided for comparison, namely, Scheme 1 (also known as case 1), Scheme 2 (also known as case 2), Scheme 3 (also known as case 3), Scheme 4 (also known as case 4) and Scheme 5 (also known as case 5), where: the initial phase of the first femtosecond laser pulse 1 is The transmission axis is parallel to the normal direction of the plasma target 5 plane, and the focal spot radius is 2 μ m, and the light intensity is 9.89× 10 18 W / cm 2 , pulse width is 100fs, the first femtosecond laser pulse 1 is a circularly polarized Gaussian laser, and the focus is above the central axis of the front surface of the target 2 μ m; the initial phase of the second femtosecond laser pulse 2 is The transmission axis is parallel to the normal direction of the plasma target 5 plane, and the focal spot radius is 2 μ m, and the light intensity is 9.89×10 18 W / cm 2 , pulse width is 100fs, the second femtosecond laser pulse 2 is a circularly polarized Gaussian laser, and the focus is 2 below the central axis of the front surface of the target μ m; the initial phase of the third femtosecond laser pulse 3 is , the transmission axis and the normal direction of the plasma target 5 plane have an angle θ , the focal spot radius is 2 μ m, and the light intensity is 9.89× 10 18 W / cm 2 , pulse width is 100fs, the third femtosecond laser pulse 3 is a circularly polarized Gaussian laser, and the focus is 6 above the central axis of the front surface of the target μ m; the initial phase of the fourth femtosecond laser pulse 4 is , the transmission axis and the normal direction of the plasma target 5 plane have an angle θ , the focal spot radius is 2 μ m, and the light intensity is 9.89× 10 18 W / cm 2 , pulse width is 100fs, the fourth femtosecond laser pulse 4 is a circularly polarized Gaussian laser, and the focus is 6 below the central axis of the front surface of the target μ m; initial phase of case 2 and case 3 Compare Leading by π, the initial phase of Case 4 and Case 5 Compare Leading by π / 2, the angle between Case 2 and Case 4 θ is 0, the angle of case 3 θ The angle of case 5 is 6°. θ is 5°.

[0040] Specifically, case 1 is based on Figure 2 (a) Implementation: In case 1, two femtosecond laser pulses with the same initial phase and incident in parallel simultaneously hit the front surface of the low-density plasma target at a close distance to generate high-energy femtosecond lasers. When incident into the target, the nonlinear effect caused by the influence of the laser field on the electrons causes the local refractive index in the target to change, and the two laser beams attract each other until they are coupled into one laser beam.

[0041] Specifically, Case 2 is based on Figure 2 (b) Implementation, in case 2: four femtosecond laser pulses with initial phase differences are simultaneously and equidistantly hit the front surface of the plasma target in parallel, wherein the outer guide light and the inner adjacent middle beam have an initial phase difference of π when hitting the front surface of the plasma target, so that the guide light and the inner adjacent middle beam have a repulsive effect in the early stage of laser transmission in the plasma target, which will make the two middle beams more inclined to be deflected to the central axis of the plasma target for transmission; the initial phase difference of the two middle beams is 0 and they are transmitted in parallel at a close distance, so that the two middle beams attract each other, and under the combined effect of the mutual attraction of the two middle beams and the repulsion of the outer guide light and the inner adjacent middle beam, the two middle beams are rapidly coupled to synthesize high-energy femtosecond lasers. Due to the combined effect of the mutual attraction of the two middle laser beams and the repulsion of the guide light on the two middle laser beams in scheme 2 (case 2), the two middle laser beams can be coupled faster than scheme 1 (case 1).

[0042] Specifically, case 3 is based on Figure 2(c) Implementation, in case 3: four femtosecond laser pulses with initial phase difference are equidistant and have an incident angle of 6° between the transmission axes and are simultaneously hit on the front surface of the plasma target, wherein the outer guide light and the inner adjacent middle beam have an initial phase difference of π when hitting the front surface of the plasma target, so that in the early stage of laser transmission in the plasma target, the guide light and the inner adjacent middle beam have a repulsive effect, which will make the two middle beams more inclined to be deflected toward the central axis of the plasma target for transmission; the initial phase difference of the two middle beams is 0 and they are transmitted in parallel at a close distance, so that the two middle beams attract each other. Under the combined effect of the mutual attraction of the two middle beams and the repulsive effect of the outer guide light and the inner adjacent middle beam, the two middle beams can be relative to scheme 1 (case 1) Fast coupling occurs faster than that of the intermediate light beam, and after a period of time of transmission in the plasma target, an optical path difference is generated due to a certain angle between the transmission axes of the outer guiding light and the intermediate light beam adjacent to the inner side. This optical path difference will produce an additional phase difference. The phase difference caused by the optical path difference will make the phase difference between the guiding light and the intermediate light beam less than π; when the phase difference is between 0 and π but does not include 0 and π, energy transfer will occur between the light beams, and the phase-advanced laser will transfer energy to the phase-lag laser, so that the guiding light will continue to transfer energy to the intermediate light beam; at the same time, due to the change in laser intensity, the phase velocity of the laser transmission in the plasma target will change, the laser intensity becomes lower and the phase velocity becomes faster, thereby bringing about a third type of phase difference in addition to the phase difference caused by the initial phase difference and the optical path difference, namely, the phase difference caused by the energy transfer between beams. And due to the angle of the transmission axis, compared with Scheme 2 (case 2), the distance between the guiding light and the optical center of the intermediate light beam in Scheme 3 (case 3) will become smaller after being transmitted for a certain distance, which will increase the interaction effect between the guiding light and the intermediate light beam, further improving the modulation effect of the guiding light and the energy transfer effect between beams. The phase difference will continuously regulate the transmission behavior of the laser. Compared with Scheme 2 (case 2), Scheme 3 (Scheme 3) increases the energy transfer between beams, allowing the guiding light to participate in the coupling process, which will further increase the energy of the synthesized high-energy femtosecond laser.

[0043] Specifically, case 4 is based on Figure 2(b) Implementation, in case 4: four femtosecond laser pulses with initial phase difference are equidistant and parallel to the front surface of the plasma target at the same time, where the outer guide light and the adjacent middle beam on the inner side have an initial phase difference of π / 2 when hitting the front surface of the plasma target. Since the initial phase difference is between 0 and π, energy transfer will occur between the beams. Therefore, in the early stage of laser transmission in the plasma target, the guide light has a repulsive effect on the middle beam and energy transfer between beams, which will make the two middle beams more inclined to be deflected to the central axis of the plasma target. The initial phase difference of the two middle beams is 0 and they are transmitted in parallel at a close distance, so that the two middle beams attract each other, prompting the two middle beams to couple rapidly and continuously obtain energy from the guide light, increasing the energy of the synthesized high-energy femtosecond laser. Due to the difference in initial phase, there is energy transfer between beams, and part of the energy of the guide light participates in the coupling process, so the energy of the high-energy femtosecond laser synthesized in scheme 4 (case 4) is higher than that in scheme 2 (case 2).

[0044] Specifically, case 5 is based on Figure 2 (c) Implementation, in case 5: four femtosecond laser pulses with initial phase difference are equidistant and have a certain incident angle of 5° between the transmission axes, and are simultaneously hit on the front surface of the plasma target. The guiding light and the two intermediate beams inside the guiding light have an initial phase difference of π / 2 when hitting the front surface of the plasma target. Since the initial phase difference is between 0 and π, there is energy transfer between beams. In the early stage of laser transmission in the plasma target, the guiding light has a repulsive effect on the intermediate beams and energy transfer between beams, which will make the two intermediate beams more inclined to be deflected to the central axis of the plasma target and continue to obtain energy from the guiding light. At the same time, the difference between scheme 5 (case 5) and other schemes is that this scheme (case 5) reduces the distance between the optical centers of the guiding light and the intermediate beams due to the phase difference and angle modulated by the optical path difference, so that the guiding light will first couple with the adjacent intermediate beams on the inside, and then the lasers formed by the coupling will be secondary coupled, and finally form a laser beam, so that more energy is coupled into the synthesized high-energy femtosecond laser. Since the coupling process of scheme 5 (case 5) is carried out twice, the process of synthesizing high-energy femtosecond laser takes longer than other schemes. At the same time, the degree of coupling is more thorough, the energy deposition process is longer, and more energy is coupled into the synthesized high-energy femtosecond laser.

[0045] The peak intensity and energy conversion efficiency of the high-energy femtosecond laser synthesized in case 2 are 2.92 × 10 19 W / cm 2 and 33%.

[0046] The peak intensity and energy conversion efficiency of the high-energy femtosecond laser synthesized in case 3 are 5.84 × 10 19 W / cm 2 and 55%.

[0047] The peak intensity and energy conversion efficiency of the high-energy femtosecond laser synthesized in case 4 are 3.74 × 10 19 W / cm 2 and 36%.

[0048] The peak intensity and energy conversion efficiency of the high-energy femtosecond laser synthesized in case 5 are 5.12 × 10 19 W / cm 2 and 62%.

[0049] Figure 3 is the normalized light field of the dual-beam femtosecond laser when the initial phase difference is π, π / 2, and 0 ( I / I 0) Distribution map, I 0=2.74×10 18 W / cm 2 , where (a)-(c) are the initial phase difference of the dual-beam femtosecond laser at 0 at time t =44T0, t =60T0, t =76T0, (d)-(f) are the normalized light field distribution diagrams of the dual-beam femtosecond laser with an initial phase difference of π / 2 at time t =44T0, t =60T0, t =76T0, (g)-(i) are the normalized light field distribution diagrams of the dual-beam femtosecond laser with an initial phase difference of π at time t =44T0, t =60T0, t =76T0. Specifically, (a)-(c) show the process from attraction to coupling between two laser beams with a phase difference of 0, (d)-(f) show the evolution of the energy transfer between two laser beams with a phase difference of π / 2, which makes the light intensity increase and decrease, and the mutual repulsion between the two beams under this phase difference, (g)-(i) show the process of mutual repulsion between two laser beams with a phase difference of π without energy interaction.

[0050] Figure 4 is the normalized light field of the dual-beam femtosecond laser when the initial phase difference is π, π / 2, and 0 ( I / I 0) distribution diagram, normalized current density ( J / J0) distribution map, normalized electron density ( n / n c ) distribution map, I 0=2.74×10 18 W / cm 2 , J 0=1×10 16 A / cm 2 , n c =1.1 × 10 21 / cm 3 . (a) is the time when the initial phase difference of the two femtosecond laser beams is 0 t =40T0 normalized light field distribution diagram, (b) the initial phase difference of the dual-beam femtosecond laser is 0 at time t =40T0, (c) the normalized current density distribution diagram of the dual-beam femtosecond laser with an initial phase difference of 0 at time t =42T0 normalized electron density distribution diagram, (d) is the initial phase difference of the double-beam femtosecond laser is π / 2 at time t =50T0 normalized light field distribution diagram, (e) is the initial phase difference of the double-beam femtosecond laser is π / 2 at time t =50T0 normalized current density distribution diagram, (f) is the initial phase difference of the double-beam femtosecond laser is π / 2 at time t =52T0 normalized electron density distribution diagram, (g) is the initial phase difference of the double-beam femtosecond laser is π at time t =40T0 normalized light field distribution diagram, (h) is the initial phase difference of the double-beam femtosecond laser is π at time t =40T0 normalized current density distribution diagram, (i) is the initial phase difference of the double-beam femtosecond laser at time π t =42T0 normalized electron density distribution diagram. Specifically, Figure 4 In (a), since the phase difference between the two laser beams is 0, the electric field values ​​at adjacent positions are the same. Under the action of the electric field force, the electrons between the two beams move horizontally ( y The electrons have the same direction of motion, which makes the polarity of the current at that position the same. Figure 4 (b) As shown in the figure, the electrons move in the same direction, so that the electrons between the beams are pushed to the inner wall of the laser, forming a low-density electron area as shown in the figure. Figure 4 As shown in (c). Since a low-density electron region is formed between the beams, the refractive index of this region is lower than that of the background plasma, which causes the laser to bend toward the central axis and attract each other, eventually coupling into a laser beam. Figure 4In (g), since the phase difference between the two laser beams is π, the electric field values ​​at adjacent positions are opposite. Under the action of the electric field force, the electrons between the two beams move horizontally ( y The electrons move in opposite directions, either accumulating on both sides or being repelled in the middle. Due to the reverse direction of electron movement, the current polarity at adjacent positions is opposite. Figure 4 (h). Under the co-extrusion of two laser beams, the electron density in the middle of the two laser beams is higher than the background plasma density, which makes the refractive index of the middle area higher, and the laser is more easily deflected and transmitted to both sides, eventually causing the two laser beams to repel each other. When the phase difference between the two laser beams is between 0 and π, the repulsive or attractive effect depends on whether the phase difference is closer to π or 0. As mentioned above, this is caused by the local refractive index change caused by different electric field values. Figure 4 In (d), when the phase difference between the two laser beams is π / 2, they repel each other and have energy transfer.

[0051] Furthermore, as described above, by utilizing the inter-beam interaction caused by the phase difference between the laser beams, the upper and lower laser beams 1 and 2 with a phase difference of 0 are added to the middle two laser beams with a phase difference of Laser 3 and Laser 4 are connected, and the transmission axes of Laser 1 and Laser 2 have an angle with the transmission axes of Laser 3 and Laser 4. The specific parameters are as described above. It is worth emphasizing that the interaction between beams generally occurs with adjacent lasers, which is due to the strict requirements of laser interaction on the ratio of focal spot radius and optical center spacing.

[0052] Figure 5 is the normalized light field of case 2 and case 3 ( I / I 0) Distribution map, I 0=2.74×10 18 W / cm 2 , where (a)-(c) are respectively the time t =44T0, t =56T0, t =76T0 normalized light field distribution diagram, (d)-(f) are respectively the case 3 (case 3) at time t =44T0, t =58T0, t=76T0. Specifically, in case 2, since the initial phases of laser 3 and laser 4 are ahead of laser 1 and laser 2 by π, laser 3 and laser 4 have a repulsive effect on the adjacent laser 1 and laser 2, causing laser 1 and laser 2 to deflect and transmit toward the central axis. At the same time, since the phase difference between laser 1 and laser 2 is 0, they attract each other and deflect and transmit toward the central axis. Under the combined effect of the two phase differences mentioned above, the transmission of localized laser 1 and laser 2 prompts laser 1 and laser 2 to couple faster. Figure 5 In (a), we can see that case 2 is faster than case 1 at 40T0. Figure 4 (a) The coupling degree is higher at 40T0, which means that the coupling of case 2 occurs earlier. Figure 5 In (b), we can see that solution 2 (case 2) has completed the coupling at 56T0, while solution 1 (case 1) has completed the coupling at 56T0. Figure 4 (b) The coupling was completed at 60T0, which was 4T0 earlier.

[0053] According to the above, in case 3, since the initial phases of laser 3 and laser 4 are ahead of laser 1 and laser 2 by π, coupling occurs in advance in case 3, as shown in Figure 5 (d)- Figure 5 As shown in (e), coupling is completed at 58T0. At the same time, due to the transmission axis angle between laser 1 and laser 2 and laser 3 and laser 4 in scheme 3 (case 3), there is an optical path difference between laser 3 and laser 4 and the adjacent laser 1 and laser 2 during the transmission process. Since the optical path of laser 3 and laser 4 is larger than that of laser 1 and laser 2, the optical path difference will reduce the phase difference. When the phase difference is slightly less than π, inter-beam energy transfer occurs between laser 3 and laser 4 and the adjacent laser 1 and laser 2, so that the energy of laser 3 and laser 4 enters the synthesized high-energy femtosecond laser, improving the laser energy conversion rate. Inter-beam energy transfer causes the energy of the laser to be compared, and the phase velocity will also change when the laser energy changes. The phase velocity of the laser with larger energy will slow down, which will bring about the third type of phase difference. Under the joint action of the above three types of phase differences, the phase between the lasers will change dynamically. Due to the existence of the angle, the distance between the optical centers of laser 3 and laser 4 and the adjacent laser 1 and laser 2 will also decrease as the transmission distance increases, which improves the intensity of the inter-beam interaction.

[0054] Figure 6 is the normalized light field of case 4 and case 5 ( I / I 0) Distribution map, I 0=2.74×10 18 W / cm2 , where (a)-(c) are respectively the time t =44T0, t =56T0, t =76T0 normalized light field distribution diagram, (d)-(f) are respectively the normalized light field distribution diagram of case 5 at time t =44T0, t =60T0, t =76T0. Specifically, in case 4, since the initial phases of laser 3 and laser 4 are π / 2 ahead of those of laser 1 and laser 2, laser 3 and laser 4 have a repulsive effect on the adjacent laser 1 and laser 2, causing laser 1 and laser 2 to deflect and transmit toward the central axis. At the same time, since the phase difference between laser 1 and laser 2 is 0, they attract each other and deflect and transmit toward the central axis. Under the combined effect of the two phase differences mentioned above, the transmission of localized laser 1 and laser 2 causes laser 1 and laser 2 to couple faster. Figure 6 In (a), we can see that case 4 is faster than case 1 at 40T0. Figure 4 (a) The coupling degree is higher at 40T0, which means that the coupling of case 4 occurs earlier. Figure 6 In (b), we can see that scheme 4 (case 4) has completed the coupling at 56T0, while scheme 1 (case 1) has completed the coupling at 56T0. Figure 4 (b) The coupling was completed at 60T0, which was 4T0 earlier. In case 4, the initial phases of laser 3 and laser 4 are π / 2 ahead of those of laser 1 and laser 2, which results in inter-beam energy transfer. The energy of laser 3 and laser 4 partially enters the synthesized high-energy femtosecond laser. As mentioned above, in case 4, the phase difference will change dynamically under the combined action of the three types of phase differences. Figure 5 (a) with Figure 6 (a) It can be seen that under the parameter conditions of Case 4, Laser 3 and Laser 4 transfer part of their energy to Laser 1 and Laser 2 in the middle, which makes Case 4 have a higher energy conversion rate than Case 2.

[0055] Since the laser in case 5 has an incident axis angle of 5°, the optical path of laser 3 and laser 4 is greater than that of laser 1 and laser 2, making the initial phase difference slightly less than π / 2. Therefore, the interaction between laser 3 and laser 4 and the adjacent laser 1 and laser 2 is attractive. At the same time, due to the existence of the transmission axis angle, the distance between the optical centers of laser 3 and laser 4 and the adjacent laser 1 and laser 2 is reduced during the transmission process. Figure 6In (d), laser 3 and laser 4 are coupled with adjacent laser 1 and laser 2 first. Then, a second coupling occurs between the beams, as shown in Figure 6 (e) As shown. Figure 6 In (f), since the coupling process is longer, more energy can be deposited into the synthesized high-energy femtosecond laser.

[0056] Figure 7 is the normalized electron density of scheme 1 (case1), scheme 2 (case2), and scheme 3 (case3) at different times ( n / n c ) distribution map, n c =1.1 × 10 21 / cm 3 , where (a)-(d) are respectively the time t =38T0, t =42T0, t =46T0, t =60T0 normalized electron density distribution diagram, (e)-(h) are respectively case 2 (case 2) at time t =34T0, t =36T0, t =40T0、 t =60T0 normalized electron density distribution diagram, (i)-(l) are respectively case 3 at time t =36T0, t =40T0、 t =44T0, t =60T0 normalized electron density distribution diagram.

[0057] Figure 8 is the normalized electron density of scheme 1 (case1), scheme 4 (case4), and scheme 5 (case5) at different times ( n / n c ) distribution map, n c =1.1 × 10 21 / cm 3 , where (a)-(d) are respectively the time t =38T0, t =42T0, t =46T0, t =60T0 normalized electron density distribution diagram, (e)-(h) are respectively case 4 at time t =36T0,t =40T0、 t =44T0, t =60T0 normalized electron density distribution diagram, (i)-(l) are respectively case 5 at time t =36T0, t =44T0, t =56T0, t = Normalized electron density distribution map of 76T0; Figure 8 (l) shows the relatively coherent plasma channel structure formed by case 5, without any longitudinal truncation.

[0058] Fig. 9 The light intensity distribution diagrams of the incident seed light, scheme 1 (case1), scheme 2 (case2), scheme 3 (case3), scheme 4 (case4), and scheme 5 (case5), where (a) is the longitudinal light intensity distribution diagram of the incident seed light, scheme 1 (case1), scheme 2 (case2), scheme 3 (case3), scheme 4 (case4), and scheme 5 (case5), and (b) is the transverse light intensity distribution diagram of the incident seed light, scheme 1 (case1), scheme 2 (case2), scheme 3 (case3), scheme 4 (case4), and scheme 5 (case5); by comparing the longitudinal and transverse light intensity distribution diagrams of the incident seed light and the high-energy femtosecond laser synthesized by schemes 1 (case1), 2 (case2), 3 (case3), scheme 4 (case4), and 5 (case5), the light intensity peaks are 9.89 × 10 18 W / cm 2 , 2.91 × 10 19 W / cm 2 , 2.92 × 10 19 W / cm 2 , 5.84 × 10 19 W / cm 2 , 3.74 × 10 19 W / cm 2 , 5.12 × 10 19 W / cm 2 , Case 5 can increase the light intensity by 6 times.

[0059] Fig.10The energy conversion efficiency diagrams of Scheme 1 (case1), Scheme 2 (case2), Scheme 3 (case3), Scheme 4 (case4), and Scheme 5 (case5), where (a) is the efficiency diagram of total input laser energy converted into electron energy of Scheme 1 (case1), Scheme 2 (case2), Scheme 3 (case3), Scheme 4 (case4), and Scheme 5 (case5), and (b) is the conversion efficiency (color bar) of total input laser energy converted into synthetic laser energy of Scheme 1 (case1), Scheme 2 (case2), Scheme 3 (case3), Scheme 4 (case4), and Scheme 5 (case5), the normalized ratio of synthetic laser to the laser with the highest synthesizable energy (black frame), and the optimal output time (point) diagram of synthetic laser. Specifically, in Fig.10 (a) shows the ratio of total laser energy to electron energy. Fig.10 (b) shows that case 5 (case5) has the longest coupling process, so more laser energy is deposited into the synthesized high-energy femtosecond laser. The optimal output times of case 2 (case2), case 3 (case3), and case 4 (case4) are 6T0, 4T0, and 6T0 earlier than case 1 (case1), respectively, while case 5 (case5) has undergone two coupling processes, so the optimal output time is delayed by 4T0. The proportion of the total incident laser energy converted to the synthesized high-energy laser is 60%, 33%, 55%, 36%, and 62%, respectively.

[0060] Fig.11 is the normalized optical center distance ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) for the intensity of high-energy femtosecond laser synthesized by Scheme 3 (case 3) and Scheme 5 (case 5) ( I ), λ 0=1 μ m. n c =1.1 × 10 21 / cm 3 , where (a) is the normalized optical center distance ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / nc ) The relationship between the intensity of the high-energy femtosecond laser synthesized by Scheme 3 (case3) and Scheme 5 (case5) and the normalized optical center distance. (b) is the normalized optical center distance ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) is the relationship between the intensity of the high-energy femtosecond laser synthesized by Scheme 3 (case3) and Scheme 5 (case5) and the angle between the guide light and the intermediate laser transmission axis. (c) is the normalized optical center spacing ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) The relationship between the intensity of the high-energy femtosecond laser synthesized by Scheme 3 (case 3) and Scheme 5 (case 5) and the angle between the guide light and the intermediate laser transmission axis. (d) is the normalized optical center spacing ( d / λ 0) The angle between the guiding light and the intermediate laser transmission axis ( θ ), the normalized intensity of the input laser ( a 0), normalized background electron density ( n / n c ) is a graph showing the relationship between the intensity of the high-energy femtosecond laser synthesized by Scheme 3 (case 3) and Scheme 5 (case 5) and the normalized background electron density. Specifically, Fig.11 (a)- Fig.11 (d) The influence of the optical center spacing, incident axis angle, normalized intensity of incident light, and normalized electron density of background plasma on the intensity of synthesized high-energy femtosecond laser. Fig.11 In (a), the increase in the distance between the optical centers will weaken the effect of the interaction between the beams, which makes the distance between the optical centers inversely proportional to the synthesized high-energy femtosecond laser intensity and proportional to the optimal output position. Fig.11 In (b), before the incident axis angle reaches the optimum, the effect on the intensity of the synthesized high-energy femtosecond laser is a positive gain, which is caused by the phase difference caused by the optical path difference and the change in the distance between the optical centers. However, after exceeding the optimum angle, the angle is too large, causing Laser 3 and Laser 4 to cross Laser 1 and Laser 2 too early, and will bounce off and transmit to both sides, bringing negative gain to the synthesized high-energy femtosecond laser intensity. Fig.11In (c), when the normalized intensity within this range is selected, the magnification and optimal output position of the synthesized high-energy femtosecond laser are relatively stable. Fig.11 In (d), if the normalized electron density of the background plasma is too small, the nonlinear effect will not be obvious, but if it is too large, the loss in the transmission process will be too high. Fig.11 A certain adjustable range of initial parameters is given, proving that the present invention allows a certain error to exist.

[0061] Matters not covered by the present invention are known technologies.

[0062] 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.

[0063] 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 patent of the present application shall be subject to the attached claims.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for generating high-energy femtosecond lasers using four femtosecond lasers, characterized in that: Four femtosecond laser pulses with initial phase differences are simultaneously hit on the front surface of the plasma target according to a certain spatial position, wherein the two femtosecond laser pulses located on the two outer sides are used as guide lights, the two femtosecond laser pulses on the inner side of the guide lights are intermediate light beams, the guide lights and the two intermediate light beams on the inner side of the guide lights have an initial phase difference when hitting the front surface of the plasma target, the transmission axes of the outer guide lights and the intermediate light beams adjacent to the inner side thereof are symmetrically distributed along the central axis of the plasma target, and the transmission axes of the outer guide lights and the intermediate light beams adjacent to the inner side thereof have a certain angle, and the angle ranges from 0° to 10°; The nonlinear effect causes the four femtosecond laser beams to interact with each other when they are transmitted in the plasma target, resulting in rapid coupling of the laser beams and synthesis of high-energy femtosecond lasers. The plasma target has an electron density range of 2.2 × 10 19 / cm 3 to 2.2 × 10 20 / cm 3 The adjustable range of the incident intensity of each femtosecond laser pulse is 1.1×10 17 W / cm 2 to 1.1× 10 21 W / cm 2 The adjustable range of the optical center distance when hitting the front surface of the plasma target is 2 µ m to 6 µ m.

2. The method for generating high-energy femtosecond lasers using four femtosecond lasers according to claim 1, characterized in that: The spatial size of the plasma target is x = 60 µ m and y = 60 µ m.

3. The method for generating high-energy femtosecond lasers using four femtosecond lasers according to claim 1 or 2, characterized in that: The four femtosecond laser pulses are circularly polarized femtosecond laser pulses. s -Polarized femtosecond laser pulses or p -Polarized femtosecond laser pulses.

4. The method for generating high-energy femtosecond lasers using four femtosecond lasers according to claim 3, characterized in that: When four femtosecond laser pulses are transmitted in the plasma target, the interactions caused by the phase difference include repulsion, attraction, energy transfer, and coupling.

5. The method for generating high-energy femtosecond lasers using four femtosecond lasers according to claim 3, characterized in that: The four femtosecond laser pulses are circularly polarized femtosecond laser pulses, and the intensity of each circularly polarized femtosecond laser is 9.89 × 10 18 W / cm 2 , pulse width is 100fs, wavelength is 1 µ m, the focal spot radius is 2 µ m, the optical center spacing when hitting the front surface of the plasma target is 4 µ m.

6. The method for generating high-energy femtosecond lasers using four femtosecond lasers according to claim 1, characterized in that: Four femtosecond laser pulses with initial phase differences are simultaneously and equidistantly hit the front surface of the plasma target in parallel, wherein the outer guide light and the inner adjacent middle light beam have an initial phase difference of π when hitting the front surface of the plasma target, so that in the early stage of laser transmission in the plasma target, the guide light and the inner adjacent middle light beam have a repulsive effect, which will make the two middle light beams more inclined to be deflected and transmitted toward the central axis of the plasma target; the initial phase difference of the two middle light beams is 0 and they are transmitted in parallel at a close distance, so that the two middle light beams attract each other, and under the combined effect of the mutual attraction of the two middle light beams and the repulsive effect of the outer guide light and the inner adjacent middle light beam, the two middle light beams are rapidly coupled to synthesize high-energy femtosecond laser.

7. The method for generating high-energy femtosecond lasers using four femtosecond lasers according to claim 1, characterized in that: Four femtosecond laser pulses with initial phase differences are equidistant and have an incident angle of 6° between their transmission axes, and are simultaneously hit on the front surface of the plasma target. The outer guide light and the inner adjacent middle light beam have an initial phase difference of π when hitting the front surface of the plasma target, so that in the early stage of laser transmission in the plasma target, the guide light and the inner adjacent middle light beam have a repulsive effect, which will make the two middle light beams more inclined to be deflected toward the central axis of the plasma target for transmission; the initial phase difference of the two middle light beams is 0 and they are transmitted in parallel at a close distance, so that the two middle light beams attract each other, and under the combined effect of the mutual attraction of the two middle light beams and the repulsive effect of the outer guide light and the inner adjacent middle light beam, the two middle light beams are rapidly coupled, and after a period of transmission in the plasma target, an optical path difference is generated due to a certain angle between the transmission axes of the outer guide light and the inner adjacent middle light beam, and this optical path difference will produce additional phase difference, and the phase difference caused by the optical path difference The difference will make the phase difference between the guiding light and the intermediate light beam less than π; when the phase difference is between 0 and π but does not include 0 and π, energy transfer will occur between the light beams, and the phase-advanced laser will transfer energy to the phase-lagging laser, so that the guiding light will continue to transfer energy to the intermediate light beam; at the same time, due to the change in laser intensity, the phase velocity of the laser transmission in the plasma target will change, and the laser intensity will decrease and the phase velocity will increase, thereby bringing about a third type of phase difference other than the phase difference caused by the initial phase difference and the optical path difference, namely, the phase difference caused by the energy transfer between beams, and due to the angle of the transmission axis, the distance between the guiding light and the optical center of the intermediate light beam will become smaller after being transmitted for a certain distance, which will increase the interaction effect between the guiding light and the intermediate light beam, further improving the modulation effect of the guiding light and the energy transfer effect between beams, and the phase difference will continuously regulate the transmission behavior of the laser, increase the energy transfer between beams, and allow the guiding light to participate in the coupling process, which will further increase the energy of the synthesized high-energy femtosecond laser.

8. The method for generating high-energy femtosecond lasers using four femtosecond lasers according to claim 1, characterized in that: Four femtosecond laser pulses with initial phase differences are simultaneously and equidistantly hit the front surface of the plasma target in parallel. The outer guide light and the inner adjacent middle light beam have an initial phase difference of π / 2 when hitting the front surface of the plasma target. Since the initial phase difference is between 0 and π, energy transfer will occur between the light beams. Therefore, in the early stage of laser transmission in the plasma target, the guide light has a repulsive effect on the middle light beam and energy transfer between the beams, which will make the two middle light beams more inclined to be deflected toward the central axis of the plasma target for transmission. The initial phase difference of the two middle light beams is 0 and they are transmitted in parallel at a close distance, which makes the two middle light beams attract each other, prompting the two middle light beams to couple rapidly and continuously obtain energy from the guide light, thereby increasing the energy of the synthesized high-energy femtosecond laser.

9. The method for generating high-energy femtosecond lasers using four femtosecond lasers according to claim 1, characterized in that: Four femtosecond laser pulses with initial phase differences are equidistant and have a certain incident angle of 5° between the transmission axes, and are simultaneously hit on the front surface of the plasma target. The guiding light and the two intermediate light beams inside the guiding light have an initial phase difference of π / 2 when hitting the front surface of the plasma target. Since the initial phase difference is between 0 and π, there is energy transfer between beams. In the early stage of laser transmission in the plasma target, the guiding light has a repulsive effect on the intermediate light beams and energy transfer between beams, which will make the two intermediate light beams more inclined to be deflected toward the central axis of the plasma target for transmission and continue to obtain energy from the guiding light; at the same time, due to the optical path difference modulation phase difference and angle, the distance between the optical centers of the guiding light and the intermediate light beams is shortened, so that the guiding light will first couple with the adjacent intermediate light beam on the inside, and then the lasers formed by the coupling will be secondary coupled to finally form a laser beam, so that more energy is coupled into the synthesized high-energy femtosecond laser.

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