A simplified u-shaped beam reverser

Abstract

This invention discloses a simplified U-shaped beam inverter, relating to the field of high-power laser technology. It includes a collimating lens (102), a right-angle mirror, an electro-optic switch (105), and a focusing lens (106). The right-angle mirror consists only of a first reflecting mirror surface (103) and a second reflecting mirror surface (104) that are perpendicular to each other, both of which form a 45° angle with the beam transmission direction. The entire right-angle mirror is rotated 45° about the beam transmission direction to simultaneously achieve a 90° symmetrical rotation of the near-field wavefront and polarization state of the beam. The beam inverter is placed directly behind the filter aperture array plate (101), eliminating the need for additional reflecting mirrors or wedge mirrors to guide the beam into and out of the main optical path. By rotating the entire right-angle mirror by 45°, this invention enables a simplified structure with only two reflecting surfaces to have wavefront rotation functionality. This allows the entire inverter module to be directly integrated into a sealed optical path, significantly simplifying the structure, reducing the number of optical components, improving system cleanliness and damage resistance while maintaining functional integrity. It is suitable for high-power laser amplification systems.

Description

Technical Field

[0001] This invention relates to the field of high-power laser technology, and more specifically to a simplified U-shaped beam inverter for an off-axis multi-pass laser amplification system. Background Technology

[0002] Beam reversers are commonly used in off-axis multi-pass amplification laser devices. Multi-pass amplification technology allows the laser pulse to pass through the amplification medium multiple times, effectively improving the energy extraction efficiency of the main amplifier. This helps reduce the output energy of the pre-amplifier, as well as the corresponding device size and cost. The off-axis design separates the far-field focusing points, ensuring only one light pass through each filter aperture. This helps avoid amplified stimulated emission (ASE) from parasitic cavities and plasma blockage caused by intense laser irradiation ablation and ionization of the filter apertures, preventing subsequent beam passage. Beam reversers can replace the complex, expensive, and fragile large-size plasma electrode electro-optic switches (Poukes cells) and polarization crystals in laser devices with smaller electro-optic switches, offering significant advantages in cost, operational performance, and reduced device size compared to full-size electro-optic switches. This technology is beneficial for laser devices realizing inertial confinement fusion and PW-level ultra-intense laser devices for fundamental physics research.

[0003] Currently, commonly used beam reversers can be classified into U-turns and L-turns based on their structure. The U-turn was proposed in 1992 by Livermore National Laboratory in the United States. Its principle involves drawing the second-stage amplified beam from near the far field using a pair of mirrors or wedges, collimating it with a lens, then reflecting it back by three pyramidal mirrors, focusing it again, and finally guiding it back into the main optical path by another pair of mirrors or wedges, thus reversing the beam. The beam reverser's optical path also includes polarizers and small-sized Polkers cells to prevent amplified stimulated emission from the parasitic cavity and back-reflected light from the lens surface. A key feature of the U-turn is that the output wavefront is rotated 90 degrees compared to the input wavefront, which helps to convert the "cylindrical" wavefront aberration (i.e., astigmatism) caused by the thermal distortion of the sheet amplifier into easily correctable "spherical" wavefront aberration (i.e., deviation). U-shaped structures are used in China's SGIII and its Technical Integration Experiment Line (TIL), and in the United States' NIF, among others. L-shaped inverters, proposed by France's CEL-V, are characterized by the shared use of mirrors, polarizers, Pockels cells, and lenses during the beam's input and output. This results in a smaller overall number of optical components and no wavefront rotation. However, because the beam passes through the Pockels cell twice, the beam transmittance decreases significantly, leading to relatively high system losses. L-shaped structures are used in France's Laser Megajoule (LMJ) and its prototype verification device, the Laser Integration Line (LIL), among others.

[0004] Based on a comprehensive analysis and comparison of various inverter configurations, this invention proposes a simplified U-shaped beam inverter, which significantly simplifies the inverter structure while ensuring all functions are maintained. Summary of the Invention

[0005] In view of this, the present invention provides a U-shaped beam inverter with an extremely simple structure.

[0006] To achieve the above objectives, the technical solution provided by the embodiments of the present invention is as follows: The present invention provides a simplified U-shaped beam reverser, the core of which is a right-angle mirror containing two orthogonal reflecting surfaces. This is simpler and clearer than the U-shaped beam reverser that uses three mirrors distributed in a pyramidal shape. Due to the simple structure of the core component, it can be directly placed within a distance of about 3 to 4 meters behind the pinhole array plate to complete the beam return and wavefront reversal, without the need to use two pairs of mirrors or wedge mirrors to guide the beam into and out of the main optical path. At the same time, this optical path arrangement does not affect the beam transmission of the other two pinholes in the pinhole array plate, thus making the overall structure of the present invention extremely simple, with lower cost and easier assembly. For beam detection, the reflectivity of one reflecting surface of the right-angle mirror can be reduced to directly extract the detection beam.

[0007] The structure of the present invention is as follows Figure 1 As shown. Figure 1 On the left is the filter aperture array plate 101, with filter apertures numbered 1 to 4, corresponding to the order in which the laser beam passes through the array plate. Figure 1 The two reflecting mirrors on the right, 103 and 104, are perpendicular to each other, forming a right-angle mirror similar to a right-angle prism. The point where the two reflecting mirrors meet is called the splicing line of the right-angle mirror (i.e., Figure 1 On the right-angle mirror OO The 'axis' is similar to the right-angled edge of a right-angled prism. When a parallel beam of light is incident on the right-angled mirror, the incident wavefront of mirror 103 and the output wavefront of mirror 104 are about the splicing line. OO Symmetrical. For example... Figure 2 As shown in (a), when the splicing line is parallel to y When the axis is in motion (i.e.) OO (The z-axis is parallel to the line connecting holes 1 and 2 on the orifice plate 101). The incident and output wavefronts of the right-angle mirror will be reversed left and right, and the beam polarization state will remain horizontal. This deflection is similar to that of an L-shaped beam inverter. When the right-angle mirror is positioned along the z-axis... xy Rotate 45° within the plane so that the splicing line is aligned with... y When the axis is at a 45° angle (i.e.) OO (The axis is parallel to the line connecting holes 1 and 4 on the small aperture plate 101). The incident and output wavefronts of the right-angle reflector will undergo a 90° symmetrical reversal, and the polarization state of the output beam will change to the vertical direction.

[0008] Horizontal polarization ( Figure 1 In xThe pre-amplified output light (direction) is injected into the main amplification cavity through the small hole 1 on the small hole plate 101. After two stages of energy amplification, it is filtered by the small hole 2 and enters the beam reversing unit. When the beam enters the reversing unit, it is first collimated by the lens 102. The collimated beam is then incident on a 45° angled right-angle mirror, and after reflection by the mirror surfaces 103 and 104, it is output. Due to the splicing line of the right-angle mirror and... y The axes are at a 45° angle, at which point both the near-field wavefront and polarization direction of the beam rotate by 90 degrees (e.g., Figure 1 Within the rectangular dashed frame, the double-headed arrows represent the beam polarization direction, and the letter "F" represents the wavefront. Upon passing through the Pockels cell 105, the beam polarization direction rotates 90 degrees again, returning to a horizontal polarization state to ensure that the polarization direction is within the incident plane when the beam is incident on the energy amplifier at the Brewster angle. The parallel beam, after being focused by lens 106, passes through aperture 3 for filtering and re-enters the main amplification cavity, thus completing beam reversal. Subsequently, the beam undergoes third and fourth stage energy amplification in the main optical path, then passes through aperture 4 for filtering and is output to the terminal optical components. Lenses 102 and 106, together with the focusing lens in the main optical path in front of the aperture array plate 101, form a 4F system, satisfying the image transmission condition. Lenses 102 and 106 themselves also mutually satisfy the 4F system condition. The aperture plate 101 is the input and output surface of this 4F system. Furthermore, the transmittance of the reflecting mirror 104 can be appropriately reduced to extract a small portion of the beam energy into the detection system for detecting the beam quality in the middle optical path. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings required in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a structural design diagram of the U-shaped wavefront inverter in this invention;

[0011] In the diagram: 101. Filtering pinhole array plate; 102. Collimating lens; 103. First reflecting surface of the right-angle mirror (the specific shape of the reflecting plane is determined according to the light path, so as not to block the light path corresponding to other pinholes); 104. Second reflecting surface of the right-angle mirror (the specific shape of the reflecting plane is determined according to the light path, so as not to block the light path corresponding to other pinholes); 105. Pockels box electro-optic switch; 106. Focusing lens.

[0012] Figure 2 The mirror splicing line of the right-angle reflector in this invention OO (a) parallel toy Axis or (b) with y The effect of a right-angle mirror reflecting the wavefront when the axis is at a 45° angle. Detailed Implementation

[0013] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0014] The hole spacing in the horizontal and vertical directions on the perforated plate 101 is taken as a To avoid blocking the light beam transmission in apertures 1 and 4, either mirror surface 103 or 104 of the right-angle mirror must be within the range of the aperture. xy The side length of the projection plane in the plane cannot exceed a Considering the effective reflection area of ​​the mirror is 90%, the side length of the beam propagating in the beam reverser cannot exceed 0.9 meters. a Let the focal length of the lens and the side length of the rectangular beam in the main optical path be respectively... f and s 1. To avoid the right-angle mirror blocking the light beam transmission through the two small holes 1 and 4, the farthest distance between the right-angle mirror (referring to the center position of the mirror surface 103 or 104) and the small hole plate 101 cannot exceed [a certain value]. L 1. Therefore, we have:

[0015] (1)

[0016] Take the side length of the parallel beam in the inverter as s 2. The distance between the focal point of lens 102 or lens 106 and the pinhole plate 101 is... L 2 (that is, the focal length of the lens), then we have:

[0017] (2)

[0018] The actual beam size in the current U-shaped inverter s 2 is around 4*4 cm and 5*5 cm, which means the spacing between the filter apertures is... a The beam length should be around 4.4 to 5.6 cm. Taking the booster amplification optical parameters in the US National Ignition Device as an example, the lens focal length is 30 m, the beam size is 35*35 cm, and the beam side length in the beam reverser is 4 cm. According to equations (1) and (2), we can obtain... L 1 and LThe distances 2 are 3.81 m and 3.43 m, respectively, meaning there is a distance of 0.38 m between the lens and the right-angle mirror, which can be used to place the Pockels box. In the LIL and LMJ designs, the rectangular beam size in the L-shaped inverter has a side length of 8 cm. In this case, the off-axis angle of the beam and the aperture spacing of the pinhole plate can be appropriately increased, or the beam size in the inverter can be decreased to correspond to the design in this invention.

[0019] As can be seen from the above technical solutions, the simplified U-shaped beam inverter disclosed in this invention greatly simplifies the structure of the U-shaped inverter while ensuring all functions.

[0020] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0021] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A simplified U-beam inverter, characterized by: It comprises a collimating lens (102), a first mirror surface (103) and a second mirror surface (104) of a right-angle reflector, an electro-optical switch (105) and a focusing lens (106); the right-angle reflector is composed of the first mirror surface (103) and the second mirror surface (104) only, the two mirror surfaces are perpendicular to each other and both form a 45° angle with the light beam transmission direction; the whole of the right-angle reflector is rotated by 45° with the light beam transmission direction as the axis, for realizing 90° symmetrical rotation of the light beam near-field wave surface and polarization state; the light beam reverser is directly placed behind a filtering pinhole array plate (101), without additional mirrors or wedge-shaped mirrors for guiding the light beam in and out of the main light path.

2. The simplified U-shaped beam inverter according to claim 1, characterized in that: The electro-optical switch (105) is a Pockels cell, for isolating the reversed laser and rotating the light beam polarization state by 90° again.

3. The simplified U-shaped beam inverter of claim 1, wherein: The reflectivity of the second mirror surface (104) is reduced, for transmitting part of the light beam for detection.

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