A laser beam shaping device and an ultrafast laser beam shaping system

Abstract

This invention discloses a laser beam shaping device and an ultrafast laser beam shaping system, including a laser and a mirror assembly, a meniscus mirror, a beam expander, a shaping mirror, and a field mirror arranged sequentially along the laser's output optical path. The meniscus mirror is used to compensate for the roundness of the beam. The mirror assembly, meniscus mirror, beam expander, and diffractive optical elements are all movable relative to their respective optical paths. In this invention, by setting up the meniscus mirror, the beam diameter in a specific direction can be fixedly changed, thereby compensating for and adjusting the roundness of the beam. Compared with the prior art that uses two mirrors to compensate for roundness, this invention avoids the need for complex optical structures to ensure the parallelism of the cylindrical mirror generatrix and the distance between the two curved surfaces, resulting in high stability and suitability for industrial production.

Description

Technical Field

[0001] This utility model relates to the field of laser equipment technology, and more specifically to a laser beam shaping device and an ultrafast laser beam shaping system. Background Technology

[0002] Most laser output beams follow a Gaussian distribution, with extremely high intensity at the center and exponentially decreasing towards the edges. This results in energy concentration in the core region and insufficient energy at the edges. This distribution causes two major problems: First, the core region is prone to overheating and ablation during processing, while the edges fail to reach the processing threshold, leading to a very small usable laser range. Furthermore, the edges of the Gaussian beam may damage areas outside the target region, thus expanding the heat-affected zone and reducing system accuracy. Second, energy utilization is low, with the ineffective edge region accounting for 30% to 50%, resulting in wasted laser energy. To address these issues, beam shaping techniques can be used to transform the Gaussian spot into a flat-topped spot.

[0003] See Figure 1 A flat-top beam profile lacks airfoil sections and features a steeper edge transition, resulting in higher intensity transmission efficiency and a smaller heat-affected zone. Using a flat-top beam for etching, welding, or cutting is more precise and causes less damage to surrounding areas.

[0004] For high-performance systems requiring efficient utilization of laser energy, beam shaping devices are typically used to shape the Gaussian beam into a flat-top beam. There are various types of beam shaping devices, including refractive, reflective, holographic, and diffractive elements. In the field of ultrafast laser processing, diffractive optical elements (DOE lenses) are generally used to output a flat-top homogenized spot. The laser beam is propagated through a mirror, then its diameter is altered by a beam expander to meet the incident size requirements of the DOE lens. After passing through the DOE lens, galvanometer, and field mirror, a flat-top homogenized spot is obtained on the focal plane below the field mirror.

[0005] In ultrafast laser beam shaping systems, the small pulse width (picosecond, femtosecond) and high peak power of ultrafast lasers make them prone to damaging optical components. Damage to these components leads to decreased stability of the optical system, affecting its performance. Improving system stability is a continuous optimization challenge for ultrafast laser systems.

[0006] Regarding the beam shaping effect of ultrafast lasers, since diffractive optical elements are usually designed to simulate ideal Gaussian light incident, but in reality, the beam in a laser system cannot achieve ideal Gaussian light output, the final homogenization effect will have some defects. Among the factors that have a significant impact on the homogenization effect are the beam quality and roundness of the incident diffractive optical elements. Currently, the improvement of these factors is mainly achieved by raising the requirements for the laser and seeking lasers that can output high-quality, high-roundness beams for application in laser beam shaping systems.

[0007] However, the drawback of this method is:

[0008] (1) The parameters of ultrafast lasers have limited room for improvement and cannot achieve 100% roundness. At the same time, the high requirements for ultrafast lasers will drive their costs up sharply. The cost of ultrafast lasers accounts for a large proportion of the entire laser system.

[0009] (2) The optical components of the laser external optical path system also affect the beam, and this effect cannot be eliminated by specifically adjusting the output beam of the laser. As a result, it is difficult to achieve the homogenization effect of ultrafast laser beam shaping in practice. Utility Model Content

[0010] The technical problem to be solved by this invention is how to improve the stability of the laser beam shaping device.

[0011] This utility model solves the above-mentioned technical problems through the following technical means: a laser beam shaping device, including a laser and a reflector group, a meniscus mirror, a beam expander, a shaping lens, and a field lens arranged sequentially along the output optical path of the laser. The meniscus mirror is used to compensate for the roundness of the beam. The reflector group, the meniscus mirror, the beam expander, and the diffractive optical elements can all move relative to their respective optical paths.

[0012] As a preferred technical solution, the laser beam shaping device further includes a meniscus mirror frame, the movable end of which is fixedly connected to the meniscus mirror and can drive the meniscus mirror to translate and / or rotate relative to the outgoing light path.

[0013] As a preferred technical solution, the orthopedic lens includes a diffractive optical element, which includes a DOE lens.

[0014] As a preferred technical solution, the laser beam shaping device further includes a DOE lens base, with the DOE lens fixed to the movable end of the DOE lens base.

[0015] As a preferred technical solution, the reflector group includes a first reflector and a second reflector arranged sequentially along the outgoing light path.

[0016] As a preferred technical solution, the mirror assembly is fixed on the mirror frame, and the mirror frame can drive the mirror assembly to adjust in four dimensions relative to the outgoing light path.

[0017] As a preferred technical solution, the meniscus mirror, beam expander, and shaping lens are all located at the center of the outgoing light path.

[0018] As a preferred technical solution, the meniscus mirror includes a concave cylindrical surface and a convex cylindrical surface located on the outgoing light path.

[0019] As a preferred technical solution, the material of the meniscus mirror is fused silica.

[0020] This invention also provides an ultrafast laser beam shaping system, including the laser beam shaping device described above.

[0021] The beneficial effects of this utility model are as follows:

[0022] (1) In this utility model, by setting the meniscus cylindrical mirror, the diameter of the beam in a specific direction can be fixed and changed, thereby compensating for and adjusting the roundness of the beam. Compared with the prior art, which uses two lenses to compensate for the roundness, this avoids the use of complex optical structures to ensure the parallelism of the cylindrical mirror generatrix and the distance between the two curved surfaces. It has high stability and is suitable for industrial production.

[0023] (2) In this utility model, no manual adjustment is required to ensure the parallelism of the cylindrical mirror generatrix and the distance between the two curved surfaces, which reduces the difficulty of system adjustment, improves the stability of the entire beam shaping system, and is conducive to integration into industrial laser processing equipment. Attached Figure Description

[0024] Figure 1 A schematic diagram of the flat-top beam principle is provided for the background technology of this utility model;

[0025] Figure 2 This is a schematic diagram of the laser beam shaping device provided in Embodiment 1 of this utility model;

[0026] Figure 3 This is a schematic diagram of the laser beam shaping device provided in Embodiment 2 of this utility model;

[0027] Figure 4 This is a top view of the laser beam shaping device provided in Embodiment 2 of this utility model;

[0028] Figure 5 This is a schematic diagram of uneven beam energy distribution provided in Embodiment 2 of this utility model;

[0029] Figure 6 This is a schematic diagram of uniform beam energy distribution provided in Embodiment 2 of this utility model;

[0030] Figure 7 This is a schematic diagram of the laser beam shaping device provided in Embodiment 3 of this utility model;

[0031] Figure 8 This is a schematic diagram of the principle structure of the meniscus mirror provided in Embodiment 3 of this utility model;

[0032] Reference numerals: 1. Laser; 2. First reflecting mirror; 3. Second reflecting mirror; 4. Meniscus mirror; 5. Beam expander; 6. Diffractive optical element; 7. Field mirror; 8. First fixed-magnification beam expander; 9. Second fixed-magnification beam expander; 10. Galvanometer mirror; 11. Cylindrical mirror group. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below in conjunction with the embodiments of this utility model. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0034] Example 1

[0035] See Figure 2 A laser beam shaping device includes a laser 1 and a first fixed-magnification beam expander 8, a mirror group, a second fixed-magnification beam expander 9, a beam expander 5, a diffractive optical element, a galvanometer 10, and a field mirror 7 arranged sequentially along the output light path of the laser 1. It should be noted that in this embodiment, the mirror group includes a first reflector 2 and a second reflector 3 arranged sequentially along the output light path, and the shaping lens is a diffractive optical element 6.

[0036] To address the issue of easily damaged optical components in the laser beam shaping device of an ultrafast laser system, a fixed-magnification beam expander, namely the first fixed-magnification beam expander 8, is introduced and placed at the laser exit to increase the beam diameter, thereby reducing the energy density of the laser acting on the optical components and effectively reducing the probability of the optical components being damaged by the laser. In addition, the optical components in the laser beam shaping device of the ultrafast laser system, such as the beam expander 5, are more expensive than the fixed-magnification beam expander, and are more difficult to replace if problems occur. After introducing the first fixed-magnification beam expander 8 and the second fixed-magnification beam expander 9, only the fixed-magnification beam expander is easily damaged, reducing the monetary and time costs of system maintenance.

[0037] Example 2

[0038] In Example 1, the fixed-magnification beam expanders, namely the first fixed-magnification beam expander 8 and the second fixed-magnification beam expander 9, are just spherical mirrors. They can only magnify the laser beam in the XY direction, and can only increase the beam diameter, but cannot change the roundness of the beam.

[0039] The difference between this embodiment and Embodiment 1 is that the first fixed-magnification beam expander 8 and the second fixed-magnification beam expander 9 are removed, and a beam adjustment device is introduced in front of the diffraction optical element in the external shaping optical path. The homogenization effect of the laser beam shaping device is greatly limited by the output beam of the laser 1 itself, and it cannot eliminate the problem of the influence of external optical devices on the beam. The introduced beam adjustment device makes roundness compensation adjustment on the beam of the incident or diffraction optical element 6, making up for the difference between the output beam of the laser system and the ideal Gaussian beam, thereby obtaining a better homogenization effect. For example, if the laser 1 is fixed to output a beam with 95% roundness, the beam adjustment device makes roundness compensation adjustment on the beam of the incident or diffraction optical element 6, making up for the difference between the output beam of the laser system and the ideal Gaussian beam, thereby obtaining a better homogenization effect.

[0040] See Figure 3 , Figure 4 The beam adjustment device includes a cylindrical lens group 11, which includes two cylindrical lenses. The two cylindrical lenses are respectively a plano-concave lens and a plano-convex lens. The two cylindrical lens groups are connected to an adjustment bracket. The adjustment bracket is provided with multiple mounting holes at different distances. The plano-concave lens and the plano-convex lens are detachably connected to different mounting holes on the adjustment bracket, thereby adjusting the distance between the two cylindrical lenses.

[0041] A cylindrical mirror is a special optical element whose core feature is that it has optical curvature only in one direction, namely the generatrix direction, while it is planar in the direction perpendicular to it, namely the axial direction. This structure determines that it can only deflect, focus, or diverge light rays propagating along the curvature direction, while having no effect on light rays propagating along the planar direction. This allows it to achieve the function of "one-dimensional shaping" of the beam or correcting specific optical aberrations. By combining two cylindrical mirrors, the beam diameter in the generatrix direction can be changed without changing the beam divergence angle, thereby achieving the effect of compensating for the roundness of the beam.

[0042] To ensure the roundness of the output beam from laser 1, the focal length combination of the two cylindrical mirrors was calculated. The distance between the curved surfaces of the two cylindrical mirrors was strictly controlled, and the generatrices of the two cylindrical mirrors were strictly parallel. In actual debugging, it was ensured that the beam was perpendicularly incident on the center of the two cylindrical mirrors. The two cylindrical mirrors were rotated synchronously around the central axis of the beam until the magnification direction of the cylindrical mirror group was consistent with the direction of the short side of the ellipse of the beam cross section. The distance between the two cylindrical mirrors was fine-tuned by observing the final homogenization effect.

[0043] It should be noted that in this embodiment, the diffractive optical element 6 uses a DOE lens. In the entire system, the cylindrical lens group 11, the beam expander 5, and the diffractive optical element 6 all need to be adjusted to have the laser center in and center out, with the mirror surface perpendicular to the optical axis. The two cylindrical mirrors in the cylindrical lens group 11 also need to ensure that their generatrices are strictly parallel. The distance between the two cylindrical mirrors is stable after adjustment. The first reflecting mirror 2 and the second reflecting mirror 3 are conventional ultrafast optical reflecting mirrors. The first reflecting mirror 2 and the second reflecting mirror 3 are both set on corresponding reflecting mirror mounts. The reflecting mirror mount can be a commercially available Lubang Optoelectronics two-dimensional adjustment mirror mount AMM3-1BP. The two cylindrical mirrors in the cylindrical lens group 11 are each equipped with a corresponding cylindrical mirror mount. The beam expander 5 is connected to the beam expander mount, and the DOE lens is connected to the DOE lens base. The cylindrical mirror mount, the beam expander mount, and the DOE lens base are all commercially available Lubang Optoelectronics four-dimensional adjustment mirror mount AMM4-LBE-M34.

[0044] Working principle: The light output from laser 1 passes through the first reflecting mirror 2 and the second reflecting mirror 3. The cylindrical mirror group 11 adjusts the beam roundness, and the beam expander 5 increases the overall beam diameter to meet the incident beam diameter requirements of the diffractive optical element 6. After passing through the galvanometer 11 and the field mirror 7, a flat-topped homogenized spot is obtained on the focal plane under the field mirror 7. The core principle of the DOE lens of the diffractive optical element 6 is to control the phase difference of the diffracted light through the design of micro-nano structures, achieving precise light field shaping through the interference and superposition of light. In the beam shaping system, it has requirements for the diameter, beam quality, beam roundness, and beam incident angle of the incident beam. The diameter of the incident beam is adjusted by the beam expander to meet these requirements, and the beam incident angle is adjusted by the four-dimensional adjustment frame. Beam quality and roundness are inherent optical parameters of a laser output. In the final homogenization effect judgment, insufficient beam roundness (beam ellipticity) will lead to uneven energy distribution in the two perpendicular directions, with a heavy energy distribution in one direction and a weak energy distribution in the other. Figure 5 As shown, by introducing the cylindrical mirror group 11, it is not necessary to disassemble the laser 1 for internal adjustments, nor is it necessary for the laser 1 to output 100% circular light. It can also compensate for the influence of the external optical path on the beam, flexibly change the roundness of the beam, and flexibly adjust the final shaping effect, making the energy distribution in the two perpendicular directions the same, resulting in a more uniform energy distribution in the overall shaping spot effect. Figure 6 As shown.

[0045] Example 3

[0046] The difference between this embodiment and Embodiment 1 is that by replacing the cylindrical mirror group 11 with a meniscus mirror 4, the beam diameter in a specific direction can be fixed and changed. Although the function of fine-tuning the magnification effect by adjusting the distance between the two cylindrical mirrors of the cylindrical mirror group 11 is sacrificed, the roundness of the output beam of the laser 1 is fixed, and the parameters of the meniscus mirror 4 are fixed. There is no need for manual adjustment to ensure the parallelism of the generatrix of the cylindrical mirror and the distance between the two curved surfaces. This simplifies the system debugging difficulty, improves the stability of the entire beam shaping system, and is conducive to the better integration of this ultrafast laser beam shaping optical system into industrial laser processing equipment.

[0047] See Figure 7 , Figure 8 A laser beam shaping device includes a laser 1 and a mirror group, a meniscus mirror 4, a beam expander 5, a shaping lens, and a field mirror 7 arranged sequentially along the output light path of the laser 1. The mirror group, the meniscus mirror 4, the beam expander 5, and the diffractive optical element 6 can all move relative to their respective light paths. In this embodiment, the mirror group, the meniscus mirror 4, the beam expander 5, and the diffractive optical element 6 are all provided with corresponding mirror frames or lens bases, which are the same as in embodiment 2 and will not be described again here. The shaping lens adopts the diffractive optical element 6, and the mirror group includes a first mirror 2 and a second mirror 3 arranged sequentially.

[0048] In this embodiment, the meniscus mirror 4 is fixed on the meniscus mirror holder, which can be the Lubang Optoelectronics four-dimensional adjustment mirror mount AMM4-LBE-M34, thereby realizing the three-dimensional adjustment of the meniscus mirror 4.

[0049] The parameters of the meniscus mirror are shown in the table below.

[0050]

[0051] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A laser beam shaping device, characterized in that, It includes a laser and a series of mirrors, meniscus mirrors, beam expanders, shaping mirrors, and field mirrors arranged sequentially along the laser's output optical path. The meniscus mirror is used to compensate for the roundness of the beam. The mirrors, meniscus mirrors, beam expanders, and diffractive optical elements can all move relative to their respective optical paths.

2. The laser beam shaping device according to claim 1, characterized in that, It also includes a meniscus mirror frame, the movable end of which is fixedly connected to the meniscus mirror and can drive the meniscus mirror to translate and / or rotate relative to the outgoing light path.

3. The laser beam shaping device according to claim 1, characterized in that, Orthopedic lenses include diffractive optical elements, which include DOE lenses.

4. The laser beam shaping device according to claim 3, characterized in that, It also includes a DOE lens base, with the DOE lens fixed to the movable end of the DOE lens base.

5. The laser beam shaping device according to claim 1, characterized in that, The reflector assembly includes a first reflector and a second reflector arranged sequentially along the outgoing light path.

6. A laser beam shaping device according to claim 1 or 5, characterized in that, The mirror assembly is fixed on the mirror mount, which can drive the mirror assembly to adjust in four dimensions relative to the outgoing light path.

7. The laser beam shaping device according to claim 1, characterized in that, The meniscus mirror, beam expander, and shaping lens are all located at the center of the outgoing light path.

8. The laser beam shaping device according to claim 1, characterized in that, A meniscus mirror consists of a concave cylindrical surface and a convex cylindrical surface located in the outgoing light path.

9. A laser beam shaping device according to claim 1, characterized in that, The crescent-shaped cylindrical mirror is made of fused silica.

10. An ultrafast laser beam shaping system, characterized in that, Includes the laser beam shaping device as described in any one of claims 1-9.

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