Field lens laser scanning system and scanning method based on cascade metasurface

Abstract

The invention discloses a cascade metasurface-based field lens laser scanning system and scanning method, and the system comprises a laser, and a collimation and beam expanding system, a laser deflection galvanometer group, an aperture diaphragm, a cascade metasurface field lens and a working platform which are sequentially arranged along an emergent light path of the laser. The cascaded metasurface field lens comprises a first metasurface and a second metasurface which are arranged in parallel at an interval. According to the invention, the deflection device can drive the two reflection galvanometers to deflect synchronously, different phase regulation and control can be realized by setting the nanorod periods and heights of the adjacent nanorod units to be different, and the size of a traditional field lens is greatly reduced by means of the planar structures of the first metasurface and the second metasurface. High-efficiency focusing and small light spot output of large-angle incident light can be achieved, the integration problem caused by the large size of a traditional optical system and the energy loss problem during large-angle scanning are effectively solved, and the system has higher machining efficiency and precision in laser scanning machining.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, and more specifically to a field lens laser scanning system and scanning method based on cascaded metasurfaces. Background Technology

[0002] Laser processing technology, due to its advantages of high precision, non-contact operation, and strong controllability, is widely used in micro-nano manufacturing, semiconductor processing, and the fabrication of precision optical devices. Traditional laser processing systems typically employ refractive methods (such as F-Theta field lenses and galvanometer systems) to achieve beam focusing and scanning. Among these, the field lens, as a core optical component, must meet requirements such as a large field of view, low distortion, and high energy utilization. However, to correct aberrations and achieve flat-field focusing, traditional field lenses usually require combinations of multiple lenses or complex aspherical designs, resulting in bulky optical systems, complex assembly and adjustment, and difficulty in simultaneously meeting the demands of high-power laser tolerance and multifunctional integration. Furthermore, traditional optical components have inherent limitations in dynamic tunability and multi-parameter coordinated control (such as wavelength, polarization, and focal position), restricting the flexibility and efficiency of laser processing.

[0003] In recent years, metasurfaces, as artificial two-dimensional materials composed of subwavelength structures, have been found to offer new insights into the miniaturization and functional integration of optical systems through localized electromagnetic manipulation, enabling functions such as anomalous refraction, polarization conversion, and multi-wavelength multiplexing. Compared to traditional refractive / diffractive optical elements, metasurfaces offer advantages such as ultrathinness, lightweight design, and high design freedom, allowing for flexible control of the phase, amplitude, and polarization of the light field, and are expected to significantly simplify the optical structure of laser processing systems.

[0004] However, existing metasurface-based laser processing solutions mostly focus on single functions (such as beam deflection or focusing), making it difficult to simultaneously meet the requirements of large field of view, high power tolerance, and complex wavefront modulation. Furthermore, single-layer metasurfaces face bottlenecks in terms of controllability and energy efficiency, while cascaded metasurfaces (i.e., multi-layer metasurface collaborative design) can achieve more complex wavefront modulation through phase superposition. However, current technologies have not effectively solved the problem of thermal stability under high-power lasers, nor the alignment and integration challenges between multi-layer metasurfaces.

[0005] Therefore, developing a field lens laser scanning system based on cascaded metasurfaces, through the synergistic design and optimization of multi-level metasurfaces, to achieve high power compatibility, aberration-free focusing over a large field of view, and multifunctional integration, is of great significance for overcoming the size limitations of traditional field lenses and improving the precision and flexibility of laser processing. This technology is expected to bring revolutionary applications in fields such as micro-nano fabrication, additive manufacturing, and the fabrication of precision optical devices. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to achieve efficient focusing of light incident at a large angle and small spot output.

[0007] The present invention solves the above-mentioned technical problems through the following technical means: a field lens laser scanning system based on cascaded metasurfaces, comprising a laser and a collimating and beam expanding system, a laser deflecting galvanometer group, an aperture stop, a cascaded metasurface field lens, and a working platform arranged sequentially along the laser's output optical path. The cascaded metasurface field lens includes a first metasurface and a second metasurface arranged in parallel at intervals. Both the first and second metasurfaces include multiple nanopillar units arranged radially from their centers. Each nanopillar unit includes multiple nanopillars arranged circumferentially along the first or second metasurface. The nanopillar periods and / or heights of adjacent nanopillar units are different. The laser deflecting galvanometer group includes two reflecting galvanometers connected to the same deflection device, which can drive the two reflecting galvanometers to deflect synchronously.

[0008] As a preferred technical solution, the adjustment angle of the reflecting mirror is adjusted by changing the driving voltage of the reflecting mirror, and the mirror deflection angle is proportional to the voltage.

[0009] As a preferred technical solution, the collimation and beam expansion system includes two convex lenses arranged along the outgoing optical path. The two convex lenses convert the diverging beam emitted by the laser into a parallel beam, and the diameter of the parallel beam is proportional to the ratio of the focal lengths of the two lenses.

[0010] As a preferred technical solution, the collimation and beam expansion system includes a concave lens and a convex lens arranged along the outgoing optical path. The concave lens and the convex lens convert the diverging beam emitted by the laser into a parallel beam, and the diameter of the parallel beam is proportional to the ratio of the focal lengths of the two lenses.

[0011] As a preferred technical solution, the cascaded metasurface field mirror also includes a silicon substrate, with the first metasurface and the second metasurface fixed on opposite sides of the silicon substrate.

[0012] As a preferred technical solution, the spacing between adjacent nanopillar units is different.

[0013] As a preferred technical solution, the deflection angle of the reflecting mirror is 0-32°.

[0014] As a preferred technical solution, the aperture stop diameter is 3mm, the substrate thickness of the cascaded metasurface field lens is 1mm, the distance between the aperture stop and the cascaded metasurface field lens is 25mm, and the distance between the working platform plane and the cascaded metasurface field lens is 30mm.

[0015] As a preferred technical solution, the working platform is a two-dimensional translation stage.

[0016] A scanning method using a cascaded metasurface-based field lens laser scanning system includes a laser emitting laser light, which is converted into a parallel beam by a collimating and expanding system and then incident on a laser deflecting galvanometer group. After being reflected by two reflecting galvanometers of the laser deflecting galvanometer group, the light is filtered by an aperture stop and then incident on a cascaded metasurface field lens, which modulates and focuses the light onto the working surface of the working platform.

[0017] The beneficial effects of the present invention are:

[0018] (1) In this invention, the two reflecting mirrors can be driven to deflect synchronously by the deflection device. By setting the period and height of the adjacent nanopillar units to be different, different phase modulation can be achieved. The planar structure of the first metasurface and the second metasurface greatly reduces the volume of the traditional field mirror, which can achieve efficient focusing of large-angle incident light and small spot output. It effectively solves the integration problem caused by the large size of the traditional optical system and the energy loss problem during large-angle scanning, so that the system has higher processing efficiency and accuracy in laser scanning processing. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the zero-voltage structure of the field lens laser scanning system provided in an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of the field lens laser scanning system with a certain voltage applied according to an embodiment of the present invention;

[0021] Figure 3 This is a schematic diagram of the collimation and beam expansion system provided in an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of the aperture stop structure provided in an embodiment of the present invention;

[0023] Figure 5 This is a schematic diagram of the cascaded metasurface field mirror structure provided in an embodiment of the present invention;

[0024] Figure 6 This is a schematic diagram showing the distribution of light spot diameter at different angles according to an embodiment of the present invention;

[0025] Reference numerals: 1. Laser; 2. Collimation and beam expansion system; 3. Laser deflection galvanometer; 4. Aperture stop; 5. First metasurface; 6. Silicon substrate; 7. Second metasurface; 8. Working platform. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] See Figure 1 , Figure 5 A cascaded metasurface-based field lens laser scanning system includes a laser 1 and a collimating and beam expanding system 2, a set of laser deflecting mirrors 3, an aperture stop 4, a cascaded metasurface field lens, and a working platform 8 arranged sequentially along the output optical path of the laser 1. The cascaded metasurface field lens includes a first metasurface 5 and a second metasurface 7 arranged in parallel at intervals. Both the first metasurface 5 and the second metasurface 7 include multiple nanopillar units arranged radially from their centers. Each nanopillar unit includes multiple nanopillars arranged circumferentially along the first metasurface 5 or the second metasurface 7. The nanopillars of adjacent nanopillar units are... Different periods and / or heights result in different phase modulations. Therefore, the planar structure of the first metasurface 5 and the second metasurface 7 significantly reduces the volume of traditional field mirrors. Furthermore, cascaded design allows for efficient focusing of lasers incident at different angles. In this embodiment, a 10.6-micrometer wavelength laser is used for design analysis. The height of the nanopillars on both the first and second metasurfaces 5 and 7 is 5.5 micrometers. By varying the nanopillar diameter within the range of 0-3 micrometers, a phase coverage of 0-2π can be achieved, meaning the desired phase modulation can be achieved within a 3-micrometer range. The maximum diameter of the nanopillars is 3 micrometers, meaning the center-to-center spacing of the nanopillars is 3 micrometers. Different nanopillar diameters correspond to different phase modulation effects, ultimately achieving a spot diameter in the range of 11-19 micrometers across the entire working plane.

[0028] It should be noted that the period in this embodiment refers to the center-to-center spacing of the nanopillars in the nanopillar unit; the focusing principle is achieved through the phase optimization design of cascaded metasurfaces. Existing technologies struggle to balance volume and small spot size when achieving large-angle focusing, resulting in severe spot distortion at large angles. Even with cascading, it's difficult to optimize a matching phase for large-angle focusing using metasurfaces, easily leading to severe distortion on the focusing plane at large angles. In this embodiment, the phase distribution characteristics of large-angle incident light are analyzed, spots at different angles are screened, and the least-damped squares method is used for optimization to obtain the final phase optimization result; see reference. Figure 6 The diagram shows the spot diameters of light rays at 0°, 7°, 14°, 21°, 26°, and 32° angles, with the spot diameters at each angle exhibiting a relatively stable distribution.

[0029] See Figure 1 Laser 1 is used to emit laser light with a certain divergence angle. Collimation and beam expansion system 2 is used to convert the divergent beam into parallel light, ensuring energy concentration during long-distance transmission. It also optimizes the spatial distribution and energy density of the beam to better suit processing requirements. In this embodiment, collimation and beam expansion system 2 includes two convex lenses. The two convex lenses convert the divergent beam emitted by the laser into a parallel beam. The diameter of the parallel beam is proportional to the ratio of the focal lengths of the two lenses. The distance between the two convex lenses is the sum of the focal lengths of the two convex lenses. Of course, a combination of concave and convex lenses can also be used to complete collimation and beam expansion. The advantage of using a combination of concave and convex lenses is that there is no focal overlap and it is more suitable for high-power lasers.

[0030] See Figure 1 A set of laser deflecting galvanometers 3 includes two laser deflecting galvanometers 3, which are composed of reflecting galvanometers. The two laser deflecting galvanometers 3 are connected to the same deflection device and deflect synchronously through an input signal. The deflection device can be a commercially available Tianchuanqi 25K laser scanning galvanometer SC25. The straight-line distance between the center points of two adjacent reflecting galvanometers is 5mm to 10mm, and the maximum deflection angle of any reflecting galvanometer is ±0.1° to ±32°.

[0031] See Figure 4 The aperture stop 4 is used to filter out light and stray light other than 3 mm in diameter, and to further adjust the beam after reflection by the galvanometer. In this embodiment, the diameter of the aperture stop 4 is 3 mm.

[0032] See Figure 1 The cascaded metasurface field mirror also includes a silicon substrate 6 with a thickness of 1 mm. The silicon substrate 6 serves as the support for the first metasurface 5 and the second metasurface 7. In this embodiment, the first metasurface 5, the silicon substrate 6, and the second metasurface 7 are all made of high-refractive-index silicon to provide better phase modulation capability and facilitate precise control of the wavefront phase through nanopillar structure parameters. Of course, other high-refractive-index materials, such as germanium and zinc selenide, can also be used.

[0033] See Figure 1 The working platform 8 can be a fixed platform or a CNC-controlled two-dimensional translation stage, which allows the processing and scanning range to be no longer limited to a fixed area. It can perform processing and scanning on 3D models and use CNC to drive the two-dimensional translation stage, which is easy to adjust. In this embodiment, the distance between the plane where the working platform 8 is located and the cascaded metasurface field mirror is 30mm, and the distance between the aperture stop 4 and the cascaded metasurface field mirror is 25mm. Of course, the diameter of the aperture stop 4, the distance between the aperture stop 4 and the cascaded metasurface field mirror, and the distance between the cascaded metasurface field mirror and the working platform 8 can also be adjusted according to different needs to balance the spatial filtering effect and the beam energy utilization rate.

[0034] Working principle: The laser emitted from laser 1 is directed into collimating and expanding system 2. The collimated and expanded parallel beam is incident on a set of reflecting galvanometers. The reflected laser passes through aperture stop 4, which performs spatial filtering on the reflected laser to filter out non-main beams and stray light. It then propagates 25mm and is incident on the cascaded metasurface field mirror. Driven by the motor of the deflection device, the reflecting galvanometer can achieve angular deflection within a range of ±32°. By controlling the driving voltage, different angles of beam scanning can be achieved. The deflection angle of the galvanometer is proportional to the voltage. Laser beams with different incident angles are irradiated at different positions of the metasurface field mirror after passing through aperture stop 4. After the coordinated phase modulation of the two metasurfaces, the beams are finally focused on the working platform 30mm away from the metasurface field mirror, achieving a focusing effect for large-angle beams (0-32°).

[0035] See Figure 1 When the voltage applied to the two reflecting mirrors is 0, the laser emitted from the collimating and beam expanding system 2 is reflected by the two reflecting mirrors and spatially filtered by the aperture stop 4 before being vertically incident on the cascaded metasurface field mirror. After being modulated by the cascaded metasurface field mirror, it is focused on the working platform 8.

[0036] See Figure 2 When a certain voltage is applied to the two reflecting mirrors, the laser emitted from the collimating and expanding beam system 2 is deflected at a certain angle after being reflected by the two reflecting mirrors. After being spatially filtered by the aperture stop 4, it is incident on different positions of the cascaded metasurface field mirror. After being modulated by the cascaded metasurface field mirror, it is focused on different positions on the working platform 8. The deflection of the angle of the two reflecting mirrors is proportional to the applied voltage.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention 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 the present invention.

Claims

1. A field-lens laser scanning system based on cascaded metasurfaces, characterized in that, The system includes a laser and a collimating and beam expanding system, a laser deflecting galvanometer assembly, an aperture stop, a cascaded metasurface field mirror, and a working platform arranged sequentially along the laser's output beam path. The cascaded metasurface field mirror includes a first metasurface and a second metasurface arranged in parallel at intervals. Both the first and second metasurfaces include multiple nanopillar units arranged radially from their centers. Each nanopillar unit includes multiple nanopillars arranged circumferentially along the first or second metasurface. The nanopillar periods and / or heights of adjacent nanopillar units are different. The laser deflecting galvanometer assembly includes two reflecting galvanometers connected to the same deflection device, which can drive the two reflecting galvanometers to deflect synchronously.

2. The field lens laser scanning system based on cascaded metasurfaces according to claim 1, characterized in that, The adjustment angle of the reflecting mirror is adjusted by changing the driving voltage of the reflecting mirror. The mirror deflection angle is proportional to the voltage.

3. The field lens laser scanning system based on cascaded metasurfaces according to claim 1, characterized in that, The collimation and beam expansion system includes two convex lenses arranged along the outgoing optical path. The two convex lenses convert the diverging beam emitted by the laser into a parallel beam, and the diameter of the parallel beam is proportional to the ratio of the focal lengths of the two lenses.

4. The field lens laser scanning system based on cascaded metasurfaces according to claim 1, characterized in that, The collimating and beam expanding system includes a concave lens and a convex lens arranged along the outgoing optical path. The concave lens and the convex lens convert the diverging beam emitted by the laser into a parallel beam. The diameter of the parallel beam is proportional to the ratio of the focal lengths of the two lenses.

5. The field lens laser scanning system based on cascaded metasurfaces according to claim 1, characterized in that, The cascaded metasurface field mirror also includes a silicon substrate, with the first metasurface and the second metasurface fixed on opposite sides of the silicon substrate.

6. The field lens laser scanning system based on cascaded metasurfaces according to claim 1, characterized in that, The spacing between adjacent nanopillar units is different.

7. The field lens laser scanning system based on cascaded metasurfaces according to claim 1, characterized in that, The deflection angle of the reflecting mirror is 0-32°.

8. The field lens laser scanning system based on cascaded metasurfaces according to claim 1, characterized in that, The aperture stop has a diameter of 3 mm, the substrate thickness of the cascaded metasurface field mirror is 1 mm, the distance between the aperture stop and the cascaded metasurface field mirror is 25 mm, and the distance between the working platform plane and the cascaded metasurface field mirror is 30 mm.

9. A field lens laser scanning system based on cascaded metasurfaces according to claim 1, characterized in that, The working platform is a two-dimensional translation stage.

10. A scanning method using a cascaded metasurface-based field lens laser scanning system as described in any one of claims 1-9, comprising: emitting laser light from a laser, converting it into a parallel beam by a collimating and expanding system, then incident on a laser deflecting galvanometer group; after reflection by two reflecting mirrors of the laser deflecting galvanometer group, the light is filtered by an aperture stop and then incident on a cascaded metasurface field lens, and focused onto the working surface of a working platform by the field lens modulation.

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