Method and equipment for processing microstructure by controlling Bessel laser side lobe partition

Abstract

The application provides a method and equipment for processing microstructures by controlling Bessel laser side lobes, and is used for solving the problem that Bessel beam side lobe energy is not effectively utilized and it is difficult to realize high-quality and high-efficiency processing in the prior art. The application specifically comprises the following steps: in a first axial region, adjusting the number of sub-pulses of a burst pulse and laser power to determine first laser parameters that can make the main lobe process deep micro-holes and inhibit the side lobe processing; in a second axial region, adjusting corresponding parameters to determine second laser parameters that can make the main lobe and the side lobe processing region fuse to form a continuous Y-shaped groove; then, according to the obtained parameters, arch-shaped scanning is carried out in the two axial regions respectively, and high-depth-ratio micro-holes and micro-taper structure arrays are sequentially processed. The application realizes accurate control and utilization of Bessel side lobes by optimizing the parameters of Bessel burst pulses in different axial regions, and provides a technical scheme for high-performance manufacturing of special antireflection optical windows in aviation and aerospace.

Description

Technical Field

[0001] This invention relates to the field of ultrafast laser manufacturing of special optical windows for aviation and aerospace, and particularly to a method and equipment for processing microstructures by controlling the sidelobe partitions of a Bessel laser. Background Technology

[0002] Integrated, film-free antireflective optical windows based on microstructures have become key components of infrared detection systems for optoelectronic pods in next-generation aerospace and marine equipment. They effectively reduce Fresnel reflection and improve infrared transmittance by constructing a gradient refractive index layer through surface subwavelength microstructures. Since the microstructure and the window body are made of the same homogeneous material, this solves the problems of low mechanical strength, poor thermal stability, and insufficient environmental resistance caused by heterogeneous materials in traditional antireflective films. Currently, the manufacturing technology of such microstructured antireflective optical windows / glasses suitable for aerospace applications has become a cutting-edge research hotspot in the field of special optical windows.

[0003] Ultrafast laser processing technology is characterized by its ultrashort pulse duration (~10). -15 s), high peak power (>10 14 W / cm 2 The infrared detection window of an optoelectronic pod has a very large aperture (typically >50 mm), and its excellent three-dimensional processing accuracy makes it an ideal means of fabricating microstructures on the surface of optical windows. However, the infrared detection window of an optoelectronic pod has a very large aperture (typically >50 mm), requiring the fabrication of large-area, highly consistent microstructures in applications. Traditional ultrafast laser Gaussian beams have limited depth of focus, making them difficult to meet processing requirements. Using a conical lens to shape the Gaussian beam into a Bessel beam can significantly extend the depth of focus, providing a solution to the above problem.

[0004] Nevertheless, the use of ultrafast laser Bessel beams in the fabrication of antireflective microstructures for optical windows still has the following limitations: First, existing methods mainly utilize the frontmost region of the Bessel beam (where the main lobe energy is significantly higher than that of the side lobes) for processing, and suppress processing defects by avoiding the side lobe effect, thus failing to fully utilize the processing advantages of the long focal depth of the Bessel beam; Second, there is a lack of systematic research on the processing behavior and influence mechanism of the side lobes in different axial regions from the front to the back of the Bessel beam, and how to actively utilize the side lobes to participate in the formation of high-quality microstructures remains a technological gap. Summary of the Invention

[0005] To address the above problems, this invention proposes a method and equipment for fabricating microstructures by controlling the sidelobe partitioning of a Bessel laser. The core of this method lies in actively controlling the energy distribution characteristics and pulse sequence parameters of different regions along the axis of a Bessel beam based on a conical lens, thereby transforming the sidelobe energy, which is traditionally considered an interference, into a controllable processing resource, thus achieving the precise and efficient fabrication of microstructures with different functions.

[0006] To achieve the above objectives, the present invention provides a method for fabricating microstructures by controlling the sidelobe partitioning of a Bessel laser, characterized by comprising the following steps:

[0007] S1. After ultrasonic cleaning and drying, the optical window is placed on a three-axis motion platform and held in place by a clamp. The pitch stage is adjusted to make the laser beam perpendicular to the surface of the optical window.

[0008] S2. Turn on the high repetition rate ultrafast laser. The laser passes through the burst pulse generator and the Bessel shaping device in sequence. The focusing system focuses the laser. The laser is observed using a side-axis high-magnification metallographic microscope. The laser focusing position is adjusted by the three-axis motion platform to select the axial processing area of ​​the Bessel beam.

[0009] S3. Adjust the laser focusing position to the first axial region of the Bessel beam. The first axial region is the region where the beam energy is concentrated and the main lobe energy is higher than that of the side lobes. By adjusting the number of sub-pulses and the laser power of the burst pulse, determine a set of first laser parameters so that the main lobe can be processed into a deep micro-hole while the side lobes have no visible processing marks.

[0010] S4. Adjust the laser focusing position to the second axial region of the Bessel beam. The second axial region is the region where the beam energy is dispersed and the side lobe energy is close to the main lobe. By adjusting the number of sub-pulses and the laser power of the burst pulse, determine a set of second laser parameters so that the processing areas of the main lobe and the side lobe are fused together to form a continuous Y-shaped groove under these parameters.

[0011] S5. According to the first laser parameters, a bow-shaped scan is performed on the surface of the optical window using the first axial region of the Bessel beam to process a large-area high aspect ratio micro-hole array; according to the second laser parameters, a bow-shaped scan is performed using the second axial region of the Bessel beam, and adjacent Y-shaped grooves are connected to each other during the scanning process, thereby processing a micro-cone structure in one step.

[0012] Furthermore, the optical window material is zinc sulfide, sapphire, fused silica, or magnesium fluoride, and the material is polished on both sides.

[0013] Furthermore, the first axial region is close to the position where the beam energy is most concentrated, the number of sub-pulses of the first laser parameter is ≥4, and the depth-to-diameter ratio of the processed deep micro-hole is ≥1:1.

[0014] Furthermore, the second axial region is far from the position where the beam energy is most concentrated, and the number of sub-pulses of the second laser parameter is ≥2.

[0015] Furthermore, the equipment for fabricating microstructures using Bessel laser sidelobe partitioning control, employing the aforementioned method for fabricating microstructures using Bessel laser sidelobe partitioning control, includes the following components:

[0016] A high repetition rate ultrafast laser is used to output pulsed lasers, wherein the wavelength of the pulsed lasers can be selected from 515 nm, 800 nm or 1030 nm, and the pulse width is between 100 fs and 10 ps.

[0017] A burst pulse generator, the input of which is connected to the output optical path of the high repetition rate ultrafast laser, is used to modulate the pulsed laser into a burst pulse sequence containing 2 to 128 sub-pulses;

[0018] The Bessel shaping device, whose optical input end is coaxially arranged with the output end of the burst pulse generator, consists of a beam expander and a conical lens, and is used to shape the spatial distribution of laser energy from a Gaussian beam into a Bessel beam.

[0019] The focusing system, whose light input end is coaxially arranged with the output end of the Bessel shaping device, consists of a convex lens and an objective lens, and is used to focus the Bessel beam.

[0020] A rangefinder metallurgical microscope, set parallel to the focusing system, is used to observe the morphology of microstructures and determine the relative position of laser focusing;

[0021] The device includes a fixture, a pitch stage, and a three-axis motion platform. The fixture is fixed to the pitch stage, and the pitch stage is mounted on the three-axis motion platform. The fixture is used to fix and level the optical window and move it so that the focused Bessel beam is processed on the surface of the optical window along a specified trajectory.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention achieves precise control and utilization of the sidelobe effect by actively identifying and separately controlling two regions with different axial energy distribution characteristics of the Bessel beam (a first axial region with concentrated energy and a dominant main lobe, and a second axial region with dispersed energy and significant sidelobe effects), and matching them with targeted optimized burst pulse parameters. In the first axial region, the micro-aperture processed by the Bessel beam burst pulse exhibits a significantly improved aspect ratio and is defect-free, while micro-apertures processed using a traditional single-pulse Bessel beam show defects, primarily due to the sidelobes of the Bessel beam reaching the processing threshold. In the second axial region, the Bessel beam burst pulse only requires a single bow-shaped scan to process a micro-cone array structure, while traditional laser beams require two cross-bow-shaped scans. In summary, this method can efficiently and continuously fabricate two types of functionalized microstructures—deep micro-aperture arrays and micro-cone structures—with high quality within the same processing system by switching the beam's active region and corresponding laser parameters, improving the integration, efficiency, and process controllability of anti-reflective microstructure fabrication for optical window surfaces. The corresponding equipment system provides reliable hardware support for this method, ensuring the repeatability and accuracy of the processing.

[0024] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is a diagram of the equipment system for processing microstructures using Bessel laser sidelobe partitioning in an embodiment of the present invention;

[0026] Figure 2 This is the spatial energy field distribution of a Bessel beam based on a conical lens in an embodiment of the present invention;

[0027] Figure 3 These are microstructures processed by a single-pulse Bessel beam at different focusing positions in embodiments of the present invention;

[0028] Figure 4 This is the microstructure fabricated by Bessel laser sidelobe partitioning in the embodiments of the present invention;

[0029] Figure 5 This refers to a large-area antireflection microporous array manufactured in the embodiments of the present invention;

[0030] Figure 6 This refers to a large-area antireflective microcone array manufactured in the embodiments of the present invention;

[0031] Explanation of reference numerals in the attached figures: 1-High repetition rate ultrafast laser; 2-Burst pulse generator; 3-Bessel shaping device; 4-Focusing system; 5-Parallel-axis metallurgical microscope; 6-Optical window; 7-Clamp; 8-Tilting stage; 9-Triaxial motion platform. Detailed Implementation

[0032] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0033] To address the limitations of current ultrafast laser Bessel beam fabrication techniques for antireflective microstructures on optical window surfaces, which fail to fully utilize the long depth of focus and systematically control the sidelobe effect, this invention provides a method and equipment for fabricating microstructures using Bessel laser sidelobe partitioning. For example... Figure 1 As shown, the equipment system used in this embodiment of the invention mainly includes the following components: a high repetition rate ultrafast laser 1, used to output pulsed laser, the wavelength of which can be selected from 515 nm, 800 nm or 1030 nm, and the pulse width range is 100 fs to 10 ps; a burst pulse generator 2, whose input end is optically connected to the output end of the high repetition rate ultrafast laser 1, used to modulate the pulsed laser into a burst pulse sequence containing 2 to 128 sub-pulses; a Bessel shaping device 3, whose optical input end is coaxially arranged with the output end of the burst pulse generator 2, the device consisting of a beam expander and a conical lens, used to shape the spatial distribution of laser energy from a Gaussian beam to a Bessel beam; and a focusing system 4, whose optical input end is coaxially arranged with the output end of the Bessel shaping device 3, consisting of a convex lens and a... The system comprises an objective lens for focusing the Bessel beam; a rangefinder metallurgical microscope 5, set parallel to the focusing system 4, for real-time observation of the morphology of the processed microstructure and assisting in determining the relative position of the laser focus; a clamp 7, a pitch stage 8, and a three-axis motion platform 9, wherein the clamp 7 is fixedly mounted on the pitch stage 8, and the pitch stage 8 is mounted on the three-axis motion platform 9, together used to clamp and level the optical window 6 and drive it to perform movement, so that the focused Bessel beam can be processed on the surface of the optical window 6 according to a preset trajectory.

[0034] Figure 2 The typical laser energy distribution of a Bessel beam generated by a conical lens in its first and second axial regions is shown. The first axial region corresponds to a segment where beam energy is relatively concentrated, and the main lobe energy is significantly higher than the side lobes. In this region, if a single-pulse Bessel beam is used to process the zinc sulfide window at a focusing position of approximately 10 μm, a relatively large micropore can be formed. However, additional microstructures will also be generated around it due to the side lobes reaching the processing threshold, such as... Figure 3 As shown, the second axial region corresponds to the section where the beam energy is relatively dispersed and the energy density of the side lobes is close to that of the main lobe. Within this region, as the focusing position moves from 10 μm to 100 μm, the size of the microstructure formed by the main lobe processing gradually decreases, while the size of the microstructure formed by the side lobe processing gradually increases.

[0035] Based on the aforementioned physical phenomena, this embodiment utilizes the Bessel laser sidelobe partitioning and microstructure processing method to achieve high-quality fabrication of antireflective microstructures on the surface of zinc sulfide optical windows. The specific implementation steps are as follows:

[0036] First, the zinc sulfide window is ultrasonically cleaned and dried, then placed on a three-axis motion platform 9 and reliably held in place by a clamp 7. The elevation stage 8 is adjusted to ensure the laser beam is perpendicular to the window surface. Next, the high-repetition-rate ultrafast laser 1 is activated, and the laser beam passes sequentially through a burst pulse generator 2 and a Bessel shaping device 3, before being focused by a focusing system 4. The zinc sulfide window is then processed at different defocus positions using the three-axis motion platform 9, and real-time observation is performed using a paraxial high-magnification metallurgical microscope 5. The effective processing range of the Bessel beam in this embodiment is determined to be approximately 110 μm.

[0037] After defining the processing range, the zonal parameters were calibrated: first, the laser focusing position was adjusted to the first axial region of the Bessel beam (corresponding to axial position z=10 μm). By adjusting the number of sub-pulses of the burst pulse to 10 and the laser power to 215 mW, the main lobe was able to process deep micropores, while the side lobes did not produce any processing marks visible under a microscope. This result is as follows: Figure 4 As shown. Next, the laser focusing position is adjusted to the second axial region of the Bessel beam (corresponding to the axial position z=90 μm). By adjusting the number of sub-pulses of the burst pulse to 8 and the laser power to 183 mW, the processing areas of the main lobe and the side lobe are merged to form a continuous Y-shaped groove structure.

[0038] Finally, scanning processing is performed based on the calibrated laser parameters: on the surface of the zinc sulfide window, a bow-shaped scan is performed using the first axial region of the Bessel beam and corresponding parameters to process a large-area, high aspect ratio micro-hole array, such as... Figure 5 As shown. Using the second axial region of the Bessel beam and corresponding parameters, a bow-shaped scan is also performed. Adjacent Y-shaped structures are connected in a single scan, thus fabricating a large-area micro-cone array structure, such as... Figure 6 As shown.

[0039] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technical principles disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for fabricating microstructures by controlling the sidelobe regions of a Bessel laser, used for fabricating anti-reflective optical windows, characterized in that... Includes the following steps: S1. After ultrasonic cleaning and drying, the optical window is placed on a three-axis motion platform and held in place by a clamp. The pitch stage is adjusted to make the laser beam perpendicular to the surface of the optical window. S2. Turn on the high repetition rate ultrafast laser. The laser passes through the burst pulse generator and the Bessel shaping device in sequence. The focusing system focuses the laser. The laser is observed using a side-axis high-magnification metallographic microscope. The laser focusing position is adjusted by the three-axis motion platform to select the axial processing area of ​​the Bessel beam. S3. Adjust the laser focusing position to the first axial region of the Bessel beam. The first axial region is the region where the beam energy is concentrated and the main lobe energy is higher than that of the side lobes. By adjusting the number of sub-pulses and the laser power of the burst pulse, determine a set of first laser parameters so that the main lobe can be processed into a deep micro-hole while the side lobes have no visible processing marks. S4. Adjust the laser focusing position to the second axial region of the Bessel beam. The second axial region is the region where the beam energy is dispersed and the side lobe energy is close to the main lobe. By adjusting the number of sub-pulses and the laser power of the burst pulse, determine a set of second laser parameters so that the processing areas of the main lobe and the side lobe are fused together to form a continuous Y-shaped groove under these parameters. S5. According to the first laser parameters, a bow-shaped scan is performed on the surface of the optical window using the first axial region of the Bessel beam to process a large-area high aspect ratio micro-hole array; according to the second laser parameters, a bow-shaped scan is performed using the second axial region of the Bessel beam, and adjacent Y-shaped grooves are connected to each other during the scanning process, thereby processing a micro-cone structure in one step.

2. The method for fabricating microstructures by controlling the sidelobe partitions of a Bessel laser according to claim 1, characterized in that, In step S1, the optical window material is zinc sulfide, sapphire, fused silica or magnesium fluoride, and the material is polished on both sides.

3. The method for fabricating microstructures by controlling the sidelobe partitions of a Bessel laser according to claim 1, characterized in that, In step S3, the first axial region is close to the position where the beam energy is most concentrated, the number of sub-pulses of the first laser parameter is ≥4, and the depth-to-diameter ratio of the processed deep micro-hole is ≥1:

1.

4. The method for fabricating microstructures by controlling the sidelobe partitions of a Bessel laser according to claim 1, characterized in that, In step S4, the second axial region is far from the position where the beam energy is most concentrated, and the number of sub-pulses of the second laser parameter is ≥2.

5. Equipment for processing microstructures by controlling the sidelobe regions of a Bessel laser, characterized in that, The method for fabricating microstructures using Bessel laser sidelobe partitioning as described in claim 1 comprises the following components: A high repetition rate ultrafast laser for outputting pulsed lasers, wherein the wavelength of the pulsed laser can be selected from 515 nm, 800 nm or 1030 nm, and the pulse width is between 100 fs and 10 ps. A burst pulse generator, the input of which is connected to the output optical path of the high repetition rate ultrafast laser, is used to modulate the pulsed laser into a burst pulse sequence containing 2 to 128 sub-pulses; The Bessel shaping device, whose optical input end is coaxially arranged with the output end of the burst pulse generator, consists of a beam expander and a conical lens, and is used to shape the spatial distribution of laser energy from a Gaussian beam into a Bessel beam. The focusing system, whose light input end is coaxially arranged with the output end of the Bessel shaping device, consists of a convex lens and an objective lens, and is used to focus the Bessel beam. A rangefinder metallurgical microscope, set parallel to the focusing system, is used to observe the morphology of microstructures and determine the relative position of laser focusing; The device includes a fixture, a pitch stage, and a three-axis motion platform. The fixture is fixed to the pitch stage, and the pitch stage is mounted on the three-axis motion platform. The fixture is used to fix and level the optical window and move it so that the focused Bessel beam is processed on the surface of the optical window along a specified trajectory.

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