A two-step processing method for optical component surface microstructure based on femtosecond laser

Abstract

The present invention provides a two-step processing method for the surface microstructure of an optical element based on a femtosecond laser, and belongs to the field of engineering optical technology. In order to solve the problem that there is a lack of processing methods for the microstructure of the surface of an optical element in the prior art, a femtosecond laser is used to process the surface of an optical element for microstructure, which often has the problem of large roughness. The method of the present invention comprises the following steps: drawing a processing trajectory image according to the microstructure processing requirements, clamping the optical element to be processed on a processing platform and accurately positioning it; adjusting the laser light path to an infrared femtosecond laser, importing the processing trajectory image into a processing system, setting processing parameters to perform femtosecond laser processing on the optical element, and obtaining an initial microstructure; moving the processing platform under a galvanometer system, adjusting the laser light path to an ultraviolet femtosecond laser, setting processing parameters, and performing flexible polishing on the initial microstructure to obtain a final microstructure. The surface microstructure of the optical element obtained by the method of the present invention has high quality.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering optics, and in particular to a two-step processing method for the surface microstructure of an optical element based on a femtosecond laser. Background Art

[0002] The surface microstructure of optical components is widely used in optical communication, optical signal processing, light field control, laser confinement fusion and other fields due to its good imaging performance and the advantages of miniaturization and lightness. In particular, the various special functions of organisms are caused by the different shapes, sizes and arrangements of the micro-nano structures on their surfaces. Therefore, research on bionic engineering has been carried out to process different structures on the surface of optical components to achieve hydrophilic / hydrophobic surface modification and process optical compound eyes for military equipment research and development. In addition, fields such as integrated circuits, optical waveguides and new energy are also highly dependent on the preparation of micro-nano structures. The research results on the surface microstructure of optical components reveal the physical mechanism of material modification at the microscopic scale. As a cutting-edge technology in modern manufacturing, the importance of microstructure preparation is self-evident.

[0003] At present, microstructure processing methods mainly include: optical etching, plasma etching, vapor deposition, template method, etc. It is difficult to process microstructures on the surface of hard and brittle optical components. Scholars at home and abroad have proposed different methods for processing microstructures. Currently, the more commonly used method is micro-milling using tiny tools. This method is difficult to process tiny structures due to tool limitations, and the hardness and brittleness of the components have also become an obstacle to the development of micro-milling methods; CO 2 Although the laser processing method overcomes the influence of the hard and brittle optical component material itself, its laser spot is large, it cannot process tiny structures, and the processing efficiency is low.

[0004] Femtosecond lasers have revolutionized material processing with their unique characteristics of ultrashort pulse width and extremely high peak intensity. Short pulse width suppresses the formation of heat-affected zones, which is critical for ultra-high precision manufacturing, while high peak intensity allows the induction of nonlinear interactions such as multiphoton absorption and tunneling ionization in transparent materials, which provides versatility in processable materials. Femtosecond laser processing has the following advantages: (1) The instantaneous power is extremely high. The peak power of the laser pulse after multi-stage chirp amplification can reach 10 15 W, power density exceeds 10 21 W / cm 2, which is hundreds of times the total power generated in the world. (2) The damage area of ​​femtosecond laser is stable. The damage of femtosecond laser is mainly determined by multi-photon ionization. Its power density reaches the ionization threshold only in a very small area around the center of the spot. Therefore, the irradiation damage range of the surface of the material is stable. (3) High processing accuracy. Femtosecond laser breaks the diffraction limit with its ultra-short pulse and can perform ultra-fine processing of materials at sub-micron or even nanometer scales. (4) Small thermal effect. The pulse width of femtosecond laser is much smaller than the energy relaxation time, so the lattice is not heated up by the electroacoustic interaction. The temperature in the action area will not increase significantly, and the thermal effect of damage can be ignored. Femtosecond laser processing technology does not require strict environmental factors, does not involve chemical reagents and sample contamination in the preparation process, and is widely applicable to a variety of dielectric transparent materials. Since the microstructure roughness of the surface of optical components is relatively large when femtosecond laser is used for microstructure processing on the surface of optical components, the application of femtosecond laser for microstructure processing on the surface of hard and brittle optical components is greatly limited. Therefore, there is an urgent need for a method for microstructure processing on the surface of optical components based on femtosecond laser to achieve precise microstructure processing on the surface of optical components with low roughness. Summary of the invention

[0005] The technical problems to be solved by the present invention are:

[0006] The prior art lacks a method for processing microstructures on the surface of optical components, and the use of femtosecond lasers to process microstructures on the surface of optical components often results in a problem of large roughness.

[0007] The present invention adopts the following technical solutions to solve the above technical problems:

[0008] The present invention provides a two-step processing method for the surface microstructure of an optical element based on femtosecond laser. The method is based on a femtosecond laser processing system. The laser of the femtosecond laser processing system includes an infrared femtosecond laser path and an ultraviolet femtosecond laser path. The femtosecond laser processing system is provided with a galvanometer system. The method comprises the following steps:

[0009] S1. Draw a processing trajectory image according to the processing requirements of the surface microstructure of the optical element, clamp the optical element to be processed on the processing platform, and accurately position the element;

[0010] S2, adjusting the laser optical path to an infrared femtosecond laser, importing the processing trajectory image into the processing system, setting processing parameters, and performing femtosecond laser processing on the optical element according to the processing trajectory to obtain an initial microstructure;

[0011] S3. Move the processing platform under the galvanometer system, adjust the laser light path to ultraviolet femtosecond laser, set the processing parameters, perform flexible polishing on the initial microstructure, and obtain the final microstructure.

[0012] Furthermore, the wavelength of the S2 mid-infrared femtosecond laser is 1030 nm.

[0013] Furthermore, the wavelength of the ultraviolet femtosecond laser in S3 is 257 nm.

[0014] Furthermore, the microstructure is a pyramidal microstructure with a diameter of 100 μm and a depth of 50 μm.

[0015] Furthermore, S2 comprises the following steps:

[0016] S21, adjusting the laser optical path to an infrared femtosecond laser, setting the infrared laser wavelength, and determining the laser processing focal plane at the wavelength;

[0017] S22, importing the processing trajectory image into a processing system and setting processing parameters;

[0018] S23, moving the component to the processing center, and performing femtosecond laser processing on the optical component according to the processing trajectory. During the processing, after each layer is processed, check whether the focal plane is offset. If offset occurs, re-determine the focal plane until the processing is completed;

[0019] S24. After the processing is completed, the characteristic morphology of the processed area is observed. If the expected processing effect is achieved, the processing is completed. If the expected effect is not achieved, the previous steps are repeated to perform the processing operation to obtain the initial microstructure.

[0020] Furthermore, setting the processing parameters in S22 includes setting the laser frequency, single pulse energy and scanning speed, wherein the scanning speed is 5 mm / s.

[0021] Furthermore, S3 comprises the following steps:

[0022] S31, moving the processing platform under the galvanometer system, adjusting the laser optical path to ultraviolet femtosecond laser, setting the infrared laser wavelength, and determining the laser processing focal plane at the wavelength;

[0023] S32, setting processing parameters;

[0024] S33, moving the component to a machining center, and performing flexible polishing on the initial microstructure according to the machining trajectory to obtain a final microstructure.

[0025] Furthermore, the S32 setting of processing parameters includes setting laser frequency, single pulse energy and galvanometer scanning speed, wherein the galvanometer scanning speed is 45 mm / s.

[0026] Furthermore, in S1, the optical element to be processed is ultrasonically cleaned and then clamped to the processing platform.

[0027] White light interferometry was used to detect the surface roughness of the initial microstructure and the final microstructure.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention discloses a two-step processing method for the surface microstructure of an optical element based on a femtosecond laser. The femtosecond laser is used to process the surface of the optical element in two steps. First, an infrared femtosecond laser with a large absorption rate of the optical element is used to perform preliminary processing on the element to obtain an initial microstructure. Then, an ultraviolet femtosecond laser with a small absorption rate of the optical element is used to perform flexible polishing on the initial microstructure to reduce the roughness of the side wall of the microstructure, thereby obtaining a microstructure with better quality and improving the quality of the microscopic morphology of the microstructure processed by the femtosecond laser.

[0030] Second, the method of the present invention can realize "cold processing" of the microstructure on the surface of the optical element, which can avoid the influence of other factors such as thermal stress on the element after processing; according to the characteristics of the femtosecond laser method, the method of the present invention can realize stable and high-precision processing of the optical element, and obtain a microstructure with higher precision, and the error between the theoretical processing size is smaller;

[0031] 3. The infrared and ultraviolet femtosecond laser processing of the method of the present invention is carried out on a processing platform and at the same processing position. There is no need to disassemble components, which improves processing efficiency and reduces the risk of component damage due to component disassembly. The entire processing process is simple and easy to achieve large-scale processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of a two-step processing method of a surface microstructure of an optical element based on a femtosecond laser in an embodiment of the present invention;

[0033] Figure 2 A schematic diagram of a femtosecond laser processing system in an embodiment of the present invention;

[0034] Figure 3 A white light interferometer image of the surface microstructure of an optical element obtained in an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of a processing trajectory in an embodiment of the present invention;

[0036] Figure 5 Schematic diagram of infrared and ultraviolet femtosecond laser processing in an embodiment of the present invention;

[0037] Figure 6 It is a comparison diagram of two-step microstructure processing in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] In the description of the present invention, it should be noted that the terminology nouns in the various embodiments, such as "up", "down", "front", "back", "left", "right", etc., which indicate directions, are only for simplifying the description of the positional relationship based on the drawings in the specification, and do not mean that the referred elements and devices must be operated according to the specific directions and defined operations and methods and structures in the specification. Such directional nouns do not constitute a limitation on the present invention.

[0039] In the description of the present invention, it should be noted that the terms "first", "second", and "third" mentioned in the embodiments of the present invention are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features.

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0041] like Figure 1 As shown in FIG. 1 , the present invention provides a two-step processing method for the surface microstructure of an optical element based on a femtosecond laser. The femtosecond laser processing system of the method of the present invention adopts the femtosecond laser processing experimental system in the cited document [1], including: a femtosecond laser generator, a laser transmission and focusing lens group, a displacement platform system and a paraxial observation system; the schematic diagram of the processing system is shown in FIG. Figure 2 As shown; the optical element used is a fused quartz optical element with a specification of 50mm×50mm×10mm;

[0042] like Figure 4 and Figure 5 As shown, the surface microstructure of the optical element to be processed is a cone structure with a diameter of 100 μm and a depth of 50 μm. A CAD image of the processing trajectory is drawn according to the processing requirements of the microstructure. Specifically, the cone angle α=20° and the depth of each layer Δh=1.7 μm are set, and then the processing radius of each layer ΔR=cotα×Δh is obtained.

[0043] Start the femtosecond laser processing system, clamp the optical component to be processed on the processing platform, observe the component through the CCD camera of the paraxial observation system, and accurately position the component; adjust the infrared femtosecond laser in the laser optical path, and set the wavelength of the infrared femtosecond laser to 1030nm; determine the laser processing focal plane at this wavelength, specifically, use the parameters of laser frequency of 20KHz and single pulse energy of 2μJ to determine the processing focal plane on the silicon wafer.

[0044] The CAD image of the processing trajectory is imported into the processing system, and the processing parameters are set, including setting the laser frequency to 500KHz, the single pulse energy to 2μJ, and the scanning speed to 5mm / s. The component is moved to the processing center, and the optical component is processed by femtosecond laser according to the processing trajectory. During the processing, after each layer is processed, it is checked whether the focal plane is offset. If offset occurs, the focal plane is re-determined until the processing is completed.

[0045] After processing is completed, the characteristic morphology of the processing area is observed through the CCD camera of the paraxial observation system. If the expected processing effect is achieved, the processing is completed. If the expected effect is not achieved, the previous steps are repeated to obtain the initial microstructure.

[0046] The initial microstructure was measured using white light interferometry and the surface roughness after high-pass filtering was 34 nm.

[0047] Move the processing platform under the galvanometer system, adjust the laser optical path to ultraviolet femtosecond laser, and set the wavelength of the ultraviolet femtosecond laser to 257nm; determine the laser processing focal plane at this wavelength, specifically: use the parameters of laser frequency of 20KHz and single pulse energy of 2μJ to determine the processing focal plane on the silicon wafer.

[0048] Set the processing parameters, including setting the laser frequency to 40KHz, the single pulse energy to 2μJ, and the galvanometer scanning speed to 45mm / s;

[0049] The component is moved to the machining center, and the initial microstructure is flexibly polished according to the machining trajectory to obtain the final microstructure.

[0050] like Figure 3 As shown, the surface roughness of the final microstructure measured by white light interferometry after high-pass filtering is 13.69 nm, and the surface quality is improved by nearly 60%.

[0051] like Figure 6 As shown, the method of the present invention firstly adopts infrared femtosecond laser processing to obtain the initial microstructure, and then adopts ultraviolet femtosecond laser to perform flexible polishing on the microstructure, which can greatly improve the quality of the microstructure and provide a high-precision and efficient processing method for improving the surface microstructure processing of optical elements.

[0052] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

[0053] The cited literature of the present invention is: [1] Ding Ye. Research on femtosecond laser preparation technology of functional microstructure on the surface of alloy materials. Wanfang Platform, 2020-12-03.

Claims

1. A two-step processing method for the surface microstructure of an optical element based on femtosecond laser, the method is based on a femtosecond laser processing system, the laser of the femtosecond laser processing system includes an infrared femtosecond laser path and an ultraviolet femtosecond laser path, and the femtosecond laser processing system is provided with a galvanometer system, characterized in that The method comprises the following steps: S1. Draw a processing trajectory image according to the processing requirements of the surface microstructure of the optical element. The microstructure is a cone microstructure with a diameter of 100 μm and a depth of 50 μm. The processing trajectory is drawn by setting the cone angle α=20° and the layer depth Δh=1.7 μm. The processing radius of each layer ΔR=cotα×Δh is obtained, and the optical element to be processed is clamped on the processing platform, and the element is accurately positioned; S2, adjusting the laser optical path to infrared femtosecond laser, importing the processing trajectory image into the processing system, setting processing parameters, and performing femtosecond laser processing on the optical element according to the processing trajectory to obtain an initial microstructure; comprising the following steps: S21, adjusting the laser optical path to an infrared femtosecond laser, setting the infrared laser wavelength, and determining the laser processing focal plane at the wavelength; S22, import the processing trajectory image into the processing system, set the processing parameters, including setting the laser frequency, single pulse energy and setting the scanning speed to 5mm / s S23, moving the component to the processing center, and performing femtosecond laser processing on the optical component according to the processing trajectory. During the processing, after each layer is processed, check whether the focal plane is offset. If offset occurs, re-determine the focal plane until the processing is completed; S24, after the processing is completed, the characteristic morphology of the processing area is observed. If the expected processing effect is achieved, the processing is completed. If the expected effect is not achieved, the previous steps are repeated to perform the processing operation to obtain an initial microstructure; S3, moving the processing platform under the galvanometer system, adjusting the laser light path to ultraviolet femtosecond laser, setting processing parameters, and performing flexible polishing on the initial microstructure to obtain the final microstructure; comprising the following steps: S31, moving the processing platform under the galvanometer system, adjusting the laser optical path to ultraviolet femtosecond laser, setting the wavelength of the ultraviolet laser, and determining the laser processing focal plane under the wavelength; S32, setting processing parameters, including setting laser frequency, single pulse energy and setting the galvanometer scanning speed to 45 mm / s; S33, moving the component to a machining center, and performing flexible polishing on the initial microstructure according to the machining trajectory to obtain a final microstructure.

2. The two-step processing method of optical element surface microstructure based on femtosecond laser according to claim 1, characterized in that The wavelength of the S2 mid-infrared femtosecond laser is 1030nm.

3. The two-step processing method of optical element surface microstructure based on femtosecond laser according to claim 2, characterized in that The wavelength of the ultraviolet femtosecond laser in S3 is 257nm.

4. The two-step processing method of optical element surface microstructure based on femtosecond laser according to claim 1, characterized in that In S1, the optical element to be processed is ultrasonically cleaned and then clamped to the processing platform.

5. The two-step processing method of optical element surface microstructure based on femtosecond laser according to claim 1, characterized in that White light interferometry was used to detect the surface roughness of the initial microstructure and the final microstructure.

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