Optical element applied to Gaussian laser homogenization and design method thereof

Abstract

The invention relates to the technical field of laser, in particular to an optical element applied to Gaussian laser homogenization and a design method of the optical element. The method specifically comprises the steps of determining technical input of a Gaussian laser homogenization system, determining an arrangement mode of a metasurface array on an optical element, designing a nano-structure unit according to the wavelength of input Gaussian laser, determining an incident plane nano-brick steering angle of a nano-brick on a laser incident plane, and determining a super-structure unit according to the incident plane nano-brick steering angle. The intensity distribution of the homogenized Gaussian laser is determined according to the technical input of the Gaussian laser homogenization system, and the emergent surface nano brick steering angles of the nano bricks at different positions on the laser emergent surface are calculated according to the intensity distribution of the homogenized Gaussian laser and the intensity of the input Gaussian laser. Therefore, the super-structure surface device for realizing Gaussian laser homogenization is obtained. Point-by-point modulation of intensity is realized by changing the steering angle of the nano-structure unit, and finally, high-efficiency and high-performance homogenization of Gaussian laser is realized on the premise of ensuring that wave aberration is not introduced in the homogenization process of the Gaussian laser.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser technology, in particular to an optical element applied to Gaussian laser homogenization and a design method thereof. BACKGROUND

[0002] Laser is a widely used technology, covering all aspects of national security, enterprise production and social life, and therefore has extremely important research significance and value. Generally, the laser generated by a fiber laser is Gaussian distribution, which is related to the position and presents a situation of high center and low periphery. However, in many precision machining, optical imaging detection, medical beauty and other application scenarios, the unevenness of laser energy will introduce many problems, such as different machining sizes, reduced precision, increased safety risks and the like, and therefore it is necessary to shape the Gaussian distributed laser and homogenize its intensity distribution.

[0003] There are various existing laser homogenization schemes, which can be summarized as follows: one is a laser homogenization scheme based on diffractive optical elements, which re-modulates the energy distribution of the incident laser by selecting a specially designed lens array combination to achieve energy homogenization in the far field; two is a laser homogenization scheme based on refractive optical elements, which designs the optical parameters of the refractive element to divide the incident laser into multi-order / lateral diffraction light by using the characteristics of the refractive element, and realizes the purpose of beam homogenization by interference superposition in the far field; three is a laser homogenization scheme based on the principle of diffuse reflection, which realizes the homogenization of laser by multiple diffuse reflections.

[0004] Although the above-mentioned schemes realize the homogenization of laser, there are still a series of problems in actual use: first, the device integration is not high, the optical path is complex, and there are many optical elements, which cannot be used in application scenarios with high integration requirements; second, the optical system stability introduced by multiple optical elements is insufficient, the incident angle of the incident laser is relatively sensitive, and the use environment of the optical system has a greater impact on the homogenization efficiency; finally, especially in application scenarios with special requirements for laser wavefront, such as Hartmann wavefront detection system, the laser homogenization scheme based on diffractive / refractive / diffuse reflection optical elements will inevitably introduce wave aberration, resulting in a large deviation between the measurement result and the actual value, and an optimized Gaussian laser homogenization technology is urgently needed to solve the above technical difficulties. SUMMARY

[0005] Based on the above, the purpose of the present application is to solve the technical problem that the wave aberration is introduced by the laser homogenization scheme based on the diffraction / reflection / diffuse reflection optical element in the Gaussian laser wavefront detection system, and an optical element design method applied to Gaussian laser homogenization is proposed, which selects a metasurface with precise control ability for the incident wave front as a technical platform, carries out optical element design work according to the laser homogenization requirement of Gaussian laser, realizes point-by-point modulation of intensity by changing the steering angle of the nano structure unit, and finally realizes efficient and high-performance homogenization of Gaussian laser under the premise of ensuring that the Gaussian laser homogenization process does not introduce wave aberration.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] An optical element design method applied to Gaussian laser homogenization, comprising the following steps:

[0008] Determine the wavelength, beam size, intensity of the input Gaussian laser and the size of the region to be homogenized;

[0009] Determine the arrangement mode of the metasurface array on the optical element, the metasurface array is composed of a plurality of nano structure units arranged in two dimensions, each nano structure unit includes a nano brick and a base working surface, the base working surface is divided into a laser incident surface and a laser exit surface, a nano brick is arranged on each of the laser incident surface and the laser exit surface, the steering angle of the nano brick on each laser incident surface is the incident surface nano brick steering angle, and the steering angle of the nano brick on each laser exit surface is the exit surface nano brick steering angle;

[0010] According to the wavelength of the input Gaussian laser, the design of the nano structure unit is carried out, the material of the nano structure unit is selected, and when the linearly polarized light is vertically incident on the nano structure unit of the metasurface array, the extinction performance of the exit linearly polarized light is used as the optimization object by using an electromagnetic simulation tool, so that the structure parameters of the nano structure unit with the highest efficiency of exit co-linearly polarized light and the lowest efficiency of exit orthogonal linearly polarized light are obtained;

[0011] Determine the incident surface nano brick steering angle of the nano brick on the laser incident surface;

[0012] According to the size of the region to be homogenized of the input Gaussian laser, the intensity distribution after Gaussian laser homogenization is determined, and the exit surface nano brick steering angle of the nano brick at different positions on the laser exit surface is calculated according to the intensity distribution after Gaussian laser homogenization and the intensity of the input Gaussian laser.

[0013] As a preferred scheme of the design method of the optical element applied to Gaussian laser homogenization, the x-axis and the y-axis are respectively set as the directions parallel to the two edges of the substrate working surface, and the xoy coordinate system is established with the center of the super-structured surface array as the origin, and the nanobrick is coincided with the projection of the center of the substrate working surface on the xoy plane.

[0014] As a preferred scheme of the design method of the optical element applied to Gaussian laser homogenization, the size parameters of the nano-structure unit include the long axis L, the short axis W and the height H of the nanobrick and the size of the substrate working surface edge length C, the height H is perpendicular to the long axis L and the short axis W, and the long axis L is not equal to the short axis W.

[0015] As a preferred scheme of the design method of the optical element applied to Gaussian laser homogenization, the long axis L and the short axis W are arranged on the plane parallel to the nanobrick and the substrate working surface, and the turning angle is the included angle between the long axis L of the nanobrick and the positive direction of the x-axis.

[0016] As a preferred scheme of the design method of the optical element applied to Gaussian laser homogenization, as a preferred scheme of the design method of the optical element applied to Gaussian laser homogenization, the incident plane nanobrick turning angles of the nanobricks at different positions on the laser incident surface are the same and are constant values.

[0017] As a preferred scheme of the design method of the optical element applied to Gaussian laser homogenization, the exit plane nanobrick turning angles of the nanobricks at different positions on the laser exit surface are:

[0018]

[0019] In the formula, θ1(x, y) is the exit plane nanobrick turning angle, I lim is the intensity distribution after Gaussian laser homogenization, I inc (x, y) is the intensity of the input Gaussian laser.

[0020] An optical element applied to Gaussian laser homogenization, wherein the super-structured surface device is obtained according to the design method of the optical element applied to Gaussian laser homogenization.

[0021] The beneficial effects of the present application are:

[0022] In view of the technical problem that the laser homogenization scheme based on diffraction / refraction / diffuse reflection optical elements in a Gaussian laser wavefront detection system will introduce wave aberration, a design method of optical elements applied to Gaussian laser homogenization is provided, the method selects a superstructure surface with precise control ability on the incident wavefront as a technical platform, carries out optical element design work according to the Gaussian laser homogenization requirement, realizes point-by-point modulation of intensity by changing the steering angle of the nano structure unit, and finally realizes efficient and high-performance homogenization of Gaussian laser under the premise of ensuring that the Gaussian laser homogenization process does not introduce wave aberration. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments of the present application will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the contents of the embodiments of the present application and the drawings.

[0024] Figure 1 is a schematic diagram of the superstructure surface array arrangement in the optical element in the embodiments of the present application;

[0025] Figure 2 is a structural schematic diagram of the nano structure unit of the superstructure surface array in the optical element in the embodiments of the present application;

[0026] Figure 3 is the scanning optimization result of the structural parameters of the nano structure unit in the embodiments of the present application;

[0027] Figure 4 is the laser intensity distribution diagram before and after the optical element carries out Gaussian laser homogenization in the embodiments of the present application.

[0028] DRAWINGS:

[0029] 1-nanobrick; 2-base working surface. DETAILED DESCRIPTION

[0030] The present application will be further described in detail below in combination with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that, in order to facilitate the description, only the parts related to the present application are shown in the drawings, but not all the structures.

[0031] In the description of the present application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0032] In the present application, unless otherwise explicitly specified and limited, "on" or "under" the first feature of the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "above" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0033] In the description of the present embodiment, the terms "up", "down", "left", "right" and other orientation or position relationships are based on the orientation or position relationship shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more. In addition, the terms "first", "second" are only used to distinguish in the description, and have no special meaning.

[0034] A design method of an optical element applied to Gaussian laser homogenization, applied to a Gaussian laser homogenization system, comprising the following steps:

[0035] S1, determining the technical input of the Gaussian laser homogenization system, including inputting the wavelength λ of the Gaussian laser inc , inputting the beam size L inc ×L inc of the Gaussian laser inc (x, y), inputting the size L lim ×L lim of the Gaussian laser homogenization region to be homogenized;

[0036] S2, determining the arrangement mode of the superstructure surface array on the optical element, such as Figure 1As shown, the metasurface array consists of multiple two-dimensional periodically arranged nanostructure units. Each nanostructure unit includes a nanobrick 1 and a substrate working surface 2. The substrate working surface 2 is divided into a laser incident surface and a laser exit surface. A nanobrick 1 is disposed on both the laser incident surface and the laser exit surface. The turning angle θ of the nanobrick 1 on each laser incident surface is the incident surface nanobrick turning angle θ0(x, y), and the turning angle θ of the nanobrick 1 on each laser exit surface is the exit surface nanobrick turning angle θ1(x, y). Figure 1 The image on the inner left is a side view of the metasurface array. Figure 1 The image in the middle shows the arrangement of nano-bricks 1 on the laser incident surface. Figure 1 The inner right side shows the arrangement of nano-bricks 1 on the laser emission surface;

[0037] S3. Based on the wavelength λ of the input Gaussian laser. inc The design of nanostructure units was carried out, the materials of the nanostructure units were selected, and electromagnetic simulation tools were used to simulate and optimize the nanostructure units in the metasurface array based on linearly polarized light to obtain the structural parameters of the nanostructure units. Using electromagnetic simulation tools, when linearly polarized light is incident perpendicularly on the nanostructure units on the metasurface array, the extinction performance of the emitted linearly polarized light is used as the optimization object to obtain the structural parameters of the nanostructure units with the highest efficiency of emitted linearly polarized light in the same direction and the lowest efficiency of emitted linearly polarized light.

[0038] S4. Determine the incident surface nanobrick 1's orientation angle θ0(x, y) on the laser incident surface;

[0039] S5. Based on the size L of the region to be homogenized by the input Gaussian laser... lim ×L lim Determine the intensity distribution after Gaussian laser homogenization I lim Intensity distribution I after Gaussian laser homogenization lim and the intensity I of the input Gaussian laser inc (x, y) Calculate the nanobrick turning angle θ1(x, y) of the nanobrick 1 at different positions on the laser emission surface.

[0040] Preferably, such as Figure 2 As shown, the x-axis and y-axis are defined as the directions parallel to the two sides of the substrate working surface 2, respectively. An xoy coordinate system is established with the center of the metasurface array as the origin. The projections of the nanobrick 1 and the corresponding center of the substrate working surface 2 onto the xoy plane coincide. The intensity I of the input Gaussian laser is... inc The xoy coordinate system is used to calculate the turning angles of the nanobricks at different positions on the laser emission surface, including (x, y) and θ1(x, y).

[0041] Specifically, refer again Figure 2The size parameters of the nano-structure unit include the length L, the width W and the height H of the nano-brick 1, and the length C of the working surface 2 of the substrate, the height H is perpendicular to the length L and the width W, and the length L is not equal to the width W. The length L and the width W are arranged on the plane parallel to the nano-brick 1 and the working surface 2 of the substrate, and the turning angle θ is the included angle between the length L of the nano-brick 1 and the positive direction of the x-axis.

[0042] More specifically, in step S3, the outgoing co-directional linearly polarized light refers to the vibration direction of the outgoing linearly polarized light being the same as the vibration direction of the incoming linearly polarized light; and the outgoing orthogonal linearly polarized light refers to the vibration direction of the outgoing linearly polarized light being perpendicular to the vibration direction of the incoming linearly polarized light.

[0043] Further, in the foregoing, the “super-structure array is composed of a plurality of nano-structure units arranged in a two-dimensional periodic manner” refers to that the nano-structure units are arranged in a fixed period in the x-axis and y-axis directions, and the period is equal to the length C of the working surface 2 of the substrate.

[0044] Further, the size of the super-structure array composed of the plurality of nano-structure units arranged in a two-dimensional periodic manner is matched with the beam size L inc ×L inc of the input Gaussian laser, and the specific number of the nano-structure units is calculated accordingly.

[0045] Specifically, the nano-brick turning angle θ0(x, y) of the nano-brick 1 at different positions on the laser incidence surface is the same and a constant value.

[0046] Further, the nano-brick turning angle θ1(x, y) of the nano-brick 1 at different positions on the laser incidence surface is calculated according to the intensity distribution I lim of the homogenized Gaussian laser and the intensity I inc (x, y) of the input Gaussian laser, and is:

[0047]

[0048] In the formula, θ1(x, y) is the nano-brick turning angle on the incidence surface, I lim is the intensity distribution of the homogenized Gaussian laser, and I inc (x, y) is the intensity of the input Gaussian laser.

[0049] An optical element applied to Gaussian laser homogenization, wherein the super-structure device is obtained according to the design method of the optical element applied to Gaussian laser homogenization in any one of the above.

[0050] Preferably, the metasurface device embeds wave aberration correction in the design through electromagnetic simulation software, which can calculate a nanometer structure unit arrangement scheme that can achieve homogenization without introducing wave aberration. Since the nanometer structure unit is subwavelength, it can suppress high-order diffraction, all energy is concentrated in the designed zero-order diffraction, the efficiency is high, there is no stray light and high-order noise, and the generation of wave aberration is further prevented, thereby ensuring the homogenization of Gaussian laser without introducing wave aberration.

[0051] In a specific embodiment, the detailed homogenization process of Gaussian laser is as follows:

[0052] S1, determine the technical input of the Gaussian laser homogenization system, including the wavelength λ of the input Gaussian laser inc = 620 nm, the beam size L inc × L inc = 136 mm × 136 mm, the size L lim × L lim = 80 mm × 80 mm of the input Gaussian laser to be homogenized, the intensity I inc (x, y) can be represented as:

[0053]

[0054] In the formula: I0is the intensity of the input Gaussian laser I inc at the (0, 0) position, I0= 1 is selected; ω is the beam waist radius of the input Gaussian laser, ω = 50 mm is selected.

[0055] S2, determine the arrangement mode of the metasurface array, in this embodiment, the metasurface array is as shown in Figure 1 The incident surface nanobrick turning angle θ0(x, y) of the nanobrick 1 on the laser incident surface is the same and a constant value, and the exit surface nanobrick turning angle θ1(x, y) of the nanobrick 1 on the laser exit surface is determined based on the respective positions. Figure 2 is a structural schematic diagram of the nanometer structure unit, which gives a base working surface 2 with an edge length C and a nanobrick 1 located on the base working surface 2. The long axis of the nanobrick 1 is L, the short axis is W, and the height is H, wherein the center of the nanobrick 1 and the base working surface 2 coincide in the projection on the xoy plane.

[0056] S3, according to the working wavelength λ inc selected in step S1, design the nanometer structure unit, select the material of the nanometer structure unit, and use electromagnetic simulation tools to simulate and optimize the nanometer structure unit in the metasurface array based on linearly polarized light, to obtain the structural parameters of the nanometer structure unit.

[0057] Specifically, the operating wavelength of the nanostructure unit based on linearly polarized light is selected as the visible light band, and λ is selected. inc =620nm is the main wavelength, according to the working wavelength λ inc The structural parameters of nanobrick 1 were optimized based on the performance requirements of the nanostructure units.

[0058] Optionally, the material of nanobrick 1 is silver, and the material of substrate working surface 2 is silicon dioxide.

[0059] In this embodiment, the operating wavelength of the metasurface is selected as λ = 620 nm, where the structural parameters of the nanostructure unit are H = 70 nm and C = 340 nm. The length L and width W of the nanobrick 1 in the metasurface are selected as the independent variables for structural parameter scanning in electromagnetic simulation. The optimization results of the structural parameter scanning are as follows: Figure 3 As shown: When L = 140nm and W = 85nm, the transmission and reflection coefficients of the long-axis reflection are relatively flat and high throughout the entire wavelength band, while the transmission and reflection coefficients of the long-axis transmission are relatively flat and low throughout the entire wavelength band. The transmission and reflection coefficients of the short-axis transmission reach a peak at 620nm, and the transmission and reflection coefficients of the short-axis reflection reach a trough at 620nm. This means that when a set of orthogonally linearly polarized light with mutually perpendicular vibration directions is incident perpendicularly onto the nanostructure unit, the linearly polarized light in one vibration direction cannot pass through the nanostructure unit, while the linearly polarized light in the other vibration direction can pass through the nanostructure unit, and the transmission efficiency is the highest at a wavelength of 620nm. In other words, the optimized nanostructure unit can be equivalent to a miniature polarizer. This step is completed using an existing electromagnetic simulation software platform.

[0060] S4. Determine the incident surface nanobrick 1's orientation angle θ0(x,y) = 90°.

[0061] S5. Based on the size L of the region to be homogenized by the input Gaussian laser... lim ×L lim =80mm×80mm, and by substituting the aforementioned data into formula (2), the intensity distribution I after Gaussian laser homogenization can be obtained. lim =0.528, the intensity distribution I after Gaussian laser homogenization lim and the intensity I of the input Gaussian laser inc The turning angle θ1(x,y) of the nanobrick 1 at different positions on the laser emission surface is calculated using (x,y). Simultaneously, the turning angle of the nanobrick 1 outside the homogenization region is set to 0°. The homogenized result is as follows: Figure 4 As shown, the Gaussian beam was successfully homogenized into a flat-top beam with high efficiency.

[0062] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the features disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the disclosure being indicated by the following claims.

[0063] It should be understood that the present disclosure is not limited to the precise structures herein described and illustrated in the drawings, and that various modifications and changes can be made without departing from its scope. The present disclosure is limited only by the claims that follow.

Claims

1. A design method for an optical element applied to Gaussian laser homogenization, characterized in that, Includes the following steps: Determine the wavelength, beam size, intensity, and size of the region to be homogenized from the input Gaussian laser. The arrangement pattern of the metasurface array on the optical element is determined. The metasurface array is composed of multiple nanostructure units arranged in a two-dimensional periodic manner. Each nanostructure unit includes a nanobrick (1) and a substrate working surface (2). The substrate working surface (2) is divided into a laser incident surface and a laser exit surface. A nanobrick (1) is provided on both the laser incident surface and the laser exit surface. The turning angle of the nanobrick (1) on each laser incident surface is the incident surface nanobrick turning angle, and the turning angle of the nanobrick (1) on each laser exit surface is the exit surface nanobrick turning angle. The design of the nanostructure unit is carried out based on the wavelength of the input Gaussian laser. The material of the nanostructure unit is selected. Using electromagnetic simulation tools, when the nanostructure unit is perpendicularly incident on the metasurface array with linearly polarized light, the extinction performance of the emitted linearly polarized light is optimized to obtain the structural parameters of the nanostructure unit with the highest efficiency of emitted linearly polarized light in the same direction and the lowest efficiency of emitted linearly polarized light. Determine the incident surface nanobrick orientation angle of the nanobrick (1) on the laser incident surface; The intensity distribution after Gaussian laser homogenization is determined based on the size of the region to be homogenized by the input Gaussian laser. The turning angle of the nano-brick (1) at different positions on the laser emission surface is calculated from the intensity distribution after Gaussian laser homogenization and the intensity of the input Gaussian laser.

2. The design method of an optical element for Gaussian laser homogenization according to claim 1, characterized in that, The x-axis and y-axis are set as the two sides parallel to the working surface (2) of the substrate, respectively. The xoy coordinate system is established with the center of the metasurface array as the origin. The projection of the nanobrick (1) and the center of the corresponding working surface (2) of the substrate coincides in the xoy plane.

3. The design method of an optical element for Gaussian laser homogenization according to claim 2, characterized in that, The dimensional parameters of the nanostructure unit include the major axis L, minor axis W and height H of the nanobrick (1) and the side length C of the working surface (2) of the substrate. The height H is perpendicular to the major axis L and the minor axis W, and the major axis L and the minor axis W are not equal.

4. The design method of an optical element for Gaussian laser homogenization according to claim 3, characterized in that, The major axis L and the minor axis W are arranged on the plane parallel to the nanobrick (1) and the working surface of the substrate (2), and the turning angle is the angle between the major axis L of the nanobrick (1) and the x-axis rotating counterclockwise in the positive direction.

5. A design method for an optical element applied to Gaussian laser homogenization according to claim 1. Its characteristic is that... The nano-bricks (1) at different positions on the laser incident surface have the same and constant turning angle.

6. The design method of an optical element for Gaussian laser homogenization according to claim 1, characterized in that, The turning angle of the nanobrick (1) at different positions on the laser emission surface is: In the formula: θ1(x, y) is the turning angle of the exit surface nanobrick, I lim The intensity distribution after Gaussian laser homogenization, I inc (x, y) represents the intensity of the input Gaussian laser.

7. An optical element for Gaussian laser homogenization, a metasurface device obtained by the design method of an optical element for Gaussian laser homogenization according to any one of claims 1-6.

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