An optical system that outputs a circularly symmetrical light spot

Abstract

This invention discloses an optical system for outputting a circularly symmetrical light spot. The optical system includes a light source, a shaping unit, and a focusing unit placed sequentially along the optical path. The shaping unit uses a homogenized circularly symmetrical mirror to change the light spot distribution pattern of the Gaussian beam generated by the light source, shaping it into an initial circularly symmetrical light spot with adjustable size. The focusing unit uses a rotating ellipsoidal mirror to focus the initial circularly symmetrical light spot onto a preset position on the working surface to form a target three-dimensional circularly symmetrical light spot. The phase of the reflecting surface is determined as follows: based on the energy distribution of the Gaussian beam and the target three-dimensional circularly symmetrical light spot, and the point-to-point ray mapping relationship, the surface equation of the shaping unit is constructed. Then, based on the energy distribution, the mirror illumination area and the corresponding divergence angle are determined. Different mirror illumination areas are superimposed with corresponding lateral and longitudinal offset phases. This achieves the output of a highly uniform circularly symmetrical light spot with adjustable intensity and size, adapting to the needs of different scenarios in actual processing.

Description

Technical Field

[0001] This invention belongs to the field of laser processing, and more specifically, relates to an optical system that outputs a circularly symmetrical light spot. Background Technology

[0002] Conventional Gaussian focused laser beams, with their high energy at the center and low energy at the edges, are prone to causing defects such as overheating, porosity, and spatter at the center, as well as insufficient melting and incomplete processing at the edges during laser processing. For example, in laser glass thin-film technology, the energy in the center region of a Gaussian laser processing is much higher than the ablation threshold, which can damage the substrate material. Conversely, the energy at the falling edge of a Gaussian distribution is lower than the ablation threshold, which can generate thermal effects and damage the thin film structure. An intensity-adjustable circularly symmetric laser beam can significantly improve this energy matching with the ablation threshold. By using this ablation threshold, excess energy above the threshold and excess energy in the falling edge can be reduced, avoiding potential damage to the substrate and adjacent areas below the laser scribing line, thus greatly improving processing efficiency. The rectangular footprint generated by a flat-top laser can produce straight walls with very little overlap, thereby increasing the processing speed of laser micromachining.

[0003] Currently, there are various methods for generating intensity-tunable circularly symmetric laser spots in the field of laser processing. However, some methods are not suitable for high-power laser processing scenarios, such as spatial light modulators. At present, intensity-tunable circularly symmetric laser spot solutions suitable for high-power processing scenarios can be divided into two categories: one is based on flat-top fiber lasers with special fiber structures, which can directly output a ring-shaped laser spot; the other is based on external optical path shaping using optical elements, which obtains an intensity-tunable circularly symmetric laser spot by shaping the Gaussian beam output from a general laser.

[0004] Coherent has introduced flat-top laser products that can achieve high-uniformity flat-top laser output. However, these lasers all have the following drawbacks: First, they are expensive; the price of fiber lasers that can output intensity-tunable circularly symmetrical beams is much higher than that of ordinary fiber lasers. Second, their application scenarios are limited; the flat-top beam shaping method based on the special structure of optical fibers is only applicable to fiber lasers, but there are still many scenarios in laser processing where it is not suitable to use fiber lasers as processing light sources. Third, the beam size is limited; it can only output a preset intensity-tunable circularly symmetrical beam size and cannot adjust other types of intensity-tunable circularly symmetrical beam modes, such as concave beams.

[0005] In external optical path shaping based on beam-shaping elements, various beam-shaping elements are used, which can be roughly divided into two categories: The first category is transmissive beam-shaping elements, such as microlenses, beam-shaping DOEs, and many other transmissive optical beam-shaping elements with beam-shaping functions, such as Edmund's AdlOpticaπShaper flat-top beam shaper. However, current transmissive optical beam-shaping elements have the following drawbacks: a low damage threshold, therefore, in ultra-high power laser processing, the stability and lifespan of transmissive optical elements are insufficient; many transmissive optical beam-shaping elements have complex mirror shapes, making them difficult and costly to manufacture. The second category is reflective beam-shaping elements, such as aspherical mirrors. Compared with transmissive optical beam-shaping elements, reflective beam-shaping elements have a higher damage threshold because the main material can be metal and a built-in water-cooling channel can be incorporated, and the manufacturing technology is also more mature. However, the current disadvantages of intensity-adjustable circular symmetric spot shaping optical paths based on reflective shaping elements are: the mirror shaping effect is singular, and the processing precision requirements for complex functional mirrors are high, making the processing difficult.

[0006] In summary, one approach to achieving extremely high-power flat-top beam shaping is to simplify the optical path as much as possible based on reflective shaping elements, thereby satisfying diverse shaping modes while reducing manufacturing complexity and improving stability and applicability. Summary of the Invention

[0007] In view of the shortcomings of related technologies, the purpose of this invention is to provide an optical system that outputs a circularly symmetrical light spot, aiming to solve the problem of how to simplify the optical path as much as possible, meet the diverse shaping modes while reducing the processing complexity, and improving stability and applicability.

[0008] To achieve the above objectives, the present invention provides an optical system for outputting a circularly symmetrical light spot, comprising: a light source, a shaping unit, and a focusing unit arranged sequentially along the optical path;

[0009] The light source is used to generate a Gaussian beam;

[0010] The shaping unit employs a homogenized circularly symmetrical mirror to change the spot distribution pattern of the incident Gaussian beam, shaping it into an initial circularly symmetrical spot with adjustable size, and then projecting it onto the focusing unit.

[0011] The phase and reflective surface shape of the shaping unit are determined in the following way: based on the energy distribution of the incident Gaussian beam and the energy distribution of the target three-dimensional circularly symmetrical spot, and based on the point-to-point ray mapping relationship of the rotating ellipsoidal mirror, the surface equation of the shaping unit is constructed, and then the mirror illumination area and the corresponding divergence angle are determined based on the energy distribution. Different mirror illumination areas are superimposed with the corresponding lateral offset phase and longitudinal offset phase.

[0012] The center of the focusing unit is located on the central axis of the beam emitted by the shaping unit, and is used to focus the initial circularly symmetrical light spot after being shaped by the shaping unit onto a preset position on the working surface to form a target three-dimensional circularly symmetrical light spot; the phase of the reflecting surface of the focusing unit is determined by the following method: based on the preset front focal length and preset back focal length of the focusing unit, the point-to-point ray mapping relationship, the focusing phase is superimposed on the plane mirror to determine the positional correspondence from the light source to the working surface, and the surface equation of the focusing unit is constructed.

[0013] Optionally, the shaping unit is used to change the light intensity distribution of the target three-dimensional circularly symmetrical light spot obtained after shaping by adjusting the lateral offset phase. The target three-dimensional circularly symmetrical light spot includes: a flat-top light spot, a concave ring light spot, and a convex ring light spot.

[0014] Optionally, the shaping and focusing unit is used to change the focal plane position of different spot portions in the target three-dimensional circularly symmetrical spot by adjusting the longitudinal offset phase.

[0015] Optionally, the focusing unit is a rotating ellipsoidal mirror, a focusing lens, or a combination of a plane mirror and a focusing lens placed along the optical path.

[0016] Optionally, the focusing unit employs a rotating ellipsoidal reflector, which includes a focal point in the incident direction and a focal point in the exit direction, denoted as the front focal point and the rear focal point, respectively; the focal plane corresponding to the front focal point is denoted as the front focal plane; the focal plane corresponding to the rear focal point is denoted as the rear focal plane; the sum of the distances from the center point of the shaping unit to the center point of the focusing unit through the front focal point is the front focal length, and the distance from the rear focal point to the center point of the focusing unit is the rear focal length;

[0017] According to the principle of equal optical path in light propagation, the input beam energy at point r on the reflecting mirror surface of the shaping unit corresponds to a light ring with radius R on the working surface. The correspondence between the light ring with radius R at the target three-dimensional circularly symmetric spot and the light ring with radius r at the initial circularly symmetric spot is as follows:

[0018]

[0019] Where F1 is the preset front focal length; F2 is the preset back focal length; I s (r, θ) represents the polar coordinate distribution of the incident circular beam intensity, which, for a Gaussian beam, satisfies a two-dimensional Gaussian distribution; I t (r,θ) represents the polar coordinate distribution of the light intensity of the target flat-top circular spot. For a target three-dimensional circularly symmetric spot with adjustable intensity, it is a normalization constant.

[0020] Optionally, the boundaries of different regions of the reflective surface of the shaping unit are homogenized to make the mirror surface smooth and without grooves; the mirror surface of the shaping unit is homogenized in the following way: radial lines are drawn from the center of the mirror surface along the radius, and the phase difference value is subtracted from the processing points located in different shaping regions on the same line.

[0021] Optionally, the light source is a laser.

[0022] Optionally, the shape of the reflecting surface of the shaping unit is a non-rotationally symmetric freeform surface.

[0023] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0024] 1. This invention provides an optical system for outputting a circularly symmetrical light spot. The shaping unit uses a homogenized circularly symmetrical mirror. Based on the energy distribution of the incident Gaussian beam and the spot distribution pattern of the target light field, a mapping relationship between the energy distribution of the incident light field and the target light field is set. Combining the principle of equal optical path and the principle of energy conservation, a surface equation of the phase of the reflecting surface of the homogenized circularly symmetrical mirror corresponding to the target three-dimensional circularly symmetrical light spot with adjustable intensity is constructed. At the same time, based on the preset front focal length and preset back focal length of the focusing unit, a surface equation of the focusing unit is constructed. This invention achieves beam collimation, shaping, and focusing through a combination of two mirrors, obtaining an intensity-adjustable circularly symmetrical light spot from a laser source. Without the need for other optical components, it can achieve the output of a highly uniform, intensity-adjustable, and size-adjustable circularly symmetrical light spot with fewer optical components and a simplified optical path structure. Moreover, different spot parts are located on the same / different planes, adapting to the needs of different scenarios in actual processing.

[0025] 2. This invention provides an optical system for outputting a circularly symmetrical light spot. The shaping unit uses a homogenized circularly symmetrical mirror. Homogenization of the mirror surface solves the continuity problem of the entire mirror surface when multiple curved surfaces are combined, reducing the difficulty of processing complex surface shapes. Furthermore, this invention offers a variety of light spot shaping modes, not limited to highly uniform and intensity-adjustable circularly symmetrical light spots, but including more complex programmable intensity distribution circularly symmetrical light spots, such as concave annular light spots and convex annular light spots; and the energy proportion of each part of the concave annular light spot and the convex annular light spot is adjustable.

[0026] 3. The embodiments of the present invention provide an optical system for outputting circularly symmetrical light spots. The optical system is constructed with fewer optical components, making the adjustment of the optical system easier, the optical path stability better, and the damage threshold higher. The fewer optical components required to output circularly symmetrical light spots of different sizes and intensities reduces the accumulation of processing or assembly errors of each component, enabling the light spot shaping system in the present invention to obtain more stable and accurate output. At the same time, the optical path volume is reduced, resulting in a more streamlined optical path structure and stronger anti-interference ability. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of an optical system that outputs a flat-top light spot according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram showing the change in the position of the light spot when the longitudinal offset phase of the shaping unit provided in the embodiment of the present invention changes;

[0029] Figure 3 This is a schematic diagram of the shaping unit provided in an embodiment of the present invention;

[0030] Figure 4 This is a side view of the reflecting mirror surface of the shaping unit provided in an embodiment of the present invention;

[0031] Figure 5 This is a front view of the reflective mirror surface of the shaping unit provided in an embodiment of the present invention;

[0032] Figure 6 This is a schematic diagram of the target spot energy distribution of an optical system that outputs a flat-top light spot according to Embodiment 1 of the present invention;

[0033] Figure 7 This is a schematic diagram of the target spot energy distribution of an optical system that outputs a flat-top light spot according to Embodiment 2 of the present invention;

[0034] Figure 8 This is a schematic diagram of the target spot energy distribution of an optical system that outputs a flat-top light spot, provided in Embodiment 3 of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0036] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0037] like Figure 1 As shown, an optical system for outputting a flat-top light spot includes: a light source 1, a shaping unit 3, and a focusing unit 5 arranged sequentially along the optical path;

[0038] The light source 1 is used to generate a Gaussian beam 2;

[0039] The shaping unit 3 uses a homogenized circular symmetric mirror to change the spot distribution pattern of the incident Gaussian beam, shaping it into an initial circular symmetric spot with adjustable size, and then projecting it onto the focusing unit 5.

[0040] The phase of the reflecting surface of the shaping unit 3 is determined in the following way: based on the energy distribution of the incident Gaussian beam and the energy distribution of the target three-dimensional circularly symmetrical spot, and based on the point-to-point ray mapping relationship of the rotating ellipsoidal mirror, the surface equation of the shaping unit is constructed, and then the mirror illumination area and the corresponding divergence angle are determined based on the energy distribution. Different mirror illumination areas are superimposed with the corresponding lateral offset phase and longitudinal offset phase.

[0041] The center of the focusing unit 5 is located on the central axis of the beam emitted from the shaping unit 3. It is used to focus the initial circularly symmetrical light spot shaped by the shaping unit 3 onto a preset position on the working surface 7 to form a target three-dimensional circularly symmetrical light spot. The phase of the reflecting surface of the focusing unit 5 is determined by the following method: based on the preset front focal length and preset back focal length of the focusing unit, the point-to-point ray mapping relationship, the focusing phase is superimposed on the plane mirror to determine the positional correspondence from the light source to the working surface, and the surface equation of the focusing unit is constructed.

[0042] Optionally, the focusing unit is a rotating ellipsoidal mirror, a focusing lens, or a combination of a plane mirror and a focusing lens placed along the optical path. In this embodiment, preferably, the focusing unit is a rotating ellipsoidal mirror.

[0043] This invention provides an optical system for outputting a flat-top beam, a simple beam shaping system that relies on a dual-mirror combination to output an intensity-adjustable circularly symmetrical beam. The core of this optical system is a homogenized circularly symmetrical mirror as the shaping unit and a rotating ellipsoidal mirror as the focusing unit. The homogenized circularly symmetrical mirror shapes the input Gaussian beam, and its mirror surface shape is obtained by solving for given parameters. The rotating ellipsoidal mirror collimates and focuses the shaped beam, and its reflective surface shape is given by a preset focal length. This embodiment of the optical system provides the ability to output an intensity-adjustable and size-adjustable circularly symmetrical beam. Simultaneously, it achieves collimation, shaping, and focusing functions through two mirrors, reducing the number of optical components. The discontinuities in the curved surface of the homogenized circularly symmetrical mirror are homogenized, resulting in a smooth, groove-free mirror surface, reducing manufacturing difficulty, and allowing it to withstand high-power laser effects. The intensity of the target beam can be adjusted to achieve an adjustable energy distribution of the circularly symmetrical beam.

[0044] With the shape of the reflecting surface completely determined, the optical system has a definite incident direction and an exit direction. The rotating ellipsoidal mirror includes a focal point in the incident direction and a focal point in the exit direction, denoted as the front focal point and the rear focal point, respectively. The focal plane corresponding to the front focal point is denoted as the front focal plane; the focal plane corresponding to the rear focal point is denoted as the rear focal plane; the sum of the distances from the center point of the shaping unit to the center point of the focusing unit through the front focal point is the front focal length, and the distance from the rear focal point to the center point of the focusing unit is the rear focal length. Since the shaping unit shapes the Gaussian beam into an initial circularly symmetric spot, the phase of the homogenized circularly symmetric mirror exhibits a non-uniform gradient. When the shape of the reflecting surface of the homogenized circularly symmetric mirror is different (i.e., the phase setting is different), the distribution pattern of the circularly symmetric spot obtained by the optical system is also different. Adjusting the phase of the reflecting surface of the shaping unit 3 changes the distribution of the circularly symmetric spot obtained after shaping. The circularly symmetric spot includes: a flat-top spot, a concave annular spot, and a convex annular spot. Based on the surface equation of the shaping unit, the energy distribution of the target light spot on the preset focal plane can be used as a condition to solve the problem and determine its shape as a non-rotationally symmetric free surface.

[0045] like Figure 1 As shown, the shaping unit 3 shapes the input beam 2 emitted by the light source 1 into an intermediate beam 4. The focusing unit 5 collimates the intermediate beam 4 through a reflective surface and then emits an outgoing beam 6. The outgoing beam 6 is focused onto the back focal plane 7, resulting in a target intensity adjustable circular symmetrical spot 8 of a defined size on the back focal plane 7. The focusing unit 5 uses a rotating ellipsoidal reflector, which has both collimation and focusing functions.

[0046] The light rays that make up the input beam pass through or approximately pass through the front focal point and are then input into the homogenized circularly symmetrical reflector, and the incident direction of the input beam is perpendicular to the front focal plane; preferably, the input beam is a Gaussian beam emitted by the light source 1 located at the front focal point, and exemplarily, the light source 1 is a laser.

[0047] The shape of the reflective surface of the shaping unit 3 is determined in the following way: based on the preset spot intensity distribution of the preset target light field, and based on the point-to-point ray mapping relationship of light propagation, a non-uniform gradient phase is set on the reflective mirror surface. According to the principle of energy conservation, the incident light rays at different positions on the mirror surface correspond to the positions of the target spot with the same energy. The surface equation of the reflective surface shape corresponding to the target intensity adjustable circular symmetric spot is constructed. The spot distribution pattern of the target light field corresponds to the desired intensity adjustable circular symmetric spot.

[0048] Specifically, the mapping relationship between the incident light field and the target light field energy distribution is determined by dividing the incident light field into multiple parts according to the energy ratio requirement of the target intensity adjustable circular symmetrical light spot, and mapping the energy of each part to the corresponding position on the back focal plane. Figure 1In the middle, the narrow light ring 9 on the reflective surface of the shaping unit 3 corresponds to the narrow light ring 10 on the back focal plane 7 (working surface).

[0049] The energy mapping relationship between the incident light field and the target light field is determined based on conditions such as the energy distribution of the incident light field and the energy distribution of the target light field. Its meaning is as follows: The incident light field is divided into multiple narrow circular rings, such as… Figure 1 The middle ring 9 divides the target light field into multiple narrow rings, such as Figure 1 The middle ring 10; the energy of each part of the incident light field is mapped to a certain part of the target light field, that is, the light in that part of the incident light field will reach the corresponding part of the target light field after passing through the optical path. This energy correspondence is the energy mapping relationship between the incident light field and the target light field. The specific manifestation of the above mapping relationship in the shape of the reflecting surface is as follows: the reflecting surface is based on a plane mirror, and corresponding gradient phases are added at various points on the plane, so that each part of the outgoing light from the light source is deflected to the target radius of the back focal plane, while maintaining energy correspondence; the light beam incident on the reflecting surface can therefore be regarded as being divided into multiple parts. The light beams incident on different positions on the mirror surface are respectively shaped into a part corresponding to the intensity-adjustable circularly symmetrical light spot, and all parts together constitute the target intensity-adjustable circularly symmetrical light spot.

[0050] The shape of the reflecting surface of the rotating ellipsoidal mirror in focusing unit 5 is determined in the following way:

[0051] Based on the preset front focal length and preset back focal length of the rotating ellipsoidal mirror, and according to the point-to-point ray mapping relationship of the rotating ellipsoidal mirror, a corresponding rotating ellipsoidal phase is added to the mirror surface to determine the positional correspondence from the light source to the target surface. The surface equation of the rotating ellipsoid that satisfies the preset conditions is constructed so that the target light spot is located at the preset position.

[0052] It should be noted that the adjustment effects caused by customizing the shape of the reflective surface and replacing the mirror with a homogenized circularly symmetrical reflector with different mirror shapes include: adjustable energy distribution of the circularly symmetrical light spot on the focal plane, adjustable spot size, and adjustable front and rear focal lengths of the optical system.

[0053] Furthermore, the intensity distribution of the target three-dimensional circularly symmetrical spot is changed by adjusting the lateral offset phase, and the focal plane position of different spot parts in the target three-dimensional circularly symmetrical spot is changed by adjusting the longitudinal offset phase.

[0054] like Figure 2 As shown, the focal plane where the spot was located before the longitudinal offset phase was adjusted is called the old target, and the focal plane where the spot was located after the adjustment is called the new target.

[0055]

[0056] Where l is the distance from a point on the mirror to the center, F2 is the focusing distance, d is the longitudinal offset distance, θ1 is the angle between a point on the mirror and the new target and the axis, θ2 is the angle between a point on the mirror and the old target and the axis, and Δθ is the difference between the two angles.

[0057] From the reflection relationship, we can know Finally, the longitudinal offset phase f(l) at point l can be obtained.

[0058] Furthermore, the method for dividing the reflective surface of shaping unit 3 into regions involves segmenting the point light source with a divergence angle of θ0 to determine the energy proportion of different parts. A cone with a divergence angle of θ0 emitted from the point light source will form a light gray region S0 on the reflective surface, while a cone with a divergence angle of θ1 emitted from the point light source will form a dark gray region S1 and its boundary L on the reflective surface. S0-S1 also becomes an approximately circular light gray region. Superimposing more shaping phases on the mirror surface will result in a higher energy proportion and corresponding circular regions.

[0059] like Figure 3 As shown in the figure, the dark gray area is the illumination area S1 of the light source with an energy percentage of dot_part. The dark gray and light gray areas together constitute the total illumination area S0 of the point light source. The radius of the light source divergence angle on the reflecting surface is F1*tanθ0, which is the size of the light gray area S0; the radius of the boundary divergence angle on the reflecting surface is F1*tanθ1, which is the size of the dark gray area S1.

[0060] Given the total divergence angle θ0 and the energy percentage (dot_part) of the dark gray region S1, according to the formula:

[0061]

[0062] Therefore, the boundary divergence angle θ1 to be determined is:

[0063]

[0064] For different energy regions, the phase is calculated based on the surface equation; the phase is the same for the same energy region.

[0065] Furthermore, the mirror design of the reflecting surface of the shaping and focusing unit 3, such as... Figure 4 In the schematic diagram of the mirror shown, the angle between the line connecting the light source to the center of the mirror and the line connecting the target point to the center of the mirror is 90°. Based on the distance F1 from the light source to the center of the mirror, the distance F2 from the target three-dimensional circular symmetrical spot to the center of the mirror, and the angle α between the incident ray and the outgoing ray, the curve equation of the focusing mirror can be uniquely determined, that is, the focusing mirror can be designed according to the application requirements.

[0066] The final equation of the ellipsoid can be obtained as follows:

[0067]

[0068] Where x', y', and z' are the coordinates of points on the mirror surface, respectively.

[0069] Furthermore, the reflective surface of the shaping unit 3 is homogenized. Specifically, the boundaries of different regions of the reflective surface of the shaping unit are homogenized to make the mirror surface smooth and without grooves. Figure 3 In the schematic diagram of the mirror surface shown, when different phases are superimposed on the dark gray region S1 and the light gray region S0-S1, a height difference L at the boundary between the different regions will occur. This height difference varies unevenly with the angle, resulting in scratches in the center of the final processed mirror surface. This defect is exacerbated when there are many partitions in the mirror surface, severely affecting the shaping effect of the reflector and reducing its power threshold. A method for optimizing the boundary height difference of the reflector surface is proposed, such as... Figure 5 As shown, 1000 radial lines are drawn from the center of the mirror along the radius. Figure 5 The diagram illustrates one of the regions, R1. R1 intersects the boundary L at point D2. Point D1 of region S1 lies on R1, and point D3 of region S0-S1 lies on R1. The equation for region S1 is H1, and the equation for region S0-S1 is H2. The height of the two region boundaries on the radiation line R1 is...

[0070] Δ(R1) = H2(D2) - H1(D2)

[0071] Therefore, the height of points within region S1 remains unchanged, still H1(D1), and the height of points within the S0-S1 region minus the boundary height difference, i.e., H2(D3) - Δ(R1), achieves mirror homogenization on R1. This operation is performed on all 1000 radiation lines, ultimately achieving homogenization of the entire mirror surface. Even when the mirror surface has more than two sections, homogenization can still be performed using this method without affecting the mirror's optical performance.

[0072] This invention provides an optical system for outputting a circularly symmetrical light spot. The shaping unit employs a homogenized circularly symmetrical mirror, and the focusing unit employs a rotating ellipsoidal mirror. Based on preset front focal length, preset back focal length, and the light spot distribution pattern of the target light field, a mapping relationship between the energy distribution of the incident light field and the target light field is established. Combining the principles of equal optical path length and energy conservation, the surface equations of the reflecting surfaces of the circularly symmetrical mirror and the rotating ellipsoidal mirror corresponding to the target intensity-adjustable circularly symmetrical light spot are constructed. The Gaussian beam emitted from the light source is shaped, collimated, and focused before being used to generate a target three-dimensional circularly symmetrical light spot on the working surface. Furthermore, adjusting the phase of the reflecting surface of the circularly symmetrical mirror correspondingly adjusts the shape and energy distribution of the generated target three-dimensional circularly symmetrical light spot. This system solves the technical problem of simplifying the optical path as much as possible, satisfying diverse shaping modes while reducing processing complexity, and improving stability and applicability. With fewer optical components and a simplified optical path structure, it achieves the output of a highly uniform and intensity-adjustable target three-dimensional circularly symmetrical light spot. The size of the target three-dimensional circularly symmetrical light spot is arbitrarily adjustable, adapting to the needs of different scenarios in actual processing.

[0073] In one specific embodiment, referred to as Embodiment 1, the optical system is as follows: Figure 1 As shown, the uncollimated Gaussian beam 2 output from the laser as light source 1 is incident on the shaping unit 3 and shaped into an intermediate beam 4. The intermediate beam 4 is then collimated and focused by the focusing unit 5 to become the output beam 6. The light field distribution of the output beam 6 on the back focal plane 7 is flat-topped. The mirror shape of the shaping unit 3 is calculated from the spot pattern and energy mapping relationship of the intensity-adjustable circularly symmetrical spot on the back focal plane; the mirror shape of the focusing unit 5 is calculated from the collimation focal length F1 and the focusing focal length F2.

[0074] Based on the principle of equal optical path length in light propagation, a non-uniform gradient phase is introduced on the reflecting mirror surface. This gradient phase can transform the Gaussian intensity distribution of the incident light from the target into a uniform intensity distribution, so that the energy of the input beam at point r on the mirror surface corresponds to a ring of radius R in the target plane light spot. Furthermore, based on the principle of energy conservation, the mapping relationship of the light rays is solved. The correspondence between the ring of radius R in the target's three-dimensional circularly symmetric light spot and the ring of radius r in the initial circularly symmetric light spot is as follows:

[0075]

[0076] Where F1 is the preset front focal length; F2 is the preset back focal length, I s (r,θ) represents the initial circularly symmetric polar coordinate distribution of the beam intensity, which, for a Gaussian beam, satisfies a two-dimensional Gaussian distribution; I t (r,θ) represents the polar coordinate distribution of the light intensity of the target three-dimensional circularly symmetric spot. For a circularly symmetric spot with adjustable intensity, it is a normalization constant.

[0077] The equation for the surface z = f(r, w) corresponding to the reflecting surface of the homogenized circularly symmetric mirror can be solved based on the above equation.

[0078] Specifically, in this embodiment, the front focal length of the rotating ellipsoidal reflector is 150mm, the back focal length is 300mm, the radius of the intensity-adjustable circularly symmetrical light spot is 10mm, and the energy distribution of the light spot on the back focal plane is as follows. Figure 6 As shown.

[0079] In another specific embodiment, referred to as Embodiment 2, a dual-mirror intensity-tunable circularly symmetric spot optical system with an output concave spot having a center energy lower than the surrounding energy is provided. The overall structure of this optical system is the same as that of Embodiment 1, except that the polar coordinate distribution of the target three-dimensional circularly symmetric spot intensity is different. t (r,θ) is changed to a preset target light intensity distribution, and I is used in Example 1. t (r,θ) is a normalization constant, so the side view of the light spot shows a uniform intensity distribution. In this embodiment, I is changed. t (r,θ) allows the light intensity of the target three-dimensional circularly symmetrical spot to change with the target spot radius, and the mirror shape of the shaping unit changes accordingly, including but not limited to flat-top, concave, and convex spots. The mirror shape of the rotating ellipsoidal reflector is the same as in Example 1.

[0080] In this embodiment, the calculation method for the surface equation of the reflecting surface of the homogenized circularly symmetrical mirror is the same as that in the above embodiment. It is also based on the principle of equal optical path and the principle of energy conservation, and the energy of the light spot on the reflecting mirror surface is matched one by one with the energy of the light spot on the target surface from the inside to the outside. This will not be elaborated here.

[0081] Specifically, in this embodiment, the front focal length of the rotating ellipsoidal mirror is 150mm, the back focal length is 300mm, the radius of the concave spot is 10mm, and the intensity distribution of the concave spot satisfies I∝R. 2 The energy distribution of the light spot on the back focal plane is as follows Figure 7 As shown.

[0082] In another specific embodiment, referred to as Embodiment 3, a dual-mirror intensity-tunable circularly symmetric spot optical system is provided, characterized by an output annular convex spot with a center energy higher than the surrounding energy. The overall structure of this optical system is the same as that of Embodiment 1, the only difference being the polar coordinate distribution of the target three-dimensional circularly symmetric spot intensity. t (r,θ) is changed to a preset target light intensity distribution, whose light intensity changes with the radius of the target light spot, and the mirror shape of the shaping unit changes accordingly. The mirror shape of the rotating ellipsoidal reflector is the same as in Example 1. The calculation method of the surface equation of the reflector in this embodiment is the same as in Example 2, and will not be repeated here.

[0083] Specifically, in this embodiment, the front focal length is 150mm, the rear focal length is 300mm, the radius of the annular convex spot is 10mm, and the intensity distribution of the annular convex spot satisfies I∝(-R). 2 +25). The energy distribution of the light spot on the back focal plane is as follows: Figure 8 As shown.

[0084] In Example 1, the flat-top spot has a more uniform light intensity distribution, which will not lead to partial overexposure and partial underexposure, making it suitable for micro-nano processing in fields such as solar panels; in Example 2, the concave spot has a temperature field distribution that is closer to the flat-top distribution because the intensity at the center of the spot is lower than that at the periphery, making it suitable for preheating of highly reflective materials and composite laser processing; in Example 3, the convex spot has a gentler intensity gradient than the Gaussian spot, and the obtained temperature field distribution is close to the trapezoidal distribution, making it suitable for laser cutting, welding and other processing scenarios of temperature-sensitive non-metallic materials.

[0085] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An optical system for outputting a circularly symmetrical light spot, characterized in that, include: The light source, shaping unit, and focusing unit are placed sequentially along the optical path; The light source is used to generate a Gaussian beam; The shaping unit employs a homogenized circularly symmetrical mirror to change the spot distribution pattern of the incident Gaussian beam, shaping it into an initial circularly symmetrical spot with adjustable size, and then projecting it onto the focusing unit. The phase of the reflecting surface of the shaping unit is determined in the following way: based on the energy distribution of the incident Gaussian beam and the energy distribution of the target three-dimensional circularly symmetrical spot, as well as the point-to-point ray mapping relationship of the rotating ellipsoidal mirror, the surface equation of the shaping unit is constructed, and then the mirror illumination area and the corresponding divergence angle are determined according to the energy distribution. Different mirror illumination areas are superimposed with the corresponding lateral offset phase and longitudinal offset phase. The center of the focusing unit is located on the central axis of the beam emitted by the shaping unit, and is used to focus the initial circularly symmetrical light spot after being shaped by the shaping unit onto a preset position on the working surface to form a target three-dimensional circularly symmetrical light spot; the phase of the reflecting surface of the focusing unit is determined by the following method: based on the preset front focal length and preset back focal length of the focusing unit, the point-to-point ray mapping relationship, the focusing phase is superimposed on the plane mirror to determine the positional correspondence from the light source to the working surface, and the surface equation of the focusing unit is constructed.

2. The optical system as described in claim 1, characterized in that, The shaping unit is used to change the light intensity distribution of the target three-dimensional circularly symmetrical light spot obtained after shaping by adjusting the lateral offset phase. The target three-dimensional circularly symmetrical light spot includes: a flat-top light spot, a concave ring light spot, and a convex ring light spot.

3. The optical system as described in claim 1, characterized in that, The shaping unit is used to change the focal plane position of different spot portions in the target three-dimensional circularly symmetrical spot by adjusting the longitudinal offset phase.

4. The optical system as claimed in claim 1, characterized in that, The focusing unit is a rotating ellipsoidal mirror, a focusing lens, or a combination of a plane mirror and a focusing lens placed along the optical path.

5. The optical system as described in claim 4, characterized in that, The focusing unit employs a rotating ellipsoidal reflector, which includes a focal point in the incident direction and a focal point in the exit direction, denoted as the front focal point and the rear focal point, respectively. The focal plane corresponding to the front focal point is denoted as the front focal plane, and the focal plane corresponding to the rear focal point is denoted as the rear focal plane. The sum of the distances from the center point of the shaping unit to the center point of the focusing unit via the front focal point is the front focal length, and the distance from the rear focal point to the center point of the focusing unit is the rear focal length. According to the principle of equal optical path in light propagation, the input beam energy at point r on the reflecting mirror surface of the shaping unit corresponds to a light ring with radius R on the working surface. The correspondence between the light ring with radius R at the target three-dimensional circularly symmetric spot and the light ring with radius r at the initial circularly symmetric spot is as follows: in, The polar coordinate distribution of the incident circular beam intensity is given. For a Gaussian beam, it satisfies a two-dimensional Gaussian distribution. The polar coordinate distribution of the light intensity of the target flat-topped circular light spot.

6. The optical system as claimed in claim 1, characterized in that, The boundaries of different regions of the reflective surface of the shaping unit are homogenized to make the mirror surface smooth and without grooves; the mirror surface of the shaping unit is homogenized in the following way: radial lines are drawn from the center of the mirror surface along the radius, and the phase difference value is subtracted from the processing points located in different shaping regions on the same line.

7. The optical system as claimed in claim 1, characterized in that, The light source is a laser.

8. The optical system as claimed in claim 1, characterized in that, The shape of the reflective surface of the shaping unit is a non-rotationally symmetric freeform surface.

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