Diffractive optical element for generating point-ring point light spot array and laser optical system

Abstract

The invention discloses a diffractive optical element for generating a point-ring point light spot array, which is used for applying a phase distribution on a transverse beam profile of a laser beam, the applied phase distribution forms a first region and a second region, phases in the first region are equal, and the first region is an equiphase region; and the second region is an optical wedge phase region, is obtained by modulating an optical wedge phase, is used for generating a central light spot when the laser beam passes through the first region, and is used for generating an annular point light spot when the laser beam passes through the second region. According to the diffractive optical element, predetermined phase distribution is applied to the incident laser beam through the equiphase region and the optical wedge phase region, a point-ring point light spot array can be realized on a working plane in a laser optical system, and the ring point light spot array can realize the same preheating effect as an annular light spot at relatively low power; and the total laser output energy during laser welding is reduced.

Description

Technical Field

[0001] The invention belongs to the field of laser processing and relates to a diffraction optical element and a laser optical system for modulating a laser beam into a central Gaussian spot and a ring-point spot array. Background Art

[0002] Laser welding has the advantages of large weld depth-to-width ratio, high welding precision and high speed, and is widely used in automobile manufacturing, aerospace and other fields.

[0003] Laser welding is divided into deep penetration welding and heat conduction welding based on the way the material melts and the energy transfer mechanism during the welding process. Deep penetration welding is a high-energy-density welding mode in which the laser beam forms a small hole on the surface of the material. The laser energy is transferred directly into the material through the small hole, causing the material to melt and evaporate rapidly. Its characteristics include large welding depth and fast welding speed, making it widely used in scenarios requiring high-strength and high-sealing welding. However, in the deep penetration welding state, the Gaussian distribution of the laser beam results in high temperatures in the center of the spot and low temperatures in the edge areas. This can easily lead to keyhole instability during high-speed welding and produce welding defects such as spatter.

[0004] The spot ring light preheats the welding material through the ring light, and the Gaussian light in the center maintains deep penetration welding. By combining the light spots, the temperature gradient of the welding material is smoothed, which can effectively eliminate welding defects and improve welding quality. There are two main ways to generate spot ring light: spot ring laser and external optical path shaping. The spot ring laser generates point light and ring light through a circular fiber core and a ring fiber core. The power of the point light and ring light can be adjusted independently. However, the cost of the spot ring laser is high and the original optical path needs to be modified. It is mainly used for high-power laser welding. External optical path shaping is based on spiral phase plates or axicons. Among them, the radius of the ring light generated by the spiral phase plate has a low degree of freedom; the radius of the ring light generated by the axicon is adjustable, but the spot shape before and after the focal plane is inconsistent. In addition, the ring light covers a large area, which reduces the peak power density of the ring light. To achieve the preheating function, a larger amount of laser energy needs to be allocated to the ring light.

[0005] In summary, in the field of laser processing, the cost of point ring lasers is high and the optical path needs to be modified. The radius of the ring light in the point ring spot generated by external optical path shaping cannot be taken into account at the same time as the focal depth. The focal plane of the point ring spot is asymmetric front to back, and maintaining a certain peak power density of the ring spot requires a higher energy ratio of the ring area. Summary of the Invention

[0006] In view of the defects and improvement requirements of the prior art, the present invention provides a diffractive optical element for generating a dot-ring dot spot array, which is used to apply a phase distribution on the transverse beam profile of a laser beam. The applied phase distribution forms a first region and a second region, wherein the phase in the first region is equal, which is an equal-phase region; the second region is a wedge phase region, which is obtained by modulating the wedge phase. When the laser beam passes through the first region, it is used to generate a central spot, and when the laser beam passes through the second region, it is used to generate a ring dot spot.

[0007] The present invention provides a laser optical system, including: a laser source that outputs a laser beam, and the laser beam serves as an incident laser beam;

[0008] The diffractive optical element as described above, a focusing lens, and a working plane, wherein the diffractive optical element is arranged in the beam path of the incident laser beam to apply a phase distribution on the incident laser beam. By constructing a first region and a second region on the diffractive optical element, it is realized that when the incident laser beam passes through the first region, a central spot is formed on the working plane, and the laser beam passing through the second region forms a ring dot spot array on the working plane.

[0009] Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0010] (1) Compared with the existing dot-ring lasers, at the same power, the peak power density of the ring dots is higher than that of the annular spot. When the peak power density of the annular spot is the same as that of the annular dot array, the annular dot array requires less energy and can achieve the same preheating effect as the annular spot with a lower power, reducing the total laser output energy during laser welding.

[0011] (2) By changing the wedge phase gradient applied in the second region, the position of the ring dots generated by the diffractive optical element in the present invention is adjustable.

[0012] (3) By changing the area of the equal-phase region, the energy ratio of the dot-ring dots can be adjusted. In addition, by changing the distance between the laser and the diffractive optical element, the spot size incident on the diffractive optical element can be changed, thereby changing the energy ratio of the dot-ring dots.

[0013] (4) By etching a wedge phase with an opposite gradient in the wedge phase region of the diffractive optical element, the number of ring dots generated by the positive wedge phase and the negative wedge phase is equal. Before and after the focal plane, the ring dots with the negative wedge phase deflect towards the optical axis in the direction of light, and the ring dots with the positive wedge phase deflect away from the optical axis. Therefore, the power density of the ring dots near the focal plane is more stable, and it has better defocus processing quality. Description of the Drawings

[0014] Figure 1 Schematic diagram of the optical wedge element with positive and negative phase gradients in the diffractive optical element of the present invention;

[0015] Figure 2 Schematic diagram and phase diagram of the diffractive optical element that generates dot-ring dots after etching the optical wedge phase region of the diffractive optical element with a negative optical wedge phase structure.

[0016] Figure 3 Schematic diagram and phase diagram of the diffractive optical element that generates dot-ring dots after etching the optical wedge phase region of the diffractive optical element with a positive optical wedge phase structure;

[0017] Figure 4 Schematic diagram of etching the phase structure alternately in the angular and axial directions in the diffractive optical element;

[0018] Figure 5 Schematic diagram of the laser optical system that realizes the combined spot of dot-ring dots;

[0019] Figure 6 Schematic diagram of another laser optical system that realizes the combined spot of dot-ring dots;

[0020] Figure 7 Schematic diagram of yet another laser optical system that realizes the combined spot of dot-ring dots;

[0021] Figure 8 Shows based on Figure 6 Schematic diagram of the dot-ring dot light field distribution of the diffractive optical element after etching the negative optical wedge phase in the laser optical system;

[0022] Figure 9 Shows based on Figure 6 Schematic diagram of the dot-ring dot light field distribution of the diffractive optical element after etching the positive optical wedge phase in the laser optical system;

[0023] Figure 10 Shows the diffractive optical element in Figure 6 Schematic diagram of the area ratio and energy ratio of the equal phase region and the optical wedge phase region of the dot-ring dots at different positions in the laser optical system shown;

[0024] Figure 11 Schematic diagram and phase distribution diagram of the diffractive optical element when both the central equal phase region and the optical wedge phase region are angularly distributed;

[0025] Figure 12 Schematic diagram and phase diagram of the dot-ring dot diffractive optical element generated based on the optical wedge phase with opposite phase gradients alternately etched in the angular direction;

[0026] Figure 13 Shows based on Figure 12Schematic diagram of the point-ring point light field distribution of the diffraction optical element;

[0027] Figure 14 Schematic diagram and phase diagram showing a point-ring point diffraction optical element generated by the phase of an optical wedge based on opposite phase gradients with angular etching alternation;

[0028] Figure 15 Showing based on Figure 14 Schematic diagram of the point-ring point light field distribution of the diffraction optical element in;

[0029] Figure 16 Schematic diagram and phase diagram showing a point-ring point diffraction optical element generated by the phase of an optical wedge based on opposite phase gradients with axial etching alternation;

[0030] Figure 17 Schematic diagram and phase diagram showing a diffraction optical element generating point-ring points by the phase of an optical wedge based on opposite phase gradients with axial and angular etching alternation;

[0031] Figure 18 Schematic diagram and phase diagram showing a diffraction optical element based on the phase of an axicon with opposite phase gradients with axial etching alternation;

[0032] Figure 19 Schematic diagram and phase diagram showing a diffraction optical element based on the phase of an axicon with opposite phase gradients with angular etching alternation;

[0033] Figure 20 Schematic diagram of the point-ring segment light field distribution of a diffraction optical element based on the phase of an axicon with opposite phase gradients with angular etching alternation;

[0034] Figure 21 Schematic diagram and phase diagram showing a diffraction optical element based on the phase of an axicon with opposite phase gradients with angular diagonal etching alternation;

[0035] Figure 22 Schematic diagram of the point-ring segment light field distribution of a diffraction optical element based on the phase of an axicon with opposite phase gradients with angular diagonal etching alternation;

[0036] Figure 23 Schematic diagram and phase diagram showing a diffraction optical element based on the phase of an axicon with opposite phase gradients with axial and angular etching alternation;

[0037] Figure 24 Schematic diagram and phase diagram showing the height of a diffraction optical element based on the phase of an axicon with opposite phase gradients with angular etching alternation after removing the equal phase region;

[0038] Figure 25 Schematic diagram and phase diagram showing the height of an equivalent diffraction optical element obtained by superimposing two diffraction optical elements;

[0039] Figure 26 Schematic diagram of the height and phase diagram of the equivalent diffractive optical element obtained by rotating two diffractive optical elements by 1 / 2 sector phase superposition after removing the equal-phase region;

[0040] Figure 27 Schematic diagram of the height and phase diagram of the equivalent diffractive optical element obtained by rotating two diffractive optical elements by 4 / 5 sector phase superposition after removing the equal-phase region. Detailed implementation manners

[0041] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present 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 only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] In the present invention, terms such as "first" and "second" in the present invention and the accompanying drawings (if any) are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence.

[0043] The present invention discloses a diffractive optical element, which modulates the phase region of the diffractive optical element so that an incident laser beam generates a dot-ring-dot spot array on the working plane.

[0044] Embodiment 1:

[0045] Figure 1 Schematic diagram of the optical wedge element with positive and negative phase gradients in the diffractive optical element of the present invention. Where m is a negative optical wedge, high at the edge and low at the center; n is a positive optical wedge, high at the center and low at the edge. The optical wedge is a prism composed of two non-parallel planes, and the included angle of the planes is called the wedge angle α (similar to the base angle of an axicon). When a laser is vertically incident on the optical wedge, due to the linear change of the optical wedge thickness in a specific direction, a linearly varying phase delay is introduced. After passing through the optical wedge, the propagation direction of the light beam deflects, and the deflection angle δ is determined by the wedge angle and the refractive index n of the lens. By modulating the diffractive optical element, the diffractive optical element has an optical wedge phase in some regions, and then a dot-ring-dot spot array is modulated.

[0046] The diffractive optical element in the present invention is used to apply a phase distribution to the transverse beam profile of a laser beam. The applied phase distribution forms a first region and a second region, which are obtained by modulating with a prism element. The phase in the first region is equal, being an equal-phase region; the second region is a prism phase region, which is used to add a preset prism phase to the incident laser beam to obtain the first region and the second region. In other words, the diffractive optical element is divided into multiple regions according to the functions corresponding to different phases, namely the first region and the second region. The first region is also called the equal-phase region, and the second region is obtained after prism phase modulation and is also called the prism phase region, specifically including a first prism phase region and / or a second prism phase region. After the equal-phase region receives the incident laser, a Gaussian spot is formed at the center of the working plane in the laser optical system; when the incident laser passes through the first prism phase region and / or the second prism phase region, an off-center Gaussian spot is formed on the working plane, forming an annular spot beam. In an embodiment of the present invention, both the first prism phase region and the second prism phase region are called prism phase regions, which are respectively obtained by modulating with a positive prism and a negative prism, and are used to add a preset angle of prism phase to the incident laser to form an annular spot beam on the working plane, where the deflection angles of the positive and negative prisms are the same but the directions are opposite.

[0047] Specifically, Figure 2 The schematic diagram and phase diagram of the diffractive optical element that shows the generation of a point-annular spot after etching a negative prism on the diffractive optical element Figure 3 The schematic diagram and phase diagram of the diffractive optical element that shows the generation of a point-annular spot after etching a positive prism on the diffractive optical element. Figure 2 and Figure 3 The phase shift values (phases in radians) based from 0 to 2π are shown in gray shading and the gray shading is expressed as phase values. The relative height of the lens in the figure is represented by a blue-to-yellow gradient, with the lens height represented from 0 to 1, where yellow represents the highest with a height of 1 and blue represents the lowest with a height of 0. Taking Figure 2 as an example, Figure 2 The left figure in shows the relative height of the lens of the diffractive optical element. Blue represents the horizontal plane, indicating that the lens height is 0, and yellow represents the highest point 1 of the lens. The diffractive optical element is a circular lens, and the center of the diffractive optical element is also called the center of the circle, which has the effect of phase offset on the laser beam. As can be seen from the figure, the central point region a of the diffractive optical element is an equal-phase region, and the lens height in the equal-phase region remains unchanged, such as constantly being 0. Here, it is just a schematic number and can also be other constant height values. The equal-phase region a is a circle centered on the center; b is the negative prism phase region, and the height of the lens of the diffractive optical element gradually increases along the center line direction of the fan-shaped ring region, and the height in the region perpendicular to the center line within the fan-shaped ring region is the same. b is a fan-shaped ring, and the center of the fan-shaped ring coincides with the center point. The fan-shaped ring b is arranged along the outer edge of the equal-phase region a. Similar to the following examples, they will not be elaborated. Figure 2In the right-middle figure, a' shows the phase distribution of the equal-phase region corresponding to region a; region b' shows the phase distribution corresponding to region b, and the phase varies in the range of 0 - 2π. Figure 2 The diffraction optical element in the middle includes an equal-phase region a and a negative optical wedge phase region composed of multiple repeated fan-shaped ring regions b, also known as the first optical wedge phase region. When the incident laser passes through the equal-phase region a, a Gaussian spot is formed at the center of the working plane in the laser optical system. When the incident laser passes through the negative optical wedge phase region, a ring spot is formed on the working plane in the laser optical system. The number of ring spots is determined by the number of divided fan-shaped ring regions. For example, Figure 2 as shown, where 10 fan-shaped ring regions b form the negative optical wedge phase region. Figure 3 Similarly, it shows the schematic diagram and phase diagram of a diffraction optical element that etches a positive optical wedge to generate point-ring spots. In this element, the height of the equal-phase region lens is constant, and the height of the lens within the optical wedge phase gradually decreases along the center line direction of the fan-shaped ring region, and the height in the region perpendicular to the center line is the same, which is opposite to the negative optical wedge phase.

[0048] Figure 2 and Figure 3 in the two optical wedge phase gradients in the middle change at the same speed but in opposite directions. Figure 2 and Figure 3 the two etched optical wedge phase gradients in the middle change at the same speed but in opposite directions. In addition, the diffraction optical element in the present invention can obtain a point-ring spot beam on the working plane based on any combination modulation of positive and negative optical wedges. The diffraction optical element in the present invention can obtain a point-ring spot beam on the working plane based on any combination etching modulation of positive and negative optical wedges. In an optional mode, only one of the positive and negative optical wedges can be selected, or both can be used. In an optional embodiment, the number of the first optical wedge phase region and the second optical wedge phase region constructed by selecting positive and negative optical wedges is equal, and the arrangement can be randomly arranged or alternately arranged. Preferably, the positive and negative optical wedges are etched alternately, that is, the first optical wedge phase region and the second optical wedge phase region appear alternately, such as axially alternating arrangement or angularly alternating arrangement of the first optical wedge phase region and the second optical wedge phase region. For example, Figure 4 as shown, where region a (center) represents the equal-phase region, regions b and c respectively represent the etched opposite optical wedge phase regions. The left figure shows angular staggering (the reference circle center is staggered on the outer ring of region a), and the right figure shows axial staggering (taking the radius as the reference, staggering from the center along the radius outwards). Based on etching the optical wedge element to construct the central equal-phase region and the optical wedge phase region in the diffraction optical element, when the laser passes through the diffraction optical element, a point-ring spot array can be generated on the working plane of the laser optical system.

[0049] Those skilled in the art should understand that the actual height of the lens is at the micron level and the lens size is at the millimeter level. To facilitate the demonstration of the design concept, the actual height of the lens etching is scaled to a relative height of 0 - 1, where the phase value of 2π corresponds to a height of 1; the phase value of 0 corresponds to a height of 0.

[0050] Based on the above, the diffractive optical element in the present invention has multiple phase regions. The equal-phase region is used to receive the incident light beam and form a Gaussian spot at the center of the working plane. The wedge phase region is used to form an annular spot at the working plane after receiving the incident light beam. The wedge phase region includes a first wedge phase region and a second wedge phase region. Whether the first wedge phase region and the second wedge phase region exist individually, are randomly arranged in two regions, or are alternately arranged, a dot-ring dot matrix spot can be obtained.

[0051] Furthermore, when the diffractive optical element is provided with an equal-phase region, after etching the above-mentioned wedge phase on the diffractive optical element, such as a positive wedge phase and / or a negative wedge phase, the incident laser generates a dot-ring dot spot after passing through the diffractive optical element. By changing the fan-ring area and phase gradient of the etched wedge phase, the position and intensity of the annular spot can be changed. Further, when alternating positive and negative wedge phases are etched on the diffractive optical element, the generated dot-ring dot spot has better defocus characteristics. Here, the alternating etching arrangement can adopt an axial arrangement, an angular arrangement, or a combination of both. Secondly, the equal-phase region in the diffractive optical element is adjustable. Adjusting the size of the equal-phase region can change the energy ratio of the dot-ring dot spot. In addition, when a divergent laser beam is incident on the diffractive optical element, by adjusting the distance from the incident laser to the diffractive optical element, the spot area of the incident laser on the diffractive optical element can be changed, thereby changing the energy ratio of the dot-ring dot. That is, it is only necessary to adjust the position of the diffractive optical element on the laser beam path, or in other words, adjust the distance from the diffractive optical element to the laser emission point.

[0052] In another alternative embodiment, when the above positive and negative alternating positive and negative wedge phases are replaced with positive and negative axicon phases, the incident laser generates a dot-ring segment spot array with a long depth of focus after passing through the diffractive optical element. Specifically, refer to the following description.

[0053] The equal-phase region in the above-mentioned Embodiment 1 is also referred to as the first region in the diffractive optical element, and the wedge phase region is referred to as the second region. The second region is formed by a positive wedge phase, a negative wedge phase, or a combination of positive and negative wedge phases.

[0054] Embodiment 2

[0055] As Figure 5A schematic diagram of a laser optical system for realizing a point-ring point combined light spot is shown, which includes: a diffractive optical element 1, a focusing lens 2, and a working plane 3. The diffractive optical element is arranged in the beam path of the laser, applies a wedge phase to the incident laser, focuses the incident laser with the aid of the focusing lens 2, and constructs a point-ring dot matrix light spot in the working plane 3. When the incident laser beam (emitted from the laser emission point P, i.e., the laser source) passes through the equal-phase region in the diffractive optical element, a Gaussian light spot (point light spot) located at the center of the working plane 3 is correspondingly formed in the working plane 3. On the wedge phase region formed after applying the wedge phase, after the incident laser passes through, a ring point light spot is correspondingly formed. The wedge phase region here refers to the description in Embodiment 1. To avoid redundancy, it will not be elaborated further. The diffractive optical element 1 in Embodiment 2 uses the diffractive optical element disclosed in Embodiment 1.

[0056] Specifically, the laser beam generated by the laser source is used as the incident laser beam; the diffractive optical element is arranged in the beam path of the incident laser beam to apply a phase distribution to the incident laser beam, which is realized by constructing a first region and a second region on the diffractive optical element: when the incident laser beam passes through the first region, a central light spot is formed in the working plane, and the laser beam passing through the second region forms a ring point light spot array in the working plane. Further, based on Figure 5 the laser optical system, a collimating lens 4 is further included, which is used to collimate and expand the incident laser. Optionally, the collimating lens 4 is located between the diffractive optical element 1 and the focusing lens 2, and the diffractive optical element 1 can be adjusted along the beam path direction of the incident laser, specifically as Figure 6 and 7 shown, the diffractive optical element 1 is arranged in the beam path direction of the incident laser, and can be located at any position before the focusing lens 2, that is, before or after the collimating lens 4. Specifically, referring to Figure 6 When the diffractive optical element 1 moves in the beam path direction and continuously moves from the dotted line position to the solid line region, the point light spot on the working plane 3 changes to a point-ring point, and as the diffractive optical element 1 moves, the peak power density of the ring point gradually increases, and the peak power density of the central point gradually decreases. The area of the incident light spot irradiated on the diffractive optical element and the corresponding light spot energy distribution change as Figure 10 shown, and for the point-ring point combined light spot, the point-ring point power ratio is continuously adjustable with the position change of the diffractive optical element 1, continuously adjusting the energy ratio between the point and the ring point. In addition, when the laser optical system is the Figure 7 structure, that is, when the diffractive optical element 1 moves between the collimating lens 4 and the focusing lens 2, the point-ring point light spot on the working plane 3 does not change with the position change of the diffractive optical element 1 (constant stable state).

[0057] It should be noted that when the collimating lens 4 is located between the light output position P of the laser and the diffractive optical element 1, the divergent light beam output by the laser forms a certain width after propagating in free space for a certain distance and then enters the collimating lens 4, turning into a quasi-parallel light beam. The offset of the point-ring spot generated in this way with respect to the incident spot is more stable. By adjusting the focal length of the collimating lens 4, the spot radius of the quasi-parallel light incident on the diffractive optical element can be changed, and thus the energy ratio of the point-ring spot can be changed.

[0058] The laser optical system using the diffractive optical element 1 of the present invention generates a point-ring spot on the working plane 3, which is also called the effect of a Gaussian spot and an annular dot matrix spot. Figure 8 and Figure 9 show Figure 6 Schematic diagrams of the point-ring light field distributions generated by diffractive optical elements etched with negative and positive optical wedge phases respectively in the laser optical system based on Figure 8 and 9 are shown, which display the distributions of the central point and the ring point in the focal plane and before and after it. Referring to

[0059] In order to better understand the effects of diffractive optical elements etched with positive and negative optical wedge phases alternately, the structural characteristics and phase distributions of diffractive optical elements etched axially in the angular direction in different designs, the following will describe the schematic diagrams of the diffractive optical elements in the present invention realizing a point-ring array through different designs.

[0060] Figure 11 Schematic diagrams and phase diagrams of diffractive optical elements with equal-phase regions and optical wedge phases arranged angularly are shown; there are two functional regions in this lens. Region a is an equal-phase region, with a fan shape, and the center of the fan corresponds to the central point, generating a central Gaussian spot, corresponding to a' in the phase diagram. Region b is an optical wedge phase region, with a fan shape, and the center of the fan corresponds to the central point. When the laser passes through it, a ring point is generated, corresponding to b' in the phase diagram.

[0061] Both the equal-phase region and the optical wedge phase region of the diffractive optical element are arranged angularly, and the energy ratio of the generated point-ring spot is fixed. The energy ratio is independent of the position of the diffractive optical element 1 in the laser optical system. The magnitude of the energy ratio is determined by the area ratio or the angle ratio of the equal-phase region and the optical wedge phase region, that is, the energy ratio is not affected by the change in the position of the diffractive optical element in the optical path and the characteristics of the laser output spot.

[0062] Figure 12 Schematic diagrams and phase diagrams of a point-ring diffractive optical element generated by etching optical wedge phases with opposite phase gradients alternately in the angular direction are shown; Figure 12The diffractive optical element in [it] is divided into three functional regions, an equal-phase region, a first wedge phase region, and a second wedge phase region. Both the first wedge phase region and the second wedge phase region have four sectors, and they are arranged alternately. As shown in the figure, region a is the equal-phase region, which is circular. Multiple repeated sector ring regions b form the first wedge phase region, and multiple repeated sector ring regions c form the second wedge phase region. The sector rings b and c are arranged along the outer edge of region a. The following examples are similar. Refer to Figure 12 In the right figure in [it], the gray shadow shows that the adjacent sector ring regions b and region c are phase complementary, that is, a negative and positive phase gradient design. a' is the phase value of the equal-phase region corresponding to region a; region b' is the phase change diagram corresponding to region b, and region c' is the phase change diagram corresponding to region c. b' and c' are complementary. The schematic diagram of the defocused morphology of the specific point-ring point spot can be referred to Figure 13 As shown, on the focal plane (the middle plane, that is, the working plane), there is a central spot (Gaussian spot), and eight ring points are respectively generated by the lasers of the first wedge phase region composed of four sector ring regions b and the second wedge phase region composed of four sector ring regions c. Specifically, half of the ring points near the focal plane are close to the optical axis and half are far from the optical axis. Therefore, the peak power density of the light field before and after the focal plane is nearly the same, and the positions of the ring points have changed. In the figure, the light intensity is represented by color. The red 1 represents the maximum light intensity in the whole plane, and the blue 0 represents the minimum light intensity. Among them, the blue plane in the middle is the focal plane, that is, the working plane is the plane above, and the plane below is the post-focal plane.

[0063] Figure 14 Shows a schematic diagram and a phase diagram of a diffractive optical element that generates point-ring points based on angularly alternating etching of opposite phase gradients of the wedge phase and opposite phase gradients of the diagonal sector rings; and Figure 12 Similar, except that both the first wedge phase region and the second wedge phase region have five sectors, that is, the sector ring regions b and the sector ring regions c are equal and odd. The above design of 5 is just one implementation. Other odd numbers can also achieve similar effects, that is, the ring points generated by the diagonal sectors coincide on the focal plane (the middle plane), and the schematic diagram of the specific spot defocused morphology can be referred to Figure 15 As shown. This is because the phases of the diagonal etching regions are opposite. After the incident laser passes through the diagonal etching regions, the light ray inclination angles are the same. After being focused by the focusing lens, they converge at a point, and an odd number of uniformly distributed ring points can be generated. At this time, the ring points generated by the diagonal regions coincide on the working plane, and the ring points have more stable defocus characteristics. When the incident light spot deviates, the influence on the ring points on the working plane is smaller. Therefore, when the number of sector rings in the first wedge phase region and the number of sector rings in the second wedge phase region are the same, and the number of sectors is odd, and after angularly alternating etching of negative and positive wedges, the ring points generated on the focal plane coincide, and at this time the ring points have more stable defocus characteristics. Specifically, refer to Figure 15, the light fields before and after the focal plane are completely consistent, and each ring point on the focal plane consists of two ring points, one close to the optical axis and the other far from the optical axis; after defocusing, one of the two ring points that make up this ring point moves away from the optical axis and the other moves closer to the optical axis, and the front and back of the focal plane are completely consistent. Therefore, during laser processing, the tolerance for positive and negative defocus of the light field is greater, and it has the characteristic of long depth of focus.

[0064] The proportion of the aperture and the angle of the optical wedge on the diffractive optical element can be changed for each etching area, and the position and intensity of each ring point can be customized individually.

[0065] Furthermore, Figure 16 The schematic diagram and phase diagram of the point-ring point diffractive optical element generated based on the optical wedge phase with axially alternating etching of opposite phase gradients are shown; as can be seen from the figure, when the first optical wedge phase region and the second optical wedge phase region are arranged axially staggered, the diffractive optical element can also generate a point-ring point light spot array with long depth of focus on the working plane. Among them, a is the equal phase region, which generates a central Gaussian light spot; b and c are the optical wedge phase regions, which are arranged axially alternately; b is the negative fan-shaped ring optical wedge phase, c is the positive fan-shaped ring optical wedge phase, a' is the phase value of the equal phase region corresponding to region a; the b' region is the phase change diagram corresponding to region b, and the c' region is the phase change diagram corresponding to region c.

[0066] Figure 17 The schematic diagram and phase diagram of the diffractive optical element that generates point-ring points based on the optical wedge phase with axial and angular alternating etching of opposite phase gradients are shown; this embodiment combines Figure 12 the angular direction in Figure 16 and the axial staggered arrangement in Figure 17 The designed diffractive optical element can also generate a point-ring point light spot array with long depth of focus on the working plane.

[0067] Example 3:

[0068] Combining the above Example 1 and Example 2, when the optical wedge phase in the diffractive optical element of Example 2 is replaced with an axicon phase, the laser optical system realizes the effect of a point-ring segment light spot array, that is, when the diffractive optical element with an etched axicon phase is placed in the laser optical system, a point-ring segment light spot array can be generated on the working plane. The specific structure of the diffractive optical element is as follows.

[0069] The laser optical system shown in Example 3 is similar to that in Example 2, and the specific working process is similar, so it will not be described in detail to avoid redundancy.

[0070] Example 4:

[0071] Figure 18Schematic diagram and phase diagram of a diffractive optical element showing the axicon phase based on axially etched alternating opposite phase gradients; the phase shift changes from large to small from the center of the circle outward, with periodicity. As shown in the figure, a is the equal-phase region, which generates a central spot, and b and c are the axicon phase regions, which appear alternately along the axis; b is the positive axicon phase region, c is the negative axicon phase region, b and c have opposite phases, and the diffractive optical element consists of the equal-phase region a, the positive axicon phase region composed of multiple identical fan rings b, and the negative axicon phase region composed of multiple identical fan rings c, and the fan rings b and c are arranged alternately axially.

[0072] Figure 19 Schematic diagram and phase diagram of a diffractive optical element showing the axicon phase based on angularly etched alternating opposite phase gradients; Figure 20 Schematic diagram of the point-ring segment light field distribution of a diffractive optical element showing the axicon phase based on angularly etched alternating opposite phase gradients. After angular or axial alternate etching of positive and negative axicons, the ring segment spots generated on the working plane coincide. At this time, the ring segment spot array has a more stable defocus characteristic, similar to the wedge phase. Similar to Figure 12 and 14 When the positive and negative axicons are alternately etched and the number is equal and even, after passing through the diffractive optical element, a point-ring segment spot array is formed on the working plane, that is, a Gaussian spot at the center and a beam composed of ring segments on the ring. Referring to Figure 20 After the incident laser is defocused, half of the ring segment spots in front of and behind the focal plane are close to the optical axis, and half of the ring light is far from the optical axis. Therefore, the peak power density of the light fields in front of and behind the focal plane is close to the same, and the position of the ring segment spots has changed.

[0073] Example 5:

[0074] Figure 21 Schematic diagram and phase diagram of a diffractive optical element showing the axicon phase based on angularly etched alternating opposite phase gradients and with opposite phase gradients for the diagonal fan rings; Figure 22 Show Figure 21 Schematic diagram of the point-ring segment light field distribution of the diffractive optical element shown. As Figure 21 shown, the diffractive optical element lens has three functional regions. a is the equal-phase region, which generates a central spot; b and c are the axicon phase regions, and multiple identical fan rings b form the positive axicon phase region; multiple identical fan rings c form the negative axicon phase region, where the number of the fan ring regions b and c is equal and odd, and the fan rings b and c are arranged alternately angularly. Figure 22As shown, each ring of light on the focal plane consists of two rings, one close to the optical axis and the other far from the optical axis; after defocusing, one of the two ring-segment light spots that make up this ring-segment light spot moves away from the optical axis and the other moves closer to the optical axis, and it is exactly the same before and after the focal plane. During laser processing, it has greater tolerance for positive and negative defocus of the light field and has the characteristic of long focal depth. In other words, when the number of phase fan rings with alternating opposite phase gradients is equal and odd, it has the characteristic of long focal depth. Here, the phase can be the axicon phase or the prism phase, and the alternating method is not limited to angular or axial. During axial etching, the energy of the incident light spot is Gaussian distributed, and the areas of the phase regions with different phase gradients need to be different to achieve better long focal depth characteristics.

[0075] Example 6:

[0076] ​ Schematic diagrams and phase diagrams showing the generation of point-ring segments by an axicon phase based on alternating opposite phase gradients in axial and angular etching; the diffractive optical element includes an equal-phase region, a negative axicon phase region, and a positive axicon phase region, and the arrangement of the negative axicon phase region and the positive axicon phase region does not have the regularity of a single angular or single axial distribution. This embodiment combines the ​ angular direction in ​ and the ​ axial staggered arrangement in

[0077] Example 7:

[0078] ​ Height schematic diagrams and phase diagrams of a diffractive optical element based on an axicon phase with alternating opposite phase gradients in angular etching after removing the equal-phase region are shown; ​ will be described in combination with ​ Comparing the two figures, it can be seen that the diffractive optical element in ​ includes a positive axicon phase region and a negative axicon phase region, which are arranged in a staggered manner and extend to the central region. The central region does not include an equal-phase region. The diffractive optical element is divided into ten regions in the angular direction, that is, a positive axicon phase region composed of five identical first sectors and a negative axicon phase region composed of five other identical second sectors. The sizes of the first sector and the second sector are the same. Further, ​Shows the height schematic diagram and phase diagram of the equivalent diffractive optical element obtained by superimposing two diffractive optical elements; when the number of positive and negative phase regions in the diffractive optical element is odd, the equivalent height schematic diagram and phase diagram after superposition. As shown in the figure, the period of the equivalent diffractive optical element lens is denser, the deflection effect on light is increased, and the radius of the ring light (the degree of deviation of the position of the ring light from the central region of the lens) is larger. Specifically, two identical ​ The shown diffractive optical elements are placed in the optical path of the incident laser. One of the diffractive optical elements is fixed, and the other diffractive optical element is rotated along the laser optical axis. When the relative rotation angle of the two diffractive optical elements is 0, the axicon phases of the same sectors are superimposed on each other, as ​ shown, is the equivalent height schematic diagram and phase diagram after superposition. Since both diffractive optical elements apply the same axicon phase to the incident light beam, the phase period after superposition is halved, and the position of the ring-ring array spot will expand outward by a factor of two.

[0079] ​ Shown after removing the equal-phase region, select ​ The height schematic diagram and phase diagram of the equivalent diffractive optical element obtained by rotating and superimposing the two diffractive optical elements in []. Here, the relative rotation is 1 / 2 sector angle. One of the diffractive optical elements is fixed, and the other diffractive optical element is rotated. The rotation angle is half of the sector ring angle in the diffractive optical element. As shown in the figure, the superimposed diffractive optical element includes an equal-phase region, a positive axicon phase region, and a negative axicon phase region, where a is the positive axicon phase region, c is the negative axicon phase region, and b is the equal-phase region. The sizes of the sector rings a, b, and c are equal and the numbers are the same. The three regions appear alternately in the angular direction, generating a long depth of focus point-ring segment spot array. Specifically, the overlapping regions generate different types of phase regions including the following situations. For example, when the positive axicon phase of one diffractive optical element exactly cancels the negative axicon phase of another diffractive optical element, an equal-phase region a is formed, so that the light beam passing through this region remains straight and forms a central Gaussian spot on the focal plane. In the uncanceled region, the positive axicon phase region of one diffractive optical element is superimposed on the positive axicon region of another diffractive optical element; the negative axicon phase region is superimposed on the negative axicon phase region of another diffractive optical element. At this time, the light beam still maintains a circular distribution on the working plane, generating a long depth of focus point-ring segment spot array.

[0080] ​ Shown after removing the equal-phase region, select ​Schematic diagram of the height and phase diagram of the equivalent diffractive optical element obtained by rotating two diffractive optical elements in [[ ]] and superposing the 4 / 5 sector phases. Here, the relative rotation is 4 / 5 of the sector angle. Fix one diffractive optical element and rotate the other diffractive optical element. The rotation angle is 4 / 5 of the sector ring angle in the diffractive optical element. As shown in the figure, compared with Embodiment 8, the area of the equal-phase region increases. At this time, the proportion of the central light energy increases, and the increase proportion is related to the area (or angle) of the equal-phase region in the lens. Further, if ​ When rotating continuously under the shown rotation angle, for example, when rotating by one sector angle, point light spots are generated after the two diffractive optical elements are superposed. When the lens rotation angle is 0 - (one sector angle) - (two sector angles), the corresponding target light field presents the state of: complete ring segment light - complete point light - complete ring segment light, corresponding to the change trend within one period. When the rotation angle is a multiple of the sector, only point light or ring segment light can be achieved. For other rotation angles, a point - ring segment light spot array can be achieved.

[0081] In summary, after dividing the diffractive optical element into regions with different functions by etching the prism phase or axicon phase, when applying the above different types of diffractive optical elements to ​ the laser optical system in [[ ]], various different effects such as point - ring point light spots, long - depth - of - focus point - ring point light spots, point - ring segment light spots, and long - depth - of - focus point - ring segment light spots can be achieved on the working plane.

[0082] When generating ring points by etching the prism phase, by changing the area and phase gradient of the etched prism phase region, the position and intensity of the ring points can be changed. When the phase region of the diffractive optical element includes an equal - phase region and a prism phase region, a point - ring point combined light spot is generated. When preferably etching the prism phase with alternating positive and negative phase gradients, the generated point - ring point light spots have better defocus characteristics. The etched alternating positive and negative phase gradients can be axial or angular or a combination of both.

[0083] By changing the equal - phase region in the diffractive optical element, the energy ratio between the point and the ring point can be changed. When a divergent light beam is incident on the diffractive optical element, by changing the distance from the incident light spot to the diffractive optical element, the area of the light spot incident on the diffractive optical element can be changed, thereby changing the energy ratio of the point - ring point.

[0084] Etching positive and negative alternating opposite phase gradients is applicable not only to the prism phase but also to the axicon phase. When changing the positive prism phase and negative prism phase etched in the phase - shift region to a positive axicon phase and a negative axicon phase, a point - ring segment light spot array with long depth of focus can be generated.

[0085] By setting two identical diffractive optical elements with etched alternating axicon phases in the incident laser path, and without setting a central equal-phase region for these two identical diffractive optical elements, by rotating to change the relative positions of the two diffractive optical elements, when the incident laser passes through the superimposed diffractive optical elements, a point-ring array spot with a long depth of focus can be generated, and the energy ratio of the point-ring light can be adjusted by changing the deflection angles of the two diffractive optical elements.

[0086] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A diffractive optical element for generating a dot-ring dot spot array, which is used to impose a phase distribution on the transverse beam profile of a laser beam, characterized in that, The applied phase distribution forms a first region and a second region, where the phase in the first region is equal, being an equal-phase region; the second region is a wedge phase region, obtained by modulating the wedge phase. When the laser beam passes through the first region, it is used to generate a central spot, and when the laser beam passes through the second region, it is used to generate an annular spot.

2. The diffractive optical element for generating a dot-ring dot light spot array according to claim 1, wherein The first region is located in the central region of the diffractive optical element, being a circle centered at the center. The second region is composed of multiple fan-shaped rings, each fan-shaped ring having the same size, and the fan-shaped rings are arranged along the outer edge of the first region centered at the center.

3. The diffractive optical element for generating a dot-ring dot spot array according to claim 2, characterized in that, The second region is a positive wedge phase region or a negative wedge phase region, where the positive wedge phase region is a region obtained by modulating on a positive wedge element, and the negative wedge phase region is a region obtained by modulating on a negative wedge element.

4. The diffractive optical element for generating a dot-ring dot light spot array according to claim 2, characterized in that, The second region is a phase region composed of a positive wedge phase region and a negative wedge phase region, where the number of fan-shaped rings included in the positive wedge phase region is equal to the number of fan-shaped rings included in the negative wedge phase region, and the positive wedge phase region and the negative wedge phase region are arranged alternately.

5. The diffractive optical element for generating a point-ring spot array according to claim 4, wherein, The number of fan-shaped rings in the positive wedge phase region and the number of fan-shaped rings in the negative wedge phase region are odd numbers.

6. The diffractive optical element for generating a point-ring spot array according to claim 1, wherein The first region is composed of multiple identical first sectors, and the second region is composed of multiple identical second sectors. The first sector and the second sector have the same shape and size, and the center of the first sector is the same as the center of the second sector, being the center of the first region. The first sector and the second sector are arranged alternately.

7. The diffractive optical element for generating a point-annular spot array according to claim 1, etching the wedge phase to obtain the second region, including angular etching and axial etching.

8. A laser optical system, characterized in that, Comprising: A laser source that outputs a laser beam, and the laser beam serves as an incident laser beam; A diffractive optical element according to any one of claims 1-7, a focusing lens, and a working plane. The diffractive optical element is arranged in the beam path of the incident laser beam to apply a phase distribution to the incident laser beam, which is achieved by constructing a first region and a second region on the diffractive optical element: when the incident laser beam passes through the first region, a central spot is formed on the working plane, and when the laser beam passes through the second region, an annular spot array is formed on the working plane.

9. The laser optical system according to claim 8, wherein The laser optical system further includes: a collimating lens that collimates and expands the incident laser beam.

10. The laser optical system according to claim 8, characterized in that, Adjusting the distance between the diffractive optical element and the incident laser beam along the optical axis is used to change the area ratio of the incident beam irradiating the first region and the second region of the diffractive optical element, and continuously adjusting the energy ratio of the point and the annular spot.

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