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

Abstract

The invention discloses a diffractive optical element for generating a point-ring section light spot array and a laser optical system, belongs to the field of laser processing, and is used for applying phase distribution on a transverse beam profile of a laser beam, and the applied phase distribution forms an equiphase region, a positive axicon phase region and a negative axicon phase region. Wherein the phases of the equiphase regions are equal, the positive-axis pyramid phase regions and the negative-axis pyramid phase regions are arranged in a staggered manner, when a laser beam passes through the equiphase regions, the equiphase regions generate a central light spot, and when the laser beam passes through the positive-axis pyramid phase regions and the negative-axis pyramid phase regions, the central light spot generates a central light spot. The positive axicon phase region and the negative axicon phase region generate an annular segment light spot array. According to the diffraction optical element, a point-ring section light spot array with long focal depth can be generated in a laser optical system, and the peak power density of a ring light area can be improved.

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 segment 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 automotive manufacturing, aerospace and other fields.

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

[0004] The spot ring spot preheats the welding material through the ring light, and the Gaussian light in the center maintains deep fusion welding. By combining the light spots, the temperature gradient of the welding material is smooth, 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 spot light and ring light through a circular fiber core and a ring fiber core, and the power of the spot light and the 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 in 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 low 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 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 produced by external optical path shaping cannot be taken into account at the same time as the telephoto 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 deficiencies of the prior art and the improvement requirements, the present invention provides a diffractive optical element for generating a point-ring segment spot array, which is used to apply a phase distribution on the transverse beam profile of a laser beam. The applied phase distribution forms an equal-phase region, a positive axial pyramid phase region, and a negative axial pyramid phase region. The positive axial pyramid phase region and the negative axial pyramid phase region are obtained by positive axial pyramid and negative axial pyramid phase modulation respectively. Among them, the phases in the equal-phase region are equal, and the positive and negative axial pyramid phase regions are arranged alternately. When the laser beam passes through the equal-phase region, it is used to generate a central spot. When the laser beam passes through the positive axial pyramid phase region and the negative axial pyramid phase region, it is used to generate ring segment spots.

[0007] The present invention discloses a laser optical system, including: a laser source that outputs a laser beam, and the laser beam serves as an incident laser beam; the above-mentioned diffractive optical element, a focusing lens, and a working plane. Among them, 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 an equal-phase region, a positive axial pyramid phase region, and a negative axial pyramid phase region on the diffractive optical element, it is realized that: when the incident laser beam passes through the equal-phase region, a central spot is formed on the working plane, and the laser beams passing through the positive axial pyramid phase region and the negative axial pyramid phase region form a ring segment spot array on the working plane.

[0008] The present invention also discloses a laser optical system, including: a laser source that outputs a laser beam, and the laser beam serves as an incident laser beam; two diffractive optical elements, where the diffractive optical element is a special case of the above-mentioned diffractive optical element, that is, the case where the area of the equal-phase region is 0, a focusing lens, and a working plane. Among them, the two diffractive optical elements are arranged in the beam path of the incident laser beam to apply a phase distribution on the incident laser beam. When the first diffractive optical element is fixed and the second diffractive optical element is rotated around the optical axis, by constructing an equal-phase region, a positive axial pyramid phase region, and a negative axial pyramid phase region on the two superimposed diffractive optical elements, it is realized that: when the incident laser beam passes through the equal-phase region, a central spot is formed on the working plane, and the laser beams passing through the positive axial pyramid phase region and the negative axial pyramid phase region form a ring segment spot array on the working plane, where the angle of rotation of the second diffractive optical element relative to the first diffractive optical element is any angle except for multiples of the first sector or the second sector angle in (0, 2π).

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

[0010] (1) When the diffractive optical element uses positive axial pyramid phase and negative axial pyramid phase alternately, a point-ring segment spot array with a long depth of focus can be generated;

[0011] (2) Secondly, the point-ring segment light spot discretizes the ring light. When the number of fan rings in the diffractive optical element is twice an odd number, the peak power density in the ring light region can be increased on the working plane;

[0012] (3) By setting two identical diffractive optical elements with etched alternating axicon phases in the incident laser path, without setting the central equal-phase region for these two identical diffractive optical elements, by rotating to change the phase superposition state of the two diffractive optical elements, when the incident laser passes through the superimposed diffractive optical elements, a point-ring segment light spot array with a long depth of focus can be generated, and the energy ratio of the point-ring segment light spot can be adjusted by changing the deflection angles of the two diffractive optical elements. Brief Description of the Drawings

[0013] Figure 1 Schematic diagram of the light wedge element with positive and negative phase gradients in the diffractive optical element of the present invention;

[0014] Figure 2 Schematic diagram and phase diagram of the diffractive optical element that generates point-ring points after etching the negative light wedge phase structure in the light wedge phase region of the diffractive optical element.

[0015] Figure 3 Schematic diagram and phase diagram of the diffractive optical element that generates point-ring points after etching the positive light wedge phase structure in the light wedge phase region of the diffractive optical element;

[0016] Figure 4 Schematic diagram of the diffractive optical element etched with phase structures alternately in the angular and axial directions;

[0017] Figure 5 Schematic diagram of the laser optical system that realizes the combined spot of point-ring points;

[0018] Figure 6 Schematic diagram of another laser optical system that realizes the combined spot of point-ring points;

[0019] Figure 7 Schematic diagram of yet another laser optical system that realizes the combined spot of point-ring points;

[0020] Figure 8 Showing based on Figure 6 Schematic diagram of the point-ring point light field distribution of the diffractive optical element after etching the negative light wedge phase in the laser optical system;

[0021] Figure 9 Showing based on Figure 6 Schematic diagram of the point-ring point light field distribution of the diffractive optical element after etching the positive light wedge phase in the laser optical system;

[0022] Figure 10 Showing the diffractive optical element atFigure 6 Schematic diagrams of the area ratio and energy ratio between the equal-phase region of the point-ring point and the optical wedge phase region of the laser optical system shown at different positions;

[0023] Figure 11 Schematic diagram of a diffractive optical element and a phase distribution diagram when both the central equal-phase region and the optical wedge phase region are angularly distributed;

[0024] Figure 12 Schematic diagram and phase diagram of a point-ring point diffractive optical element generated based on the optical wedge phase with opposite phase gradients alternating in angular etching;

[0025] Figure 13 Showing based on Figure 12 Schematic diagram of the point-ring point light field distribution of the diffractive optical element in

[0026] Figure 14 Schematic diagram and phase diagram of a point-ring point diffractive optical element generated based on the optical wedge phase with opposite phase gradients alternating in angular etching;

[0027] Figure 15 Showing based on Figure 14 Schematic diagram of the point-ring point light field distribution of the diffractive optical element in

[0028] Figure 16 Schematic diagram and phase diagram of a point-ring point diffractive optical element generated based on the optical wedge phase with opposite phase gradients alternating in axial etching;

[0029] Figure 17 Schematic diagram and phase diagram of a diffractive optical element generating a point-ring point based on the optical wedge phase with opposite phase gradients alternating in axial and angular etching;

[0030] Figure 18 Schematic diagram and phase diagram of a diffractive optical element based on the axicon phase with opposite phase gradients alternating in axial etching;

[0031] Figure 19 Schematic diagram and phase diagram of a diffractive optical element based on the axicon phase with opposite phase gradients alternating in angular etching;

[0032] Figure 20 Schematic diagram of the point-ring segment light field distribution of a diffractive optical element based on the axicon phase with opposite phase gradients alternating in angular etching;

[0033] Figure 21 Schematic diagram and phase diagram of a diffractive optical element based on the axicon phase with opposite phase gradients alternating in angular diagonal etching;

[0034] Figure 22Schematic diagram of the point-ring segment light field distribution of a diffractive optical element showing the axicon phase based on alternating opposite phase gradients of angular diagonal etching;

[0035] Figure 23 Schematic diagram and phase diagram of a diffractive optical element showing the axicon phase based on alternating opposite phase gradients of axial and angular etching;

[0036] Figure 24 Height schematic diagram and phase diagram of a diffractive optical element showing the axicon phase based on alternating opposite phase gradients of angular etching after removing the equal phase region;

[0037] Figure 25 Height schematic diagram and phase diagram of an equivalent diffractive optical element obtained by superimposing two diffractive optical elements;

[0038] Figure 26 Height schematic diagram and phase diagram of an equivalent diffractive optical element obtained by superimposing two diffractive optical elements after rotating 1 / 2 sector phase and removing the equal phase region;

[0039] Figure 27 Height schematic diagram and phase diagram of an equivalent diffractive optical element obtained by superimposing two diffractive optical elements after rotating 4 / 5 sector phase and removing the equal phase region. Detailed implementation method

[0040] 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.

[0041] In the present invention, terms such as "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects and do not necessarily describe a specific order or sequence.

[0042] 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 point-ring spot array on the working plane.

[0043] Example 1:

[0044] Figure 1Schematic diagram of a light wedge element with positive and negative phase gradients in the diffractive optical element of the present invention is shown. Where m is a negative light wedge, with a high edge and a low center; n is a positive light wedge, with a high center and a low edge. A light wedge is a prism formed by two non-parallel planes, and the included angle between the planes is called the wedge angle α (similar to the base angle of an axicon). When a laser is incident perpendicularly on the light wedge, due to the linear variation of the light wedge thickness along a specific direction, a linearly varying phase delay is introduced. After passing through the light 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, a part of the diffractive optical element has a light wedge phase, and then a dot-ring dot spot array is modulated.

[0045] The diffractive optical element in the present invention 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, and the first region and the second region are modulated by a light wedge element. The phases in the first region are equal, which is an equal-phase region; the second region is a light wedge phase region, which is used to add a preset light wedge 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 light wedge phase modulation, and is also called the light wedge phase region, specifically including the first light wedge phase region and / or the second light wedge 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 light wedge phase region and / or the second light wedge phase region, an off-center Gaussian spot is formed on the working plane, forming a ring dot beam. In the embodiments of the present invention, both the first light wedge phase region and the second light wedge phase region are called light wedge phase regions, and are respectively modulated by a positive light wedge and a negative light wedge, which are used to add a preset angle of light wedge phase to the incident laser, and a ring dot beam is formed on the working plane, where the deflection angles of the positive and negative light wedges are the same but the directions are opposite.

[0046] Specifically, Figure 2 Schematic diagram and phase diagram of a diffractive optical element that generates dot-ring dots after etching a negative light wedge on the diffractive optical element are shown. Figure 3 Schematic diagram and phase diagram of a diffractive optical element that generates dot-ring dots after etching a positive light wedge on the diffractive optical element are shown. Figure 2 and Figure 3 The phase shift values (phases in radians) based on 0 to 2π are shown in gray shading, and the gray shading is expressed as a phase value. The relative height of the lens in the figure is represented by a blue-to-yellow gradient, and the lens height is represented by 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 2The left figure in [figure number] shows the relative height of the diffractive optical element lens. The blue color represents the horizontal plane, indicating that the lens height is 0, and the yellow color 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 shift on the laser beam. As can be seen from the figure, the central point area a of the diffractive optical element is an equal-phase area, and the lens height in the equal-phase area remains unchanged. For example, it is constantly 0. Here, only a schematic number is shown, and it can also be other constant height values. The equal-phase area a is a circle centered on the center; b is the negative optical wedge phase area. The height of the lens of the diffractive optical element gradually increases along the center line direction of the fan-shaped ring area, and the height of the area perpendicular to the center line in the fan-shaped ring area is the same. b is a fan-shaped ring, and the center of the circle corresponding to the fan-shaped ring coincides with the center point. The fan-shaped ring b is arranged along the outer edge of the equal-phase area a. Similar to the following examples, they will not be elaborated. Figure 2 In the right figure in [figure number], a' is the phase distribution of the equal-phase area corresponding to area a; area b' is the phase distribution corresponding to area b, and the phase changes in the range of 0 - 2π. Figure 2 In [figure number], the diffractive optical element includes an equal-phase area a and a negative optical wedge phase area composed of multiple repeated fan-shaped ring areas b, which is also called the first optical wedge phase area. When the incident laser passes through the equal-phase area 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 area, an annular spot is formed on the working plane in the laser optical system. The number of annular spots is determined by the number of divided fan-shaped ring areas. As Figure 2 shown, where 10 fan-shaped ring areas b form the negative optical wedge phase area. Figure 3 Similarly, it shows the schematic diagram and phase diagram of the diffractive optical element that etches a positive optical wedge to generate point-annular spots. The height of the lens in the equal-phase area is constant, and the height of the lens in the optical wedge phase gradually decreases along the center line direction of the fan-shaped ring area, and the height of the area perpendicular to the center line is the same, which is opposite to the negative optical wedge phase.

[0047] Figure 2 and Figure 3 In [figure number] and [figure number], the change speeds of the two optical wedge phase gradients are the same, but the directions are opposite. Figure 2 and Figure 3The phase gradient change rates of the two optical wedges in the middle etching are the same, but the directions are opposite. In addition, the diffractive optical element in the present invention can obtain a point-ring-point beam on the working plane after being modulated based on any combination of positive and negative optical wedges. The diffractive optical element in the present invention can obtain a point-ring-point beam on the working plane after being etched and modulated based on any combination of positive and negative optical wedges. In an alternative mode, only one of the positive and negative optical wedges can be selected, or both can be selected. In an alternative embodiment, the number of the first optical wedge phase region and the second optical wedge phase region constructed by selecting the positive and negative optical wedges is equal, and the arrangement can be random arrangement or alternating arrangement. 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. As Figure 4 shown, where region a (center) represents the equal-phase region, and regions b and c respectively represent the etched opposite optical wedge phase regions. The left figure is angular interleaving (the reference circle center is interleaved on the outer ring of region a), and the right figure is axial interleaving (referring to the radius, interleaving from the center along the radius outwards). Based on the etched optical wedge element, when constructing the central equal-phase region and the optical wedge phase region in the diffractive optical element, when the laser passes through the diffractive optical element, a point-ring-point spot array can be generated on the working plane of the laser optical system.

[0048] Those skilled in the art should understand that the actual lens height is in the micron level and the lens size is in the millimeter level. For the convenience of reflecting the design idea, the actual height of the lens etching is scaled, and the relative height is changed to 0-1. The phase value of 2π corresponds to the height of 1; the phase value of 0 corresponds to the height of 0.

[0049] 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 beam and form a Gaussian spot at the center of the working plane, and the optical wedge phase region is used to form a ring-point spot on the working plane after receiving the incident beam. The optical wedge phase region includes the first optical wedge phase region and the second optical wedge phase region. The first optical wedge phase region and the second optical wedge phase region can exist individually, be randomly arranged in two regions or be alternately arranged, and a point-ring-point array spot can be obtained.

[0050] Further, 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 light spot after passing through the diffractive optical element. By changing the sector ring area and phase gradient of the etched wedge phase, the position and intensity of the ring-dot light spot can be changed. Further, when alternating positive and negative wedge phases are etched on the diffractive optical element, the generated dot-ring-dot light spot has better defocus characteristics. The arrangement of the alternating etching 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, and adjusting the size of the equal-phase region can change the energy ratio of the dot-ring-dot light spot. In addition, when a divergent laser beam is incident on the diffractive optical element, by adjusting the distance between the incident laser and the diffractive optical element, the spot area of the incident laser on the diffractive optical element can be changed, and thus the energy ratio of the dot-ring-dot can be changed. That is, it is only necessary to adjust the position of the diffractive optical element in the laser beam path, or in other words, adjust the distance between the diffractive optical element and the laser emission point.

[0051] In another alternative embodiment, when the above-mentioned 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 light spot array with a long depth of focus after passing through the diffractive optical element. Specifically, refer to the following description.

[0052] The equal-phase region in the above-mentioned Embodiment 1 is also called the first region in the diffractive optical element, and the wedge phase region is called 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.

[0053] Embodiment 2

[0054] As Figure 5 FIG. shows a schematic diagram of a laser optical system for realizing a dot-ring-dot combined light spot, 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 dot-ring-dot array light spot in the working plane 3. When the incident laser beam (emitted from the laser emission point P, that is, the laser source) passes through the equal-phase region in the diffractive optical element, a Gaussian light spot (dot 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-dot light spot is correspondingly formed. The wedge phase region here refers to the description in Embodiment 1, and for the sake of brevity, it will not be described in detail. The diffractive optical element 1 in Embodiment 2 uses the diffractive optical element disclosed in Embodiment 1.

[0055] 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 impose a phase distribution on the incident laser beam. This 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 the laser beam passing through the second region forms an array of ring spot on the working plane. Further, based on Figure 5 in 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 direction of the beam path of the incident laser, specifically as Figure 6 and 7 shown. The diffractive optical element 1 is arranged in the direction of the beam path of the incident laser, and it 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 direction of the beam path, continuously moving from the dotted line position to the solid line area, the spot on the working plane 3 changes from a point spot to a point-ring spot. And as the diffractive optical element 1 moves, the peak power density of the ring spot gradually increases, and the peak power density of the central point gradually decreases. The area of the incident spot irradiating on the diffractive optical element and the corresponding spot energy distribution change as Figure 10 shown, and for the point-ring spot combination spot, the point-ring spot power ratio is continuously adjustable with the change of the position of the diffractive optical element 1, continuously adjusting the energy ratio between the point and the ring spot. In addition, when the laser optical system is the Figure 7 structure in, that is, when the diffractive optical element 1 moves between the collimating lens 4 and the focusing lens 2, the point-ring spot on the working plane 3 does not change with the change of the position of the diffractive optical element 1 (constant stable state).

[0056] 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 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 beam. The spot-ring spot generated in this way is more stable with respect to the offset of the incident spot. 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.

[0057] The laser optical system using the diffractive optical element 1 in 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 based on Figure 6Schematic diagram of the diffraction optical element that etches the negative optical wedge and positive optical wedge phases respectively in the laser optical system to generate a point-ring point light field distribution, showing the distribution of the central point and ring points in the focal plane and before and after. Refer to Figure 8 and 9 , the light fields before and after the focal plane are inconsistent, and the ring points show a contracting or diverging trend before and after the focal plane. At this time, it will lead to different laser processing effects under positive and negative defocus.

[0058] In order to better understand the effects of the diffraction optical element based on the staggered etching of positive and negative optical wedge phases, the structural characteristics and phase distribution of the diffraction optical element etched angularly and axially in different designs, the following will describe the schematic diagram of the diffraction optical element in the present invention to achieve a point-ring point array through different designs.

[0059] Figure 11 Schematic diagram and phase diagram showing the diffraction optical element with equal-phase regions and optical wedge phases arranged angularly; there are two functional regions in this lens. Region a is the equal-phase region, with a fan shape. 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 the optical wedge phase region, with a fan shape. The center of the fan corresponds to the central point, and ring points are generated when the laser passes through, corresponding to b' in the phase diagram.

[0060] Both the equal-phase region and the optical wedge phase region of the diffraction optical element are arranged angularly, and the energy ratio of the generated point-ring points is fixed. The energy ratio is independent of the position of the diffraction optical element 1 in the laser optical system. The size of the energy ratio is determined by the area ratio or angle ratio of the equal-phase region and the optical wedge phase region, that is, the energy ratio is not affected by the change of the position of the diffraction optical element in the optical path and the characteristics of the laser output spot.

[0061] Figure 12 Schematic diagram and phase diagram showing the point-ring point diffraction optical element generated by etching optical wedge phases with opposite phase gradients alternately angularly; Figure 12 The diffraction optical element in [[ ]] is divided into three functional regions: an equal-phase region, a first optical wedge phase region, and a second optical wedge phase region. Among them, both the first optical wedge phase region and the second optical wedge phase region are composed of four sectors and are arranged staggeredly. As shown in the figure, region a is the equal-phase region, which is circular. Multiple repeated fan-shaped ring regions b form the first optical wedge phase region, and multiple repeated fan-shaped ring regions c form the second optical wedge phase region. The fan-shaped 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 [[ ]], the gray shadow shows that the phases of adjacent fan-shaped ring regions b and region c are 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. For the specific schematic diagram of the defocus morphology of the point-ring point light spot, refer to Figure 13As shown, on the focal plane (the middle plane, i.e., the working plane), there is a central spot (Gaussian spot), and eight ring points are generated by the laser of the first wedge phase region composed of four fan-shaped ring regions b and the second wedge phase region composed of four fan-shaped 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 fields 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. The plane above is the pre-focal plane, and the plane below is the post-focal plane.

[0062] Figure 14 Schematic diagram and phase diagram of a diffractive optical element showing point-ring points generated based on angularly alternating etching of opposite-phase gradients of wedges and opposite-phase gradients of diagonal fan rings; and Figure 12 Similar, the difference is that both the first wedge phase region and the second wedge phase region are five sectors, that is, the fan-shaped ring regions b and c are equal and odd numbers. The above design of 5 is just one implementation, and 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). For the specific off-focus morphology schematic diagram of the spot, reference can be made to Figure 15 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 off-focus characteristics. When the incident light spot deviates, the influence on the ring points on the working plane is smaller. Therefore, when the number of fan-shaped rings in the first wedge phase region is the same as that in the second wedge phase region, 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. At this time, the ring points have more stable off-focus characteristics. Specifically, referring to Figure 15 , the light fields before and after the focal plane are completely the same, and each ring point on the focal plane is composed of two ring points, one close to the optical axis and one far from the optical axis; after off-focus, the two ring points forming this ring point, one is far from the optical axis and the other is close to the optical axis, and it is completely the same before and after the focal plane. Therefore, during laser processing, the tolerance for positive and negative off-focus of the light field is greater, and it has the characteristic of long focal depth.

[0063] The aperture ratio and the angle of the wedge of each etching region on the diffractive optical element can be changed, and the positions and intensities of each ring point can be customized individually.

[0064] Furthermore, Figure 16Schematic diagram and phase diagram showing a point-ring point diffractive optical element generated based on the optical wedge phase with axially alternating etched opposite phase gradients; 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 spot array with a long depth of focus on the working plane. Among them, a is the equal phase region, generating a central Gaussian spot; b and c are the optical wedge phase regions, arranged alternately along the axis; 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; region b' is the phase change diagram corresponding to region b, and region c' is the phase change diagram corresponding to region c.

[0065] Figure 17 Schematic diagram and phase diagram showing a diffractive optical element generating a point-ring point based on the optical wedge phase with axially and angularly alternating etched opposite phase gradients; 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 spot array with a long depth of focus on the working plane.

[0066] Example 3:

[0067] 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 achieves the effect of a point-ring segment spot array, that is, when the diffractive optical element with the etched axicon phase is placed in the laser optical system, it can generate a point-ring segment spot array on the working plane. The specific structure of the diffractive optical element is as follows.

[0068] 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.

[0069] Example 4:

[0070] Figure 18 Schematic diagram and phase diagram showing a diffractive optical element with an 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, generating a central spot, b and c are the axicon phase regions, appearing alternately along the axis; b is the positive axicon phase region, c is the negative axicon phase region, the phases of b and c are opposite, and the diffractive optical element consists of the equal phase region a, the positive axicon phase region composed of multiple identical fan-shaped rings b, and the negative axicon phase region composed of multiple identical fan-shaped rings c. The fan-shaped rings b and c are arranged alternately axially.

[0071] Figure 19Schematic diagram and phase diagram showing a diffractive optical element with an axicon phase based on angularly alternating etching of opposite phase gradients; Figure 20 Schematic diagram of the point - ring segment light field distribution of a diffractive optical element with an axicon phase based on angularly etched alternating opposite phase gradients. After angular or axial alternating etching of positive and negative axicons, the ring segment light spots generated on the working plane coincide. At this time, the ring segment light spot array has a more stable defocus characteristic, similar to the optical 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 light spot array is formed on the working plane, that is, a Gaussian light spot at the center and a light beam composed of ring segments on the ring. Referring to Figure 20 , after the incident laser is defocused, half of the ring segment light spots in front of and behind the focal plane are close to the optical axis and half of the ring light is away from the optical axis. Therefore, the peak power densities of the light fields in front of and behind the focal plane are close to the same, and the positions of the ring segment light spots have changed.

[0072] Example 5:

[0073] Figure 21 Schematic diagram and phase diagram showing a diffractive optical element with an axicon phase based on angularly alternating etching of opposite phase gradients and with opposite phase gradients for the angular fan rings; Figure 22 Showing Figure 21 Schematic diagram of the point - ring segment light field distribution of the diffractive optical element shown in Figure 21 As shown in Figure 21 , the diffractive optical element lens has three functional regions. Region a is an equal - phase region that generates a central light spot; regions b and c are axicon phase regions. Multiple identical fan rings b form a positive axicon phase region; multiple identical fan rings c form a negative axicon phase region, where the number of fan ring regions b and c is equal and odd, and the fan rings b and c are arranged alternately in the angular direction. Figure 22 As shown, each ring light on the focal plane is composed of two rings, one close to the optical axis and one away from the optical axis; after defocusing, the two ring segment light spots that make up this ring segment light spot, one is away from the optical axis and one is close to the optical axis, and it is exactly the same in front of and behind the focal plane. During laser processing, it has a greater tolerance for positive and negative defocus of the light field and has a long focal depth characteristic. In other words, when the number of phase fan rings with alternately etched opposite phase gradients is equal and odd, it has a long focal depth characteristic. Here, the phase can be an axicon phase or an optical wedge phase, and the alternating method is not limited to angular or axial. When axially 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 a better long - focal - depth characteristic.

[0074] Example 6:

[0075] Figure 23Schematic diagram and phase diagram showing a diffractive optical element that generates a point-ring segment of an axicon phase based on alternating opposite phase gradients of 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 and single axial distribution. This embodiment combines Figure 18 the angular direction in Figure 19 with the axial staggered arrangement in Figure 17 . That is, half of the sectors are axially etched and half are angularly etched. Similar to

[0076] Example 7:

[0077] Figure 24 Height schematic diagram and phase diagram of a diffractive optical element of axicon phase based on alternating opposite phase gradients of angular etching after removing the equal-phase region; Figure 24 will be described in combination with Figure 21 . Comparing the two figures, it can be seen that Figure 24 the diffractive optical element in Figure 25 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 identical second sectors. The sizes of the first sector and the second sector are the same. Further, Figure 24 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 of the sectors in the diffractive optical element is odd, the superimposed equivalent height schematic diagram and phase diagram. As shown in the figure, the period of the equivalent diffractive optical element lens is more dense, the deflection effect on the light beam increases, 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 Figure 25 diffractive optical elements shown are placed in the optical path of the incident laser. One diffractive optical element 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. As

[0078] Figure 26 After the equal-phase region is removed as shown, select Figure 24 The height schematic diagram and phase diagram of the equivalent diffractive optical element obtained by rotating two diffractive optical elements in [[ ]] by 1 / 2 sector phase superposition. Here, the relative rotation is 1 / 2 sector angle. Fix one diffractive optical element and rotate the other diffractive optical element. 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-axis pyramid phase region, and a negative-axis pyramid phase region. Among them, a is the positive-axis pyramid phase region, c is the negative-axis pyramid phase region, and b is the equal-phase region. The sizes and numbers of the sector rings a, b, and c are equal, and the three regions appear alternately in the angular direction, generating a long-depth-of-field point-ring segment spot array. Specifically, different types of phase regions are generated in the overlapping regions, including the following situations. For example, when the positive-axis pyramid phase of one diffractive optical element exactly cancels out the negative-axis pyramid phase of another diffractive optical element, an equal-phase region a is formed, so that the light beam passing through this region maintains a straight propagation and forms a central Gaussian spot on the focal plane. In the uncanceled region, the positive-axis pyramid phase region of one diffractive optical element is superimposed on the positive-axis pyramid region of another diffractive optical element; the negative-axis pyramid phase region is superimposed on the negative-axis pyramid phase region of another diffractive optical element. At this time, the light beam still maintains an annular distribution on the working plane, generating a long-depth-of-field point-ring segment spot array.

[0079] Figure 27 After the equal-phase region is removed as shown, select Figure 24 The height schematic diagram and phase diagram of the equivalent diffractive optical element obtained by rotating two diffractive optical elements in [[ ]] by 4 / 5 sector phase superposition. Here, the relative rotation is 4 / 5 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 Figure 27 Under the shown rotation angle, continue to rotate. For example, when rotating by one sector angle, point spots are generated after the two diffractive optical elements are superimposed. When the lens rotation angle is 0 - (one sector angle) - (two sector angles), the corresponding target light field presents a state of: complete ring segment light - complete point light - complete ring segment light, corresponding to the change trend within one cycle. 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 spot array can be achieved.

[0080] In summary, by etching the light wedge phase or the axicon phase method, after dividing the diffractive optical element into regions with different functions, applying the above different types of diffractive optical elements to Figures 5 - 7When it is in the laser optical system, it can achieve various different effects such as point-ring point spot, long focal depth point-ring point spot, point-ring segment spot, and long focal depth point-ring segment spot on the working plane.

[0081] When generating a ring point by etching the phase of the optical wedge, by changing the area and phase gradient of the etched optical wedge phase region, the position and intensity of the ring point can be changed. And when the phase region of the diffractive optical element includes an equal phase region and an optical wedge phase region, a point-ring point combined spot is generated. When preferably etching the optical wedge phase with alternating positive and negative phase gradients, the generated point-ring point spot has better defocus characteristics. The etched alternating positive and negative phase gradients can be axial, angular, or a combination of both.

[0082] 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.

[0083] Etching alternating positive and negative opposite phase gradients is applicable not only to the optical wedge phase but also to the axicon phase. When changing the positive optical wedge phase and negative optical wedge phase etched in the phase shift region to a positive axicon phase and a negative axicon phase, a point-ring segment spot array with a long focal depth can be generated.

[0084] By setting two identical diffractive optical elements with etched alternating axicon phases in the incident laser path, and when the two identical diffractive optical elements do not have a central equal phase region, by rotating to change the relative position 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 focal depth 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.

[0085] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A diffractive optical element for generating a dot-ring segment light 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 an equal-phase region, a positive axicon phase region, and a negative axicon phase region, where the phase in the equal-phase region is equal, and the positive axicon phase region and the negative axicon phase region are arranged alternately. When the laser beam passes through the equal-phase region, the equal-phase region generates a central spot, and when the laser beam passes through the positive axicon phase region and the negative axicon phase region, the positive axicon phase region and the negative axicon phase region generate an annular segment spot array.

2. The diffractive optical element for generating a point-ring segment light spot array according to claim 1, wherein The equal-phase region is located in the central region of the diffractive optical element and is a circle centered on the center of the diffractive optical element. The positive axicon phase region is composed of a plurality of first fan-shaped rings, each first fan-shaped ring having the same size and arranged concentrically around the center; and the negative axicon phase region is composed of a plurality of second fan-shaped rings, each second fan-shaped ring having the same size and arranged concentrically around the center, where the first fan-shaped rings and the second fan-shaped rings are arranged alternately along the outer edge of the equal-phase region and are axicon phases with opposite phase gradients.

3. The diffractive optical element for generating a point-ring segment light spot array according to claim 2, wherein The number of first fan-shaped rings included in the positive axicon phase region is equal to the number of second fan-shaped rings included in the negative axicon phase region.

4. The diffractive optical element for generating a point-ring segment light spot array according to claim 3, characterized in that The number of first fan-shaped rings in the positive axicon phase region and the number of second fan-shaped rings in the negative axicon phase region are odd numbers.

5. The diffractive optical element for generating a point-ring segment light spot array according to claim 1, characterized in that, The positive axicon phase region and the negative axicon phase region are obtained by etching the positive axicon phase and the negative axicon phase, and the etching methods include angular interleaved etching and / or axial interleaved etching.

6. The diffractive optical element for generating a spot-ring segment light spot array according to claim 2, wherein When the area of the central region of the equal-phase region is zero, the positive axicon phase region is composed of a plurality of first sectors, each sector arranged concentrically around the center, and the negative axicon phase region is composed of a plurality of second sectors, each sector arranged concentrically around the center, where the first sectors and the second sectors are arranged alternately as axicon phases with positive and negative opposite phase gradients.

7. 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 as described in any one of claims 1-5, a focusing lens, and a working plane, where 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, and is achieved by constructing an equal-phase region, a positive axicon phase region, and a negative axicon phase region on the diffractive optical element: when the incident laser beam passes through the equal-phase region, a central spot is formed on the working plane, and when the laser beam passes through the positive axicon phase region and the negative axicon phase region, an annular segment spot array is formed on the working plane.

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; Two diffraction optical elements as described in claim 6, a focusing lens, and a working plane, wherein the two diffraction optical elements are arranged in the beam path of the incident laser beam to impose a phase distribution on the incident laser beam. When the first diffraction optical element is fixed and the second diffraction optical element is rotated about the optical axis, an equal-phase region, a positive-axis pyramid phase region, and a negative-axis pyramid phase region are constructed on the two superimposed diffraction optical elements to achieve: when the incident laser beam passes through the equal-phase region, a central spot is formed on the working plane, and the laser beams passing through the positive-axis pyramid phase region and the negative-axis pyramid phase region form an annular segment spot array on the working plane, wherein the angle by which the second diffraction optical element rotates relative to the first diffraction optical element is any angle in (0, 2π) excluding multiples of the first sector angle or the second sector angle.

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