Astigmatism correction method and system for laser beam, and astigmatism correction device

Abstract

The present invention provides an astigmatism correction method and system for a laser beam, and an astigmatism correction device. The astigmatism correction method for a laser beam includes: emitting a laser beam; obtaining the beam waist sizes of the laser beam in two directions and the beam waist positions in the two directions; where the two directions include a first direction and a second direction, and the first direction is perpendicular to the second direction; adjusting the astigmatism correction device to make the beam waist sizes of the laser beam in the two directions consistent and the beam waist positions coincide. According to the method, system and device of the present invention, astigmatism correction of the laser beam can be achieved, thereby improving the quality of precision laser processing.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser precision machining, and is particularly applicable to the correction of laser beam aberration. Specifically, the present invention relates to an astigmatism correction method and system for a laser beam, and an astigmatism correction device. Background Art

[0002] In existing laser precision machining, generally, a laser is used in combination with a beam expander to expand the beam to an appropriate diameter, and then a focusing head is used in combination with a table movement or a galvanometer is used in combination with a field lens for scanning machining. Currently, most of the optical elements used in the focusing system adopt a transmissive focusing system. The smaller the focal length of the lens, the smaller the focused focal spot, which is beneficial to increasing the laser power density. However, for any laser in practical applications, its output beam cannot be an ideal fundamental mode Gaussian beam with 100%. Thus, the focusing ability of the laser beam will be affected by the laser beam quality. Precision machining technology has high requirements for the laser beam quality, which are mainly reflected in aspects such as the laser beam diffraction factor, beam roundness, and astigmatism. When the roundness of the original laser beam is not good or the astigmatism control is not good, it will result in a poor roundness of the focused laser spot and a poor focusing effect, affecting the quality of laser machining.

[0003] In fact, the astigmatism of the laser beam has an obvious impact on the precision machining quality. When using a focusing head in combination with a moving table for machining, due to the existence of laser beam astigmatism, the spot cannot be focused to the minimum simultaneously in the transverse and longitudinal directions. In actual laser machining, only an optimal position with the best roundness can be selected for machining; when transverse and longitudinal machining is required, the requirement for the roundness of the spot will be higher, and the machining effects in the two directions will be inconsistent, which is reflected in aspects such as machining line width and ablation depth.

[0004] In addition, when using a galvanometer in combination with a field lens for machining, due to the existence of laser beam astigmatism, there will be problems similar to those of using a focusing head in combination with a moving table at the center of the scanning area; since the focal plane of the field lens is not a perfect plane, but a curved surface with different field curvatures in the meridional direction and the sagittal direction, the inconsistent field curvatures in the meridional direction and the sagittal direction constitute the astigmatism of the field lens itself. When large-area machining is required, the focusing effect of the spot at the edge of the area is simultaneously affected by the superposition of the field lens astigmatism and the laser beam astigmatism, which will have a more significant impact on the machining quality. When the laser beam astigmatism is too large, even the spot at the edge of the area cannot form a focus. Summary of the Invention

[0005] Problems to be Solved by the Invention

[0006] In laser processing, due to the existence of laser beam astigmatism, there are different processing effects in the transverse and longitudinal directions, and there is a technical problem that the light spot cannot be focused to the minimum in both the transverse and longitudinal directions simultaneously. The existing technologies generally adopt a compromise solution, that is, adjusting the sizes of the light spot in the X and Y directions to be the same. At this time, the light spot has better roundness, but it is not the smallest focused light spot, and the focused energy density of the laser does not reach the optimum; or the light spot can also be adjusted to have the smallest size in the X or Y direction, but in this case, the light spot is an obvious ellipse and the processing quality is poor.

[0007] In the application of galvanometer scanning processing, there is astigmatism (i.e., the field curvatures in the X and Y directions are inconsistent) at the edge of the processing system composed of the galvanometer and the field lens. The superposition of this astigmatism and the astigmatism of the laser beam will further affect the quality of the light spot at the edge of the field, resulting in poor focusing effect or even inability to focus of the light spot at the edge of the field.

[0008] An object of one aspect of the present invention is to propose an astigmatism correction method and system for a laser beam in order to improve the processing quality of the laser beam, thereby significantly improving the quality of laser processing.

[0009] In the astigmatism correction method, system and astigmatism correction device for a laser beam according to one aspect of the present invention, considering that different lasers have different astigmatism values, the cylindrical lens group also has a certain focusing range.

[0010] The present invention proposes an astigmatism correction method for a laser beam, including: emitting a laser beam;

[0011] Obtaining the waist sizes of the laser beam in two directions and the waist positions in two directions; wherein, the two directions include a first direction and a second direction, and the first direction and the second direction are perpendicular;

[0012] Adjusting the astigmatism correction device to make the waist sizes of the laser beam in two directions consistent and the waist positions coincide.

[0013] Further, the above astigmatism correction method further includes obtaining the ratio of the waist sizes of the laser beam in the first direction and the second direction, the absolute difference between the waist positions of the laser beam in the first direction and the second direction, and the ratio K of the diffraction factors of the laser beam in the first direction and the second direction;

[0014] The step of making the waist sizes of the laser beam in two directions consistent and the waist positions coincide includes: making the ratio of the waist sizes approach K N , and the absolute difference approaches zero; wherein, N is a number greater than 0 and less than 1.

[0015] Further, the astigmatism correction device includes three cylindrical lens groups with adjustable distances between each pair, and each cylindrical lens group includes at least one cylindrical lens;

[0016] Among them, the three cylindrical lens groups are the first cylindrical lens group, the second cylindrical lens group, and the third cylindrical lens group in sequence. The distance between the first cylindrical lens group and the second cylindrical lens group is the first distance, and the distance between the second cylindrical lens group and the third cylindrical lens group is the second distance;

[0017] Initially adjust the first distance and the second distance so that the ratio of the beam waist sizes approaches K N ;

[0018] Further, the first distance and the second distance in the initial adjustment are determined by the magnification factor, and the magnification factor is the reciprocal of the ratio of the beam waist sizes in the first direction and the second direction multiplied by K N .

[0019] Further, the N is 0.5.

[0020] Further, after initially adjusting the first distance and the second distance, finely adjust the second distance so that the absolute difference approaches zero.

[0021] Further, each cylindrical lens group includes one cylindrical lens.

[0022] On the other hand, the present invention also discloses an astigmatism correction system for a laser beam, including:

[0023] A laser for emitting a laser beam;

[0024] An astigmatism correction device for correcting the laser beam so that the beam waist sizes in two directions of the laser beam are the same and the beam waist positions coincide; among them, the two directions include a first direction and a second direction, and the first direction and the second direction are perpendicular;

[0025] The astigmatism correction device is located behind the laser.

[0026] Further, it further includes: a parameter measurement device for obtaining the beam waist sizes of the laser beam in two directions and the beam waist positions in two directions; among them, the parameter measurement device is located behind the astigmatism correction device.

[0027] On the other hand, the present invention discloses an astigmatism correction device, and the astigmatism correction device includes three cylindrical lens groups with adjustable distances between each pair, and each cylindrical lens group includes at least one cylindrical lens.

[0028] The astigmatism correction method, system and device for a laser beam implemented according to the present invention have the following beneficial effects:

[0029] (1) The present invention provides an astigmatism correction method and system for a laser beam. After obtaining the waist sizes and waist positions in two directions, the astigmatism correction device is adjusted to make the waist sizes in two directions consistent and the waist positions coincide, thereby achieving the correction of the astigmatism of the laser beam, and improving the quality of precision laser processing. When transverse and longitudinal processing is required, the processing effects in two directions can be made more consistent; moreover, for a scanning system with a galvanometer and a field lens, when large-area processing is performed, the spot focusing effect at the edge of the large area can also be improved, thereby improving the processing quality over the entire large area.

[0030] (2) The astigmatism correction method for a laser beam proposed by the present invention can not only improve the effect of laser precision processing. For example, for an elliptical spot, it can be corrected into a circular spot with a very high roundness after correction; for a circular spot, the spot size can be reduced.

[0031] Moreover, for the corrected laser beam obtained by this method, after being transmitted over a certain distance, the roundness of the beam will not change significantly.

[0032] (3) According to the astigmatism correction method and system for a laser beam proposed by the present invention, the technical concept involved is applicable to a wide range of laser processing. The astigmatism correction device for the laser can be designed according to specific processing requirements (such as spot size) and laser parameters (such as wavelength, beam diameter), and can also be adaptively designed according to the correction of the spot shape.

[0033] (4) The present invention provides an astigmatism correction device that makes full use of the directional refractive characteristics of a cylindrical lens to correct the parameters of the beam in a single direction. Applied to laser precision processing, it can achieve the effect of maintaining a very high roundness of the spot under a small focusing size, improving the quality and efficiency of laser processing;

[0034] At the same time, by using the method of making the distances between two of the three cylindrical lens groups adjustable, the device has a certain magnification adjustment range, and also has stronger adaptability to the directions of the major and minor axes of the elliptical spot, improving the adaptability of the astigmatism correction of the laser beam.

[0035] Additional aspects and advantages of the application will be given in part in the following description, will become apparent in part from the following description, or will be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings forming a part of this application are used to provide a further understanding of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application.

[0037] In the drawings:

[0038] Figure 1 Schematic flow chart of an astigmatism correction method for a laser beam according to an embodiment proposed by the present invention;

[0039] Figure 2 Schematic diagram showing the variation of the laser beam size with the beam position before astigmatism correction;

[0040] Figure 3 Schematic diagram showing the variation of the laser beam size with the beam position obtained after astigmatism correction;

[0041] Figure 4 Schematic structural diagram of an astigmatism correction system for a laser beam according to an embodiment proposed by the present invention;

[0042] Figure 5 Schematic structural diagram of another astigmatism correction system for a laser beam according to an embodiment proposed by the present invention;

[0043] Figure 6 Schematic structural diagram of an astigmatism correction device according to an embodiment proposed by the present invention;

[0044] Figure 7 Schematic diagram showing the relationship between the magnification of an astigmatism correction device implemented according to the present invention and the first distance and the second distance;

[0045] Figure 8 Configuration diagram of an astigmatism correction device implemented according to the present invention under different magnification adjustments;

[0046] Figure 9 Schematic structural diagram of an application scenario using the astigmatism correction device proposed by the present invention;

[0047] Figure 10 Schematic structural diagram of another application scenario using the astigmatism correction device proposed by the present invention;

[0048] Figure 11 Schematic diagram showing the variation of the laser beam size with the beam position before astigmatism correction in Embodiment 1;

[0049] Figure 12 Schematic diagram showing the variation of the laser beam size with the beam position after astigmatism correction in Embodiment 1;

[0050] Figure 13 Schematic diagram showing the variation of the laser beam size with the beam position before astigmatism correction in Embodiment 2;

[0051] Figure 14 Schematic diagram showing the variation of the laser beam size with the beam position after astigmatism correction in Embodiment 2.

[0052] Figure 15 It is the spot image before astigmatism correction in Embodiment 3;

[0053] Figure 16 It is the spot image after astigmatism correction in Embodiment 3. Detailed implementation manners

[0054] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0055] The following further describes the present invention in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present invention.

[0056] The following describes an astigmatism correction method and system for a laser beam, and an astigmatism correction device according to embodiments of the present application with reference to the drawings.

[0057] As Figure 1 shown, an astigmatism correction method for a laser beam is proposed, including: emitting a laser beam; obtaining the waist sizes of the laser beam in two directions and the waist positions in two directions; wherein, the two directions include a first direction and a second direction, and the first direction is perpendicular to the second direction; adjusting an astigmatism correction device to make the waist sizes of the laser beam in the two directions consistent and the waist positions coincide. Wherein, the first direction and the second direction can be the X direction (horizontal direction) and the Y direction (vertical direction). Of course, the first direction can also have a certain angle with the horizontal direction (such as 45° etc.). Generally speaking, it is sufficient that the first direction is perpendicular to the second direction. In this embodiment, the first direction and the second direction are the X direction and the Y direction, and the waist sizes in the two directions can be expressed as W 0x 、W 0y , and the waist positions in the two directions can be expressed as Z 0x 、Z 0y . In addition, the coincidence of the waist positions here means that the absolute difference between the waist positions in the two directions tends to 0.

[0058] Generally, before the astigmatism of the laser beam is corrected, the waist sizes of the laser beam in the two directions are different and the waist positions do not coincide, as Figure 2 shown. The astigmatism correction method for the laser beam proposed by the present invention obtains W 0x 、W 0y 、Z 0x 、Z 0y and then adjusts an astigmatism correction device independent of the laser (for emitting the laser beam) to make the waist sizes of the laser beam in the two directions consistent and the waist positions coincide. The result is as Figure 3 shown. Thus, the astigmatism of the laser beam can be corrected, and the quality of laser processing can be improved.

[0059] In addition, the astigmatism correction method can make the processing effects in the horizontal and vertical directions more consistent at the same time; and for the scanning system with a galvanometer mirror and a field lens, when performing large-format processing, it can also improve the spot focusing effect at the edge of the large format, thereby improving the processing quality of the entire large format. Moreover, this method can not only improve the laser precision processing effect. For example, for an elliptical spot, it can be corrected into a circular spot with a very high roundness after correction; for a circular spot, the spot size can be reduced (for example, a rectangular spot can be corrected into a square spot). Furthermore, for the corrected laser beam obtained by this method, after being transmitted over a certain distance, the roundness of the beam will not change significantly.

[0060] It should be noted that for the astigmatism correction method of this laser beam, the technical concept involved is applicable to a wide range of laser processing. The laser astigmatism correction device can be designed according to specific processing requirements (such as spot size) and laser parameters (such as wavelength, beam diameter), and can also be adaptively designed according to the correction of the spot shape.

[0061] As another embodiment, the astigmatism correction method of this laser beam further includes obtaining the ratio (W 0x / W 0y ) of the beam waist sizes of the laser beam in the first direction and the second direction, the absolute difference |Z 0x -Z 0y | of the beam waist positions of the laser beam in the first direction and the second direction, and the ratio K of the diffraction factors of the laser beam in the first direction and the second direction, where K = M 2 x / M 2 y , M 2 x represents the diffraction factor in the X direction, and M 2 y represents the diffraction factor in the Y direction; making the beam waist sizes of the laser beam in the two directions consistent and the beam waist positions coincide includes: making the ratio W 0x / W 0y of the beam waist sizes approach K N , and the absolute difference |Z 0x -Z 0y | approach zero; where N is a number greater than 0 and less than 1. Here, the ratio W 0x / W 0y of the beam waist sizes approaching K N means approaching K N ± 0.001 (determined by the accuracy of the test instrument for obtaining the beam waist size, beam waist position, and diffraction factor, such as the M 2 tester), and the absolute difference |Z 0x -Z0y Approaching zero means that the absolute difference is less than 0.01 times the average Rayleigh length Z R . λ is the laser wavelength.

[0062] Among them, the diffraction factor M is selected 2 as the reference object for the target approaching value of W 0x / W 0y because it is considered that the diffraction factor can reflect the quality of the laser beam, and the value of the diffraction factor does not change during the astigmatism correction process. At the same time, by adjusting the astigmatism correction, the ratio of the beam waist size W 0x / W 0y approaches K N , and the absolute difference |Z 0x -Z 0y | approaches zero, which can achieve the consistency of the focusing positions in two correction directions. It can also well ensure that after the laser beam propagates a certain distance, the beam is still very round, making it more suitable for precision laser processing systems with high requirements for the light spot.

[0063] The laser beam in this embodiment is a Gaussian beam. According to the characteristics of the Gaussian beam, the product of the beam waist size W0 and the divergence angle θ0 corresponding to the beam waist is a constant value A: W 0x θ 0x =A x , W 0y θ 0y =A y , A is proportional to the diffraction factor (M 2 ), that is, there is: K = A x / A y , so that W 0x / W 0y approaches K N , then at the same time θ 0x / θ 0y approaches K N . From this, it can be ensured that the ratio of the beam radii W xd / W yd =(W 0x +dθ 0x ) / (W 0y +dθ 0y approaches K N . At the same time, the difference in the beam waist positions (|Z 0x -Z 0y |) reflects the difference in the divergence angle θ0, that is, the beam radii after correction reach the processing object with the same ratio after a certain propagation distance. That is, after propagating a certain distance, the roundness of the beam does not change significantly. The above corrected laser beam can obtain the best focusing effect and spot roundness.

[0064] In addition, the above-mentioned waist size W 0x 、W 0y , the waist position Z 0x 、Z 0y , the diffraction factor M 2 x 、M 2 y , as the initial parameters for calibration and the final judgment basis, can all be directly measured by a standard M 2 tester. The M 2 tester is a standard instrument often used by those skilled in the art to measure laser beam parameters, and will not be elaborated in detail here as it is prior art. When it is necessary to measure the parameters of the uncorrected laser beam by the M 2 tester, the M 2 tester can be directly placed behind the laser, as shown in Figure 4 .

[0065] As another embodiment, the astigmatism correction device in the above correction method includes three cylindrical lens groups with adjustable distances between each pair, which can make the spot size in one direction remain unchanged during laser correction, while adjusting the spot size in the other direction. The three cylindrical lens groups are the first cylindrical lens group, the second cylindrical lens group, and the third cylindrical lens group in sequence. The first cylindrical lens group and the second cylindrical lens group and the distance between them form a variable magnification group, and the third cylindrical lens group forms a compensation group to adjust the divergence angle of the outgoing beam; the distance between the first cylindrical lens group and the second cylindrical lens group is the first distance L1, and the distance between the second cylindrical lens group and the third cylindrical lens group is the second distance L2; initially adjust the first distance L1 and the second distance L2 so that the ratio of the waist sizes approaches K N . For one of the embodiments, each cylindrical lens group includes a cylindrical lens, as shown in Figure 6 .

[0066] This astigmatism correction device uses all cylindrical lenses. Utilizing the directional refractive characteristics of the cylindrical lenses, during laser correction, the laser beam is adjusted in a single direction, reducing the astigmatism of the laser beam and improving the laser processing quality. At the same time, this adjustment method with adjustable distances between each pair of the three cylindrical lens groups enables the device to have a certain range of magnification adjustment, and also makes the device more adaptable to the directions of the major and minor axes of the elliptical spot, improving the adaptability of the astigmatism correction of the laser beam.

[0067] Here, adjusting the laser beam in a single direction can be, for example, that the emitted laser beam is elliptical. If the X-axis and Y-axis respectively correspond to the major axis and minor axis of the ellipse at this time, and if the refractive correction of the cylindrical lens group is for the X direction at this time, then adjust W 0x / W 0yThe purpose should be to reduce the size in the X direction to approach the size in the Y direction, so as to keep the light spot as round as possible. Of course, the sizes in the X direction or Y direction can be adjusted separately arbitrarily according to the actual situation.

[0068] Among them, the refractive directions of the lenses in the three cylindrical lens groups are the same, the principal planes of the lenses in each cylindrical lens group are parallel to each other, the center points of the lenses are collinear, and the connecting line formed by the center points is perpendicular to the principal plane. The principal plane is a special concept in optics, representing a set of conjugate planes with an axial magnification of 1.

[0069] As another embodiment, the first distance L1 and the second distance L2 for the initial adjustment are determined by the magnification. The magnification βx is the reciprocal of the ratio of the waist sizes in the first direction and the second direction multiplied by K N , that is, βx = W 0y / W 0x *K N .

[0070] As another embodiment, each cylindrical lens group includes a cylindrical lens. This structure can achieve the astigmatism correction effect, and the number of required cylindrical lenses is the least, and the structure is the simplest.

[0071] Among them, the relationship between the magnification βx and L1, L2 can be obtained after determining the optical design parameters (such as curvature radius, thickness, refractive index) of the three cylindrical lens groups. Obtaining L1 and L2 under different magnifications belongs to the conventional technology in the optical field. The specific relationship is shown in Table 1 below. Of course, it can also be reflected in the form of a curve, such as Figure 7 shown (corresponding to Table 1). Here, only the case where each cylindrical lens group includes a cylindrical lens and the magnification range is 0.8 - 1.2 is listed, and the corresponding L1, L2 are given. When it is necessary to obtain L1 and L2 corresponding to other magnifications, the optical parameters can be redesigned according to the specific situation.

[0072] It should be particularly noted that each cylindrical lens group of the present application may further include multiple cylindrical lenses. For example, the first cylindrical lens group includes two cylindrical lenses. When designing the optical parameters, the focal length formed by the two cylindrical lenses included in the first cylindrical lens group is equal to the focal length when the first cylindrical lens group only includes one cylindrical lens. The distance between the cylindrical lens groups is also correspondingly matched according to the optical design structure parameters. When adjusting this multi-piece astigmatism correction device, the distance L1 between the first cylindrical lens group and the second cylindrical lens group and the distance L2 between the second cylindrical lens group and the third cylindrical lens group are also adjusted, and the distance between the two cylindrical lenses in the first cylindrical lens group remains unchanged. The lens group composed of two cylindrical lenses can enable the astigmatism correction device to have a better correction effect. Moreover, this multi-piece design has a better spherical aberration correction effect for a larger incident light beam. The reason is that for a larger incident light beam size, the requirement for spherical aberration correction is relatively higher, and the more the number of lenses, the higher and more flexible the operability of spherical aberration correction.

[0073] In addition, each cylindrical lens group may further include three, four or more cylindrical lenses, which is specifically determined according to requirements. Moreover, each cylindrical lens group may also include multiple cylindrical lenses simultaneously according to specific requirements, as long as it satisfies that the focal length formed when each cylindrical lens group includes multiple lenses is equal to the focal length when including one lens, and the astigmatism adjustment method is the same. When each cylindrical lens group includes multiple cylindrical lenses, the optical parameter design ideas are interlinked and will not be elaborated here.

[0074] Table 1 Magnification and corresponding L1, L2 values

[0075] Magnification factor L1 L2 0.8 112.792 48.453 0.9 102.666 54.656 1 92.551 59.608 1.1 82.451 63.649 1.2 72.372 67.004

[0076] Among them, Figure 8 is the configuration diagram of the astigmatism correction device under different magnification adjustments. Here, the situation where each cylindrical lens group includes one cylindrical lens is also listed. When each cylindrical lens group includes multiple cylindrical lenses, the adjustment methods of L1 and L2 are the same, and the distance between the cylindrical lenses inside each cylindrical lens group remains unchanged. One adjustment method presented in this figure is that the position of the second cylindrical lens remains unchanged, and the first cylindrical lens and the second cylindrical lens are changed to adjust L1 and L2. Of course, it is also possible to keep the position of the first cylindrical lens or the third cylindrical lens unchanged and adjust the other two cylindrical lenses.

[0077] As another embodiment, N is 0.5. This value comprehensively considers the balance of the waist size and divergence angle in the X and Y directions, and at this time, the astigmatism correction effect is the best.

[0078] As another embodiment, after initially adjusting the first distance and the second distance, the second distance is further finely adjusted so that the absolute difference |Z 0x -Z0y approaches zero. The present invention further takes into account the consistency problem of the focusing positions in two correction directions. Therefore, in the correction method, the second distance is further finely adjusted to make the foci in the two directions as consistent as possible. This is especially applicable to the processing and use environment of a scanning field lens, so that the foci in the two directions can be kept as little affected by the non-uniform focal field under the action of the astigmatism device, thus avoiding the problem of inability to focus. Among them, the method of finely adjusting the second distance can be: according to the relative positions of Z 0x and Z 0y , when Z 0x is on the right side of Z y0y , it is necessary to reduce θx, and the adjustment direction is to increase the second distance; otherwise, the second distance is reduced. In this way, continuous adjustment is made to make the absolute difference tend to 0.

[0079] As another embodiment, the present invention provides an astigmatism correction system for a laser beam, including: a laser for emitting a laser beam; an astigmatism correction device for correcting the laser beam so that the beam waist sizes in two directions of the laser beam are the same and the beam waist positions coincide; where the two directions include a first direction and a second direction, and the first direction is perpendicular to the second direction; and the astigmatism correction device is located behind the laser. Through this system, astigmatism adjustment of the laser beam can be achieved, and the quality of laser processing can be improved.

[0080] Actually, for the astigmatism correction system of a laser beam implemented according to the present invention, the application scenarios mainly involve laser processing. As shown in Figure 9 , a schematic structural diagram of an application scenario includes: a laser 101, an astigmatism correction device 102 implemented according to the present invention, a beam expander 103, an optical system mirror 104 for guiding the direction of the laser, and a condenser lens 105 for condensing the laser. As shown in Figure 10 , a schematic structural diagram of another application scenario includes: a laser 101, an astigmatism correction device 102 implemented according to the present invention, an optical system mirror 104 for guiding the direction of the laser, a beam expander 103, and a scanning assembly 106 of a galvanometer and a field lens located behind the optical path of the beam expander 103. In actual application, the astigmatism correction device with L1 and L2 determined is placed in the system, and there is no need to adjust the device again. Direct laser processing can be carried out using the corrected laser.

[0081] As another embodiment, as shown in Figure 5 , the above astigmatism correction system for a laser beam further includes a parameter measurement device for obtaining the beam waist sizes of the laser beam in two directions and the beam waist positions in two directions; where the two directions include a first direction and a second direction, and the first direction is perpendicular to the second direction; and the parameter measurement device is located behind the astigmatism correction device. Among them, the parameter measurement device can be an M 2 tester. When passing throughFigure 4 After the device obtains the initial laser beam parameters, L1 and L2 of the astigmatism correction device are calculated and obtained through the foregoing method, and the astigmatism correction system (the astigmatism correction device is placed between the laser and the M Figure 5 tester) is used to finely adjust the second distance. Each time the second distance is finely adjusted, the M 2 tester obtains the new waist sizes in two directions and the waist positions in two directions after the fine adjustment, and determines whether |Z 2 -Z 0x -Z 0y | approaches zero. If not, the fine adjustment and parameter acquisition are repeated until the absolute difference tends to 0.

[0082] As another embodiment, the present invention also provides an astigmatism correction device. As Figure 6 shown, the astigmatism correction device includes three cylindrical lens groups with adjustable distances between each other. Each cylindrical lens group includes at least one cylindrical lens. This device has a certain magnification adjustment range, making it more adaptable to the directions of the major and minor axes of the elliptical light spot and improving the adaptability of astigmatism correction of the laser beam.

[0083] As another embodiment, each cylindrical lens group includes one cylindrical lens. The three cylindrical lens groups are the first cylindrical lens, the second cylindrical lens, and the third cylindrical lens in sequence. The surface of the first cylindrical lens facing the laser beam emission direction is convex, so that the first cylindrical lens realizes light condensation.

[0084] Among them, the first cylindrical lens group, the second cylindrical lens group, and the distance between them form a variable magnification group, and the third cylindrical lens group forms a compensation group to adjust the divergence angle of the outgoing beam.

[0085] Preferably, the first cylindrical lens has a positive refractive power, the second cylindrical lens has a negative refractive power, and the third cylindrical lens has a positive refractive power. Among them, the second cylindrical lens can correspond to various shapes of lenses such as plano-convex, double-convex, and meniscus. The third cylindrical lens can correspond to various shapes of lenses such as plano-concave, double-concave, and meniscus. Through reasonable distribution of the optical powers of the three cylindrical lenses, it only needs to meet the design requirement that the wavefront error is less than 0.25 times the wavelength, and this device has good optical performance.

[0086] Preferably, the three cylindrical lenses are three single cylindrical lenses, and their surfaces along the laser beam emission direction are convex-flat, concave-flat, and convex-flat respectively. The astigmatism correction device with this structure can save more costs.

[0087] It should be noted that the core of the variable magnification cylindrical lens group implemented according to the present invention is to achieve the correction in the refractive axis direction. In fact, it makes the placement position requirement of the above lens group in the optical axis direction not exceed 2° from the direction to be corrected in the spot cross-section direction to be corrected, that is, to ensure the placement position of the cylindrical lens group as much as possible, without bringing a complicated calculation amount to the orthogonal decomposition calculation of the optical axis, and also making the astigmatism correction effect reach the best.

[0088] The present invention provides the optical design parameters of an astigmatism correction device in an embodiment, which is applicable to a 355 nm wavelength ultraviolet laser, as shown in Table 2 below.

[0089] Table 2 Optical Design Parameters of Astigmatism Correction Device

[0090]

[0091]

[0092] The astigmatism correction device of this embodiment can achieve a continuously adjustable magnification of 0.8 - 1.2x.

[0093] Among them, the radius of curvature of the front surface of the first cylindrical lens is 126.308 mm, and the radius of curvature of the rear surface is ∞; the radius of curvature of the front surface of the second cylindrical lens is -32.252 mm, and the radius of curvature of the rear surface is ∞; the radius of curvature of the front surface of the third cylindrical lens is 83.714 mm, and the radius of curvature of the rear surface is ∞; the allowable tolerance of all radii of curvature is 10%, the upper deviation is +5%, and the lower deviation is -5%. The central thickness of the three cylindrical lenses is 5 mm each, and the allowable tolerance of the central thickness is 10%, the upper deviation is +5%, and the lower deviation is -5%; the refractive indices of the three cylindrical lenses are all 1.458, and the allowable tolerance of the refractive index is 10%, the upper deviation is +5%, and the lower deviation is -5%;

[0094] Through the above optical parameter settings, the wavefront error of the astigmatism correction device can be minimized within the entire magnification range.

[0095] Preferably, the Abbe numbers of the three cylindrical lenses are all 67.8, and the allowable tolerance of the Abbe number is 10%, the upper deviation is +5%, and the lower deviation is -5%. Among them, the material and coating of the cylindrical lens need to be determined in combination with the specific application scenario (laser parameters, processing effect). The material of the embodiment of the present invention is the optimized design result at a wavelength of 355 nm, and for other wavelength bands, the optical design can be adjusted accordingly.

[0096] In the correction based on the astigmatism correction device involved in the present invention, there are requirements for the field of view range of the incident light beam. The diameter of the optical incident light beam of the cylindrical lens within 13 mm can meet the diffraction limit requirements, that is, the astigmatism correction device allows the incident diameter φ ≤ 13 mm.

[0097] Among them, the adjustment methods of L1 and L2 can be electric adjustment or can be adjusted through a manual cam structure. The total length of the above structure < 165 mm, the structure is compact and easy to integrate.

[0098] The embodiments in the above table are a set of preferred optical design parameters in one of the implementation manners of the present invention, which are the results of comprehensively considering factors such as correction quality, total system mechanical length, processing cost, etc.; by changing conditions such as lens material, lens curvature, total system length limit, etc., there are theoretically multiple feasible optical design schemes.

[0099] According to the astigmatism correction method and the astigmatism correction device implemented in the embodiment of the present invention, it is applicable to the case where the astigmatism value of the light beam before correction is less than 50%, the astigmatism value after correction is less than 1%, and the ratio of the beam waist sizes is corrected from 80 - 120% and approaches K N (extremely close to 1). Among them, the astigmatism value of the light beam Ast = |Z 0x -Z 0y | / Z R * 100%, Z R represents the average Rayleigh length, λ is the laser wavelength. For application scenarios beyond this range, it is necessary to re - design the optical structure of the astigmatism correction device, and the astigmatism correction relationship between the above - mentioned optical structure and the light spot can be calculated according to specific optical design parameters.

[0100] The corresponding relationship between the magnification obtained by the cylindrical lens group with the above - mentioned optical design parameters and L1, L2 is as Figure 7 shown, corresponding to Table 1 in the above text. Usually, the values of L1 and L2 are determined by the parameters of the cylindrical lens group (lens material, radius of curvature), which is a conventional optical design idea. Figure 8 It is a configuration diagram for different magnification adjustments.

[0101] Example 1

[0102] This example is directed to the scenario of precision laser processing with a focusing head (that is, the lens in this example) cooperating with a moving table.

[0103] Among them, the focusing head refers to an optical device that can focus a laser beam into a very small - sized beam, having a certain focal length and working distance, and is widely used in laser processing. It can be a single - piece type or a multi - piece type.

[0104] Using a UV laser with a wavelength of 355 nm, before astigmatism correction, as measured by M 2 the tester, the waist sizes of the laser beam in the x and y directions are 1.8 mm and 2 mm respectively (before using a lens for focusing), the diffraction factors of the beam are 1.05 and 1.03 respectively, and the astigmatism value of the beam is about 20%. Using a lens with f = 100 mm for focusing, the size change of the laser beam near the focal length of the lens is as Figure 11 shown. It can be seen from the figure that the waist position and waist size in the x direction are 100.017 mm and 6.5 μm, and the waist position and waist size in the y direction are 100.065 mm and 5.7 μm; the difference in the waist positions in the two directions is 48 μm. When the focused spot is circular, the corresponding position is 99.845 mm (obtained from the data at the first intersection point of the two lines in Figure 11 , and at this time, the intersection indicates that the sizes in the x and y directions are the same), and the spot radius is 7.3 μm. During actual processing, it is impossible to focus the spot to the minimum in both directions, that is, the best processing effect cannot be obtained.

[0105] Using an astigmatism correction device to correct the astigmatism of the laser beam, the size change near the focal point of the lens after correction is as Figure 12 shown. The calculated magnification β = 1.12 is obtained. According to the relationship diagram between the magnification and the distance in Figure 7 , the corresponding values of L1 and L2 are 82.451 and 71.84 respectively. Then, by finely adjusting the second distance, the astigmatism value of the corrected beam < 1%. It can be seen from the figure that the waist positions in the x and y directions are both corrected to 99.975 mm, the waist sizes in the x and y directions are 5.69 μm and 5.65 μm respectively, and the roundness of the focused spot is 99%. Processing can be carried out under the condition that both the best roundness and the best focusing effect are satisfied with the laser beam after astigmatism correction.

[0106] Example 2

[0107] The difference between this example and Example 1 is that the astigmatism value of the laser beam of the initial laser is different.

[0108] Using a UV laser with a wavelength of 355 nm for processing, before astigmatism correction, as measured by M 2 the tester, the waist sizes of the laser beam in the x and y directions are 1.8 mm and 2 mm respectively, the diffraction factors of the beam are 1.05 and 1.03 respectively, and the astigmatism value of the beam is about 10%. Using a lens with f = 100 mm for focusing, the size change of the laser beam near the focal length of the lens is as Figure 13 shown.

[0109] From Figure 13It can be seen that the waist position and waist size in the x direction are 100.010 mm and 6.58 μm, respectively, and the waist position and waist size in the y direction are 100.034 mm and 5.77 μm, respectively; the difference in the waist positions in the two directions is 24 μm. When the focused spot is circular, the corresponding position is 99.764 mm, and the spot radius is 7.93 μm. During actual processing, it is impossible to focus the spot to the minimum in both directions, that is, the best processing effect cannot be obtained.

[0110] An astigmatism correction device is used to correct the astigmatism of the laser beam. The size change near the lens focus after correction is as Figure 14 shown. The calculated magnification β = 1.12 is used, and the corresponding values of L1 and L2 are 82.451 and 71.265, respectively. Then, the second distance is finely adjusted, and the astigmatism value of the corrected beam < 1%. It can be seen from the figure that the waist positions in the x and y directions are both corrected to 100.75 mm, the waist sizes in the x and y directions are 5.78 μm and 5.76 μm, respectively, and the roundness of the focused spot is 99%. Processing can be carried out under the condition that the best roundness and the best focusing effect are simultaneously satisfied.

[0111] Example 3

[0112] This example is aimed at the scenario of precision laser processing when a galvanometer is paired with a field lens (i.e., the scanning lens in this example) as the scanning component.

[0113] A UV laser with a wavelength of 355 nm is used for processing. Before astigmatism correction, the waist sizes of the laser beam in the x and y directions measured by the M 2 tester are 1.8 mm and 2 mm, respectively, the diffraction factors of the beam are 1.05 and 1.03, respectively, the astigmatism value of the beam is about 20%, and a galvanometer is used in combination with a scanning lens with f = 200 mm for focusing and scanning processing. The effective scanning area of the system is 125 mm x 125 mm.

[0114] Before astigmatism correction, due to the existence of beam astigmatism, the size of the circular spot obtained at the center of the field is not small enough, and the spot size is 49.477 μm, as Figure 15 (the left figure in the processing effect diagram of the laser beam hitting the processing object). Due to the superposition of the beam astigmatism and the astigmatism of the field lens, the difference in the waist positions in the x and y directions is too large when the spot at the edge of the field is focused, and good focusing cannot be achieved. The spot shows a significant ellipse, as Figure 15 shown in the right figure, the major axis size is 55.526 μm, and the minor axis size is 49.184 μm. It should be noted that the spots around the edge of the spot in the figure are caused by material sputtering, but this does not affect the roundness of the spot.

[0115] Using an astigmatism correction device, the calculated magnification is 1.12. Adjust the values of L1 and L2 to 84.451 and 71.265 respectively, and then finely adjust the second distance to achieve the correction of astigmatism in two directions. After correction, the astigmatism value of the beam < 1%. After completing the astigmatism correction, the processing quality across the entire surface is improved. The results are as Figure 16 (The processing effect diagram of the laser beam hitting the processing object) shown. The size of the focused spot at the center of the image plane decreases, from the original Figure 15 49.477 μm in Figure 16 the left figure in Figure 16 decreasing to 44.715 μm, and the spot at the edge is adjusted to the same size and roundness as the central spot ( Figure 16 the right figure in

[0116] ). Its roundness is good, the spot size is 44.217, the focusing effect is good, and the spot size is small. The above content is only a preferred exemplary embodiment of the present invention and is not used to limit the implementation of the present invention. Those of ordinary skill in the art can easily make corresponding adaptations or modifications according to the main concept and spirit of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope required by the claims.

Claims

1. An astigmatism correction method for a laser beam, characterized in that, Including: Emitting a laser beam; Obtaining the waist sizes of the laser beam in two directions and the waist positions in two directions; wherein, the two directions include a first direction and a second direction, and the first direction is perpendicular to the second direction; further including obtaining the ratio of the waist sizes of the laser beam in the first direction and the second direction, the absolute difference between the waist positions of the laser beam in the first direction and the second direction, and the ratio K of the diffraction factors of the laser beam in the first direction and the second direction; Adjust the astigmatism correction device to make the waist sizes of the laser beam in two directions consistent and the waist positions coincide. The process of making the waist sizes of the laser beam in two directions consistent and the waist positions coincide includes: making the ratio of the waist sizes approach K N , and the absolute difference approaches zero; where N is a number greater than 0 and less than 1.

2. The astigmatism correction method of a laser beam as described in claim 1, characterized in that The astigmatism correction device includes three cylindrical lens groups with adjustable distances between each other, and each of the cylindrical lens groups includes at least one cylindrical lens; Wherein, the three cylindrical lens groups are successively a first cylindrical lens group, a second cylindrical lens group, and a third cylindrical lens group, the distance between the first cylindrical lens group and the second cylindrical lens group is a first distance, and the distance between the second cylindrical lens group and the third cylindrical lens group is a second distance; Initially adjust the first distance and the second distance so that the ratio of the waist sizes approaches K N .

3. The astigmatism correction method of a laser beam according to claim 2, characterized in that, The first distance and the second distance of the initial adjustment are determined by a magnification factor, which is the reciprocal of the ratio of the waist sizes in the first direction and the second direction multiplied by K N .

4. The astigmatism correction method for a laser beam according to any one of claims 1 to 3, characterized in that, The N is 0.

5.

5. The method for correcting the astigmatism of a laser beam according to claim 2, characterized in that, After initially adjusting the first distance and the second distance, the second distance is further finely adjusted to make the absolute difference approach zero.

6. The method for correcting the astigmatism of a laser beam according to claim 5, wherein, Each of the cylindrical lens groups includes one cylindrical lens.

7. An astigmatism correction system for a laser beam, characterized in that, Including: A laser for emitting a laser beam; An astigmatism correction device is used to correct the laser beam so that the beam waist sizes of the laser beam in two directions are the same and the beam waist positions coincide. The two directions include a first direction and a second direction, and the first direction is perpendicular to the second direction. Making the beam waist sizes of the laser beam in the two directions the same and the beam waist positions coincide includes: making the ratio of the beam waist sizes of the laser beam in the two directions approach K N , and the absolute difference between the beam waist positions of the laser beam in the first direction and the second direction approaches zero; where N is a number greater than 0 and less than 1; The astigmatism correction device is located behind the laser.

8. The astigmatism correction system for a laser beam according to claim 7, characterized in that, Further including: A parameter measurement device for obtaining the waist sizes of the laser beam in two directions and the waist positions in two directions; Wherein, the parameter measurement device is located behind the astigmatism correction device.

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