CN115138963A

CN115138963A - Astigmatism correction method and system for laser beam and astigmatism correction device

Info

Publication number: CN115138963A
Application number: CN202110835663.5A
Authority: CN
Inventors: 程晓伟; 朱凡; 陆红艳
Original assignee: Dier Laser Technology Wuxi Co ltd
Current assignee: Dier Laser Technology Wuxi Co ltd
Priority date: 2021-07-23
Filing date: 2021-07-23
Publication date: 2022-10-04

Abstract

The invention provides an astigmatism correction method and system for a laser beam and an astigmatism correction device, wherein the astigmatism correction method for the laser beam comprises the following steps: emitting a laser beam; acquiring beam waist sizes of laser beams in two directions and beam waist positions in the two directions; the two directions comprise a first direction and a second direction, and the first direction is vertical to the second direction; and adjusting the astigmatism correction device to enable the beam waist sizes of the laser beams in the two directions to be consistent and the beam waist positions to be superposed. According to the method, the system and the device, the correction of the astigmatism of the laser beam can be realized, so that the precision laser processing quality can be improved.

Description

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

Technical Field

The invention belongs to the technical field of laser precision machining, and particularly relates to an astigmatism correction method and system and an astigmatism correction device for a laser beam, which are particularly suitable for correcting laser beam aberration.

Background

The existing laser precision machining generally uses a laser to cooperate with a beam expander to expand a light beam to a proper diameter, and then uses a scheme that a focusing head cooperates with a table top to move or a vibrating mirror cooperates with a field lens to scan and machine. The precision machining technology has high requirements on the quality of laser beams, and is mainly embodied in the aspects of laser beam diffraction factors, beam roundness, astigmatism and the like. When the roundness of the original laser beam is not good or the astigmatism control is not good, the roundness of a laser spot obtained by focusing is not good, the focusing effect is not good, and the laser processing quality is affected.

Actually, astigmatism of a laser beam has a remarkable influence on precision machining quality, when a focusing head is used for being matched with a moving table for machining, due to the existence of the astigmatism of the laser beam, a light spot cannot be focused to be minimum in the transverse direction and the longitudinal direction at the same time, and only an optimal roundness position can be selected for machining in actual laser machining; when the transverse and longitudinal processing is needed, the requirement on the roundness of the light spot is higher, the processing effects in two directions are inconsistent, and the processing line width, the ablation depth and the like are reflected.

In addition, when a galvanometer is used for being matched with a field lens for processing, the problem of matching motion of the similar focusing head exists at the center of the scanning breadth due to the existence of laser beam astigmatism; because the focal plane of the field lens is not a perfect plane but a curved surface with different field curvature distributions in the meridian direction and the sagittal direction, the inconsistent field curvatures in the meridian direction and the sagittal direction form astigmatism of the field lens, when large-format processing is required, the light spot focusing effect at the edge of the breadth is simultaneously influenced by the superposition of the astigmatism of the field lens and the astigmatism of the laser beam, more remarkable influence is generated on the processing quality, and even the light spot at the edge of the breadth cannot form focusing when the astigmatism of the laser beam is too large.

Disclosure of Invention

Problems to be solved by the invention

In laser processing, due to the existence of laser beam astigmatism, the technical problems that processing effects in the transverse direction and the longitudinal direction are different, and light spots cannot be focused to the minimum in the transverse direction and the longitudinal direction at the same time exist, the prior art generally adopts a compromise scheme, namely the sizes of the light spots in the X direction and the Y direction are adjusted to be the same, the light spots have better roundness but are not the minimum focused light spots, and the focusing energy density of laser is not optimal; alternatively, the spot size may be adjusted to be the smallest in the X or Y direction, but in such a case, the spot is a conspicuous ellipse, and the processing quality is not good.

In the application of galvanometer scanning processing, astigmatism (namely, inconsistent field curvature in X and Y directions) exists at the edge of a web surface in a processing system formed by a galvanometer-field lens, and the astigmatism of a laser beam are superposed to further influence the quality of a light spot at the edge of the web surface, so that the focusing effect of the light spot at the edge of the web surface is poor or even the light spot cannot be focused.

An object of an aspect of the present invention is to provide a method and a system for correcting astigmatism of a laser beam, so as to improve the laser beam processing quality, thereby significantly improving the laser beam processing quality.

In the astigmatism correction method, system and apparatus for a laser beam according to an aspect of the present invention, the cylindrical lens group further has a certain focusing range in consideration of different astigmatism values of different lasers.

The invention provides an astigmatism correction method of a laser beam, which comprises the following steps: emitting a laser beam;

acquiring beam waist sizes of laser beams in two directions and beam waist positions in the two directions; the two directions comprise a first direction and a second direction, and the first direction is vertical to the second direction;

and adjusting the astigmatism correction device to enable the beam waist sizes of the laser beams in the two directions to be consistent and the beam waist positions to be superposed.

Further, the astigmatism correction method further includes obtaining a ratio of beam waist sizes of the laser beam in the first direction and the second direction, an absolute difference of beam waist positions of the laser beam in the first direction and the second direction, and a ratio K of diffraction factors of the laser beam in the first direction and the second direction;

the enabling the beam waist sizes of the laser beams in the two directions to be consistent and the beam waist positions to be coincident comprises the following steps: the ratio of the beam waist sizes approaches K ^N And the absolute difference approaches zero; wherein N is a number greater than 0 and less than 1.

Further, the astigmatism correction device comprises three cylindrical lens groups with adjustable distance between each two cylindrical lens groups, and each cylindrical lens group comprises at least one cylindrical lens;

the three cylindrical lens groups are a first cylindrical lens group, a second cylindrical lens group and a third cylindrical lens group in sequence, 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;

the first distance and the second distance are adjusted for the first time, so that the ratio of the beam waist size approaches to K ^N ；

Further, the first distance and the second distance of the primary adjustment are determined by a magnification factor, wherein the magnification factor is the inverse of the ratio of the beam waist size of the first direction and the second direction multiplied by K ^N .

Further, the N is 0.5.

Further, after the first distance and the second distance are adjusted for the first time, the second distance is fine-tuned again, so that the absolute difference value approaches zero.

Further, each of the cylindrical lens groups includes a piece of cylindrical lens.

In another aspect, the present invention further discloses an astigmatism correction system for a laser beam, comprising:

a laser for emitting a laser beam;

the astigmatism correcting device is used for correcting the laser beams to enable beam waist sizes of the laser beams in two directions to be consistent and beam waist positions to be coincident; the two directions comprise a first direction and a second direction, and the first direction is vertical to the second direction;

the astigmatism correction means is located after the laser.

Further, the method also comprises the following steps: the parameter measuring device is used for acquiring beam waist sizes of the laser beam in two directions and beam waist positions in the two directions; wherein the parameter measuring means are located after the astigmatism correcting means.

In another aspect, the invention discloses an astigmatism correction device, which comprises three cylindrical lens groups with adjustable distance between each two cylindrical lens groups, wherein each cylindrical lens group comprises at least one cylindrical lens.

The astigmatism correction method, the astigmatism correction system and the astigmatism correction device of the laser beam, which are realized according to the invention, have the following beneficial effects:

(1) The invention provides an astigmatism correction method and system for a laser beam. When the transverse processing and the longitudinal processing are required, the processing effects in two directions can be more consistent; in addition, for the scanning system with the galvanometer matched with the field lens, when large-format processing is carried out, the light spot focusing effect of the edge of the large format can be improved, and therefore the processing quality of the whole large format is improved.

(2) The astigmatism correction method of the laser beam provided by the invention can improve the laser precision processing effect, such as: for the oval light spot, the light spot can become a round light spot with high roundness after being corrected; for a circular spot, the spot size can be reduced;

moreover, the roundness of the laser beam obtained by the method after being corrected is transmitted at a certain distance can not be obviously changed.

(3) The astigmatism correction method and system for the laser beam, which are provided by the invention, have the advantages that the applicable laser processing range is wide in related technical concept, the laser astigmatism correction device can be designed according to specific processing requirements (such as spot size) and laser parameters (such as wavelength and beam diameter), and the adaptive design can be further carried out according to the correction of the spot shape.

(4) The invention provides an astigmatism correction device, which fully applies the directional refraction characteristic of a cylindrical lens to correct the parameters of a single direction of a light beam, is applied to laser precision machining, can realize the effect of keeping the roundness of a light spot under a small focusing size to be high, and improves the laser machining quality and efficiency;

meanwhile, the distance between every two of the three cylindrical lens groups can be adjusted, so that the device has a certain magnification adjusting range, the adaptability to the directions of the major axis and the minor axis of the elliptical light spot is stronger, and the adaptability of astigmatism correction of the laser beam is improved.

Additional aspects and advantages will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the application.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, are included to provide a further understanding of the application, and the description of the exemplary embodiments and illustrations of the application are intended to explain the application and are not intended to limit the application.

In the drawings:

fig. 1 is a schematic flowchart of an astigmatism correction method for a laser beam according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of the variation of laser beam size with beam position before astigmatism correction;

FIG. 3 is a schematic diagram of the size of the laser beam obtained after astigmatism correction varying with the position of the beam;

FIG. 4 is a schematic structural diagram of an astigmatism correction system for a laser beam according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of an astigmatism correction system for a laser beam according to another embodiment of the present invention;

fig. 6 is a schematic structural diagram of an astigmatism correction apparatus according to an embodiment of the present invention;

FIG. 7 is a diagram illustrating the relationship between the magnification of one of the astigmatism correction devices and the first and second distances, according to the present invention;

FIG. 8 is a configuration diagram of an astigmatism correction device implemented in accordance with the present invention at different magnification adjustments;

fig. 9 is a schematic structural diagram of an application scenario of the astigmatism correction apparatus according to the present invention;

fig. 10 is a schematic view of another application scenario of the astigmatism correction apparatus according to the present invention;

FIG. 11 is a schematic diagram showing the variation of the laser beam size with the beam position before astigmatism correction in example 1;

fig. 12 is a schematic diagram showing the variation of the laser beam size with the beam position after astigmatism correction in embodiment 1;

FIG. 13 is a schematic diagram showing the variation of the laser beam size with the beam position before astigmatism correction in example 2;

fig. 14 is a schematic diagram of the change of the laser beam size with the beam position after the astigmatism correction in embodiment 2.

FIG. 15 is a speckle image of example 3 before astigmatism correction;

fig. 16 is a spot image after astigmatism correction in example 3.

Detailed Description

It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict. The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

The present invention is described in further detail below with reference to specific examples, which are not to be construed as limiting the scope of the invention as claimed.

An astigmatism correction method and system for a laser beam and an astigmatism correction apparatus according to an embodiment of the present application are described below with reference to the drawings.

As shown in fig. 1, a method for correcting astigmatism of a laser beam is proposed, comprising: emitting a laser beam; acquiring beam waist sizes of laser beams in two directions and beam waist positions in the two directions; wherein two areThe directions comprise a first direction and a second direction, and the first direction and the second direction are perpendicular to each other; and adjusting the astigmatism correction device to enable the beam waist sizes of the laser beams in the two directions to be consistent and the beam waist positions to be superposed. In this embodiment, the first direction and the second direction may be an X direction (a horizontal direction) and a Y direction (a vertical direction), and the first direction may also have a certain angle (e.g. 45 degrees) with the horizontal direction, and generally the first direction and the second direction are perpendicular to each other _0x 、W _0y The beam waist positions in both directions can be represented as Z _0x 、Z _0y . In addition, the beam waist positions here coincide, and are expressed as the absolute difference value of the beam waist positions in the two directions tends to 0.

Generally, before astigmatism of the laser beam is not corrected, beam waists of the laser beam in two directions are different in size and do not coincide with each other, as shown in fig. 2. The astigmatism correction method of the laser beam provided by the invention obtains W _0x 、W _0y 、Z _0x 、Z _0y Then, an astigmatism correction device independent of the laser (for emitting the laser beam) is adjusted to make the beam waist sizes of the laser beams in the two directions consistent and the beam waist positions coincide, and as a result, as shown in fig. 3, the astigmatism of the laser beam can be corrected, and the laser processing quality can be improved.

In addition, the astigmatism correction method can make the processing effects in the transverse direction and the longitudinal direction more consistent; in addition, for the scanning system with the galvanometer matched with the field lens, when large-format processing is carried out, the light spot focusing effect of the edge of the large format can be improved, and therefore the processing quality of the whole large format is improved. In addition, the method can not only improve the laser precision processing effect, such as: for the oval light spot, the light spot can become a round light spot with high roundness after being corrected; for a circular spot, the spot size can be reduced (e.g., a rectangular spot can also be corrected for a square spot). Moreover, the roundness of the laser beam obtained by the method after being corrected is transmitted at a certain distance can not be obviously changed.

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

As another embodiment, the astigmatism correction method for the laser beam further includes obtaining a ratio (W) of a beam waist size of the laser beam in the first direction to the second direction _0x /W _0y ) Absolute difference value | Z of beam waist positions of laser beam in first direction and second direction _0x -Z _0y And a ratio K of 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 Denotes the diffraction factor, M, in the X direction ² _y Represents a diffraction factor in the Y direction; making the beam waist sizes of the laser beams in the two directions consistent and the beam waist positions coincident comprises: making the ratio W of the waist sizes _0x /W _0y Approaches to K ^N And absolute difference value | Z _0x -Z _0y I approaches zero; wherein N is a number greater than 0 and less than 1. Here, the ratio W of the girdling size _0x /W _0y Approaches to K ^N The finger approaches K ^N +/-0.001 (looking at the test instrument for obtaining beam waist size, beam waist position and diffraction factor, such as M) ² Accuracy determination of tester), absolute difference | Z _0x -Z _0y I approaching zero means that the absolute difference is less than 0.01 times the average Rayleigh length Z _R 。

λ is the laser wavelength.

Wherein the diffraction factor M is selected ² As W _0x /W _0y The reference object of the target approach value of (1) is to take into account 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. Meanwhile, the ratio W of the beam waist size is adjusted by adjusting the astigmatism correction _0x /W _0y Approaches to K ^N And is andabsolute difference value | Z _0x -Z _0y The method has the advantages that |, which is close to zero, can realize the consistency of the focusing positions of two correction directions, can well ensure that the laser beam is still very round after being transmitted at a certain distance, and is more suitable for a precise laser processing system with high requirements on light spots.

The laser beam in this embodiment is a gaussian beam, and the beam waist size W of the laser beam is determined according to the characteristics of the gaussian beam ₀ Divergence angle theta corresponding to beam waist ₀ The product of (c) 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) of the corresponding direction ² ) Namely, the following steps are provided: k = A _x /A _y Let W be _0x /W _0y Approaches to K ^N Then at the same time have theta _0x /θ _0y Approaches to K ^N Thereby, the ratio W of the beam radius at the position d from the beam waist can be ensured _xd /W _yd ＝(W _0x +dθ _0x )/(W _0y +dθ _0y ) Approaches to K ^N Meanwhile, the difference (| Z) in the position of the girdling waist _0x -Z _0y |) embodies the divergence angle θ ₀ The corrected beam radius keeps the same proportion when reaching the processing object after a certain propagation distance, namely, the roundness of the beam does not change obviously after being transmitted for a certain distance. The laser beam after correction can obtain the best focusing effect and the optimal spot roundness.

Further, the beam waist dimension W _0x 、W _0y Girdling position Z _0x 、Z _0y Diffraction factor M ² _x 、M ² _y As the initial parameter of calibration and the final criterion, both can pass the standard M ² The test is directly carried out by the tester. M is a group of ² The tester is a standard instrument that is often used by those skilled in the art to measure laser beam parameters and will not be described in detail herein as prior art. When necessary through M ² When the tester measures the parameters of laser beams before being corrected, M is directly measured ² The tester is placed after the laser as shown in fig. 4.

As another oneIn an embodiment, the astigmatism correction device in the correction method includes three cylindrical lens groups with adjustable distances between every two cylindrical lens groups, so that in laser correction, the spot size in one direction is kept unchanged, and the spot size in the other direction is adjusted. The three cylindrical lens groups are a first cylindrical lens group, a second cylindrical lens group and a third cylindrical lens group in sequence, the first cylindrical lens group, the second cylindrical lens group and the distance between the first cylindrical lens group and the second cylindrical lens group form a zoom group, and the third cylindrical lens group forms a compensation group for adjusting the divergence angle of the emergent light beam; the distance between the first cylindrical lens group and the second cylindrical lens group is a first distance L1, and the distance between the second cylindrical lens group and the third cylindrical lens group is a second distance L2; the first distance L1 and the second distance L2 are adjusted for the first time, so that the ratio of the beam waist sizes approaches to K ^N . For one embodiment, each cylindrical lens group includes a piece of cylindrical lens, as shown in FIG. 6.

The astigmatism correction device adopts all cylindrical lenses, and utilizes the directional refraction characteristics of the cylindrical lenses to adjust the laser beams in a single direction during laser correction, so that the astigmatism of the laser beams is reduced, and the laser processing quality is improved. Meanwhile, the adjusting mode of adjusting the distance between every two three cylindrical lens groups enables the device to have a certain magnification adjusting range, enables the adaptability to the directions of the long axis and the short axis of the elliptical light spot to be stronger, and improves the adaptability of astigmatism correction of the laser beam.

Here, the adjustment of the single direction of the laser beam may be, for example, such that the emitted laser beam is elliptical, if the X-axis and the Y-axis correspond to the major axis and the minor axis of the ellipse, respectively, at this time, and if the refractive correction of the cylindrical lens group is directed toward the X-direction at this time, W is adjusted at this time _0x /W _0y The purpose of (1) is to reduce the size in the X direction to be close to the size in the Y axis so as to keep the circularity of the spot as much as possible, but of course, the size in the X direction or the size in the Y direction may be arbitrarily adjusted according to actual circumstances.

The refraction directions of all the lenses of the three cylindrical lens groups are the same, the main planes of all the lenses of all the cylindrical lens groups are parallel to each other, the central points of all the lenses are collinear, and the connecting line formed by the central points is vertical to the main planes. The principal plane is an optically specialized concept representing a set of conjugate planes at a homeotropic magnification of 1.

As another example, the first distance L1 and the second distance L2 of the primary adjustment are determined by a magnification β x, which is the inverse of the ratio of the beam waist size in the first direction and the second direction multiplied by K ^N I.e. β x = W _0y /W _0x *K ^N 。

As another embodiment, each cylindrical lens group comprises a cylindrical lens, the astigmatism correction effect can be realized by the structure, the number of the required cylindrical lenses is minimum, and the structure is simplest.

The relationship between the magnification β x 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, and this obtaining of L1 and L2 at different magnifications belongs to the conventional technology in the optical field. The specific relationship is shown in table 1 below, but may be embodied in the form of a curve, as shown in fig. 7 (corresponding to table 1). It is only listed here that each cylindrical lens group includes a cylindrical lens, and when the magnification is in the range of 0.8 to 1.2, L1 and L2 correspond to each other. When the L1 and the L2 corresponding to other magnifications need to be acquired, the optical parameters can be redesigned according to specific conditions.

It should be noted that each cylindrical lens group of the present application may further include a plurality of cylindrical lenses, for example, the first cylindrical lens group includes two cylindrical lenses, and when designing the optical parameters, a focal length formed by two cylindrical lenses included in the first cylindrical lens group is equal to a focal length when the first cylindrical lens group includes only one cylindrical lens. The distance between the cylindrical lens groups is also matched according to the optical design structure parameters. When adjusting the multi-plate 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 is maintained. The lens group consisting of the two cylindrical lenses can enable the astigmatism correcting device to have a better correcting effect, and the multi-piece design has a better spherical aberration correcting effect aiming at larger light beam incidence, the reason is that the requirements on spherical aberration correction are relatively higher for larger incident light beam size, and the operability on spherical aberration correction is higher and more flexible when the number of the lenses is larger.

In addition, each cylindrical lens group may further include three, four or more cylindrical lenses, as required. Moreover, each cylindrical lens group can also simultaneously comprise a plurality of cylindrical lenses according to specific requirements, only the requirement that the focal length formed when each group of cylindrical lens groups comprises a plurality of lenses is equal to the focal length formed when each group of cylindrical lens groups comprises one lens is met, and the astigmatism adjusting modes are the same. When each cylindrical lens group comprises a plurality of cylindrical lenses, the optical parameter design concept is communicated, and the details are not described herein.

TABLE 1 magnification factor and corresponding L1, L2 values

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

Fig. 8 is a configuration diagram of the astigmatism correction apparatus under different magnification adjustments, which is also a case where each cylindrical lens group includes one cylindrical lens, and when each cylindrical lens group includes a plurality of cylindrical lenses, the adjustment manners of L1 and L2 are the same, and the distance between the cylindrical lenses in each cylindrical lens group is maintained to be constant. In the adjustment mode shown in the figure, the position of the second cylindrical mirror is unchanged, the first cylindrical mirror and the second cylindrical mirror are changed to adjust the L1 and the L2, and certainly, the position of the first cylindrical mirror or the third cylindrical mirror can be kept unchanged, and the adjustment modes of the other two cylindrical mirrors are all possible.

As another example, N is 0.5, which is a value that takes into account the balance of the beam waist size and the divergence angle in both X and Y directions, where the astigmatism correction effect is the best.

As another embodiment, after the first distance and the second distance are adjusted for the first time, the second distance is fine-tuned to make the absolute difference value | Z _0x -Z _0y I approaches zero. The invention further considers the problem of consistency of the focusing positions in the two correction directions, so that the second distance is designed to be further finely adjusted in the correction method, the focuses in the two directions are kept consistent as much as possible, and the method is particularly suitable for being used in the processing and using environment of a scanning field lens, so that the focuses in the two directions can be kept free from being influenced by non-uniform focal fields as much as possible under the action of an astigmatism device, and the problem of incapability of focusing is caused. The method for fine tuning the second distance may be: according to Z _0x And Z _0y When relative position of Z _0x At Z _y0y When the right side is needed, theta x needs to be reduced, and the direction is adjusted to increase the second distance; otherwise, the second distance is reduced, and the absolute difference value is driven to 0 by continuously adjusting the distance.

As another embodiment, the present invention provides an astigmatism correction system for a laser beam, including: a laser for emitting a laser beam; the astigmatism correcting device is used for correcting the laser beams to ensure that the beam waist sizes of the laser beams in two directions are consistent and the beam waist positions are superposed; the two directions comprise a first direction and a second direction, and the first direction is vertical to the second direction; wherein the astigmatism correcting means is located after the laser. By the system, the astigmatism adjustment of the laser beam can be realized, and the laser processing quality is improved.

In fact, according to the astigmatism correction system for laser beam implemented by the present invention, the application scenario mainly relates to laser processing, as shown in fig. 9, a schematic structural diagram of the application scenario includes: a laser 101, an astigmatism correction device 102 realized according to the present invention, a beam expander 103, an optical system mirror 104 for guiding the direction of the laser beam, and a condensing lens 105 for condensing the laser beam. As shown in fig. 10, another schematic structural diagram of an application scenario includes: a laser 101, an astigmatism correction device 102 implemented in accordance with the invention, an optical system mirror 104 to direct the laser light, and a beam expander 103, and a galvanometer and field lens scanning assembly 106 positioned after the beam expander 103. In practical application, the astigmatism correction device with the determined L1 and L2 is placed in a system, the device does not need to be adjusted, and the laser after correction is directly adopted for processing.

As another embodiment, as shown in fig. 5, the astigmatism correction system for laser beam further includes a parameter measuring device for obtaining the beam waist sizes of the laser beam in two directions and the beam waist positions in two directions; the two directions comprise a first direction and a second direction, and the first direction is vertical to the second direction; wherein the parameter measuring device is located after the astigmatism correcting device. Wherein the parameter measuring device can be M ² And (4) a tester. After the initial laser beam parameters are obtained by the apparatus shown in FIG. 4, the astigmatism correction system described in FIG. 5 (with the astigmatism correction devices placed between the laser and M) is used to calculate and obtain L1, L2 of the astigmatism correction device by the method described above ² Between the testers), carry outFine-tuning the second distance, and every time fine-tuning the second distance, using M ² The tester obtains the new beam waist sizes in two directions and the beam waist positions in two directions after fine adjustment, and judges the | Z _0x -Z _0y And if not, repeating fine adjustment and parameter acquisition until the absolute difference value approaches to 0.

As another embodiment, the present invention further provides an astigmatism correction apparatus, as shown in fig. 6, the astigmatism correction apparatus includes three cylindrical lens groups with adjustable distances therebetween, and each cylindrical lens group includes at least one cylindrical lens. The device has a certain magnification adjusting range, so that the adaptability to the directions of the major axis and the minor axis of the elliptical light spot is stronger, and the adaptability of astigmatism correction of the laser beam is improved.

As another embodiment, each cylindrical lens group includes a cylindrical lens, the three cylindrical lens groups are sequentially a first cylindrical lens, a second cylindrical lens and a third cylindrical lens, and a curved surface of the first cylindrical lens, which faces the emission direction of the laser beam, is a convex surface, so that the first cylindrical lens realizes light condensation.

The first cylindrical lens group, the second cylindrical lens group and the distance between the first cylindrical lens group and the second cylindrical lens group form a zoom group, and the third cylindrical lens group forms a compensation group to adjust the divergence angle of the emergent light beam.

Preferably, the first cylindrical mirror has positive diopter, the second cylindrical mirror has negative diopter, the third cylindrical mirror has positive diopter, wherein the second cylindrical mirror can correspond to lenses in various shapes such as plano-convex, biconvex and meniscus, the third cylindrical mirror can correspond to lenses in various shapes such as plano-concave, biconcave and meniscus, through reasonable focal power distribution of the three cylindrical mirrors, the design requirement that the wavefront error is less than 0.25 times of wavelength is finally met, and the device has good optical performance.

Preferably, the three cylindrical lenses are three single cylindrical lenses, and the curved surfaces thereof along the emission direction of the laser beam are respectively convex flat, concave flat and convex flat. The astigmatism correcting device with the structure can save more cost.

It is worth noting that the core of the variable power cylindrical lens group realized according to the present invention is to realize the correction in the direction of the dioptric axis, in fact, the placing position of the lens group in the direction of the optical axis and the direction to be corrected in the direction of the cross section of the light spot to be corrected are required to be not more than 2 °, that is, the placing position of the cylindrical lens group is ensured as much as possible, so that the complex calculation amount is not brought to the orthogonal decomposition calculation of the optical axis, and the astigmatism correction effect is also optimized.

The present invention provides optical design parameters of an astigmatism correction device under an embodiment, which is suitable for an ultraviolet laser with a wavelength of 355nm, and is specifically shown in the following table 2.

TABLE 2 optical design parameters for astigmatism correction devices

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

Wherein the radius of curvature of the front surface of the first cylindrical mirror is 126.308mm, 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 mirror is 83.714mm, and the radius of curvature of the rear surface of the third cylindrical mirror is infinity; the allowable tolerance for all radii of curvature is 10%, with an upper deviation of +5% and a lower deviation of-5%. The central thicknesses of the three cylindrical mirrors are all 5mm, the allowable tolerance of the central thicknesses is 10%, the upper deviation is +5%, and the lower deviation is-5%; the refractive indexes of the three cylindrical mirrors are all 1.458, the allowable tolerance of the refractive indexes is all 10%, the upper deviation is +5%, and the lower deviation is-5%;

with the above-described optical parameter settings, the wavefront error of the astigmatism correction device can be minimized over the entire magnification range.

Preferably, the abbe numbers of the three cylindrical mirrors are all 67.8, the allowable tolerance of the abbe numbers are all 10%, the upper deviation is +5%, and the lower deviation is-5%. The material and coating of the cylindrical mirror are determined by combining specific application scenarios (laser parameters and processing effects). The material of the embodiment of the invention is an optimized design result under the wavelength of 355nm, and the optical design can be correspondingly adjusted aiming at other wave bands.

In the correction based on the astigmatism correction device, the field range of an incident beam is required, and the diffraction limit requirement can be met within 13mm of the optical incident beam diameter of the cylindrical lens, namely the allowable incident diameter phi of the astigmatism correction device is less than or equal to 13mm.

The adjustment modes of L1 and L2 can be electric adjustment or manual cam structure adjustment. The total length of the structure is less than 165mm, the structure is compact, and the integration is easy.

The examples of the above tables are a preferred set of optical design parameters in one of the embodiments according to the present invention, as a result of comprehensively considering factors such as calibration quality, total system mechanical length, machining cost, etc.; by changing the conditions of lens material, lens curvature, total system length limitation, etc., there are theoretically many possible optical design schemes.

The astigmatism correction method and the astigmatism correction device realized in the embodiment of the invention are suitable for enabling the astigmatism value of the beam before being uncorrected to be less than 50%, the astigmatism value after being corrected to be less than 1%, and the beam waist size ratio to be close to K after being corrected by the laser beam with the beam waist size of 80-120% ^N (very close to 1). Wherein the astigmatism value of the light beam Ast = | Z _0x -Z _0y |/Z _R *100％，Z _R The average rayleigh length is expressed as,

λ is the laser wavelength. For applications beyond this range, the optical configuration of the astigmatism correction device needs to be redesigned, and the astigmatism correction relationship between the optical configuration and the beam spot can be calculated according to specific optical design parameters.

The correspondence between the magnification and L1, L2 obtained by using the cylindrical lens group with the above optical design parameters is shown in fig. 7, which corresponds to table 1 above, and the values of L1, L2 are usually determined by the cylindrical lens group parameters (lens material, curvature radius), which is a conventional optical design idea. Fig. 8 is a configuration diagram under different magnification adjustments.

Example 1

This embodiment is directed to a scenario where the focusing head (i.e., the lens in this embodiment) is used in conjunction with a moving stage for precision laser machining.

The focusing head refers to an optical device capable of focusing a laser beam into a beam with a small size, has a certain focal length and working distance, is widely applied to laser processing, and can be of a single-chip type or a multi-chip type.

Using an ultraviolet laser with a wavelength of 355nm, from M, without astigmatism correction ² The tester measured that the beam waist sizes of the laser beam in the x and y directions were 1.8mm and 2mm, respectively (before focusing with no lens), the diffraction factors of the beam were 1.05 and 1.03, respectively, the astigmatism value of the beam was about 20%, focusing was performed with a lens of f =100mm, and the size change of the laser beam near the focal length of the lens is shown in fig. 11. It can be seen from the figure that the beam waist position and the beam waist size in the x direction are 100.017mm and 6.5 μm, and the beam waist position and the beam waist size in the y direction are 100.065mm and 5.7 μm; the beam waist positions in the two directions differ by 48 μm. When the focused spot is circular, the corresponding position is 99.845mm (based on the data obtained from the first intersection of the two lines in fig. 11, where the intersection indicates the dimensions in the x and y directions are consistent), and the spot radius is 7.3 μm. In actual processing, the light spot cannot be focused to the minimum in two directions, i.e. the best processing effect cannot be obtained.

The astigmatism correction device was used to correct the astigmatism of the laser beam, and the dimensional change in the vicinity of the focal point of the lens after correction was as shown in fig. 12. The calculated magnification β =1.12, corresponding values of L1 and L2 of 82.451 and 71.84, respectively, are obtained from the relationship diagram of the magnification and the distance in fig. 7, and the second distance is finely adjusted so that the astigmatism value of the corrected beam is less than 1%. It can be seen from the figure that the beam waist positions in the x direction and the y direction are both corrected to 99.975mm, the beam waist sizes in the x direction and the y direction are respectively 5.69 μm and 5.65 μm, and the roundness of the focused light spot is 99%. The machining is performed under the laser beam after the astigmatism correction, and the machining can be performed under the condition that the optimal roundness and the optimal focusing effect are simultaneously satisfied.

Example 2

The present embodiment is different from embodiment 1 in that the astigmatism value of the laser beam of the original laser is different.

Processing with an ultraviolet laser having a wavelength of 355nm, without astigmatism correction, from M ² The tester measured that the beam waist sizes of the laser beam in the x and y directions were 1.8mm and 2mm, the diffraction factors of the beam were 1.05 and 1.03, respectively, the astigmatism value of the beam was about 10%, the beam was focused using a lens with f =100mm, and the dimensional change of the laser beam near the focal length of the lens is shown in fig. 13.

It can be seen from fig. 13 that the beam waist position and the beam waist size in the x direction are 100.010mm, 6.58 μm, and the beam waist position and the beam waist size in the y direction are 100.034mm, 5.77 μm; the beam waist positions in the two directions differ by 24 μm. When the focused spot is circular, the corresponding position is 99.764mm and the spot radius is 7.93 μm. In actual processing, the light spot cannot be focused to the minimum in two directions, i.e. the best processing effect cannot be obtained.

The astigmatism correction device was used to correct the astigmatism of the laser beam, and the dimensional change in the vicinity of the focal point of the lens after correction was as shown in fig. 14. The magnification β =1.12 used is calculated, the corresponding values of L1 and L2 are 82.451, 71.265 respectively, and the second distance is then fine-tuned, the astigmatism value of the corrected beam being < 1%. It can be seen from the figure that the beam waist positions in the x direction and the y direction are corrected to 100.75mm, the beam waist sizes in the x direction and the y direction are 5.78 μm and 5.76 μm respectively, and the roundness of the focused light spot is 99%. When the machining is performed under such conditions, the machining can be performed while the optimum roundness and the optimum focusing effect are simultaneously satisfied.

Example 3

This embodiment is directed to a scenario in which precision laser processing is performed when a galvanometer field lens (i.e., a scanning lens in this embodiment) is used as a scanning component.

The processing is carried out using an ultraviolet laser with a wavelength of 355nm,before astigmatism correction, from M ² The tester measures that the beam waist sizes of the laser beams in the x direction and the y direction are 1.8mm and 2mm respectively, the diffraction factors of the laser beams are 1.05 and 1.03 respectively, the astigmatism value of the laser beams is about 20%, a galvanometer is used for matching with a scanning lens with f =200mm to carry out focusing scanning processing, and the effective scanning format of the system is 125mm x 125mm.

Before astigmatism correction, the circular spot size obtained at the center of the web is not sufficiently small due to the existence of beam astigmatism, and the spot size is 49.477 μm, as shown in the left diagram of fig. 15 (a processing effect diagram of a laser beam impinging on a processing object). Due to the superposition of the astigmatism of the beam and the astigmatism of the field lens, the beam waist positions in the x and y directions are too different when the spot at the web edge is focused, good focusing cannot be achieved, and the spot appears as a significant ellipse, as shown in the right diagram of fig. 15, with a major axis dimension of 55.526 μm and a minor axis dimension of 49.184 μm. It should be noted that the spots around the edge of the spot are shown as a result of material sputtering, but this does not affect the circularity of the spot.

And (3) calculating by using an astigmatism correction device to obtain the magnification of 1.12, adjusting the values of L1 and L2 to 84.451 and 71.265 respectively, and finely adjusting the second distance to realize the correction of astigmatism in two directions, wherein the astigmatism value of the corrected beam is less than 1%. After the astigmatism correction is completed, the processing quality on the whole web is improved, and as a result, as shown in fig. 16 (a processing effect graph of a laser beam on a processing object), the size of a central focusing light spot of the web is reduced to 44.715 μm from 49.477 μm in the original fig. 15 (a left graph in fig. 16), the size and the roundness of an edge light spot are adjusted to be consistent with those of the central light spot (a right graph in fig. 16), the roundness is good, the light spot size is 44.217, the focusing effect is good, and the light spot size is small.

The above-mentioned embodiments are merely preferred examples of the present invention, and are not intended to limit the embodiments of the present invention, and those skilled in the art can easily make various changes and modifications according to the main concept and spirit of the present invention, so that the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An astigmatism correction method for a laser beam, comprising:

emitting a laser beam;

2. An astigmatism correction method for a laser beam according to claim 1, further comprising obtaining a ratio of beam waist sizes of the laser beam in the first direction and the second direction, an absolute difference of beam waist positions of the laser beam in the first direction and the second direction, and a ratio K of diffraction factors of the laser beam in the first direction and the second direction;

3. An astigmatism correction method for a laser beam as claimed in claim 2, characterized in that said astigmatism correction means comprise three cylindrical lens groups with adjustable distance between each other, each of said cylindrical lens groups comprising at least one cylindrical lens;

the first distance and the second distance are adjusted for the first time, so that the ratio of the beam waist size approaches to K ^N 。

4. Method for astigmatism correction of a laser beam as claimed in claim 3, characterized in thatIn that the first and second distances of the primary adjustment are determined by a magnification that is K multiplied by an inverse of a ratio of the beam waist sizes of the first and second directions ^N 。

5. An astigmatism correction method for a laser beam as claimed in any one of claims 2 to 4, characterized in that N is 0.5.

6. An astigmatism correction method for a laser beam as claimed in claim 3, characterized in that after said first distance and said second distance are adjusted for the first time, said second distance is fine-tuned again so that said absolute difference approaches zero.

7. The method for astigmatic correction of a laser beam of claim 6, wherein each of the cylindrical lens groups includes a piece of cylindrical lens.

8. An astigmatism correction system for a laser beam, comprising:

a laser for emitting a laser beam;

the astigmatism correction means is located after the laser.

9. An astigmatism correction system for a laser beam as recited in claim 8, further comprising:

the parameter measuring device is used for acquiring beam waist sizes of the laser beam in two directions and beam waist positions in the two directions;

wherein the parameter measuring device is located after the astigmatism correcting device.

10. An astigmatism correction device, comprising three cylindrical lens groups with adjustable distance between each two cylindrical lens groups, wherein each cylindrical lens group comprises at least one cylindrical lens.