Patent Publication Number: US-2021162546-A1

Title: Laser cutting device and laser cutting method

Description:
CROSS REFERENCES TO RELATED APPLICATION 
     This application is a National Stage of International Application No. PCT/CN2020/097477 filed on Jun. 22, 2020 which claims priority to Chinese Patent Application No. 201910466903.1, filed on May 31, 2019, entitled “LASER CUTTING DEVICE AND LASER CUTTING METHOD” the disclosure of which is hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a laser cutting device and a laser cutting method. 
     BACKGROUND 
     In conventional laser cutting technology, a laser beam is generally converged into a focal point to cut materials such as wafers. This cutting method generally requires the laser beam to be converged at a position with a certain depth of a processed material for cutting. Since energy at a converging point of the light beam is relatively high, when the focal point moves at the position with such depth, a modified layer can be formed on a moving path. Then, by forming a plurality of modified layers inside the processed material, the processed material can be easily split along these modified layers. 
     SUMMARY 
     According to embodiments of the disclosure, the present disclosure provides: 
     A laser cutting device includes: 
     a beam expanding element provided with a plurality of lens sets, and wherein optical axes of the plurality of lens sets are on the same straight line, each lens set is provided with at least one lens, the beam expanding element converts an incident light beam into a first light beam; and 
     a spectroscopic element arranged on a light path of an emitted light of the beam expanding element, and wherein the spectroscopic element converts the first light beam into multiple second light beams that are annular and spaced apart from each other. 
     And a laser cutting method includes: 
     adjusting a spot of a laser beam emitted by a laser to have an appropriate size through a beam expanding element, such that the adjusted laser beam is capable of passing through a spectroscopic element completely; 
     forming the adjusted laser beam into multiple annular light beams by passing through the spectroscopic element; 
     passing the multiple annular light beams through a focusing lens and forming the multiple annular light beams into multiple focal points arranged spaced away on an optical axis of the focusing lens. The number of focal points is greater than or equal to two. A distance between adjacent focal points in air is less than or equal to 20 μm; and 
     distributing the multiple focal points formed by the focusing lens inside a processed material. The multiple focal points are capable of forming a plurality of modified layers inside the processed material. When the number of focus points and the range of the distance between the focal points as described above are satisfied, the laser cutting method can better cut the materials with smaller thickness such as MINI LEDs. 
     The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other potential features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawings of the present disclosure are used herein as part of the present disclosure to understand the present disclosure. Embodiments of the present disclosure and description thereof are illustrated in the accompanying drawings to explain the principle of the present disclosure. 
         FIG. 1  is a schematic view of a laser cutting device according to an embodiment of the present application. 
         FIG. 2  is a schematic view of a beam expanding element and a spectroscopic element in the laser cutting device according to an embodiment of the present application. 
         FIG. 3  is a schematic view of lens sets in a cooperating state in the laser cutting device according to an embodiment of the present application. 
         FIG. 4  is a schematic view of an adjustment of a light path of the spectroscopic element in the laser cutting device according to an embodiment of the present application. 
         FIG. 5  is a schematic view of an adjustment of a light path of a spectroscopic element in a laser cutting device according to another embodiment of the present application. 
         FIG. 6  is a schematic view showing an application scenario a laser cutting device according to an embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     After the single-focus cutting method completes the cutting at the position with a certain depth of the processed material, the depth of the focal point inside the material is further changed to perform the cutting again. Therefore, the modified layers need to be formed at a plurality of positions with different depths so that the processed material can be easily split, which greatly affects cutting efficiency. 
     In order to facilitate the understanding of the present disclosure, the present disclosure will be described more fully with reference to the relevant drawings. Preferred embodiments of the present disclosure are shown in the attached drawings. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, providing these embodiments is to make the disclosure of the present disclosure more thorough and comprehensive. 
     It should be noted that when an element is referred to as being “fixed to” another element, it can be directly on another element or there may be an intermediate element therebetween. When an element is considered to be “connected to” another element, it can be directly connected to another element or there may be an intermediate element at the same time. On the contrary, when an element is referred as to be “directly on” another element, there is no intermediate element. Terms “vertical”, “horizontal”, “left”, “right” and the like used herein are for illustrative purposes only. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of the present disclosure. The terms used in this specification are only for the purpose of describing specific embodiments, and are not intended to limit the present disclosure. Terms “and/or” as used herein includes any and all combinations of one or more related listed items. 
     Referring to  FIGS. 1 , in order to improve efficiency of a laser cutting, a laser cutting device  10  in the present application is provided with an optical device  100 . The optical device  100  includes a beam expanding element  110  and a spectroscopic element  120 . The spectroscopic element  120  is arranged on a light path of an emitted light of the beam expanding element  110 . A laser beam sequentially passes through the beam expanding element  110  and the spectroscopic element  120 . The beam expanding element  110  can adjust a spot size of an incident light beam to form a first light beam. Optionally, the first light beam with the adjusted spot size can pass through the spectroscopic element  120  completely. That is, the first light beam will not be blocked by a fixing member held by the spectroscopic element  120 . Then, the first light beam adjusted by the spectroscopic element  120  is converted into multiple (at least two) light beams that are annular and spaced apart from each other. Optionally, the first light beam is a parallel light beam. It should be noted that the above definition of “spaced apart from each other” should be understood that distances exist between the multiple second light beams when emitted from the spectroscopic element  120 , and it is not limited to that the second light beams is always separated from each other during propagation. 
     Specifically, referring to  FIG. 2 , the beam expanding element  110  includes a plurality of (at least two) lens sets  112 . Each lens set  112  is provided with at least one lens  1120 . The spectroscopic element  120  is provided to convert the light beam (the first light beam  1101 ) emitted by the beam expanding element  110  into the multiple second light beams  1201 , thereby achieving the effect of adjusting the beam shaping. When applied to the laser cutting device, the multiple second light beams  1201  can be formed into multiple (at least two) focal points of the same number to cut a processed material, such that a plurality of modified layers can be formed in the processed material at one time, improving the cutting efficiency. 
     In addition, for conventional laser multifocal cutting technology, when cutting the processed material with a smaller thickness, it is necessary to replace an optical diffractive element(s) to reduce the number of annular light beams, thereby reducing the number of focal points, such that the focal points formed by the laser beam can be all located in the processed material. When cutting the processed material with a larger thickness, the number of annular light beams needs to be increased to increase the number of focal points, such that the focal points formed by the laser beam are all located in the processed material while the formation of modified layers in the processed material is increased. However, it is too inefficient to change the number of focal points of the light beam by replacing the optical diffractive element. In addition, the replaced diffractive optical element has the problem that it is difficult to align its center with an optical axis of the incident light beam, which affects the symmetry of an emitted light beam, and finally it is difficult for the converged light beam to be converged at one point when cutting the material, which affects the cutting effect. 
     In order to avoid replacing the diffractive optical element while allowing the number of focal points formed by the laser beam to be directly and easily adjusted, in some embodiments, the optical device  100  in the laser cutting device can adjust the number of the second light beam  1201 . 
     Referring to  FIG. 2 , in some embodiments, the beam expander element  110  can adjust the spot size of the light beam such that a spot area of the emitted light beam (the first light beam  1101 ) is larger or smaller than the spot area of the incident light beam. Optionally, the first light beam  1101  propagates parallel to an optical axis A of the beam expanding element  110 . In some embodiments, the beam expanding element  110  has a magnification of 2 times to 8 times. 
     In some embodiments, the beam expanding element  110  further includes a housing  111 . The lens set  112  is arranged inside the housing  111 . The housing  111  is provided with a light entrance  1111  and a light exit  1112  that are provided oppositely. A center of the light entrance  1111  and a center of the light exit  1112  are on the same straight line as the optical axis A. The light beam can enter the inside of the housing  111  from the light entrance  1111 , and exit from the light exit  1112  after being adjusted by the plurality of lens sets  112 , and then is formed into the first light beam  1101 . 
     The spectroscopic element  120  can convert the incident light beam (the first light beam  1101 ) into the multiple second light beams  1201 . The distances exit between the adjacent second light beams  1201  when emitted by the spectroscopic element  120 . In addition, the number of the second light beams  1201  depends on the spot area of the first light beam  1101 . Specifically, the number of the second light beams  1201  is positively correlated with the spot area of the first light beam  1101 . Optionally, a spot diameter of the first light beam  1101  is about 10 mm. 
     In some embodiments, at least one lens set  112  is a fixed lens set. At least one lens is arranged in the fixed lens set. The fixed lens set is relatively fixed to the housing  111 . That is, the position of each lens  1120  of the fixed lens set in a direction of an optical axis of the housing  111  remains fixed. The fixed lens set can be connected to the housing  111  through a fixing member, or directly clamped in the housing  111 . Optionally, a side of the beam expanding element  110  away from the spectroscopic element  120  is an object side. The lens set  112  closest to the object side is a fixed lens set. The position of the fixed lens set in the beam expanding element  110  is relatively fixed. The lens set  112  closest to the object side can diverge and transmit the incident light beam to the adjacent lens set  112 . The spot area of the diverged light beam is increased, which facilitates the adjustment of the diverged light beam by the adjacent lens set  112 , and makes full use of an edge area of the lens  1120  in the adjacent lens set  112  for refraction. 
     In some embodiments, at least two lens sets  112  in the beam expanding element  110  are movable lens sets. At least one lens  1120  is arranged in each movable lens set. Specifically, the movable lens sets include a driving member  1121 . In the same movable lens set, the driving member  1121  can drive the lens  1120  in the movable lens set to reciprocate along the optical axis A relative to the housing  111 . The driving member  1121  may be a voice coil motor or a manual adjusting member. The manual adjusting member may be a sliding structure in which a slider cooperates with a sliding groove. For example, the sliding groove is provided on the housing  111 , and the sliding groove extends through the sliding groove. One side of the slider is connected to the lens  1120 , and the other side thereof extends beyond the housing  1111 . A portion of the slider extending beyond the housing  111  can slide to drive the lens in the movable lens set to move. The manual adjusting member can also be a knob structure. The knob has an annular structure. An outer side surface of the knob extends beyond the housing  111 . An inner side surface of the knob is rotatably connected to the lens  1120  in the movable lens set. The outer side surface of the knob can be rotated to drive the lens  1120  in the movable lens set to move along the direction of the optical axis A. 
     After at least two movable lens sets are arranged, the relative distance between the movable lens sets can be adjusted, such that a divergence angle or a convergence angle of the light beam in the housing  111  can be adjusted through a part of the movable lens set. Then, the other part of the movable lens set can be adjusted to performing a collimation on the above-mentioned light beam with the specific divergence angle or the convergence angle, and obtain an emitted light beam (the first light beam  1101 ) with a corresponding spot size at the same time. 
     Referring to  FIG. 2 , Optionally, three lens sets  112  are arranged inside the housing  111 , and two lens sets  112  of which adjacent to the light exit  1112  are movable lens sets, and one lens set  112  of which adjacent to the light entrance  1111  is a fixed lens set. 
     Specifically, referring to  FIG. 3 , the beam expanding element  110  is provided with three lens sets  112 . A first movable lens set L 1  providing positive refractive power, a second movable lens set L 2  providing positive refractive power, and a third fixed lens set L 3  providing negative refractive power are arranged from an image side to the object side. The third fixed lens set L 3  can diverge the incident light and increase an area of the light beam irradiating the second movable lens set L 2 , thereby facilitating the second movable lens set L 2  to adjust the light beam. Moreover, a focal point on the object side of the first movable lens set L 1  remains coincident with a converging point of the light beam on the image side of the second movable lens set L 2 , and the coincident point is F. Therefore, the first light beam  1101  emitted by the first movable lens set L 1  will become a parallel light. 
     Specifically, when the spot area of the first light beam  1101  needs to be increased, the second movable lens set L 2  can be driven such that the second movable lens set L 2  moves away from the third fixed lens set L 3 . In this case, the convergence angle of the light beam emitted by the second movable lens set L 2  will be increased. In addition, the first movable lens set L 1  is driven such that the focal point on the object side of the first movable lens set L 1  coincides with a converging point of the light beam converged by the second movable lens set L 2  at the point F. Through the above adjustment, the first light beam  1101  emitted by the first movable lens set L 1  will be emitted in parallel and have a larger spot area. 
     On the contrary, when the spot area of the first light beam  1101  needs to be reduced, the second movable lens set L 2  can be driven such that the second movable lens set L 2  moves closer to the third fixed lens set L 3 . In this case, the convergence angle of the light beam emitted by the second movable lens set L 2  will be reduced. In addition, the first movable lens set L 1  is driven such that the focal point of the first movable lens set L 1  on the object side coincide with the converging point of the light beam converged by the second movable lens set L 2  at the point F. Through the above adjustment, the first light beam  1101  emitted by the first movable lens set L 1  will be emitted in parallel and have a smaller spot area. 
     In other embodiments, the first lens set L 1  can also provide negative refractive power, the second lens set L 2  deliberately provides positive refractive power. A virtual focus on the image side of the first lens set L 1  coincides with the converging point of the light beam on the image side of the second lens set L 2 . 
     It should be noted that, the third fixed lens set L 3  can be replaced with a movable lens set in practice. Alternatively, the third fixed lens set L 3  may not be provided, but only two movable lens sets are provided in the beam expanding element. In addition, more movable lens sets or fixed lens sets can be provided in the beam expanding element. The arrangement sequence of the fixed lens set and the movable lens set can be arbitrarily provided on the premise that the emitted light beam (the first light beam  1101 ) is parallel light beam. 
     It should further be noted that, a single positive lens will produce negative spherical aberration, and a single negative lens will produce positive spherical aberration. That is, when each lens set  112  is separately arranged and has only one lens, the light beam will not be well focused on one point after passing through the lens set  112 , or a reverse extension line of the light beam during divergence cannot be well coincided with one point. Finally, the light beam cannot be formed into the parallel light beam after passing through the plurality of lens sets  112 . In order to overcome this problem, in some embodiments, at least one lens set  112  is designed as a complex lens set. The complex lens set includes at least one positive lens and at least one negative lens, so as to achieve the effect of correcting the spherical aberration. The light beam has a better converging or diverging effect after passing through the complex lens set, improving a parallelism of the light beam (the first light beam  1101 ) finally emitted from the beam expanding element  110 . Specifically, an optical adhesive can be provided in the complex lens set to adhere the lenses. 
     In some embodiments, the spectroscopic element  120  is an optical diffractive element. Specifically, the spectroscopic element  120  is provided with a plurality of concentric annular bands. According to light-transmitting properties of the annular bands, the annular belts can be divided into light-transmitting annular bands and non-light-transmitting annular bands. The light-transmitting properties of adjacent annular bands are different. Therefore, the incident light beams are formed into the multiple second light beams  1201  after passing through the plurality of light-transmitting annular bands. In this case, the multiple second light beams  1201  have higher contrast therebetween. In other embodiments, regions of the spectroscopic element  120  irradiated by the incident light beam can be light-transmissive. In this case, regions with different thicknesses can be provided on the spectroscopic element  120  such that phase difference is generated after the incident light beam passes through the regions with different thicknesses, and then incident light beam is formed into multiple concentric annular light beams through diffraction. In this case, the incident light beam can be converted into the multiple second light beams  1201  with less energy loss. 
     It can be learned from the above-mentioned structure of the spectroscopic element  120 , after the first light beam  1101  with different spot areas is incident into the spectroscopic element  120 , the light beam will be shaped and emitted. The incident light beams with different spot areas will determine the number of the second light beam  1201  emitted from the spectroscopic element  120 . 
     In addition, referring to  FIG. 4 , in some embodiments, the spectroscopic element  120  may shape the first light beam  1101  into multiple annular light beams propagating along the optical axis A. The multiple second light beams  1201  propagating parallel to each other can be respectively focused on the same straight line parallel to a propagating direction of the light path, under the action of a focusing lens, thereby forming multiple focal points. That is, the multiple focal points are arranged spaced away on the optical axis of the focusing lens. Using the multiple focal points of the laser beam to cut a chip can cut a plurality of layers in a cross-section of the chip at one time, which can inhibit a diagonal crack of a crystal lattice in the chip, and generate a vertical guiding force for the pre-crack, so as to achieve the purpose of reducing a degree of the diagonal crack. 
     Referring to  FIG. 5 , in other embodiments, the spectroscopic element  120  can not only shape the first light beam  1101  into the multiple annular light beams (the second light beam  1201 ), but can also focus the multiple second light beams  1201  on the optical axis A. As a result, multiple focal points of the same number as the second light beams  1201  are formed on the optical axis of the spectroscopic element  120 . In this case, the second light beam  1201  that has focused into the multiple focal points can be directly used to cut the processed material. Alternatively, a focusing lens may be further arranged between the spectroscopic element  120  and the processed material to further focus the light beam emitted from the spectroscopic element  120 , thereby shortening a focal length and saving working space. 
     As shown in  FIG. 1 , in some embodiments, the laser cutting device  10  includes a laser  130 . A light beam emitted by the laser  130  can sequentially enter the beam expanding element  110  and the spectroscopic element  120 . The laser cutting device  10  can be used to cut wafers, LED chips and the like, which have sapphire as a substrate, especially used to cut MINI LEDs. 
     Optionally, the laser  130  is a picosecond laser. The picosecond laser has an output power of 10 W, a pulse width in a range of 2 ps to 6 ps, and a wavelength of 1040 nm. 
     Generally, since the light beam emitted from the laser  130  is not ideally parallel light, in some embodiments, a zone plate  140  is further provided between the laser  130  and the optical device  100 . The zone plate  140  is capable of performing a collimation on the light beam emitted from the laser  130 . The laser beam is converted into a relatively ideal parallel light and then transmitted to the optical device  100 . 
     Referring to  FIGS. 4 and 1 , when the spectroscopic element  120  converts the first light beam  1101  into the multiple second light beams  1201  propagating parallel to the optical axis A, the laser cutting device  10  needs to be further provided with a focusing lens  150 , such that the multiple second light beams  1201  is focused into the multiple focal points with the same number as the second light beams  1201  and arranged spaced away on an optical axis of the focusing lens  150 , so as to cut the processed material. In some embodiments, a focal length of the focusing lens  150  is 4 mm. In addition, a distance between adjacent focal points in air is less than or equal to 20 μm, optionally in a range of 4 μm to 8 μm. When the distance between adjacent focal points satisfies the above range, it can be advantageous for cutting thinner processed materials. 
     Optionally, the number of focal points is greater than or equal to two and less than or equal to fifteen. In addition, in some embodiments, when the beam expanding element  110  is provided and the number of focal points needs to be changed, the beam expanding element  110  can be directly adjusted to change the number of the second light beams  1201 , thereby changing the number of focal points. By reasonably configuring the number of focus points and distances between the focal points, the laser cutting device  10  can better cut the MINI LEDs. 
     The conventional laser cutting device has a problem of too large distances between the focal points, and thicknesses of the MINI LED chips are smaller, such that the conventional laser cutting device cannot accurately cut the mini LED chips. When the relationship among parameters of the laser  130 , the number of focal points and the distances between adjacent focal points as described above is satisfied, the laser cutting device  10  can efficiently and accurately cut the MINI LED chips. 
     Referring to  FIG. 5 , the spectroscopic element  120  can convert the first light beam  1101  into the multiple second light beams  1201 , and focus the multiple second light beams  1201  onto the same straight line parallel to a propagating direction of the light beam, to form the multiple focal points of the same number and arranged spaced away. In this case, the multiple second light beams  1201  can be directly used to cut the processed material. That is, the multiple focal points arranged spaced away are distributed inside the processed material. When the number of focal points needs to be changed, the beam expanding element  110  can be directly adjusted to change the number of the second light beams  1201 . 
     Referring to  FIG. 1 , in some embodiments, a first lens  161  and a second lens  162  for eliminating aberrations are sequentially arranged between the optical device  100  and the focusing lens  150 . The first lens  161 , the second lens  162 , and the spectroscopic element  120  are arranged on a focal plane on an object side of the first lens  161 . A focal point on an object side of the second lens  162  coincides with a focal point on an image side of the first lens  161 . The focusing lens  150  is arranged on a focal plane on an image side of the second lens  162 . In some of the embodiments, the first lens  161  and the second lens  162  are both independent positive lenses (focusing lenses) and have the same focal length. 
     Since the second light beam emitted by the spectroscopic element  120  will have serious aberrations after propagating a certain distance, it will not be possible to accurately cut the processed material. In addition, a light entrance of the conventional focusing lens  150  is smaller and cannot receive the second light beam completely. In this case, by providing the first lens  161  and the second lens  162 , the aberration of the second light beam can be better eliminated, and the second light beam can pass through the focusing lens  150  completely. 
     Referring to  FIGS. 1 and 4 , when the second light beam  1201  emitted by the spectroscopic element  120  is the parallel light beam, the first lens  161  can converge the second light beam  1201 . Then, the second lens  162  will convert the second light beam  1201  that has been converged and then diverged again, into a parallel light beam or a focused beam and transmit it into the focusing lens  150 . Then, the focusing lens  150  converges the multiple second light beams  1201  on multiple focal points. Optionally, a focal length on the object side and a focal length on the image side of the first lens  161  are both 250 mm, and a focal length on the object side of the second lens  162  is 250 mm. 
     Continuing to refer to  FIG. 1 , in some embodiments, due to the diversity of the positions of the laser  130  and the optical device  100  in practical applications, the laser cutting device  10  is also provided with reflecting mirrors to adjust an orientation of the light path. Specifically, some laser cutting device  10  further include a first reflecting mirror  171 , a second reflecting mirror  172 , and a third reflecting mirror  173 . In some embodiments, the propagating direction of the emitted light beam of the laser  130  and the optical device  100  is perpendicular to the propagating direction of the light beam that is finally used to cut the processed material. In this case, the propagating direction of the emitted light beam in the optical device  100  can be changed by providing the reflecting mirrors. 
     Specifically, in the embodiment shown in  FIG. 1 , the laser cutting device  10  is provided with the first lens  161 , the second lens  162 , the first reflecting mirror  171 , the second reflecting mirror  172  and the third reflecting mirror  173 . The first reflecting mirror  171  is arranged between the laser  130  and the beam expanding element  110  to reflect the light beam emitted by the laser  130  into the beam expanding element  110 . In addition, the first lens  161 , the second reflecting mirror  172 , the second lens  162 , and the third reflecting mirror  173  are sequentially arranged along the emitted light path of the spectroscopic element  120 . The second reflecting mirror  172  can change an emitted light path of the spectroscopic element  120  by 90° for propagating. The third reflecting mirror  173  can also change a reflecting light path of the second reflecting mirror  172  by 90° for propagating. The emitted light path of the spectroscopic element  120 , the reflecting light path of the second reflecting mirror  172  and a reflecting light path of the third reflecting mirror  173  are perpendicular to each other. The light beams reflected by the third reflecting mirror  173  will pass through the focusing lens  150 , so as to be converged into multiple focal points. Optionally, a distance from the first lens  161  to the spectroscopic element  120  on the light path is 250 mm, a distance from the first lens  161  to the second reflecting mirror  172  on the light path is 70 mm, and a distance from the second reflecting mirror  172  to the second lens  162  on the light path is 430 mm. 
     Referring to  FIG. 6 , in some embodiments, the laser cutting device  10  will work with an imaging device  310 . When cutting the processed material  400 , the imaging device  310  can acquire surface information on the processed material  400 , so as to monitor whether the orientation of the cutting light beam is correct. Optionally, the imaging device  310  is a CCD (Charge Coupled Device). During processing, the processed material  400  is placed on an adhesive film  340 . An edge of the adhesive film  340  is connected to an iron ring  330 . The iron ring  330 , the adhesive film  340  and the processed material  400  are all arranged above a transparent carrier  320 . The adhesive film  340  may be made of a transparent or translucent material. After being processed by the laser, the chip is split by mechanical means such as a wedge. 
     In addition, this application also provides a laser cutting method to efficiently cut materials with a smaller thickness (such as a thickness of less than 100 μm) such as mini LEDs. In the laser cutting method, a spot of a laser beam emitted by the laser is adjusted to have an appropriate size by a beam expanding element, such that the adjusted laser beam can pass through a spectroscopic element completely. The laser beam adjusted by the beam expanding element is a first light beam. Then, the first light beam is adjusted by the spectroscopic element into multiple second light beams (annular light beams) spaced apart from each other. The multiple second light beams are focused by a focusing lens, so as to be formed into N (at least two) focal points arranged spaced away on an optical axis of the focusing lens. Optionally, the number of focal points is greater than or equal to two and less than or equal to fifteen. A distance between adjacent focal points in air is less than or equal to 20 μm, optionally in a range of 4 μm to 8 μm. Specifically, the multiple focal points formed by the focusing lens are distributed inside the processed material, and the multiple focal points can form a plurality of modified layers inside the processed material. When the number of focus points and the range of the distance between the focal points as described above are satisfied, the laser cutting method can better cut the materials with smaller thickness such as mini LEDs. 
     In some embodiments, under the adjustment of the beam expanding element, the first light beam can propagate parallel to a direction of an optical axis of the beam expanding element. In some embodiments, the multiple second light beams can also propagate along a direction of an optical axis of the spectroscopic element. 
     In some embodiments, the annular light beam emitted by the spectroscopic element will further pass through a first lens, which adjusts the annular light beam into a convergent light beam. The convergent light beam is reflected by a second reflecting mirror to a second lens, which will readjust the convergent light beam into multiple annular light beams. The spectroscopic element is arranged on a focal plane on an object side of the first lens. A focal plane on an object side of the second lens coincides with a focal plane on an image side of the first lens. The focusing lens is arranged on a focal plane on an image side of the second lens. The multiple annular light beams formed by the readjustment of the second lens are then reflected by a third reflecting mirror to the focusing lens. The first lens can converge the annular light beam to convert the annular light beam into the convergent light beam. According to a propagating principle of the light path, the convergent light beam will be re-magnified after be converged. After being re-magnified, the converged light beam will be readjusted into multiple annular light beams by the second lens. The number of re-formed multiple annular light beams is the same as the number of second light beams formed by the spectroscopic element. Optionally, the annular light beam formed by the adjustment of the second lens is emitted parallel to the direction of the optical axis of the second lens. In addition, the first lens and the second lens can be used as an optical 4F system to eliminate an aberration of the second light beam, and improve the quality of the focal points formed by the focusing lens, thereby improving the accuracy of the multi-focus cutting. 
     It should be noted that in some embodiments, the beam expanding element and the spectroscopic element can only form a fixed number of second light beams. Since the number of second light beams determines the number of focal points obtained by the focusing performed by the focusing lens, in this case, the number of second light beams can be changed by replacing the spectroscopic element, thereby changing the number of focal points formed by the focusing lens. In addition, in some embodiments, the first reflecting mirror, the second reflecting mirror, and the third reflecting mirror can be selected according to the actual orientating requirements (such as reducing a size of the actual device in a certain direction) of the light path, and it is not necessary for the laser beam to pass through all the reflecting mirrors. For example, the first reflecting mirror and the second reflecting mirror may be omitted, such that the light beam emitted by the laser can pass through the beam expanding element, the spectroscopic element, the first lens, the second lens, and the third reflecting mirror in a fixed direction, and then reflected by the third reflecting mirror to the focusing lens. 
     In other embodiments, the beam expanding element can cooperate with the spectroscopic element to adjust the number of second light beams, such that the number of focal points formed by the focusing lens can be changed by adjusting the beam expanding element. Specifically, the number of the annular light beams is positively correlated with the spot size of the first light beam incident into the spectroscopic element, and the number of focal points is the same as the number of second light beams. In this case, the beam expanding element is adjusted to change the spot size of the first light beam, so as to control the number of the second light beams reaching the focusing lens, thereby obtaining the required number of focal points to cut the processed material. 
     Technical features of the embodiments as described above can be arbitrarily combined. For simplifying the description, all possible combinations of technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be fallen within the scope of this description. 
     Only several implementations of the present disclosure are illustrated in the aforementioned embodiments, and the description thereof is relatively specific and detailed, but it should not be understood as a limitation on the scope of the present disclosure. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present disclosure, several modifications and improvements can be made, which all fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the appended claims.