Laser processing device, optical system of laser processing device

Abstract

To provide an optical system of a laser processing device which has high efficiency in energy utilization of laser light and in which an intensity distribution shape of laser light at an irradiation point stays unchanged even if a focal position is displaced by thermal lens effect, and a laser processing device using the optical system of the laser processing device.SOLUTION: In order to solve the problem, the laser processing device according to the present application that processes a work-piece by irradiating the work-piece with laser light comprises an optical system having an optical surface having a plurality of different focal points provided on the same optical axis. An irradiation point of the laser light in the work-piece is at a position different from the focal point. In the irradiation point, an intensity distribution of laser light in a surface perpendicular to the optical axis is at least in an annular shape with the optical axis as a center.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser processing device and an optical system of the laser processing device. [Background technology]

[0002] A laser processing device focuses laser light onto a single point and irradiates it onto the workpiece, rapidly raising the surface temperature of the workpiece and causing the irradiated surface to melt or evaporate, thereby performing processes such as cutting, drilling, and welding on the workpiece. Because the laser light is focused onto a single point, pinpoint precision and fine processing is possible. In addition, by using a higher-energy laser beam, processing time can be shortened and it is also possible to process high-hardness workpieces that are difficult to process with blades.

[0003] It is known that, in focusing laser light, the intensity distribution of the laser light at the irradiation point of the laser light is preferably annular on the plane of the irradiation point. However, if the ring diameter at the irradiation point is large, the light energy cannot be sufficiently concentrated, which can result in a long time required to melt the workpiece or a deterioration in the quality of the processed cross section. Furthermore, if the focal depth required to maintain a constant ring diameter is shallow, problems arise such as varying processing dimensions along the thickness of the workpiece.

[0004] Therefore, in Patent Document 1, a mask that blocks the laser light is placed in the center of the cross section of the laser light before it is focused, blocking the laser light at the center. As a result, the laser light that is not blocked by the mask becomes annular, and the laser processing method disclosed uses a laser irradiation head that focuses the annular laser light.

[0005] Furthermore, Patent Document 2 discloses a laser welding device that uses a focusing lens in which the central part of the convex surface of the focusing lens is cut into a concave shape to focus the laser light, thereby irradiating the laser light such that the intensity distribution of the laser light is higher in the periphery than in the center.

[0006] Furthermore, Patent Document 3 discloses a laser processing head that uses at least one of a spherical lens for converging laser light and an aspherical lens capable of generating spherical aberration, and irradiates laser light whose intensity distribution is annular, whose intensity is higher in the peripheral region than in the central region, and whose focal position is shifted from the irradiation point on the workpiece. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 07-214360 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-305581 [Patent Document 3] WO2012 / 164663 publication Summary of the Invention [Problem to be solved by the invention]

[0008] However, the optical system of the laser processing device described in Patent Document 1 obtains laser light with a ring-shaped intensity distribution by placing a mask that blocks the laser light at the center of the cross section of the laser light. As a result, when processing a workpiece with laser light, the energy of the laser light output from the laser oscillator is used inefficiently. Furthermore, a laser oscillator with a higher output is required to obtain the necessary laser light energy at the irradiation point on the workpiece.

[0009] Furthermore, the optical system of the laser processing device described in Patent Document 2 focuses laser light using a focusing lens in which the central convex portion of the focusing lens is cut into a concave shape, thereby obtaining laser light whose intensity distribution is higher at the periphery than at the center. Here, laser light passing through the concave portion of the focusing lens is refracted in a direction diverging from the center. As a result, the laser light refracted by the concave portion of the focusing lens is not focused to the irradiation point on the workpiece. In other words, when processing a workpiece with laser light, the energy of the laser light output from the laser oscillator is used inefficiently.

[0010] Furthermore, in the optical system of the laser processing device described in Patent Document 3, when the optical system that focuses the laser light is heated by the laser light, the refractive index of the heated portion of the lens that constitutes the optical system changes (thermal lens effect). If the change in refractive index causes a focus shift, the annular laser light intensity distribution changes. Specifically, the annular diameter increases, weakening the laser intensity at the processing point, or the laser light intensity distribution changes from an annular shape, which may prevent the desired processing.

[0011] The present invention aims to provide an optical system for a laser processing device that has high energy utilization efficiency of laser light and does not change the intensity distribution shape of the laser light at the irradiation point even if the focal position is shifted due to the thermal lens effect, and a laser processing device that uses the optical system of such a laser processing device. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, the present inventors have conducted extensive research and have come up with the following invention.

[0013] The laser processing device of the present invention processes a workpiece by irradiating it with laser light, and is characterized in that it comprises an optical system having an optical surface with a plurality of different focal points on the same optical axis, the irradiation point of the laser light on the workpiece is at a position different from the focal points, and at the irradiation point, the intensity distribution of the laser light in a plane perpendicular to the optical axis is at least annular with the optical axis as its center.

[0014] In addition, the optical system provided in a laser processing device that processes a workpiece by irradiating the laser light of the present application is characterized in that it has an optical surface with multiple different focal points on the same optical axis, and the optical surface with multiple different focal points is a multiple different spherical and / or aspherical surface. [Effects of the Invention]

[0015] The laser processing apparatus according to the present invention has an optical system used in the laser processing apparatus that has an optical surface with multiple foci on the same optical axis, so that the focus of the optical system is located at a position different from the irradiation point on the workpiece, and the intensity distribution of the laser light on a plane perpendicular to the optical axis at the irradiation point on the workpiece can be at least annular with the optical axis as the center. As a result, even if the focus position shifts due to the thermal lens effect, the intensity distribution shape and intensity of the laser light at the irradiation point do not change, enabling stable laser processing. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view of an optical element according to the present embodiment, which includes different aspherical surfaces on the same optical surface. [Figure 2] 1 is a schematic cross-sectional view of an optical element according to the present embodiment, which has different aspherical surfaces on two different optical surfaces. [Figure 3] 2A shows a schematic optical path of laser light between the entrance pupil and the irradiation point when the focal point of the aspherical surface 21 in the optical element shown in FIG. 1 is behind the irradiation point and the focal point of the aspherical surface 22 is in front of the irradiation point, and FIG. 2B shows a lateral aberration diagram in the entrance pupil coordinates and the irradiation point coordinates. [Figure 4] 2A shows a schematic optical path of laser light between the entrance pupil and the irradiation point when the focal point of the aspherical surface 21 in the optical element shown in FIG. 1 is in front of the irradiation point and the focal point of the aspherical surface 22 is behind the irradiation point, and FIG. 2B shows a lateral aberration diagram in the entrance pupil coordinates and the irradiation point coordinates. [Figure 5]2A shows a schematic optical path of laser light between the entrance pupil and the irradiation point when the thermal lens effect occurs in the case where the focal point of the aspherical surface 21 in the optical element shown in FIG. 1 is behind the irradiation point and the focal point of the aspherical surface 22 is in front of the irradiation point, and FIG. 2B shows a lateral aberration diagram in the entrance pupil coordinates and the irradiation point coordinates. [Figure 6] 2A shows a schematic optical path of laser light between the entrance pupil and the irradiation point when the thermal lens effect occurs in the case where the focal point of the aspherical surface 21 in the optical element shown in FIG. 1 is located in front of the irradiation point and the focal point of the aspherical surface 22 is located behind the irradiation point, and FIG. 2B shows a lateral aberration diagram in the entrance pupil coordinates and the irradiation point coordinates. [Figure 7] 1 shows a laser processing device according to the present embodiment. [Figure 8] 10 is a graph showing the relationship between the position of the optical axis in Example 1 as the origin 0, the position of the edge of the optically effective area as 1, and the position divided into 10 equal parts, and the curvature C. [Figure 9] 10 is a graph showing the relationship between the position of the optical axis in Example 2 as the origin 0, the position of the edge of the optically effective area as 1, and the curvature C when the position is divided into 10 equal parts. [Figure 10] 10 is a graph showing the relationship between the position of the optical axis in Example 3 as the origin 0, the position of the edge of the optically effective area as 1, and the position divided into 10 equal parts, and the curvature C. [Figure 11] 10 is a graph showing the relationship between the position of the optical axis in Example 4 as the origin 0, the position of the edge of the optically effective area as 1, and the curvature C when the position is divided into 10 equal parts. [Figure 12] 10 is a graph showing the relationship between the position of the optical axis in the comparative example as the origin 0, the position of the edge of the optically effective area as 1, and the curvature C when the position is divided into 10 equal parts. [Figure 13] 1 is a graph of the intensity distribution of a laser beam that serves as a reference in an optical simulation. [Figure 14] 1 is a graph showing the intensity distribution of laser light on a straight line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece in Example 1. [Figure 15] 10 is a graph showing the intensity distribution of laser light on a straight line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece in Example 2. [Figure 16]10 is a graph showing the intensity distribution of laser light on a straight line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece in Example 3. [Figure 17] 10 is a graph showing the intensity distribution of laser light on a straight line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece in Example 4. [Figure 18] 10 is a graph showing the intensity distribution of laser light on a straight line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece in the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser processing apparatus according to an embodiment of the present invention and an optical system used in the laser processing apparatus will be described below.

[0018] 1. Embodiments of a laser processing device and an optical system used in the laser processing device The laser processing apparatus and optical system used in the laser processing apparatus according to the present invention are a laser processing apparatus that processes a workpiece by irradiating it with laser light, and an optical system provided in the laser processing apparatus, the optical system having an optical surface with multiple different focal points on the same optical axis. The laser processing apparatus according to the present invention irradiates the workpiece with laser light such that the irradiation point of the laser light by the optical system is at a position different from each of the focal points, and the intensity distribution of the laser light on a plane perpendicular to the optical axis at the irradiation point is at least annular, centered on the optical axis. Furthermore, the optical system of the laser processing apparatus according to the present invention is formed so that the intensity distribution of the laser light on a plane perpendicular to the optical axis at the irradiation point of the laser light of the laser processing apparatus is at least annular, centered on the optical axis.

[0019] According to the present invention, as described below, a laser processing apparatus for processing a workpiece by irradiating it with laser light according to the present invention includes an optical system provided with an optical surface having multiple different focal points on the same optical axis, and the irradiation point of the laser light on the workpiece is located at a position different from the focal point. As a result, the intensity distribution of the laser light on a plane perpendicular to the optical axis at the irradiation point on the workpiece (hereinafter referred to as the "intensity distribution of the laser light on the plane at the irradiation point") is at least annular, centered on the optical axis. Furthermore, the intensity distribution of the laser light on a line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece (hereinafter referred to as the "intensity distribution of the laser light on the line at the irradiation point") is at least bimodal, centered on the optical axis. Furthermore, even if focus shift occurs due to the thermal lens effect, the intensity distribution of the laser light on the plane at the irradiation point (the position and peak value of the intensity peak of the laser light) remains almost constant. This maintains the processing quality of the workpiece.

[0020] 1-1. Embodiment of Optical Surface Having Multiple Different Foci The optical surface having a plurality of different focal points according to the present invention is preferably made up of a plurality of different spherical and / or aspherical surfaces, because incident light refracted at the interfaces between the plurality of different spherical and / or aspherical surfaces converges to different focal points, causing the intensity distribution of the laser light on the plane at the irradiation point to be at least annular with the optical axis as the center.

[0021] Here, it is preferable that at least one of the optical surfaces of the multiple different spherical and / or aspherical surfaces according to the present invention is an aspherical surface, since an aspherical surface can easily obtain lateral aberration that is difficult to achieve with a spherical surface, and therefore it is possible to provide different focal points on the multiple optical surfaces according to the present invention.

[0022] Furthermore, it is preferable that the plurality of different spherical and / or aspherical surfaces according to the present invention are two different optical surfaces, because this allows for a simple configuration of the optical system according to the present invention, which is made up of optical surfaces with a plurality of different focal points.

[0023] Furthermore, the plurality of different spherical and / or aspherical surfaces according to the present invention are preferably two different aspherical surfaces, because aspherical surfaces can easily achieve lateral aberration that is difficult to achieve with spherical surfaces, making it possible to simply configure an optical system according to the present invention that is made up of optical surfaces with a plurality of different focal points, and also facilitating adjustment of the focal length.

[0024] Hereinafter, a specific embodiment will be described taking an aspherical surface as an example.

[0025] 1-2. Embodiment 1 of Multiple Different Aspherical Surfaces The above-described plurality of different spherical and / or aspherical surfaces according to the present invention are preferably provided in different concentric regions on the same optical surface, centered on the optical axis. This is to focus laser light on the same optical axis. FIG. 1 shows a schematic cross-sectional view of an optical element 10 having different aspherical surfaces on the same optical surface. The optical element 10 is made of a substrate 11, and the material of the substrate 11 is not particularly limited as long as it is made of an optical material. The substrate 11 has optical surfaces 12 and 13 through which the laser light passes, and the dashed line O indicates the central axis of the optical element 10. Two aspherical surfaces, aspherical surfaces 21 and 22, are provided on the optical surface 12 in a concentric arrangement centered on the central axis O of the optical element. In this case, incident light refracted at the interface between the two concentric aspherical surfaces 21 and 22 converges to two different focal points.

[0026] 1-3. Embodiment 2 of Multiple Different Aspherical Surfaces Furthermore, the multiple different spherical and / or aspherical surfaces according to the present invention are preferably provided in multiple different concentric regions around the optical axis, each of which is a region through which a different light beam passes, on multiple different optical surfaces. This is to focus the laser light onto the same optical axis. Here, the multiple different optical surfaces may be different optical surfaces on the same optical element, or may be optical surfaces on different optical elements.

[0027] FIG. 2 shows a schematic cross-sectional view of an optical element 10' having different aspherical surfaces on two different optical surfaces of the same optical element. The optical element 10' is composed of a substrate 11'. The substrate 11' has an optical surface 12' and an optical surface 13' through which laser light passes. Then, an aspherical surface 21' is provided concentrically on the optical surface 12' and an aspherical surface 22' is provided concentrically on the optical surface 13' around the central axis O' of the optical element. At this time, the aspherical surface 21' and the aspherical surface 22' are located at positions through which different light beams pass. And the incident light refracted at the interface between the two concentric aspherical surfaces 21' and 22' converges to two different focal points respectively.

[0028] 2. Embodiments in the characteristics of a laser processing apparatus and an optical system used in the laser processing apparatus 2-1. Embodiment of focal length Among at least two aspherical surfaces of a plurality of different spherical surfaces and / or aspherical surfaces according to the present invention, the focal lengths are different from each other, and the focal length is preferably 150 mm or more and 1000 mm or less respectively. Also, it is preferable that there are two aspherical surfaces with different focal lengths from the viewpoint of not complicating the aspherical shape. Here, if the focal lengths of the plurality of different aspherical surfaces are f1 and f2 respectively, when f1 < f2, it is preferable that f1 / f2 is greater than 0.2 and less than 0.8. Also, when f1 > f2, it is preferable that f2 / f1 is greater than 0.2 and less than 0.8. However, the units of f1 and f2 are mm.

[0029] When f1 / f2 is 0.2 or less when f1 < f2, the intensity distribution of the laser light on the plane at the irradiation point of the workpiece does not become annular centered on the optical axis. When f1 / f2 is 0.8 or more when f1 < f2, the intensity distribution of the laser light on the plane at the irradiation point of the workpiece does not become annular centered on the optical axis.

[0030] Furthermore, when f1>f2, if f2 / f1 is 0.2 or less, the intensity distribution of the laser light on the plane at the irradiation point on the workpiece will not be annular about the optical axis.When f1>f2, if f2 / f1 is 0.8 or more, the intensity distribution of the laser light on the plane at the irradiation point on the workpiece will not be annular about the optical axis.

[0031] 2-2. Embodiment of curvature radius If the radii of curvature of two aspherical surfaces among the plurality of different spherical and / or aspherical surfaces according to the present invention are r1 and r2, respectively, it is preferable that the absolute value of r1 / r2 is greater than 0.5 and less than 2. However, the units of r1 and r2 are mm. If the absolute value of r1 / r2 is 0.5 or less, the intensity distribution of the laser light on the plane at the irradiation point on the workpiece will not have a ring shape centered on the optical axis. If the absolute value of r1 / r2 is 2 or more, the intensity distribution of the laser light on the plane at the irradiation point on the workpiece will not have a ring shape centered on the optical axis.

[0032] Here, the shape of an aspherical optical surface can be expressed by an even-order aspherical equation as shown in equation (1) below. z(r)=cr 2 / [1+{1-(1+k)·c 2 r 2} 1 / 2 ]+a1r 2 +a2r 4 +a3r 6 +a4r 8 +a5r 10 +a6r 12 +a7r 14 +a8r 16 ···(1) however, z(r): Surface position in the optical axis direction at a distance r perpendicular to the optical axis (amount of sag) c: Reciprocal of the central radius of curvature k: conic constant a n :n-th order aspherical coefficients.

[0033] 2-3. Curvature embodiment Regarding the curvature C at any position in the optically effective area of ​​an optical surface, in a coordinate system in which the optical axis is the z-axis and the axis perpendicular to the z-axis is the r-axis, when the position of the optical axis on the r-axis is the origin and the position up to the edge of the optically effective area is divided into 10 equal parts, the curvature at the origin is C 0.0 (m -1 ), and the curvature at the edge of the optically effective area is C 1.0 (m -1 )

[0034] In this case, in at least two aspherical surfaces among the plurality of different spherical surfaces and / or aspherical surfaces, C 0.0 >C 1.0 When 1.0 / C 0.0 The absolute value of C is preferably less than 0.9. 1.0 / C 0.0 If the absolute value of is greater than 0.9, the intensity distribution of the laser light on the plane at the irradiation point on the workpiece will not be annular with the optical axis as the center.

[0035] Also, C 0.0 <C 1.0 When 0.0 / C 1.0 The absolute value of C is preferably less than 0.9. 0.0 / C 1.0 If the absolute value of is greater than 0.9, the intensity distribution of the laser light on the plane at the irradiation point on the workpiece will not be annular with the optical axis as the center.

[0036] Next, for at least two of the plurality of different spherical and / or aspherical surfaces, the curvature at a position at 1 / 10 of the coordinate system of the r axis described above is defined as C 0.1 (m -1 ), then C 0.1 / C 0.0 The absolute value of C is preferably greater than 0 and less than 4. 0.1 / C 0.0 If the absolute value of is 4 or more, the intensity distribution of the laser light on the plane at the irradiation point on the workpiece will not be annular with the optical axis as the center.

[0037] Furthermore, for at least two aspherical surfaces among the plurality of different spherical surfaces and / or aspherical surfaces, the curvature at a position at 2 / 10 of the coordinate system of the r axis described above is defined as C 0.2 (m -1 ), and the curvature at the 8 / 10th position is C 0.8 (m -1 ), then C 0.8 / C 0.2 The absolute value of C is preferably greater than 0.5 and less than 1.5. 0.8 / C 0.2 If the absolute value of is less than 0.5, the laser beam will not be focused. 0.8 / C 0.2 If the absolute value of is 1.5 or more, an appropriate back focus cannot be obtained.

[0038] 3. Embodiment of the intensity distribution characteristics of laser light at the irradiation point of the workpiece 3-1. Intensity distribution characteristics of laser light at the irradiation point of the workpiece in the present invention First, we will explain lateral aberration. Lateral aberration is the amount of deviation from the origin of an evaluation plane on which the focusing state of incident light is to be evaluated. A lateral aberration diagram is a diagram that associates the passing coordinates of incident light on the entrance pupil plane with the arrival coordinates on the evaluation plane on which the focusing state of incident light is to be evaluated.

[0039] The laser beam refracted at the interfaces of the multiple different aspherical surfaces converges toward different focal points on the optical axis. At this time, at the irradiation point of the laser beam on the workpiece located at a position different from the focal point, the intensity distribution of the laser beam on the plane at the irradiation point is at least annular about the optical axis. Furthermore, the intensity distribution of the laser beam on the line at the irradiation point is at least bimodal about the optical axis.

[0040] 3(a) shows a schematic optical path of the laser light between the entrance pupil and the irradiation point when the focal point of aspherical surface 21 in the optical element shown in FIG. 1 is behind the irradiation point and the focal point of aspherical surface 22 is in front of the irradiation point. The hatched areas in each case represent the optical path of the laser light. The laser light refracted by aspherical surface 21 travels toward a focal point on the workpiece that is behind the irradiation point of the laser light, and converges with a constant lateral aberration at the irradiation point of the laser light on the workpiece along the way. The laser light refracted by aspherical surface 22 travels toward a focal point on the workpiece that is in front of the irradiation point of the laser light, and further intersects with the optical axis to travel and converge with the same lateral aberration as the laser light refracted by aspherical surface 21 at the irradiation point of the laser light on the workpiece.

[0041] 3(b) shows a lateral aberration diagram of the entrance pupil coordinates and the irradiation point coordinates when the focal point of aspherical surface 21 in the optical element shown in FIG. 1 is located behind the irradiation point and the focal point of aspherical surface 22 is located in front of the irradiation point. As described above, the laser beams refracted by aspherical surfaces 21 and 22 converge at the irradiation point on the workpiece with the same lateral aberration. In this case, the intensity distribution of the combined laser beams refracted by aspherical surfaces 21 and 22 on the plane at the irradiation point on the workpiece is at least annular with the optical axis as the center.

[0042] Furthermore, from the lateral aberration diagram shown in Fig. 3(b), it can be seen that the lateral aberration near the origin of the entrance pupil coordinate system changes smoothly, and that the lateral aberration is constant at entrance pupil coordinate systems other than the origin. Note that, because the optical path diagram of the laser light in Fig. 3(a) is a schematic diagram, the optical path of the incident light at the origin of the entrance pupil coordinate system and near the origin is not shown in Fig. 3(a) in relation to the change in lateral aberration described above.

[0043] 4(a) shows a schematic optical path of the laser light between the entrance pupil and the irradiation point when the focal point of aspherical surface 21 in the optical element shown in FIG. 1 is located in front of the irradiation point and the focal point of aspherical surface 22 is located behind the irradiation point. The hatched areas in each case represent the optical path of the laser light. The laser light refracted by aspherical surface 21 travels toward a focal point located in front of the irradiation point of the laser light on the workpiece, then intersects with the optical axis and travels forward, converging with a constant transverse aberration at the irradiation point of the laser light on the workpiece. The laser light refracted by aspherical surface 22 travels toward a focal point located behind the irradiation point of the laser light on the workpiece, and converges with the same transverse aberration as the laser light refracted by aspherical surface 21 at the irradiation point of the laser light on the workpiece.

[0044] 4(b) shows a lateral aberration diagram of the entrance pupil coordinates and the irradiation point coordinates when the focal point of aspherical surface 21 in the optical element shown in FIG. 1 is located in front of the irradiation point and the focal point of aspherical surface 22 is located behind the irradiation point. In this way, the laser light refracted by aspherical surfaces 21 and 22 converges at the irradiation point on the workpiece with the same lateral aberration. In this case, the intensity distribution of the laser light, which is a combination of the laser light refracted by aspherical surfaces 21 and 22 on the plane at the irradiation point on the workpiece, is at least annular with the optical axis as the center.

[0045] Furthermore, from the lateral aberration diagram shown in Fig. 4(b), it can be seen that the lateral aberration near the origin of the entrance pupil coordinate system changes smoothly, and that the lateral aberration is constant at entrance pupil coordinate systems other than the origin. Note that, because the optical path diagram of the laser light in Fig. 4(a) is a schematic diagram, the optical path of the incident light at the origin of the entrance pupil coordinate system and near the origin is not shown in Fig. 4(a) in relation to the change in lateral aberration described above.

[0046] In the case of three or more aspherical surfaces, the three or more aspherical surfaces are different from each other in the same manner as described above, and the laser light refracted by the different aspherical surfaces travels toward a focal point at a position different from the irradiation point of the laser light on the workpiece and converges with the same transverse aberration at the irradiation point of the laser light on the workpiece. At this time, the intensity distribution of the laser light, which is a combination of the laser light refracted by the different aspherical surfaces on the plane at the irradiation point of the workpiece, is at least annular with the optical axis as the center.

[0047] 3-2. Intensity distribution characteristics of laser light when thermal lens effect occurs First, let us explain the thermal lens effect. Laser processing equipment is used to process workpieces such as metals, and therefore uses very high energy laser light. In the case of transmissive optical elements, an anti-reflection coating appropriate for the wavelength of the laser light used is formed on the surface of the optical element, and these elements are used in the optical system of the laser processing equipment as optical elements with high transmittance. However, since it is difficult to achieve 100% transmittance, the energy of the laser light that does not transmit is absorbed by the substrate of the optical element, and the light energy is converted into thermal energy. The density of the substrate or anti-reflection coating of the optical element changes in areas where the temperature rises, resulting in a change in the refractive index. This is generally referred to as the thermal lens effect.

[0048] In optical elements, when the thermal lens effect causes a change in refractive index and partial convexity, the focal position shifts. While this differs depending on the optical properties, such as the refractive index of the substrate and the curvature of the aspherical surface, for example, if the focal length is 200 mm, the thermal lens effect can shorten the focal length by 5 to 10 mm. If this affects the laser light intensity distribution on the plane at the irradiation point on the workpiece, problems such as a deterioration in the processing quality of the workpiece can occur.

[0049] FIG. 5(a) shows a schematic optical path of the laser light between the entrance pupil and the irradiation point when the thermal lens effect occurs in FIG. 3(a). The hatched areas in each diagram represent the optical path of the laser light. FIG. 5(b) shows a lateral aberration diagram at the entrance pupil coordinates and the irradiation point coordinates at that time. The refractive index of the aspherical surface 22 changes due to the thermal lens effect, causing the focal point of the aspherical surface 22 to move further forward. Therefore, as shown in FIGS. 5(a) and 5(b), the laser light refracted by the aspherical surface 22 converges toward the shifted focal point and crosses the optical axis as it travels. Then, at the irradiation point of the laser light on the workpiece, the lateral aberration converges with a lateral aberration characteristic that gradually increases from the initial lateral aberration as the distance from the origin in the entrance pupil coordinates increases.

[0050] On the other hand, since aspherical surface 21 is located in the center of the substrate, it is less susceptible to thermal linear expansion, and there is almost no change in refractive index due to the thermal lens effect. Therefore, the laser light refracted by aspherical surface 21 maintains the same lateral aberration as before it was affected by heat. Therefore, even if the focal point of aspherical surface 22 moves due to the thermal lens effect, the intensity distribution of the combined laser light refracted by aspherical surfaces 21 and 22 on the plane at the irradiation point of the laser light on the workpiece changes little and remains at least annular around the optical axis. Note that the representation of the origin and vicinity of the origin of the entrance pupil coordinates in Figures 5(a) and 5(b) is the same as that described above.

[0051] Similarly, Figure 6(a) shows a schematic optical path of the laser light between the entrance pupil and the irradiation point when the thermal lens effect occurs in Figure 4(a). The hatched areas in each case represent the optical path of the laser light. Figure 6(b) also shows a lateral aberration diagram at the entrance pupil coordinates and the irradiation point coordinates at that time. The refractive index of the aspherical surface 22 changes due to the thermal lens effect, and the focal point of the aspherical surface 22 moves further back. Therefore, as shown in Figures 6(a) and 6(b), the laser light refracted by the aspherical surface 22 travels toward the moved focal point. Then, at the irradiation point of the laser light on the workpiece, the lateral aberration converges with a lateral aberration characteristic that gradually changes from the initial lateral aberration to an increasing lateral aberration as the laser light moves away from the origin in the entrance pupil coordinates.

[0052] On the other hand, since aspherical surface 21 is located in the center of the substrate, it is less susceptible to thermal linear expansion, and there is almost no change in refractive index due to the thermal lens effect. Therefore, the laser light refracted by aspherical surface 21 maintains the same lateral aberration as before it was affected by heat. Therefore, even if the focal point of aspherical surface 22 moves due to the thermal lens effect, the intensity distribution of the combined laser light refracted by aspherical surfaces 21 and 22 on the plane at the irradiation point of the laser light on the workpiece changes little and remains at least annular around the optical axis. Note that the representation of the origin and vicinity of the origin of the entrance pupil coordinates in Figures 6(a) and 6(b) is the same as that described above.

[0053] As described above, even if a focus shift occurs due to the thermal lens effect, the intensity distribution of the laser light on the plane at the irradiation point on the workpiece hardly changes. In other words, the optical system according to the present invention has a deep focal depth that maintains the annular intensity distribution of the laser light at the irradiation point on the workpiece. As a result, even if a thermal lens effect occurs during processing in the laser processing device, the processing quality of the workpiece is maintained.

[0054] 4. Laser processing device embodiment As described above, the laser processing device of the present invention, which processes a workpiece by irradiating it with laser light, is characterized in that it comprises an optical system having an optical surface with multiple different focal points on the same optical axis, the irradiation point of the laser light on the workpiece is located at a position different from the focal point, and the intensity distribution of the laser light at the irradiation point in a plane perpendicular to the optical axis is at least annular with the optical axis as its center.

[0055] FIG. 7 shows a laser processing apparatus 50 according to this embodiment. The laser processing apparatus 50 is generally composed of a laser oscillator 51, an optical path 52, an optical system 53, and a processing stage 54. A workpiece 60 is placed on the processing stage 54. The laser oscillator 51 outputs the laser beam used for processing. The type and output power of the laser beam are selected depending on the material of the workpiece 60, the thickness to be processed, and the processing accuracy. The optical path 52 transmits the laser beam output from the laser oscillator to the optical system, which may use a reflecting mirror or an optical fiber. The optical system 53 focuses the transmitted laser beam into a predetermined shape and irradiates the irradiation point on the workpiece 60. The processing stage 54 fixes the workpiece 60 and includes a device for moving the workpiece 60, the optical system 53, or both, in accordance with the movement of the irradiation point on the workpiece 60.

[0056] By using the laser processing device according to the present invention with the above-mentioned optical system 53, the intensity distribution of the laser light on a plane at the irradiation point on the workpiece 60 becomes at least annular with the optical axis as the center. Even if defocus occurs due to the thermal lens effect, the optical system according to the present invention has a deep focal depth that maintains the annular intensity distribution of the laser light at the irradiation point on the workpiece 60, so the intensity distribution of the laser light at the irradiation point on the workpiece 60 hardly changes. This maintains the processing quality of the workpiece 60.

[0057] Examples of the present invention will be described below, with each example being explained using the optical element shown in FIG. [Example]

[0058] An optical element is used in which the effective diameter of optical surface 12 is 18.5 mm. Aspherical surface 21 and aspherical surface 22 are provided concentrically on optical surface 12. As shown in FIG. 3, the focal point of aspherical surface 21 is located behind the irradiation point, and the focal point of aspherical surface 22 is located in front of the irradiation point. Using equation (1), aspherical surface 21 has a shape that satisfies the following values: c=-0.005 k=-5.0×10 5 a2=4.702×10 -3 a4=4.450×10 -8

[0059] Similarly, the aspherical surface 22 has a shape that satisfies the following numerical values ​​when formula (1) is used: c=0.005 k=-5.0×10 5 a2=4.702×10 -3 a4=4.450×10 -8

[0060] Here, on the optical surface 12, the range up to a radius of 8 mm with the optical axis as the origin is defined as an aspherical surface 21, and the range from a radius of 8 mm to a radius of 18.5 mm is defined as an aspherical surface 22. In this case, the curvature C (unit: m -1 ) are shown in Table 1. Here, distance A (unit: mm) in Table 1 is the distance from the z axis in an r-axis coordinate system in which the optical axis is the z axis and the axis perpendicular to the z axis is the r axis, and position B indicates a position on the r axis, where the position of the optical axis is the origin 0 and the position at the edge of the optical effective area is 1, and the position is divided into 10 equal parts. Also, a graph of the relationship between the curvature C and the positions on the r axis, where the position of the optical axis is the origin 0 and the position at the edge of the optical effective area is 1, is shown in Figure 8.

[0061] [Table 1]

[0062] From the above even-order aspherical formula, the paraxial focal lengths of the aspherical surfaces 21 and 22 are f1 = 505.7 mm and f2 = 154.6 mm, respectively. Since f1 > f2, the value of f2 / f1, the absolute value of the ratio r1 / r2 of the radii of curvature of the aspherical surfaces 21 and 22, and C 0.0 <C 1.0 So C 0.0 / C 1.0 The absolute value of and C 0.1 / C 0.0 The absolute value of and C 0.8 / C 0.2The absolute values ​​of are shown in Table 2.

[0063] [Table 2] [Example]

[0064] An optical element is used in which the effective diameter of optical surface 12 is 18.5 mm. Aspherical surface 21 and aspherical surface 22 are provided concentrically on optical surface 12. As shown in FIG. 4, the focal point of aspherical surface 21 is located in front of the irradiation point, and the focal point of aspherical surface 22 is located behind the irradiation point. Using equation (1), aspherical surface 21 has a shape that satisfies the following values: c=0.005 k=-5.0×10 5 a2=4.702×10 -3 a4=4.450×10 -8

[0065] Similarly, the aspherical surface 22 has a shape that satisfies the following numerical values ​​when formula (1) is used: c=-0.005 k=-5.0×10 5 a2=4.702×10 -3 a4=4.450×10 -8

[0066] Here, on the optical surface 12, the range up to a radius of 8 mm with the optical axis as the origin is defined as an aspherical surface 21, and the range from a radius of 8 mm to a radius of 18.5 mm is defined as an aspherical surface 22. In this case, the curvature C (unit: m -1 ) are shown in Table 3. Here, distance A (unit: mm) in Table 3 is the distance from the z axis in an r-axis coordinate system in which the optical axis is the z axis and the axis perpendicular to the z axis is the r axis, and position B indicates a position on the r axis, where the position of the optical axis is the origin 0 and the position at the edge of the optical effective area is 1, and the position is divided into 10 equal parts. Also, Fig. 9 shows a graph of the relationship between the curvature C and the positions on the r axis, where the position of the optical axis is the origin 0 and the position at the edge of the optical effective area is 1, and the position is divided into 10 equal parts.

[0067]

Table 3

[0068] From the above even-order aspheric formulas, the paraxial focal lengths of aspheric surface 21 and aspheric surface 22 are f1 = 154.6 mm and f2 = 505.7 mm, respectively. At this time, since f1 < f2, the value of f1 / f2, the absolute value of the ratio of the curvature radii r1 / r2 of aspheric surface 21 and aspheric surface 22, and C 0.0 > C 1.0 So C 1.0 / C 0.0 The absolute value of, C 0.1 / C 0.0 The absolute value of, and C 0.8 / C 0.2 The absolute values of are shown in Table 4.

[0069]

Table 4

Example

[0070] An optical element with an effective diameter of 18.5 mm for the optical surface 12 is used. And, on the optical surface of 12, the aspheric surface 21 and the aspheric surface 22 are provided concentrically. And, as shown in FIG. 5, the focus of the aspheric surface 21 is behind the irradiation point, and the focus of the aspheric surface 22 is in front of the irradiation point. And, the aspheric surface 21 has a shape that satisfies the following numerical values when using the formula (1). c = -0.005 k = -5.0×10[[ID=4​​​​​​​​​​​​​ a2=4.733×10 -3 a4=4.450×10 -8

[0072] Here, on the optical surface 12, the range up to a radius of 8 mm with the optical axis as the origin is defined as an aspherical surface 21, and the range from a radius of 8 mm to a radius of 18.5 mm is defined as an aspherical surface 22. In this case, the curvature C (unit: m -1 ) are shown in Table 5. Here, distance A (unit: mm) in Table 5 is the distance from the z axis in an r-axis coordinate system in which the optical axis is the z axis and the axis perpendicular to the z axis is the r axis, and position B indicates a position on the r axis, where the position of the optical axis is the origin 0 and the position at the edge of the optical effective area is 1, and the position is divided into 10 equal parts. Also, a graph of the relationship between the curvature C and the positions on the r axis, where the position of the optical axis is the origin 0 and the position at the edge of the optical effective area is 1, is shown in Figure 10.

[0073] [Table 5]

[0074] From the above even-order aspherical formula, the paraxial focal lengths of the aspherical surfaces 21 and 22 are f1 = 505.7 mm and f2 = 154.0 mm, respectively. In this case, since f1 > f2, the value of f2 / f1, the absolute value of the ratio r1 / r2 of the radii of curvature of the aspherical surfaces 21 and 22, and C 0.0 <C 1.0 So C 0.0 / C 1.0 The absolute value of and C 0.1 / C 0.0 The absolute value of and C 0.8 / C 0.2 The absolute values ​​of are shown in Table 6.

[0075] [Table 6] [Example]

[0076] An optical element is used in which the effective diameter of optical surface 12 is 18.5 mm. Aspherical surface 21 and aspherical surface 22 are provided concentrically on optical surface 12. As shown in FIG. 6, the focal point of aspherical surface 21 is located in front of the irradiation point, and the focal point of aspherical surface 22 is located behind the irradiation point. Using equation (1), aspherical surface 21 has a shape that satisfies the following values: c=0.005 k=-5.0×10 5 a2=4.702×10 -3 a4=4.450×10 -8

[0077] The aspherical surface 22 is set to have its focus shifted by +1.5 mm. In this case, the aspherical surface 22 has a shape that satisfies the following values ​​when formula (1) is used: c=-0.005 k=-5.0×10 5 a2=4.670×10 -3 a4=4.450×10 -8

[0078] Here, on the optical surface 12, the range up to a radius of 8 mm with the optical axis as the origin is defined as an aspherical surface 21, and the range from a radius of 8 mm to a radius of 18.5 mm is defined as an aspherical surface 22. In this case, the curvature C (unit: m -1 ) are shown in Table 7. Here, distance A (unit: mm) in Table 7 is the distance from the z axis in an r-axis coordinate system in which the optical axis is the z axis and the axis perpendicular to the z axis is the r axis, and position B indicates a position on the r axis, where the position of the optical axis is the origin 0 and the position at the edge of the optical effective area is 1, and the position is divided into 10 equal parts. Also, a graph of the relationship between the curvature C and the positions on the r axis, where the position of the optical axis is the origin 0 and the position at the edge of the optical effective area is 1, is shown in Figure 11.

[0079] [Table 7]

[0080] From the above even-order aspheric formula, the paraxial focal lengths of aspheric surface 21 and aspheric surface 22 are f1 = 154.6 mm and f2 = 513.2 mm, respectively. At this time, since f1 < f2, the value of f1 / f2, the absolute value of the ratio r1 / r2 of the curvature radii of aspheric surface 21 and aspheric surface 22, and C 0.0 >C 1.0 so C 1.0 / C 0.0 the absolute value of, and C 0.1 / C 0.0 the absolute value of, and C 0.8 / C 0.2 the absolute value of are shown in Table 8.

[0081]

Table 8

[0082] An optical element with an effective diameter of the optical surface of 18.5 mm is used. And, one aspheric surface is provided on the optical surface. The aspheric surface of the optical element has one focus, which is behind the irradiation point. At this time, the aspheric surface has a shape that satisfies the following numerical values when using equation (1). c = 0.0055 k = -1.327×10 6 [[ID=...]] a2 = 2.276×10 -3

[0083] At this time, the curvature C (unit m -1 ) of the aspheric surface at each position perpendicular to the optical axis is shown in Table 9. Here, the distance A (unit mm) in Table 9 is the distance from the z-axis in the r-axis coordinate system where the optical axis is the z-axis and the axis perpendicular to the z-axis is the r-axis, and the position B is the position on the r-axis that is equally divided into 10 parts with the position of the optical axis as the origin 0 and the position of the end of the optical effective region as 1. Also, a graph showing the relationship between the position equally divided into 10 parts with the position of the optical axis as the origin 0 and the position of the end of the optical effective region as 1 and the curvature C on the r-axis is shown in FIG. 12.

[0084] [[ID=4...]]

Table 9

[0085] From the above even-order aspherical formula, the paraxial focal length of the aspherical surface is f1 = 132.3 mm. 0.0 >C 1.0 So C 1.0 / C 0.0 The absolute value of and C 0.1 / C 0.0 The absolute value of and C 0.8 / C 0.2 The absolute values ​​of are shown in Table 10.

[0086] [Table 10]

[0087] [Evaluation results] Optical simulations were performed using Zemax's Optical Design Program to confirm the intensity distribution of laser light on a line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece when using the optical elements of Examples 1 to 4. The simulations were performed using a fiber laser light source, with a core diameter of 100 μm and a beam angle of 80 mrad. The simulation results are shown in Figures 14 to 17. The horizontal axis represents the coordinate position on a line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece, in units of mm. The numerical values ​​-1 mm, 0 mm, and +1 mm in Figures 14 to 17 indicate the intensity distribution of laser light at the irradiation point, with the irradiation point position shown in the transverse aberration diagrams of Figures 3(b) to 6(b) being 0 mm. The values ​​-1 mm and +1 mm indicate the laser light intensity distribution at positions -1 mm and +1 mm, respectively, along the optical axis from the irradiation point. The minus sign here indicates a position closer to the optical system than the irradiation point.

[0088] Furthermore, an optical simulation was performed using Zemax's Optical Design Program to confirm the intensity distribution of the laser light on a line including the optical axis on a plane perpendicular to the optical axis at the irradiation point on the workpiece when the optical element of the comparative example was used. The conditions for the laser light source used in the simulation were a core diameter of φ100 μm and 80 mrad. The simulation results are shown in Figure 18. The explanation for the figure is the same as above.

[0089] 13 shows the simulation results of the laser light intensity distribution at a position -3 mm from the position of the irradiation point in the comparative example. The comparative example has one aspherical surface on the optical surface, and since it has one focal point, there is a position where the laser light intensity distribution becomes a Gaussian distribution. The vertical axis of the simulation results in FIGS. 14 to 18 is plotted as the laser light intensity relative to the laser light intensity in FIG. 13.

[0090] 14 and 15, it is clear that by using the optical system according to the present application, the intensity distribution of the laser light on a straight line at the irradiation point is at least bimodal, centered on the optical axis. This means that the intensity distribution of the laser light on a plane perpendicular to the optical axis at the irradiation point on the workpiece is at least annular, centered on the optical axis. It was also revealed that the position and peak value of the intensity peak of the laser light hardly change even at positions shifted -1 mm or 1 mm from the irradiation point.

[0091] 16 and 17, it is clear that by using the optical system according to the present application, even if the focal position of the aspherical surface is shifted, the intensity distribution of the laser light on a straight line at the irradiation point is at least bimodal, centered on the optical axis. This means that on a plane perpendicular to the optical axis at the irradiation point on the workpiece, the intensity distribution of the laser light is at least annular, centered on the optical axis. It was also revealed that the position and peak value of the intensity of the laser light hardly change even at positions shifted -1 mm or 1 mm from the irradiation point.

[0092] On the other hand, Figure 18 reveals that when the optical system of the comparative example is used, the intensity distribution of the laser light is bimodal centered on the optical axis, but the position and peak value of the intensity peak of the laser light change significantly at positions shifted -1 mm and 1 mm from the irradiation point position.

[0093] In other words, by providing an optical surface with multiple foci on the same optical axis in the optical system used in the laser processing device of the present application, the focus of the optical system can be located at a position different from the irradiation point on the workpiece, and the intensity distribution of the laser light on a plane at the irradiation point can be at least annular, centered on the optical axis. Furthermore, since most of the laser light incident on the optical system of the present application can be used as annular laser light at the irradiation point, the energy utilization efficiency of the laser light is high. It has also been revealed that even if the focal position is shifted, it is possible to obtain laser light whose intensity distribution shape, intensity peak position, and peak value at the irradiation point remain unchanged. [Industrial Applicability]

[0094] The laser processing device according to the present invention can make the intensity distribution of the laser beam on a plane at the irradiation point at least annular around the optical axis, and the intensity distribution and intensity of the laser beam on the plane at the irradiation point do not change even if the focal position is shifted due to the thermal lens effect, so it is suitable for an optical system used in a laser processing device that performs processing such as cutting and drilling on a workpiece. Furthermore, by using the laser processing device according to the present invention, stable laser processing is possible and the processing quality of the workpiece is maintained. [Explanation of symbols]

[0095] 10 Optical elements (lenses) 11 Base material 12 Optical surface 13 Optical surface 21 Aspherical surface 22 Aspherical surface 10' Optical element (lens) 11' Base material 12' optical surface 13' optical surface 21' Aspherical 22' aspherical 50 Laser processing equipment 51 Laser oscillator 52 Light path 53 Optical system 54 Processing Stage 60 Workpiece

Claims

1. A laser processing device that processes a workpiece by irradiating it with laser light, an optical system having an optical surface with two different focal points on the same optical axis, At the positions of the two different focal points, the laser beams emitted from the optical surface on which the two different focal points are provided intersect with the optical axis while having lateral aberrations, a position of an irradiation point of the laser beam on the workpiece is between the positions of the two different focal points, and is at a position where the laser beams emitted from the optical surfaces on which the two different focal points are provided converge into an annular shape with substantially the same value of transverse aberration; A laser processing apparatus characterized in that, at the position of the irradiation point, the intensity distribution in a plane perpendicular to the optical axis of the laser light obtained by combining the laser light respectively emitted from the optical surfaces having the two different focal points is annular with the optical axis as the center.

2. 2. The laser processing device according to claim 1, wherein the optical surfaces having the two different focal points are two different spherical and / or aspherical surfaces.

3. 3. The laser processing device according to claim 2, wherein the two different spherical and / or aspherical surfaces are provided in two different concentric regions on the same optical surface.

4. 3. The laser processing apparatus according to claim 2, wherein the two different spherical and / or aspherical surfaces are areas through which different light beams pass on two different optical surfaces, and are provided in two different concentric areas.

5. 3. The laser processing apparatus according to claim 2, wherein at least one optical surface of the two different spherical and / or aspherical surfaces is aspherical.

6. 6. The laser processing apparatus according to claim 2, wherein the two different aspherical surfaces have different focal lengths, and when f1<f2, f1 / f2 is greater than 0.2 and smaller than 0.8, and when f1>f2, f2 / f1 is greater than 0.2 and smaller than 0.8, where f1 is the focal length of the two different aspherical surfaces and f2 is the focal length of the two different aspherical surfaces. However, the units of f1 and f2 are mm.

7. 7. The laser processing apparatus according to claim 2, wherein the absolute value of r1 / r2 is greater than 0.5 and less than 2, where r1 and r2 are the radii of curvature of the two different aspherical surfaces, respectively. However, the units of r1 and r2 are mm.

8. In the two different aspherical surfaces, C ０．０ >C １．０ In this case, C １．０ / C ０．０ The absolute value of is less than 0.9, and C ０．０ <C １．０ In this case, C ０．０ / C １．０ 8. The laser processing device according to claim 2, wherein the absolute value of is smaller than 0.

9. However, in a coordinate system in which the optical axis is the z-axis and the axis perpendicular to the z-axis is the r-axis, when the position of the optical axis is the origin on the r-axis and the position of the end of the optical effective area of ​​the two different aspherical surfaces is divided into 10 equal parts, the curvature at the origin is C ０．０ (m －１ ), the curvature at the edge of the optically effective area is C １．０ (m －１ )

9. In the two different aspherical surfaces, C ０．１ / C ０．０ 9. The laser processing device according to claim 8, wherein the absolute value of is greater than 0 and less than 4. However, in a coordinate system in which the optical axis is the z-axis and the axis perpendicular to the z-axis is the r-axis, when the position of the optical axis on the r-axis is the origin and the position up to the end of the optical effective area is divided into 10 equal parts, the curvature at a position at 1 / 10 of the 10 equal parts is C ０．１ (m －１ )

10. In the two different aspherical surfaces, C ０．８ / C ０．２ 10. The laser processing device according to claim 8, wherein the absolute value of is greater than 0.5 and less than 1.

5. However, in a coordinate system in which the optical axis is the z-axis and the axis perpendicular to the z-axis is the r-axis, when the position of the optical axis on the r-axis is the origin and the position up to the end of the optical effective area is divided into 10 equal parts, the curvature at a position at 2 / 10 of the 10 equal parts is C ０．２ (m －１ ), the curvature at the position of 8 / 10 of the 10 equal parts is C ０．８ (m －１ )

11. An optical system provided in the laser processing apparatus according to claim 1, An optical surface having two different focal points on the same optical axis, An optical system characterized in that the optical surfaces having the two different focal points are two different spherical and / or aspherical surfaces.

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