Device and method for laser-based separation of a transparent, brittle workpiece

Abstract

The present disclosure provides a device and a method for laser-based separation of a transparent, brittle workpiece, comprising a laser that emits a laser beam having an intensity (I.sub.L) along an optical axis (P), and an optical device. The optical device has at least one one-piece double axicon. The double axicon has an entrance surface and the optical device has an exit surface. The entrance surface is such that in the double axicon, a ring beam is formed. The intensity (I.sub.L) in the double axicon is lower than the threshold intensity (I.sub.S) of the material of the double axicon. The exit surface is such that a line focus having a maximum intensity (I.sub.max) and a length (L.sub.T) is generated in the direction of the laser beam behind the exit.

Claims

1. A device for the laser-based separation of a transparent, brittle workpiece, comprising: a laser that emits a laser beam with an intensity I.sub.L along an optical axis, wherein the laser beam has a pulse energy of 500 microjoules to 5 millijoules; and an optical device, wherein the optical device has at least one double axicon, wherein the double axicon has an entrance surface and the optical device has an exit surface, wherein the laser beam splits into a ring beam after passing the entrance surface, wherein the intensity I.sub.L in the double axicon is less than a threshold intensity I.sub.S of the material of the double axicon, wherein the exit surface is such that a line focus having a maximum intensity I.sub.max being higher than a threshold energy of the workpiece and a length L.sub.f arises in a direction of the laser beam after the exit surface, and wherein, after the laser beam passes the optical device, the laser beam has an aperture angle β with 5≤β≤20° and the maximum intensity I.sub.max lies in the workpiece.

2. The device according to claim 1, wherein the double axicon has an inwardly directed conical entrance surface and an outwardly directed conical exit surface.

3. The device according to claim 1, wherein the double axicon is a Kepler axicon.

4. The device according to claim 1, wherein the double axicon is monolithic.

5. The device according to claim 4, wherein the double axicon has a refractive index of 1.35≤n.sub.a≤1.9.

6. The device according to claim 1, wherein the double axicon is composed of a first planar axicon and a second planar axicon.

7. The device according to claim 6, wherein the first planar axicon and the second planar axicon are connected to each other indirectly via a transparent intermediate element or are connected directly to each other.

8. The device according to claim 7, wherein the intermediate element has a refractive index of 1.35≤n.sub.z≤1.9.

9. The device according to claim 8, wherein the refractive index n.sub.z of the intermediate element exhibits a radial dependence.

10. The device according to claim 6, wherein the first planar axicon has a refractive index n.sub.1 and the second planar axicon has a refractive index n.sub.2, wherein the following relation applies: n.sub.1=n.sub.2.

11. The device according to claim 6, wherein the first planar axicon has a refractive index n.sub.1 and the second planar axicon has a refractive index n.sub.2, wherein the following relation applies: n.sub.1≠n.sub.2.

12. The device according to claim 11, wherein the refractive index n.sub.1 and/or the refractive index n.sub.2 exhibit or exhibits a radial dependence.

13. The device according to claim 1, wherein the exit surface of the optical device is part of a lens for focusing the ring beam.

14. The device according to claim 13, wherein the lens is a convergent lens or an axicon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of a device for the separation of a transparent, brittle workpiece.

(2) FIG. 2 depicts an optical device with a Galileo axicon and a convergent lens.

(3) FIG. 3 depicts an optical device with a Kepler axicon and a convergent lens.

(4) FIG. 4 depicts an optical device with a Galileo axicon that is composed of two planar axicons having different refractive indices.

(5) FIG. 5 depicts an optical device with a Kepler axicon that is composed of two planar axicons having different refractive indices.

(6) FIG. 6 depicts an optical device with a Galileo axicon that is composed of two planar axicons and an intermediate element.

(7) FIG. 7 depicts a line focus of a Bessel-Gaussian beam formed by means of a Galileo axicon.

DETAILED DESCRIPTION OF THE DISCLOSURE

(8) In FIG. 1, a device 1 for the separation of a transparent, brittle workpiece 50 is depicted schematically. The device 1 comprises a laser 5, which emits a laser beam 6 in the form of a Gaussian beam along the optical axis P. In the beam path of the laser beam 6, there is an optical device 10 with an entrance surface 110 and an exit surface 120. The optical device 10 transforms the original Gaussian beam 6 into a ring beam 2, which is focused in a line focus 3 having a length L.sub.f. For the processing of the workpiece 50, the line focus 3 is situated completely in the workpiece 50. In the following depictions, the design of the optical device 10 will be addressed in detail.

(9) FIG. 2 shows the optical device 10 with the workpiece 50. In this embodiment, the optical device 10 is composed of a monolithic double axicon 100, which is designed as a Galileo axicon 100′, and a convergent lens 106. The exit surface of the convergent lens 106 forms the exit surface 120 of the optical device 10.

(10) The Galileo axicon 100′ has a conical entrance surface 110 and a conical exit surface 105. Both the tip 112 of the entrance surface 110 and the tip 122 of the exit surface 105 are directed along the direction of propagation of the laser beam 6 and lie on the optical axis P. The Galileo axicon 100′ has a first axicon angle α.sub.1 and a second axicon angle α.sub.2, whereby, in the present example, the two angles are the same in size. The axicon angle α.sub.1 or the axicon angle α.sub.2 is the angle between the conical surface 114 or 124, respectively, and the normal line N to the cone axis of the conical shape created by the entrance surface 110 and exit surface 105 of the double axicon 100, whereby the normal line N is oriented perpendicularly to the optical axis P.

(11) The laser beam 6, which is emitted from a high-power laser 5 (see FIG. 1) as a Gaussian beam 6, spreads out along the optical axis P and is refracted at the entrance surface 110 of the Galileo axicon 100′ in accordance with the law of refraction toward the perpendicular of the entrance surface 110, because a transition from an optically less dense medium to an optically more dense medium takes place. On account of the conical shape of the entrance surface 110, the laser beam 6 splits apart and a ring beam 2 with an inner radius R is formed in the interior of the Galileo axicon 100′. The inner radius R of the ring beam 2 is dependent on the axicon angle α.sub.1. the refractive index n.sub.a of the Galileo axicon 100′, and the path traversed within the Galileo axicon 100′.

(12) When it impinges on the exit surface 105 of the Galileo axicon 100′, the ring beam 2 is refracted away from the perpendicular of the exit surface 105 in accordance with the law of refraction, because the ring beam 2 undergoes a transition from the optically more dense medium to the optically less dense medium. If the axicon angles α.sub.1 and α.sub.2 are identical, as in the present example, then the ring beam 2 is refracted in such a way that, after exiting from the Galileo axicon 100′, it has a constant radius R.

(13) By means of a convergent lens 106, the ring beam 2 is focused behind the Galileo axicon 100′ into a line focus 3 having a length L.sub.f. The line focus 3 penetrates completely through the workpiece 50.

(14) FIG. 3 shows the optical device 10 with a workpiece 50. In this embodiment, the optical device 10 is composed of a monolithic double axicon 100, which is designed as a Kepler axicon 100′, and a convergent lens 106. The exit surface of the convergent lens 106 forms the exit surface 120 of the optical device 10.

(15) The Kepler axicon 100″ has a conical entrance surface 110 and a conical exit surface 105. The tip 112 of the entrance surface 110 is directed opposite to the direction of propagation of the laser beam 6 and the tip 122 of the exit surface 105 is directed along the direction of propagation of the laser beam 6. Both of the tips lie on the optical axis P.

(16) The Kepler axicon 100″ has a first axicon angle α.sub.1 and a second axicon angle α.sub.2, whereby, in the present example, the two angles are the same size. The axicon angle α.sub.1 and the axicon angle α.sub.2, respectively, are thereby the angles between the conical surfaces 114 and 124, respectively, and the normal line N to the cone axis of the conical shape formed by the entrance surface 110 and the exit surface 105 of the double axicon 100, whereby the normal line N is oriented perpendicularly to the optical axis P.

(17) The laser beam 6 from the high-power laser 5 (see FIG. 1), which is emitted as a Gaussian beam 6, spreads out along the optical axis P and is refracted at the entrance surface 110 of the Kepler axicon 100″ in accordance with the law of refraction toward the perpendicular of the entrance surface 112, because a transition from an optically less dense medium to an optically more dense medium takes place. On account of the conical shape of the entrance surface 110, the laser beam 6 is condensed in the interior of the Kepler axicon 100″, resulting in a beam superimposition, whereby an intermediate focus 4 having a length L.sub.z is created in the interior of the Kepler axicon 100″. Formed behind the intermediate focus 4, as in the case of the Galileo axicon 100′, is a ring beam 2, the inner radius R of which is also dependent on the axicon angle α.sub.1, the refractive index n.sub.a of the Kepler axicon 100″, and the path traversed in the Kepler axicon 100″.

(18) When it impinges on the exit surface 105 of the Kepler axicon 100″, the ring beam 2 is refracted away from the perpendicular of the exit surface 105 in accordance with the law of refraction, because the ring beam 2 undergoes a transition from the optically denser medium to the optically less dense medium. If the axicon angles α.sub.1 and α.sub.2 are identical, as in the present example, then the ring beam 2 is refracted in such a way that, after exiting from the Kepler axicon 100″, it has a constant inner radius R.

(19) As in the case of the above-described Galileo axicon 100′ (see also FIG. 2), by means of a convergent lens 106, the ring beam 2 is focused behind the Kepler axicon 100″ into a line focus 3 having a length L.sub.f. The line focus 3 penetrates completely through the workpiece 50.

(20) FIG. 4 shows an optical device 10, which is designed as a Galileo axicon 100′ that is composed of a first planar axicon 101 with a refractive index n.sub.1 and a second planar axicon 102 with a refractive index n.sub.2, whereby, in the example presented here, the refractive index n.sub.1 is higher than the refractive index n.sub.2. The two planar axicons 101, 102 are connected by being cemented to each other. The first planar axicon 101 has an axicon angle α.sub.1 and the second planar axicon 102 has an axicon angle α.sub.2, where α.sub.1 is smaller than α.sub.2. The conical surface 114 of the first planar axicon 101 forms the entrance surface 110 of the Galileo axicon 100′, while the conical surface 124 of the second planar axicon 102 forms both the exit surface 105 of the Galileo axicon 100′ and the exit surface 120 of the optical device 10.

(21) The Gaussian beam 6 that impinges on the entrance surface 110 of the Galileo axicon 100′ is split at the entrance surface 110 into a ring beam 2, the inner radius R of which becomes larger with progressive traversed path in the first planar axicon 101. At a boundary surface 104 between the first planar axicon 101 and the second planar axicon 102, the ring beam 2 is refracted once again. Because the refractive index n.sub.1 of the first planar axicon 101 is higher than the refractive index n.sub.2 of the second planar axicon 102, the ring beam 2 is further spread apart.

(22) When it impinges on the exit surface 105 of the Galileo axicon 100′, the ring beam 2 is recombined at an aperture angle β and, at the site of superimposition, creates a line focus 3 having a length L.sub.f. The workpiece 50 is arranged in this line focus L.sub.f for the processing thereof.

(23) FIG. 5 shows an optical device 10, which is designed as a Kepler axicon 100″ that is composed of a first planar axicon 101 with a refractive index n.sub.1 and a second planar axicon 102 with a refractive index n.sub.2, whereby, in the example presented here, the refractive index n.sub.1 is higher than the refractive index n.sub.2. The first planar axicon 101 has an axicon angle α.sub.1 and the second planar axicon has an axicon angle α.sub.2, where α.sub.1 is smaller than α.sub.2. The conical surface 114 of the first planar axicon 101 forms the entrance surface 110 of the Kepler axicon 100″, while the conical surface 124 of the second planar axicon 102 forms both the exit surface 105 of the Kepler axicon 100″ and the exit surface 120 of the optical device 10.

(24) The Gaussian beam that impinges on the entrance surface 110 of the Kepler axicon 100″ is refracted at the entrance surface 110 and is concentrated in the Kepler axicon 100″, on account of the cone tip 112 of the first planar axicon 101, which is oriented opposite to the direction of propagation, resulting in beam crossing and the creation of an intermediate focus 4 having the length L.sub.z.

(25) At the boundary surface 104, the laser beam 6 is refracted once again and, behind the intermediate focus 4, a ring beam 2 with the inner radius R is formed and becomes larger with progressive traversed path in the Kepler axicon 100″. On account of the low refractive index n.sub.2 of the second planar axicon 102, the ring beam 2 spreads out more strongly behind the intermediate focus 4. In this way, a steeper angle of impingement on the exit surface 105 of the Kepler axicon 100″ is achieved than, for example, in the case of the monolithic Kepler axicon 100″ that has the same dimensions. When it passes the exit surface 105 of the Kepler axicon 100″, the ring beam 2 is recombined at an aperture angle β′ and creates at the site of superimposition a line focus 3 having a length L.sub.f.

(26) A steep angle of impingement on the exit surface 105 leads to the fact that, behind the Kepler axicon 100″, the ring beam 2 has a lesser ring thickness and consequently a higher energy density. During the superimposition of the ring beam 2 in the line focus 3, this leads to the fact that the line focus used for processing the workpiece 50 is shorter in comparison to that of a monolithic Kepler axicon 100″ having the same dimensions, but has a higher energy density.

(27) The intermediate focus 4 that is created in the Kepler axicon 100″ has a length L.sub.z, which is dependent on the refractive indices n.sub.1 and n.sub.2 as well as on the axicon angle α.sub.1 of the first planar axicon 101. In the present example, the intermediate focus 4 is about three times as long as the line focus 3 and accordingly has a markedly lower energy density.

(28) FIG. 6 shows an optical device 10, which is designed as a Galileo axicon 100′ that is composed of a first planar axicon 101 with a refractive index n.sub.1 and a second planar axicon 102 with a refractive index n.sub.2, whereby, in the example presented here, the refractive index n.sub.1 is higher than the refractive index n.sub.2, and, between the two planar axicons 101, 102, an intermediate element 103 with a refractive index n.sub.z is situated. The intermediate element 103 is cemented at its lateral faces to the planar faces of the two planar axicons 101, 102.

(29) Preferably, the intermediate element 103 has a refractive index n.sub.z that exhibits a radial dependence, by way of which the intensity distribution of a line focus 4 that is to be generated in the workpiece can be adapted in such a way that it deviates from the intensity distribution of the Bessel-Gaussian beam. In FIG. 6 presented here, the refractive index n.sub.z of the intermediate element 103 was assumed to be constant for purposes of clarity of the beam guidance, wherein the following relation applies: n.sub.1>n.sub.z>n.sub.2.

(30) The first planar axicon 101 has an axicon angle α.sub.1 and the second planar axicon has an axicon angle α.sub.2, where α.sub.1 is smaller than α.sub.2. The conical surface 114 of the first planar axicon 101 forms the entrance surface 110 of the Galileo axicon 100′, while the conical surface 124 of the second planar axicon 102 forms both the exit surface 105 of the Galileo axicon 100′ and the exit surface 120 of the optical device 10.

(31) The Gaussian beam 6 that impinges on the entrance surface 110 of the Galileo axicon 100′ is split at the entrance surface 110 into a ring beam 2, the inner radius R of which becomes with progressive traversed path in the first planar axicon 101. At the boundary surface to the intermediate element 103, the ring beam 2 is refracted once again. Because the refractive index n.sub.1 of the first planar axicon 101 is greater than the refractive index n.sub.z of the intermediate element 103, the ring beam 2 is further spread apart. At the boundary surface between the intermediate element 103 and the second planar axicon 102, the Gaussian beam is refracted once again from the perpendicular of the boundary surface and further spread apart.

(32) When it impinges on the exit surface 105 of the Galileo axicon 100′, the ring beam 2 is refracted away from the perpendicular of the exit surface 105 in accordance with the law of refraction, because the ring beam 2 undergoes a transition from the optically denser medium to the optically less dense medium. In the illustrated exemplary embodiment, the axicon angles α.sub.1, α.sub.2 and the refractive indices n.sub.1, n.sub.2, n.sub.z are configured in such a way that the ring beam 2 is first focused by means of a convergent lens 106, which is arranged behind the Galileo axicon 100′, into a line focus 3 having a length L.sub.f. The line focus 3 penetrates completely through the workpiece 50.

(33) By way of example, FIG. 7 shows the intensity distribution in the line focus 3 of a Galileo axicon 100′ along the beam direction (z direction). The length L.sub.f of the line focus 3 corresponds to the width of the intensity distribution at half maximum intensity I.sub.max.

(34) The Gaussian beam 6 that is emitted from a laser has its intensity maximum in its radial center. On account of the fact that the Gaussian beam 6 fans out when it passes the Galileo axicon 100′, the intensity maximum I.sub.max of the ring beam 2 is situated on its inner side and this leads to the fact that the line focus 3 has a higher intensity in the front region of the illustrated intensity distribution.

(35) In the case of the Kepler axicon 100″, in contrast, the intensity maximum is situated in the back region of the intensity distribution (not illustrated), because, on account of the beam crossing in the Kepler axicon 100″, the maximum intensity I.sub.max of the ring beam 2 is situated on the outer side thereof.

LIST OF REFERENCE CHARACTERS

(36) 1 device 2 ring beam 3 line focus 4 intermediate focus 5 laser 6 laser beam, Gaussian beam 10 optical device 50 workpiece 100 double axicon 100′ Galileo axicon 100″ Kepler axicon 101 first planar axicon 102 second planar axicon 103 intermediate element 104 boundary surface 105 exit surface of the double axicon 106 convergent lens 110 entrance surface 112 tip 114 conical surface 120 exit surface of the optical device 10 122 tip 124 conical surface P optical axis R inner radius of the ring beam α.sub.1 first axicon angle α.sub.2 second axicon angle β, β′ aperture angle L.sub.f length of the line focus L.sub.z length of the intermediate focus N normal line to the cone axis