EP4263113A1

EP4263113A1 - Apparatus and method for cutting a material

Info

Publication number: EP4263113A1
Application number: EP21801071.8A
Authority: EP
Inventors: Daniel FLAMM; Julian Hellstern; Jonas Kleiner
Original assignee: Trumpf Laser und Systemtechnik GmbH
Current assignee: Trumpf Laser und Systemtechnik GmbH
Priority date: 2020-12-18
Filing date: 2021-10-25
Publication date: 2023-10-25
Also published as: WO2022128214A1; US20230364705A1; CN116783025A; KR20230117753A; DE102020134195A1

Abstract

The invention relates to a method and an apparatus for cutting a workpiece (1) containing a transparent material, wherein material modifications (5) are introduced into the transparent material of the workpiece (1) along a cutting line (4) by means of ultrashort laser pulses of an ultrashort pulse laser, whereupon the material of the workpiece (1) is cut, in a cutting step, along the material modification area (50) formed thereby, the laser pulses being applied to the workpiece (1) at an angle of attack (α), the optical aberration of the laser pulses during the transition into the material of the workpiece (1) being reduced by an aberration correction device (7), the laser beam (20) having a radially asymmetrical transverse intensity distribution (220), said transverse intensity distribution (220) being elongate along a first axis (A) compared to a second axis (B), the second axis (B) running perpendicularly to the first axis (A).

Description

Device and method for separating a material

technical field

The present invention relates to a device and a method for separating a material using ultra-short laser pulses.

State of the art

In recent years, the development of lasers with very short pulse lengths, especially pulse lengths of less than a nanosecond, and high average powers, especially in the kilowatt range, has led to a new type of material processing. The short pulse length and high pulse peak power or the high pulse energy of a few microjoules to 100 pJ can lead to non-linear absorption of the pulse energy in the material, so that materials that are actually transparent or essentially transparent for the laser light wavelength used can also be processed.

A particular area of application for such laser radiation is cutting and processing in front of workpieces. In this case, the laser beam is preferably introduced into the material with vertical incidence, since reflection losses on the surface of the material are then minimized. For the processing of materials at an angle of attack, for example for chamfering a material edge, or the creation of chamfer and/or bevel structures with angles of attack of more than 30°, there is still an unsolved problem, especially because the high angle of attack on the Material edge lead to a strong aberration of the laser beam and so no targeted energy deposition can take place in the material.

Presentation of the invention

Proceeding from the known prior art, it is an object of the present invention to provide an improved device for separating a workpiece and a corresponding method. The object is achieved by a method for separating a workpiece with the features of claim 1. Advantageous developments of the method result from the dependent claims and the present description and the figures.

Accordingly, a method for separating a workpiece comprising a transparent material is proposed, wherein material modifications are introduced into the transparent material of the workpiece along a separating line by means of ultra-short laser pulses of an ultra-short pulse laser and the workpiece is then separated in a separating step along the resulting material modification surface. According to the invention, the laser pulses are applied to the workpiece at an angle of incidence and the optical aberration of the laser pulses is reduced by an aberration correction device at the transition to the material of the workpiece, the laser beam having a non-radially symmetrical transverse intensity distribution and the transverse intensity distribution elongating in a first axis in the Compared to a second axis, the second axis is perpendicular to the first axis.

The ultra-short pulse laser provides ultra-short laser pulses. In this case, ultra-short can mean that the pulse length is between 500 picoseconds and 10 femtoseconds, for example, and in particular between 10 picoseconds and 100 femtoseconds. The ultra-short laser pulses move in the beam propagation direction along the laser beam formed by them.

When an ultrashort laser pulse is focused into a material of the workpiece, the intensity in the focus volume can result in non-linear absorption by, for example, multiphoton absorption and/or electron avalanche ionization processes. This non-linear absorption leads to the generation of an electron-ion plasma, which can induce permanent structural changes in the material of the workpiece when it cools down. Since energy can be transported into the bulk of the material by nonlinear absorption, these structural changes can be generated inside the sample without affecting the surface of the workpiece.

A transparent material is understood herein to mean a material that is essentially transparent to the wavelength of the laser beam of the ultrashort pulse laser. The terms "material" and "transparent material" are used interchangeably here - the material mentioned here is therefore always to be understood as material that is transparent to the laser beam of the ultrashort pulse laser. The material modifications introduced into transparent materials by ultrashort laser pulses are divided into three different classes, see K. Itoh et al. "Ultrafast Processes for Bulk Modification of Transparent Materials" MRS Bulletin, vol. 31 p.620 (2006): Type I is an isotropic refractive index change; Type II is a birefringent refractive index change; and Type III is a so-called void. The material modification produced depends on laser parameters such as the pulse duration, the wavelength, the pulse energy and the repetition frequency of the laser, on the material properties such as the electronic structure and the thermal expansion coefficient, as well as on the numerical aperture (NA) of the focussing.

The type I isotropic refractive index changes are attributed to localized melting caused by the laser pulses and rapid resolidification of the transparent material. For example, with fused silica, the density and refractive index of the material is higher when the fused silica is rapidly cooled from a higher temperature. So if the material in the focus volume melts and then cools down quickly, the quartz glass has a higher refractive index in the areas of material modification than in the unmodified areas.

The type II birefringent refractive index changes can arise, for example, as a result of interference between the ultrashort laser pulse and the electric field of the plasma generated by the laser pulses. This interference leads to periodic modulations in the electron plasma density, which leads to a birefringent property, i.e. direction-dependent refractive indices, of the transparent material when it solidifies. A type II modification is also accompanied, for example, by the formation of so-called nanogratings.

The voids (cavities) of the type III modifications can be produced, for example, with a high laser pulse energy. The formation of the voids is attributed to an explosive expansion of highly excited, vaporized material from the focus volume into the surrounding material. This process is also known as a micro-explosion. Because this expansion occurs within the bulk of the material, the microexplosion leaves behind a less dense or hollow core (the void), or submicron or atomic-scale microscopic defect, surrounded by a densified shell of material. Due to the compression at the impact front of the microexplosion, stresses arise in the transparent material, which can lead to spontaneous cracking or can promote cracking. In particular, the formation of voids can also be associated with type I and type II modifications. For example, Type I and Type II modifications can arise in the less stressed areas around the introduced laser pulses. Therefore, if a type III modification is introduced, then in any case a less dense or hollow core or a defect is present. For example, in a type III modification of sapphire, the microexplosion does not create a cavity, but rather an area of lower density. Due to the material stresses that occur in a type III modification, such a modification is often accompanied by cracking or at least promotes it. The formation of type I and type II modifications cannot be completely prevented or avoided when introducing type III modifications. Finding "pure" Type III modifications is therefore not likely.

At high repetition rates of the laser, the material cannot cool completely between pulses, so that cumulative effects of the introduced heat from pulse to pulse can influence the material modification. For example, the repetition frequency of the laser can be higher than the reciprocal of the heat diffusion time of the material, so heat accumulation can take place in the focal zone by successive absorption of laser energy until the melting temperature of the material is reached. In addition, a larger area than the focus zone can be melted due to the thermal transport of the heat energy into the areas surrounding the focus zone. After the introduction of the ultra-short laser pulses, the heated material cools rapidly, so that the density and other structural properties of the high-temperature state are effectively frozen in the material.

The material modifications are introduced into the material along a parting line. The parting line describes the line of impact of the laser beam on the surface of the workpiece. By means of a feed, for example, the laser beam and the workpiece are shifted relative to one another at a feed rate, so that the laser pulses hit the surface of the workpiece at different points over time. In this case, the feed rate and/or the repetition rate of the laser is selected in such a way that the material modifications in the material of the workpiece do not overlap, but are separate from one another in the material. Displaceable relative to one another means here that both the laser beam can be displaced translationally relative to a stationary workpiece and that the workpiece can be displaced relative to the laser beam. It may also be the case that both the workpiece and the laser beam move. During workpiece and the laser beam are moved relative to one another, the ultra-short pulse laser emits laser pulses into the material of the workpiece at its repetition frequency.

A characteristic of the material modifications in the beam propagation direction creates an area in the material of the workpiece in which all material modifications lie and which intersects the surface of the workpiece along the parting line. The area in which the material modifications lie is called the material modification area. In particular, the material modification surface can also be curved, so that material modifications that form, for example, the outer surface of a cylinder or a cone are also located in a material modification surface.

The laser pulses are introduced into the material of the workpiece at a so-called angle of incidence. The angle of attack is given here as the angle difference between the laser beam and the surface normal of the workpiece to be cut. When the angle of attack is non-zero, the material modification surface is also inclined with respect to the surface normal of the workpiece. It should be noted here that, given a non-vanishing angle of incidence, the laser beam is refracted according to Snell's law of refraction depending on the refractive index of the surrounding medium, preferably air, and the material of the workpiece. As a result, the beam propagation direction in the material of the workpiece can deviate from the beam propagation direction before entering the material of the workpiece.

In particular, as a result, the material modification surface can also be tilted at an angle other than the angle of impact with respect to the surface normal.

The laser beam also has a non-radially symmetric transverse intensity distribution, where the transverse intensity distribution appears elongated in a first axis compared to a second axis, the second axis being perpendicular to the first axis.

In this case, non-radially symmetrical means that the transverse intensity distribution, ie the intensity distribution perpendicular to the direction of beam propagation, depends not only on the distance from the optical axis, but also at least on the polar angle around the direction of beam propagation.

A non-radially symmetrical transverse intensity distribution can mean, for example, that the transverse intensity distribution is, for example, cross-shaped, or is triangular or N-angled, for example is pentagonal. A non-radially symmetrical transverse intensity distribution can also include further rotationally symmetrical and mirror-symmetrical beam cross sections. In particular, a non-radially symmetrical transverse intensity distribution can also have an elliptical shape, the ellipse having a long axis A and an associated vertical short axis B has. An elliptical transverse intensity distribution is accordingly present when the ratio A/B is greater than 1, in particular when A/B=1.5. The elliptical transverse intensity distribution of the laser beam can correspond to an ideal mathematical ellipse. However, the non-radially symmetrical transverse intensity distribution of the laser beam can also only have the above-mentioned ratios of long main axis and short main axis, but have a different contour - for example an approximated mathematical ellipse, a dumbbell shape or another symmetrical or asymmetrical contour that is derived from a mathematically ideal ellipse.

Since the laser beam hits the material of the workpiece at an angle of attack, different angles of incidence result for the partial laser beams for a focused beam or a non-diffracting beam. According to Snell's law of refraction, the partial laser beams are refracted to different extents due to the different angles of incidence. Accordingly, different amplitude, phase and direction variations result for individual partial laser beams in the material. This effect is called aberration. As a result, partial laser beams close to the edge, for example, cover a different optical path length to a focal point under the material surface than axial partial laser beams, which can result in phase differences, for example. Ultimately, this leads to the original intensity distribution of the laser beam being distorted, so that the introduction of a material modification is only possible on the length scale of a few micrometers, or is actually prevented or not at all.

An aberration correction device can correct these beam aberrations. For example, an optical wedge, such as a three-sided prism, may be oriented with a second side parallel to the surface of the workpiece and may rest on the workpiece or be at a small distance of up to one millimeter or up to 10mm above the surface of the material. The first side of the three-sided prism is in this case employed by the prism angle to the second side. In addition, the laser beam falls perpendicularly onto the first prism surface.

Because the laser beam is not or only slightly refracted when it enters the three-sided prism due to the vertical incidence, the laser beam is hardly refracted at the transition from the three-sided prism into the material of the workpiece because of the small difference in refractive index and because the propagation lengths in media with different refractive indices are reduced, the optical aberration is significantly reduced. Therefore, ideally, the distance from the prism to the material surface is kept as small as possible. Optical aberrations, in particular phase aberrations, can be described, for example, by astigmatism or coma, which originate in particular from the optical structure used to carry out the method. The aberration correction device can thus compensate for a large number of optical aberrations.

For this purpose, the first side of the aberration correction device in the beam propagation direction can have a cylindrical shape or be cylindrically curved. In particular, the effect of the first side of the aberration correction device thus corresponds to that of a cylindrical lens. A cylindrical lens breaks the laser beam in an asymmetrical way, so that the development of astigmatism and coma can be counteracted. The cylindrical lens can, for example, be a commercially available cylindrical lens, so that expensive custom-made products do not have to be used to implement the aberration correction device.

The second side of the aberration correction device can also have a cylindrical shape, but it can also be flat as in the example above. In any case, the second side of the aberration correction device is the last surface in the path of the laser beam before the laser pulses are introduced into the material of the workpiece. This rules out any further optical influence on the intensity distribution by optical elements in the beam path. Accordingly, with the aberration correction device, a higher and aberration-reduced laser beam shape can be made available in the material of the workpiece, so that high-quality material processing, in particular separation, can take place.

In particular, the aberration correction device can also be designed in one piece in the form of a cylindrical wedge.

As a result, the first side and the second side of the aberration correction device are provided with a single optical element, so that the adjustment effort, the device costs and the maintenance costs can be reduced

The material modifications introduced by the laser pulses can be type III modifications, which are associated with cracking of the transparent material.

As a result, predetermined breaking points can be produced in the material, or the material can be virtually perforated along the material modification surface. The formation of cracks promoted by the voids makes it possible for cracks to propagate between adjacent ones Material modifications can take place, as will be explained in more detail below. This crack formation preferably takes place in the material modification surface, so that the material modification surface becomes the parting surface.

Due to the non-radially symmetrical transverse intensity distribution, the material modification in the cross section perpendicular to the direction of beam propagation in the material also becomes non-radially symmetrical. The shape of the material modification corresponds to the intensity distribution of the non-diffracting beam in the material of the workpiece.

In the case of non-diffracting rays, there are in particular areas of high intensity that interact with the material and introduce material modifications, and areas that lie below the so-called modification threshold. The non-radially symmetrical transverse intensity distribution relates to the intensity maxima that are above the modification threshold.

The non-radially symmetrical Type III material modifications therefore have a preferred direction that runs parallel to the elongated axis of the material modifications. Crack formation or crack induction typically takes place along this preferred direction. For example, crack propagation occurs mainly in the direction of a long axis of an elliptical type III material modification, since the contour of the material modification has a smaller curvature there, so that the stress peaks relax here preferably in the form of a crack in the material.

In particular, targeted crack guidance can thus be favored by a corresponding orientation of the non-radially symmetrical material modifications in the material, so that, for example, crack formation is oriented tangentially to the parting line due to the orientation of the preferred direction.

For example, if the feed direction between the non-diffracting laser beam and the workpiece is parallel to the short axis of the transversal intensity distribution, it is unlikely that the cracks in neighboring material modifications will meet, since the crack formation tends to run perpendicular to the feed direction. On the other hand, if the feed direction is parallel to the long axis about which cracking occurs preferentially, then the cracks of adjacent material modifications are likely to meet and coalesce. Due to the orientation of the beam cross section and/or the workpiece, targeted crack guidance over the entire length of the dividing line can be ensured even with curved dividing lines. This makes it possible to separate the material along dividing lines of any shape. In this case, the separation along the material modification surface is carried out by a separation step, so that the workpiece is divided into the bulk part and the so-called section of the workpiece.

In this case, the separating step can comprise a mechanical separation and/or an etching process and/or a thermal treatment and/or a self-separation step.

A thermal impact can be, for example, heating of the material or the parting line. For example, the dividing line can be heated locally using a continuous wave CO2 laser, so that the material in the material modification area expands differently compared to the untreated or unmodified material. However, it can also be the case that thermal stress is implemented by means of a stream of hot air, or by baking on a hot plate, or by heating the material in an oven. In particular, temperature gradients can also be applied in the separation step. The cracks favored by the material modification experience crack growth as a result, so that a continuous and non-jammed separating surface can form, through which the parts of the workpiece are separated from one another.

A mechanical separation can be produced by applying a tensile or bending stress, for example by applying a mechanical load to the parts of the workpiece separated by the dividing line. For example, a tensile stress can be applied when opposite forces act on the parts of the workpiece separated by the dividing line in the material plane at one force application point each pointing away from the dividing line. If the forces are not aligned parallel or antiparallel to one another, this can contribute to the development of bending stress. As soon as the tensile or bending stresses are greater than the binding forces of the material along the interface, the workpiece is separated along the interface. In particular, a mechanical change can also be achieved by a pulsating effect on the part to be separated. For example, a lattice vibration can be generated in the material by an impact. The deflection of the lattice atoms can also generate tensile and compressive stresses that can trigger cracking.

The material can also be separated by etching with a wet-chemical solution, with the etching process preferably starting the material at the material modification, i.e. the targeted material weakening. Because the parts of the workpiece weakened by the material modification are preferably etched, this leads to the workpiece being separated along the separating surface. In particular, a so-called self-separation can also be carried out by targeted crack guidance through the orientation of the material modifications in the material. The formation of cracks from material modification to material modification enables the two parts of the workpiece to be separated over the entire surface without having to carry out a further separating step.

This has the advantage that an ideal cutting method can be selected for the respective material of the workpiece, so that a cutting of the workpiece is accompanied by a high quality of the cutting edge.

The material modifications can penetrate two sides of the workpiece, which lie in intersecting planes, and produce a shaped edge, preferably a chamfer and/or a bevel, through the separating step.

Two sides lie in intersecting planes if the face normals of the planes are not parallel to each other. For example, a box has two sides that lie in intersecting planes if the sides can be connected by an edge of the box. In the case of a disc-shaped material, the peripheral surface of the disc is, as it were, in an intersecting plane with the top and bottom of the disc. Viewed at least locally, a rectangular cross-section also results in a pane in the plane of incidence of the laser beam.

The material modifications penetrate both abutting sides. Penetration here means that the material modification begins on one side and ends on the other side in the direction of beam propagation. However, it can also mean that the material modification only runs within the material of the workpiece in order to avoid material breakouts on the surface. In this case, however, much of the path of the laser between the two sides must be modified with material modifications.

For example, strategically sensible positioning of the material modifications in the material may suffice to introduce material modifications on only one third of the distance. However, it is also possible that a material modification is continuous over the entire route between the pages.

This creates a section of the workpiece in the plane of incidence of the laser beam, in which the incident and the refracted beam lie. For example, in the case of a cuboid, this section can be triangular. A triangular section of the workpiece has a so-called hypotenuse, opposite the edge to be separated. The length of the hypotenuse is given by the length of the material modifications in the workpiece. In addition, the distance from a side adjoining the hypotenuse of the section is given by the distance from the dividing line to the edge of the workpiece.

With the material modifications penetrating two sides of the material, the predetermined breaking point is introduced over the entire length of the hypotenuse. As a result, in a subsequent separating step, the workpiece is separated along the material modification surface.

The material modification surface becomes the so-called shaped edge of the material after cutting. A shaped edge of the workpiece is subdivided into so-called chamfers and bevels. A chamfering of the workpiece is understood here as a folding in which the original edge of the cuboid is replaced by two edges. This softens the original edge or creates a transition area from a first cuboid side to a second cuboid side. On the other hand, a bevel is generated when either the hypotenuse of the section coincides with an edge of the workpiece or generally when one side of the triangular section coincides with at least one side length of the workpiece running parallel thereto.

The hypotenuse of the chamfer and/or the bevel can be between 50pm and 2mm.

This has the advantage that the workpiece can be chamfered in a way that is visually particularly appealing and appears to be of high quality. In addition, thicker workpieces can also be chamfered. By providing a shaped edge, a chamfer or a bevel, a more stable edge can also be achieved that does not chip off as easily as an edge with a 90° angle during further processing, installation or use by an end customer.

The laser beam can be a non-diffractive laser beam.

Non-diffracting rays and/or Bessel-like rays are to be understood in particular as rays in which a transverse intensity distribution is propagation-invariant. In particular, in the case of non-diffracting rays and/or Bessel-type rays, a transverse intensity distribution is essentially constant along a longitudinal direction and/or direction of propagation of the rays. A transversal intensity distribution is to be understood as meaning an intensity distribution which lies in a plane oriented perpendicularly to the longitudinal direction and/or direction of propagation of the beams. In addition, the intensity distribution is always understood to be that part of the intensity distribution of the laser beam that is greater than the modification threshold of the material. This can mean, for example, that only a few or just a few intensity maxima of the non-diffracting beam can introduce a material modification into the material of the workpiece. Accordingly, the word focal zone can also be used for the intensity distribution in order to make it clear that this part of the intensity distribution is provided in a targeted manner and that an intensity increase in the form of the intensity distribution is achieved by focusing.

With regard to the definition and properties of non-diffracting rays, reference is made to the book "Structured Light Fields: Applications in Optical Trapping, Manipulation and Organization", M. Wördemann, Springer Science & Business Media (2012), ISBN 978-3-642-29322- 1 referenced. This is expressly and fully referred to.

Accordingly, non-diffracting laser beams have the advantage that they can have an intensity distribution that is elongated in the direction of beam propagation and that is significantly larger than the transverse dimensions of the intensity distribution. In particular, material modifications that are elongated in the beam propagation direction can be produced as a result, so that they can penetrate two sides of the workpiece in a particularly simple manner.

In particular, non-diffracting beams can be used to generate elliptical non-diffracting beams that have a non-radially symmetrical transverse intensity distribution. Elliptical non-diffracting beams have special properties that result from the analysis of the beam intensity. For example, elliptical quasi-non-diffracting rays have a main maximum that coincides with the center of the ray. The center of the beam is given by the place where the main axes intersect. In particular, elliptical, quasi non-diffracting beams can result from the superimposition of a plurality of intensity maxima, in which case only the envelope of the intensity maxima involved is elliptical. In particular, the individual intensity maxima do not have to have an elliptical intensity profile.

In the projection of the non-radially symmetrical transverse intensity distribution onto the surface of the workpiece, the first axis and the second axis can appear to be of equal size due to the angle of incidence. The mathematical projection of the non-radially symmetrical transverse intensity distribution under the angle of attack onto the surface of the workpiece can lead to distortions of the intensity distribution. For example, an originally elliptical intensity distribution can result in a round intensity distribution on the workpiece. In particular, however, it can also be achieved in this way that an elliptical projection is realized on the surface of the workpiece by means of an originally round intensity distribution. As a result, material modifications are introduced into the material, which have the intensity distribution that result from the projection at the angle of attack onto the surface of the workpiece.

However, it is also possible that the projection of a previously selected preferred direction distorts the non-radially symmetrical transverse intensity distribution and the preferred direction thus deviates from the actually effective intensity distribution.

In one embodiment, it is therefore preferred that the non-radially symmetrical transverse intensity distribution appears round due to the angle of attack. In particular, this means that in the case of an originally elliptical transverse intensity distribution, the long axis A and the short axis B of the ellipse appear to be of equal size due to the projection. As a result, a round intensity distribution effectively acts to generate the material modifications.

The projection of the non-radially symmetrical intensity distribution onto the surface of the workpiece can be elongated in the feed direction.

This makes it possible to control the distortion by projecting the intensity distribution onto the surface of the workpiece in such a way that the preferred direction of the effective beam profile points in the feed direction. Since the preferred direction points in the direction of the feed direction and thus runs parallel to the separating line, the workpiece can be separated particularly easily and with particularly high quality along the resulting material modification surface.

The ratio of the first axis to the second axis of the non-radially symmetric transverse intensity distribution may be greater than the reciprocal of the cosine of the angle of attack.

Suppose a laser beam is incident on a surface at the angle of incidence where the first axis of the transverse intensity distribution is parallel to the surface of the workpiece and perpendicular to the plane of incidence of the laser beam and the second axis is in the plane of incidence. Furthermore, let the first axis be the long axis and the second axis the short axis of the non- radially symmetric transverse intensity distribution. Then, by projecting the second axis onto the surface of the workpiece, the effective length is increased by a factor of the reciprocal of the angle of attack.

For example, if the second axis is 10pm and the angle of incidence is 60°, then the projection of the second axis onto the surface of the workpiece is 10pm / cos (60°) = 20pm.

Furthermore, the first axis of the transverse intensity distribution is not enlarged by the projection, since it is perpendicular to the plane of incidence. Accordingly, the beam profile has a first axis of equal size.

For example, if the first axis in the example above is 20pm, then after the projection it will also be 20pm. Overall, however, this results in a round beam shape on the surface of the workpiece.

For example, if the first axis in the example above is 15pm, then after the projection it is also 15pm, but the second axis has grown to 20pm. Material modifications are thus produced which have a preferred direction which lies in the plane of incidence of the laser beam. In particular, the preferred direction has rotated from the first axis to the second axis as a result of the projection.

Choosing the ratio of the first to the second axis, which is greater than the reciprocal of the cosine of the angle of attack, ensures that the originally intended orientation of the intensity distribution is retained even when the beam is projected onto the surface of the workpiece.

The ratio of the first axis to the second axis can be greater than V2.

This ensures, in particular at an angle of attack of 45°, that the originally intended alignment of the transversal intensity distribution is retained. In particular, 1 Zcos(45°) = V2 applies, so that the axis ratio is chosen accordingly. As a result, the preferred direction is retained by the material modification even when the beam is projected onto the surface of the workpiece.

The pulse energy of the laser pulses can be between 10pJ and 50mJ, and/or the average laser power can be between 1W and 1 kW, and/or the laser pulses can Individual laser pulses or part of a laser burst and/or the wavelength of the laser can be between 300 nm and 1500 nm, in particular 1030 nm.

This has the advantage that optimal laser parameters can be provided for different materials.

For example, the ultra-short pulse laser can provide single laser pulses with a pulse energy of 100pJ, with the average laser power being 5W and the wavelength of the laser being 1030nm.

A laser burst can comprise 2 to 20 laser pulses, with the laser pulses of the laser burst having a time interval of 10 ns to 40 ns, preferably 20 ns.

For example, a laser burst can include 10 laser pulses and the time interval between the laser pulses can be 20 ns. In this case, the repetition frequency of the laser pulses is 50 MHz. In this case, the laser bursts can be emitted with the repetition frequency of the individual laser pulses in the order of 100 kHz.

By using laser bursts, the material-specific thermal properties can be addressed, so that a shaped edge with a particularly high surface quality can be produced.

The incident laser beam can be polarized parallel to the plane of incidence.

The refraction of the laser beam at the transition from the surrounding medium to the material does not only depend on the angle of attack and the refractive indices. The polarization of the laser beam also plays a major role here. The so-called Fresnel equations can be used to show that the transmission of a laser beam polarized parallel to the plane of incidence through a material for an angle of incidence of more than 10° is always greater than the transmission of a laser beam polarized perpendicular to the plane of incidence.

In particular, with P-polarization, reflection losses of the laser beam can be minimized in order to achieve an optimal energy yield for the cutting process in the material. In addition, a particularly advantageous coupling of energy into the material can be achieved when the laser beam is incident at the Brewster angle. The object set above is also achieved by a device for separating a workpiece having the features of claim 9 . Advantageous developments result from the dependent claims, the description and the figures.

Accordingly, a device for separating a workpiece comprising a transparent material is proposed, comprising an ultra-short pulse laser that is set up to provide ultra-short laser pulses, processing optics that are set up to introduce the laser pulses into the transparent material of the workpiece, and a feed device that is set up to do so is to move the laser beam from laser pulses and the workpiece relative to each other along a dividing line with a feed and to orient the optical axis of the processing optics relative to the surface of the workpiece at an angle of incidence. According to the invention, an aberration correction device is set up to reduce the aberration of the laser pulses when they enter the material of the workpiece, the laser pulses being applied to the workpiece at an angle of attack and the laser beam having a non-radially symmetrical transverse intensity distribution, the transverse intensity distribution being in a first Axis appears elongated compared to a second axis, the second axis being perpendicular to the first axis.

Processing optics can be an optical imaging system, for example. For example, processing optics can consist of one or more components. A component can be a lens, for example, or an optically imaging free-form surface or a Fresnel zone plate. In particular, the depth of insertion of the intensity distribution into the material of the workpiece can be determined by the processing optics. To a certain extent, the placement of the focal zone in the direction of beam propagation can be adjusted. For example, by adjusting the processing optics, a focus zone can be placed on the surface of the workpiece, or preferably placed in the material of the workpiece. For example, the focus zone can be set in such a way that the laser beam penetrates two adjacent sides, thus resulting in a material modification that allows the workpiece to be separated over the entire surface by means of one separating step.

The feed device can be an XY or an XYZ table, for example, in order to vary the point of impact of the laser pulses on the workpiece. In this case, the feed device can move the workpiece and/or the laser beam in such a way that the material modifications can be introduced next to one another into the material of the workpiece along the parting line. A feed device can also have an angular adjustment, so that the workpiece and the laser beam can be rotated through all Euler angles relative to one another. In this way it can be ensured in particular that the angle of attack can be maintained along the entire dividing line.

In particular, the angle between the optical axis of the processing optics and the surface normal of the material of the workpiece is also understood as the setting angle. The setting angle of the optical axis of the processing optics and the surface normal can be between 0 and 60°, for example.

Beam shaping optics can form a non-diffracting laser beam from the laser beam.

The beam shaping optics can be designed, for example, as a diffractive optical element (DOE), a free-form surface in a reflective or refractive design, or an axicon or a microaxicon, or contain a combination of several of these components or functionalities. If the beam shaping optics forms a non-diffracting laser beam from the laser beam in front of the processing optics, then the depth of penetration intensity distribution into the material can be determined by focusing the processing optics. However, the beam shaping optics can also be designed in such a way that the non-diffracting laser beam is only generated by imaging with the processing optics.

A diffractive optical element is set up to influence the incident laser beam in one or more properties in two spatial dimensions. A diffractive optical element is a fixed component that can be used to produce exactly one intensity distribution of a non-diffracting laser beam from the incident laser beam. Typically, a diffractive optical element is a specially shaped diffraction grating, whereby the incident laser beam is brought into the desired beam shape by the diffraction.

An axicon is a conically ground optical element that forms a non-diffracting laser beam from an incident Gaussian laser beam as it passes through. In particular, the axicon has a cone angle α, which is calculated from the beam entry surface to the lateral surface of the cone. As a result, the edge rays of the Gaussian laser beam are refracted to a different focal point than rays close to the axis. This results in particular in an intensity distribution that is elongated in the beam propagation direction. The transverse intensity distribution of the non-diffractive laser beam can be non-radially symmetric, wherein the non-radially symmetric transverse intensity distribution can be elongated in a first axis compared to a second axis, and the second axis is perpendicular to the first axis.

The processing optics can include the aberration correction device.

This means that the aberration correction device with the processing optics can be moved relative to the material in order to introduce the material modifications into the material of the workpiece.

In particular, this can also mean that the aberration correction device can also be part of the processing optics and can therefore also take over tasks of a processing optics, in particular can provide optical images of the laser beam. The aberration correction device can therefore also be designed as an integral part of the processing optics and not just as a separate correction element in the beam path.

In contrast to a sacrificial wedge fixed to the material, more flexible material processing can be achieved with an appropriately shaped aberration correction device.

The processing optics can include a telescope system which is set up to introduce the laser beam into the material of the workpiece in a reduced and/or enlarged manner.

Enlarging and/or reducing the laser beam or its transverse intensity distribution allows the laser beam intensity to be distributed over a large or small focal zone. The intensity is adjusted by distributing the laser energy over a large or small area, so that it is possible to choose between modification types I, II, and III, in particular by enlarging and/or reducing the size.

In particular, enlarged or reduced material modifications can also be introduced into the material of the workpiece by enlarging or reducing the non-radially symmetrical transverse intensity distribution. Because the, for example, an elliptical transverse intensity distribution is introduced into the material in reduced form, the radius of curvature of the material modifications introduced thereby is also reduced. In other words, a given curvature becomes more acute as it decreases. This can promote the formation of cracks in the material of the workpiece. In addition, through an enlargement or a Reduction, the optical system can be adapted to the given processing conditions, so that the device can be used more flexibly.

The feed device can comprise an axis device and a workpiece holder, which are set up to move the processing optics and the workpiece along three spatial axes in a translatory manner and in a rotary manner about at least two spatial axes.

An axis device can be a 5-axis device, for example. For example, the axis device can also be a robotic arm that guides the laser beam over the workpiece or moves the workpiece relative to the laser beam.

Since the laser beam and the workpiece are moved relative to each other in order to be able to introduce the material modifications along the dividing line, maintaining the angle of incidence relative to the dividing line requires that the laser beam or the workpiece also be rotated locally. In the case of a curved parting line, for example, it is possible for the material modification surface to always have the same angle to the surface of the workpiece.

In particular, such an axis device also makes it possible at the same time to orient a non-radially symmetrical transverse intensity distribution relative to the dividing line, so that material modifications are produced whose preferred direction runs parallel to the dividing line and promote crack formation along it.

Furthermore, an axis device can also comprise fewer than 5 movable axes, as long as the workpiece holder can be moved about the corresponding number of axes. If, for example, the axis device can only be displaced in XYZ directions, then the workpiece holder can have two rotary axes, for example, in order to rotate the workpiece relative to the laser beam.

The beam components of the laser beam can hit the workpiece at a maximum angle of incidence of 80° to the surface normal of the workpiece.

Through the processing optics, the laser pulses converge to the optical axis, which is oriented at the angle of incidence to the surface normal of the workpiece. The partial laser beams of the beam bundle are at an angle to the optical axis of the processing optics. In particular, these angles can have very large or very small angles due to the numerical aperture. Since these enveloping partial laser beams of the laser beam bundle do not fall on the surface of the workpiece at an angle of more than 80°, large reflection losses can be avoided. According to the Fresnel formulas, the reflection and transmission of the laser beam on the surface of the workpiece depends on the angle of incidence and the refractive index. In the case of a grazing incidence of the laser beam, only a small amount of laser light can couple into the material, so that effective material processing is not possible. In addition, this can adversely affect the shape of the non-diffracting beam.

Polarization optics, preferably comprising a polarizer and a wave plate, can be set up to adjust the polarization of the laser beam relative to the plane of incidence of the laser beam, preferably parallel to the plane of incidence.

A wave plate, in particular a so-called lambda/2 plate, can rotate the direction of polarization of linearly polarized light by a selectable angle. This makes it possible to bring the laser beam into a desired polarization.

A polarizer can be a thin-film polarizer, for example. The thin-film polarizer only transmits laser radiation of a specific polarization.

The state of polarization of the laser radiation can therefore always be controlled by a combination of wave plate and polarizer.

According to the Fresnel formulas, polarization of the laser beam parallel to the plane of incidence has the advantage that the transmission for an angle of incidence of more than 10° is always greater than when the laser beam is polarized perpendicularly to the plane of incidence. In particular, the transmission in the case of a parallel polarized laser beam is more constant and more uniform over a large range of angles of incidence than in the case of perpendicularly polarized light. As a result, processing optics that have a large numerical aperture can also be used. In the case of a vertically polarized laser beam, an asymmetrical beam reflection would occur on the surface of the workpiece, so that optical aberrations degrade the quality of the material modifications and thus the quality of the interface.

A beam guidance device can be set up to guide the laser beam to the workpiece, with the beam being guided via a mirror system and/or an optical fiber, preferably a hollow-core fiber. A so-called free beam guidance uses a mirror system to guide the laser beam of a stationary ultrashort pulse laser in different spatial dimensions to the beam shaping optics. A free beam guidance has the advantage that the entire optical path is accessible, so that, for example, further elements such as a polarizer and a wave plate can be installed without any problems.

A hollow core fiber is a photonic fiber that can flexibly transmit the laser beam of the ultrashort pulse laser to the beam shaping optics. The hollow-core fiber eliminates the need to adjust mirror optics.

Control electronics can be set up to trigger a laser pulse emission of the ultrashort pulse laser based on the relative positions of the laser beam and the workpiece.

In the case of curved or angular feed trajectories, it can make sense to reduce the feed rate locally. With a constant repetition frequency of the laser, however, this can lead to neighboring material modifications overlapping or the material being unintentionally heated and/or melted. For this reason, control electronics can regulate the pulse output depending on the relative position of the laser beam and the workpiece.

For example, the feed device can have a position-resolving encoder that measures the position of the feed device and the laser beam. Based on the location information, the pulse output of a laser pulse can be triggered in the ultra-short pulse laser via a corresponding triggering system of the control electronics.

In particular, computer systems can also be used to implement the triggering of the pulse. For example, the locations of the laser pulse emission can be specified for the respective dividing line before the material is processed, so that an optimal distribution of the material modifications along the dividing line is ensured.

This ensures that the distance between the material modifications is always the same, even if the feed rate varies. In particular, this also means that a uniform parting surface can be produced and the chamfer or bevel has a high surface quality.

The workpiece holder can have a surface that does not reflect and/or scatter the laser beam. In particular, this can prevent the laser beam from being guided into the material again after it has penetrated the material and again causing a material modification there. In particular, a non-reflecting and/or non-scattering surface can also increase occupational safety.

Brief description of the figures

Preferred further embodiments of the invention are explained in more detail by the following description of the figures. show:

Figure 1A, B, C, D, E is a schematic representation of the process;

FIG. 2A, B, C shows a schematic representation of chamfer and bevel structures;

FIG. 3A, B, C, D, E, F another schematic representation of chamfer and bevel structures;

Figure 4A, B, C, D, E, F is a schematic representation of the non-diffractive laser beam and the principle of operation of the aberration correction device;

Figure 5A, B, C, D, E is another schematic representation of non-diffracting laser beams;

FIG. 6A, B shows a schematic representation of the formation of cracks around a material modification;

Figure 7A, B is a schematic representation of the beam projection on the

material surface;

Figure 8A, B, C, D another schematic representation of the beam projection on the

material surface;

FIG. 9 is a graph showing the transmission as a function of

polarization and angle of attack;

Figure 10A, B is a schematic representation of the device for performing the

method with aberration correction device; and

Figure 11 A, B, C further schematic representations of the device for carrying out the

procedure. Detailed description of preferred embodiments

Preferred exemplary embodiments are described below with reference to the figures. Elements that are the same, similar or have the same effect are provided with identical reference symbols in the different figures, and a repeated description of these elements is sometimes dispensed with in order to avoid redundancies.

FIG. 1 schematically shows the method for separating a workpiece 1 comprising a transparent material. FIG. 1A shows a cross section of a workpiece 1 onto which the laser beam 20 of an ultrashort pulse laser 2 is incident. In this case, the laser beam 20 is introduced onto the workpiece 1 at an angle of attack a, which corresponds to the optical axis of the processing optics 3 shown later.

The laser beam 20 is refracted at the surface 10 of the workpiece 1 according to Snell's law of refraction during the transition into the workpiece 1, so that the laser beam 20 continues in the material of the workpiece 1 at the angle β to the surface normal N. By introducing the laser pulses into the workpiece 1 via the laser beam 20 , the material of the workpiece 1 is heated in the focal zone 220 of the laser beam 20 . The material of the workpiece 1 is vaporized in the focus zone, so that this plasma state expands explosively into the surrounding material of the workpiece 1 . Due to the compression at the impact front of this so-called microexplosion, material stresses occur there, while a less dense or even empty space (void) remains in the original focus zone 220 of the laser beam. The modification of the material of the workpiece 1 in the focal zone 220 is called material modification 5, the material modification 5 being in particular a type III material modification. Finally, as a result of the material stresses, cracking in the material of the workpiece 1 is promoted.

The pulse energy of the laser pulses can be between 10pJ and 50mJ, and/or the average laser power can be between 1W and 1 kW, and/or the laser pulses can be individual laser pulses or part of a laser burst and/or the wavelength of the laser can be between be 300nm and 1500nm in size. It can also be the case that a laser burst comprises 2 to 20 laser pulses, with the laser pulses of the laser burst having a time interval of 10 ns to 40 ns, preferably 20 ns.

While the ultrashort pulse laser 2 emits laser pulses, the laser beam 20 and the workpiece 1 are moved relative to one another with a feed rate V, as shown in FIG. 1B. This advance V is guided along a parting line 4, which determines where the workpiece 1 is to be parted on the upper side 10. Because the laser beam 20 propagates in the material of the workpiece 1 at the angle β, the material modification 5 is also introduced into the material of the workpiece 1 at the angle β. In particular, the material modifications 5 can be shaped differently depending on the extent and shape of the focal zone 220 or the intensity distribution, in particular they can be elongated in the beam propagation direction.

In the case of a material modification 5 that is elongated in the direction of beam propagation, a so-called material modification surface 50 is produced in the material of the workpiece 1 by the simultaneous feed V of the laser beam 20, in which the material modification 5 lies. It must be taken into account here that the material modifications 5 do not overlap but are separate from one another. The workpiece 1 is separated into the so-called bulk workpiece T and the so-called section 12 by the material modification surface 50 . For example, the material modification surface 50 can be inclined at an angle β of up to 35° relative to the surface 10 of the workpiece 1 .

The material of the workpiece 1 is perforated to a certain extent by the material modifications 5 in the material modification area 50 , so that the workpiece 1 and the section 12 can be separated particularly easily along this material modification area 50 .

The actual separation can be realized by specific separation steps. For example, spontaneous crack growth can be initiated by a mechanical action on the section 12, so that the section 12 can be separated from the bulk workpiece T over a large area.

Section 12 may also be separated from bulk workpiece T in a chemical bath, as shown in Figure 1C. For example, it may be that the material modifications 5 introduced are particularly susceptible to an etching solution, so that the etching process in the material modification area 50 separates the section 12 from the bulk workpiece T. FIG.

For example, it can also be the case that the section 12 is separated from the bulk workpiece T as a result of a thermal effect, as shown in FIG. 1D. For this purpose, the workpiece 1 is heated, for example, with a heating plate 42 or a heating laser (not shown), so that the workpiece 1 undergoes thermal expansion. Due to the thermal expansion of the workpiece 1, cracks can form due to the material stresses already present in the material modification surface 50, so that the bulk workpiece T and the section 12 are separated from one another over the entire surface. It is also possible for the workpiece 1 to separate due to spontaneous crack formation, so-called self-separation, without external influence. The material modifications of type III introduce material stresses into the workpiece 1 which are already associated with crack formation per se. The bulk workpiece 1 and the section 12 can accordingly already be separated as a result of this spontaneous crack formation.

As a result of the separating step described above, a so-called chamfer and/or a bevel is formed on the bulk workpiece T, as shown in FIG. 1E. The edging of the workpiece 1 is also known as a shaped edge of the workpiece 1 . The chamfer or bevel are formed by the material modification surface 50, so that the angle of incidence α of the laser beam 20, the refractive indices of the surrounding medium and the workpiece 1 result in the angle of refraction ß and thus also the alignment of the material modifications 5 and finally the chamfer or bevel.

In order to produce a shaped edge 14, it is advantageous if the material modification 5 penetrates those sides of the workpiece 1 which form the edge to be chamfered. For example, in Figure 1A, sides 10 and 11 form edge 110 to be chamfered. The sides 10 and 11 of the workpiece 1 lie in particular in spatial planes which intersect, the line of intersection of the planes being the edge 110 of the workpiece 1 .

Various possible shaped edges of the material are shown in Figures 2A to 2C. In Figure 2A, the material modification surface 50 intersects the workpiece 1 with the height of the chamfer being less than the height of side 11 and the width of the chamfer being less than side 10. Accordingly, the chamfering replaces the edge 110 with two edges 110' and 110''. As a result, the original edge 110 in particular is blunted or flattened.

In Figure 2B, the material modification surface 50 intersects the workpiece 1, with the height of section 12 corresponding to the height of side 11, and the material modification surface 50 and the edge 130 formed by the underside 13 of workpiece 1 and side 11 coincide. In this example, the number of edges remains constant, but the angle at which sides 13 and 11 meet becomes more acute. Accordingly, the workpiece 1 can be sharpened and/or pointed by forming a bevel 12 .

In Figure 2C, the material modification surface 50 cuts the workpiece 1, wherein the

Material modification surface both the top 10 and the bottom 13 of the workpiece 1 cuts. As a result, the length of the workpiece 1 is reduced overall and the workpiece 1 is also sharpened, as in FIG. 2B.

In each case shown, the so-called hypotenuse H of section 12 is given by the length of the material modifications in the material.

Even if the previous description has been reduced to the cutting of cuboids, it is also possible to cut round materials 1 or rounded materials with the method. For example, in Figure 3A, B a workpiece 1 is shown in the form of a disc. The so-called plane of incidence is defined by the laser beam 20 incident at the angle of incidence α and the laser beam 20 refracted at the angle β. At this level of inspiration, the previous description can be taken over verbatim.

FIG. 3C also shows that the chamfering of the disk from FIGS. 3A, B leads to a conically tapering element, so that it is possible to produce a wide variety of shapes on shaped edges through the material modifications 5 introduced.

Another example is shown in Figure 3D. Material modifications 5 were introduced circumferentially into the workpiece 1, with the parting line 4 being curved and the angle of attack a in the plane of incidence always being kept constant. This results in a rounded chamfer or bevel after the separation step, which has a high optical quality.

Another example is shown in Figure 3E. In contrast to FIG. 3D, no rounded dividing line 4 was used here. The workpiece 1 was successively chamfered on all four sides, so that a crystal-shaped chamfer results at the corners of the workpiece 1 after the cutting step. The method is therefore also suitable for giving the workpiece 1 a qualitatively particularly high-quality impression.

FIG. 3F shows the cross section of the materials 1 from FIGS. 3D and 3F. The cross section clearly shows the formation of a chamfer 14.

So-called non-diffracting laser beams 20 are suitable for producing material modifications 5 in a particularly simple manner, which penetrate the workpiece 1 at least in sections. Since the length L of the focal zone 220 is greater than the length of the desired hypotenuse H of the section 12, the workpiece 1 can be chamfered in a particularly simple and effective manner. In FIG. 4A, a laser beam 20 processed by beam-shaping optics is shown schematically. The partial laser beams 200 of the laser beam 20 fall on the workpiece 1 at an angle α′ to the optical axis 30 , each partial laser beam 200 being refracted according to its angle α′ to the optical axis 30 . Overall, however, the optical axis 30 in this example of the laser beam 20 is perpendicular to the surface 10 of the workpiece 1, so that the angle of incidence is 0°. The partial laser beams 200 are superimposed in the workpiece 1 to form a non-diffracting beam which has an elongated focal zone 220 with the length L. FIG.

In Figure 4B, the same beam is shown schematically as in Figure 4A, but with a non-vanishing angle of attack a and with an aberration correction device 7. In the example shown, the aberration correction device 7 is a so-called cylinder wedge 70, the first side 700 of which is cylindrical and the second side 702 is planar is trained. As a result, the optical aberrations that arise when the laser beam 20 is introduced into the material of the workpiece 1 are significantly reduced. However, it is also possible for the aberration correction device 7 to have a multi-part design, with the first side 700 being provided by a first cylindrical lens and the second side 702 being provided by a second optical element, for example a second cylindrical lens or a concave-planar lens or a convex one -plan lens.

The various longitudinal intensity distributions that can be achieved by using an aberration correction device 7 are shown in FIGS. 4C to 4F. FIG. 4C shows the longitudinal intensity distribution of a non-diffracting laser beam 20 with vertical incidence, that is to say with a vanishing angle of incidence a, on the workpiece 1. The intensity distribution that is elongated in the beam propagation direction makes it possible to produce material modifications 5 that are elongated in the beam propagation direction and penetrate, for example, sides 10, 11 of the workpiece 1 that are in contact with one another. However, as soon as the laser beam 20 is switched on without an aberration correction device 7, as shown in FIG. 4D for a=15°, the partial laser beams 200 begin to diverge in the material of the workpiece 1. When the laser beam 20 strikes obliquely, i.e. at a non-vanishing angle of incidence α, aberrations occur in the material since the upper half of the beam falls on the workpiece 1 at an angle a+a′ and the lower half of the beam at an angle aa′. As a result, the focus zone 220 can be shortened or distorted, as can be seen clearly in comparison with FIG. 4C. Furthermore, the laser beam 20 begins to fray after the focal zone 220, whereas the intensity only decreases in FIG. 4C. FIG. 4E shows the longitudinal intensity distribution for a non-diffracting laser beam for an angle of incidence of a=35°. The laser beam 20 is no longer able to penetrate the material here of the workpiece 1 to form a focal zone 220 which allows the introduction of a material modification 5 into the workpiece. However, if the aberration correction device 7 from FIG. 4B is placed in the beam path of the laser beam in front of the material of the workpiece 1 for the same angle of incidence a=35°, the longitudinal intensity distribution of the non-diffracting beam can be produced for an angle of incidence of a=0° from FIG. 4C . The aberration effects are significantly reduced here, so that a high-quality separating surface can be produced.

FIG. 5A shows the transverse intensity distribution or the focal zone 220 of a non-diffracting laser beam 20. The non-diffracting laser beam 20 is a so-called Bessel-Gaussian beam, with the transverse intensity distribution being radially symmetrical in the x-y plane, so that the intensity of the non-diffracting laser beam 20 only depends on the radial distance from the optical axis 30 . In particular, the diameter of the transverse intensity distribution is between 0.25 pm and 10 pm. FIG. 5B shows the longitudinal beam cross section, ie the longitudinal intensity distribution. The longitudinal intensity distribution shows an elongated region of high intensity, about 3mm in size. The longitudinal extent of the focal zone 220 is thus significantly larger than the transverse extent.

Analogously to FIG. 5A, FIG. 5C shows a non-diffracting laser beam which has a non-radially symmetrical transverse intensity distribution. In particular, the transverse intensity distribution in the y-direction appears stretched and almost elliptical. The longitudinal intensity distribution of the laser beam 20 is shown in FIG. 5D, the focus zone 220 again having an extent of L=3 mm. FIG. 5E shows an enlarged section of the transversal intensity distribution from FIG. 5C, the different intensity maxima resulting from the superimposition of the different partial laser beams 200. FIG. In particular, the focal zone 220 is significantly elongated in the horizontal direction A compared to the vertical direction B, with both directions being perpendicular to one another.

If a laser beam 20 with such a focal zone 220 is introduced into the workpiece 1, the resulting material modification 5 has the same shape. This is shown in Figure 6A. In particular, the material modification 5 thereby has a pointed side and a flat side, the pointed sides being found in the long axis A direction and the blunt sides being found in the short axis B direction. Cracking 52 through the material modification 5 is achieved in the direction of the long axis A, since the stress peaks are greatest there. Accordingly, it is preferred that the long axis A of the non-radially symmetrical transverse intensity distribution is oriented along the dividing line 4 , for example oriented tangentially to the dividing line 4 , so that the induced cracking follows the dividing line 4 . If, as in FIG. 6B, the material modifications 5 are now oriented on the dividing line 4 so that the cracks 52 of adjacent material modifications 5 overlap, then the bulk workpiece T and section 12 can self-separate. If the material modifications 5 are further apart, a separation step may be necessary, as described above.

If a laser beam 20 with a round or a non-radially symmetrical transverse intensity distribution is projected onto a surface 10 of the workpiece 1 at an angle of incidence α, then the intensity distribution is distorted in the plane of incidence. This is shown in Figure 7. In FIG. 7A, B, the laser beam 20 impinges on the surface 10 of the workpiece 1 with a non-radially symmetrical transverse intensity distribution. It can thereby be achieved that the formation of cracks 52 will preferably run in the feed direction V. However, due to the projection of the short axis B onto the surface 10, the intensity of the short axis B is distributed over the length B/cos a, so that the short axis B becomes longer as a result of the projection as the angle of attack increases. In particular, the case can be achieved in this way that the projection of the short axis B corresponds to the length of the long axis A. The material modification 5 that is produced then no longer has a preferred direction for crack formation.

For example, at an angle of attack of 45°, the short axis increases to V2ß. Therefore, if the ratio A/B before the projection is greater than V2, the orientation of the long axis A relative to the dividing line 4 is retained during the projection.

Further examples of the influence of the projection are shown in FIG. FIG. 8A shows a Bessel-Gauss beam from FIG. 5A perpendicularly incident on the surface 10 of the workpiece 1. FIG. With a non-vanishing angle of incidence a, shown in FIG. 8B, the radially symmetrical intensity distribution on the surface 10 of the workpiece 1 becomes an intensity distribution that is elongated in one direction, so that the material modifications 5 resulting therefrom have a preferred direction. Accordingly, a preferred direction of the material modification 5 can be set or changed by the projection of the laser beam 20 onto the surface 10 of the workpiece 1 . FIG. 8C shows the Bessel beam from FIG. 5C. Due to the projection onto the surface 10 of the workpiece 1, the orientation of the long axis A is retained, so that the orientation of the preferred direction of crack propagation of the resulting material modification 5 does not change. The A/B is smaller than the reciprocal of the cosine of the angle of attack a.

The laser beam 20 can in particular be polarized, preferably polarized parallel to the plane of incidence, in order to minimize reflection losses. FIG. 9 shows the transmission of laser radiation through a workpiece 1 with parallel and perpendicular polarization to the plane of incidence according to Fresnel's formulas. In this case, the angle of attack a is shown in particular on the X-axis, but the partial laser beams 20 according to FIG. 4A have a convergence angle a' relative to the optical axis 30.

For example, at an angle of attack a=50° and a convergence angle of a −20°, the partial laser beams 200 fall on the surface 10 of the workpiece 1 in an angular range from a−a −30° to a+a′=70° parallel incidence between 96% and 94% while at normal incidence it varies between 95% and 70%. The variation for laser beams 20 polarized perpendicularly to the plane of incidence is therefore significantly greater than for light polarized parallel to the plane of incidence. In order to reduce reflection losses, it is therefore particularly advantageous if the partial laser beams 200 strike the workpiece 1 at an angle of less than 80° to the normal N to the surface.

FIG. 10A shows an embodiment of the device for carrying out the method. In this case, the laser pulses are provided by the ultra-short pulse laser 2 and are directed through polarization optics 32 through beam-shaping optics 34 . The laser beam 20 is directed to the aberration correction device 7 by the beam shaping optics 34 , the optical axis 30 of the processing optics 3 being oriented at the angle of incidence α to the surface normal N of the workpiece 1 .

In this case, the polarization optics 32 can comprise a polarizer, which polarizes the laser beam 20 emitted by the ultrashort pulse laser 2, so that it only has a well-defined polarization. A subsequent lambda/2 plate can then finally rotate the polarization of the laser beam 20 in such a way that the laser beam 20 can be introduced into the workpiece 1 preferably polarized parallel to the plane of incidence.

In the example shown, the beam-shaping optics 34 are an axicon in order to shape the incident laser beam 20 into a non-diffracting laser beam. However, other elements can be substituted for the axicon to create a non-diffracting beam. The axicon generates from the preferably collimated input beam, a conically tapering laser beam 20. The beam-shaping optics 34 can also impress the incident laser beam 20 with a non-radially symmetrical intensity distribution.

Finally, the non-diffracting laser beam 20 is introduced into the material of the workpiece 1 via the aberration correction device 7 .

An alternative embodiment is shown in Figure 10B. Here, the non-diffracting laser beam is imaged in the workpiece 1 via a telescopic optics 36, which here consists of two optical elements 360, 362, with the image being able to be an enlarging or a reducing image. In particular, the aberration correction device 7 is part of the processing optics or of the second optical element 362.

In both FIGS. 10A, B, the cylindrical side of the aberration correction device 7 is also the first side 700 in the beam propagation direction. In addition, the second side 702 is flat and is the last surface in the beam path of the laser beam 20 before the laser beam 20 is introduced into the material of the workpiece 1. This can prevent further aberrative influence of subsequent optical elements.

In addition, the aberration correction device 7 is installed in a slide-in cassette 72 so that it can be changed. If the aberration correction device 7 is arranged close to the focal zone 22, it can be exposed to particularly high thermal loads, so that it is damaged or modified itself as the processing time progresses. In order to enable the aberration correction device 7 to be changed easily, an aberration correction device 7 can be changed via a slide-in cassette 72 without the optical adjustment having to be carried out from scratch. However, the optical adjustment is preferably retained.

FIG. 11A shows a feed device 6 which is set up to move the processing optics 3 and the workpiece 1 in a translatory manner along three spatial axes and to move them in a rotary manner about two spatial axes. The laser beam 20 of the ultra-short pulse laser 2 is directed onto the workpiece 1 by processing optics 3 . In this case, the workpiece 1 is arranged on a support surface of the feed device 6 , the support surface preferably neither reflecting nor absorbing the laser energy, which the material does not absorb, nor strongly scattering it back into the workpiece 1 . In particular, the laser beam 20 can be coupled into the processing optics 3 by a beam guidance device 38 . Here, the beam guiding device can be a free-space path with a lens and mirror system, as shown in FIG. 11A. However, the beam guidance device 38 can also be a hollow-core fiber with coupling-in and coupling-out optics, as shown in FIG. 11B.

In the present example in FIG. 11A, the laser beam 20 is guided in the direction of the workpiece 1 by a mirror construction and introduced into the workpiece 1 by the processing optics 3 . The laser beam 20 causes material modifications 5 in the workpiece 1. The processing optics 3 can be moved and adjusted relative to the material with the feed device 6, so that, for example, a preferred direction or an axis of symmetry of the transverse intensity distribution of the laser beam 20 can be adapted to the feed trajectory and thus the dividing line 4 .

In this case, the feed device 6 can move the workpiece 1 under the laser beam 20 with a feed rate V, so that the laser beam 20 introduces material modifications 5 along the desired parting line 4 . In particular, in the shown FIG. 11A, the feed device 6 has a first axis system 60, with which the workpiece 1 can be moved along the XYZ axes and, if necessary, rotated. In particular, the feed device 6 can also have a workpiece holder 62 which is set up to hold the workpiece 1 . If necessary, the workpiece holder can also have degrees of freedom of movement, so that the long axis of a non-radially symmetrical transverse intensity distribution can always be oriented perpendicularly to the beam propagation direction tangentially to the desired dividing line 4 .

For this purpose, the feed device 6 can also be connected to control electronics 64 , the control electronics 64 converting the user commands of a user of the device into control commands for the feed device 6 . In particular, predefined cutting patterns can be stored in a memory of the control electronics 64 and the processes can be automatically controlled by the control electronics 64 .

The control electronics 64 can in particular also be connected to the ultrashort pulse laser 2 . The control electronics 64 can request or trigger the output of a laser pulse or laser pulse train. The control electronics 64 can also be connected to other components mentioned and thus coordinate the material processing. In particular, a position-controlled pulse triggering can be implemented in this way, with an axis encoder 600 of the feed device 6 being read out, for example, and the axis encoder signal being able to be interpreted by the control electronics 64 as location information. It is thus possible for the control electronics 64 to automatically trigger the delivery of a laser pulse or laser pulse train if, for example, an internal adder unit that adds the distance covered reaches a value and resets itself to 0 after reaching it. For example, a laser pulse or laser pulse train can be emitted automatically into the workpiece 1 at regular intervals.

Since the feed speed V and the feed direction and thus the dividing line 4 can also be processed in the control electronics 64, the laser pulses or laser pulse trains can be emitted automatically.

The control electronics 64 can also use the measured speed and the fundamental frequency made available by the laser 2 to calculate a distance or location at which a laser pulse train or laser pulse should be emitted. In this way it can be achieved in particular that the material modifications 5 in the workpiece 1 do not overlap.

Since the laser pulses or pulse trains are emitted in a position-controlled manner, there is no need for time-consuming programming of the cutting process. In addition, freely selectable process speeds can be easily implemented.

FIG. 11C also shows a feed device 6, in which the processing optics are guided over the workpiece 1 via a 5-axis arm in order to introduce material modifications 5 into the workpiece 1. The combination of rotation arms makes it possible to move the processing optics along three spatial axes and to rotate them around two spatial axes.

As far as applicable, all individual features that are presented in the exemplary embodiments can be combined with one another and/or exchanged without departing from the scope of the invention.

1 workpiece

T bulk workpiece

10 surface

11 top

110 edge

12 section

13 bottom

130 edge

14 Molded Edge, Chamfer, Bevel

2 ultrashort pulse lasers

20 laser beam

200 partial laser beam

220 focus zone

3 processing optics

30 optical axis

32 polarization optics

34 beam shaping optics

36 telescope

38 beam guiding device

360 first lens

362 second lens

4 dividing line

40 chemical bath

42 hotplate

5 material modification

50 material modification surface

52 cracks

6 feed device

60 axis device

62 workpiece holder

64 control electronics

7 aberration correction device

70 cylinder key 700 first surface

702 second surface

72 slide-in cassette a setting angle ß refraction angle

A first axis

B second axis

N surface normal

V Feed H Hypotenuse

Claims

Expectations

1 . Method for separating a workpiece (1) having a transparent material, wherein material modifications (5) are introduced into the transparent material of the workpiece (1) along a separating line (4) by means of ultra-short laser pulses of an ultra-short-pulse laser (2) and the material of the workpiece (1 ) is then separated in a separating step along the resulting material modification surface (50), characterized in that the laser pulses are applied to the workpiece (1) at an angle (a) and the optical aberration of the laser pulses during the transition into the material of the workpiece ( 1) is reduced by an aberration correction device (7) and the laser beam (20) has a non-radially symmetrical transverse intensity distribution (220), the transverse intensity distribution (220) being elongated in a first axis (A) compared to a second axis (B ) appears with the second axis (B) perpendicular to the first axis (A).

2. The method according to claim 1, characterized in that the material modifications (5) penetrate two sides of the workpiece (1) which lie in intersecting planes and through the separating step a shaped edge (14), preferably a chamfer and/or a bevel , is generated, the hypotenuse (H) of the chamfer (14) and/or the bevel (14) preferably being between 50 μm and 2 mm in size.

3. The method according to claim 1 or 2, characterized in that the type III material modifications introduced by the laser pulses are modifications associated with crack formation in the material of the workpiece, and/or the separating step involves mechanical separation and/or an etching process and/or or a thermal challenge and/or a self-separation step.

4. The method according to any one of the preceding claims, characterized in that the laser beam is a non-diffracting laser beam.

5. The method according to claim 4, characterized in that in a projection of the non-radially symmetrical transverse intensity distribution (220) onto the workpiece (1), the first axis (A) and the second axis (B) are the same through the angle of attack (a). appear, and/or the projection of the non-radially symmetric transverse

Intensity distribution (220) is elongated on the workpiece (1) in the feed direction (V). Method according to one of the preceding claims, characterized in that the pulse energy of the laser pulses is between 10pJ and 50mJ, and/or the average laser power is between 1 W and 1 kW, and/or the laser pulses are individual laser pulses or part of a laser burst, with a Laser burst comprises 2 to 20 laser pulses, the laser pulses of the laser burst having a time interval of 10 ns to 40 ns, preferably 20 ns, and/or the wavelength of the laser is between 300 nm and 1500 nm, in particular 1030 nm, and/or the incident laser beam (20 ) is polarized parallel to the plane of incidence. Device for separating a workpiece (1) comprising a transparent material, comprising an ultra-short pulse laser (2) which is set up to provide ultra-short laser pulses, processing optics (3) which are set up to introduce the laser pulses into the material of the workpiece (1), and a feed device

(6), which is set up to move the laser beam (20) from laser pulses and the workpiece (1) relative to one another along a parting line (4) with a feed (V) and the optical axis (30) of the processing optics (3) relative to the surface (10) of the workpiece (1) at an angle (a), characterized in that an aberration correction device

(7) is provided and set up to reduce the aberration of the laser pulses when entering the material of the workpiece (1), the laser pulses being applied to the workpiece (1) at an angle (a) and the laser beam (20) having a non-radially symmetrical transverse intensity distribution (220), wherein the transverse intensity distribution (220) appears elongated in a first axis (A) compared to a second axis (B), the second axis (B) being perpendicular to the first axis (A) stands.

8. The device according to claim 7, characterized in that a beam shaping optics (34) from the laser beam (20) forms a non-diffracting laser beam (20).

9. Device according to one of Claims 7 or 8, characterized in that the aberration correction device (7) has a first surface (700) and a second surface (702), the first surface (700) being in front of the second surface (702 ) stands, the first surface (700) is cylindrically curved and the second surface (702) is cylindrically curved or flat, and the second surface (702) is the last surface in the beam path of the laser beam (20) before the laser pulses enter the material of the workpiece (1) and/or the aberration correction device (7) is designed in one piece in the form of a cylindrical wedge (70) and/or the distance between the second surface (702) and the material surface is less than 1 mm and/or the aberration correction device ( 7) is exchangeably held in a slide-in cassette (72).

10. Device according to one of claims 7 to 9, characterized in that the processing optics (3) comprises the aberration correction device (7) and/or the processing optics (3) comprises a telescope system (36) which is set up for the laser beam (20) reduced and / or enlarged in the material of the workpiece (1) to introduce.

11. Device according to one of claims 7 to 10, characterized in that the feed device (6) comprises an axis device (60) and a workpiece holder (62), which are set up for the processing optics (3) and the workpiece (1) along three Spatial axes can be moved translationally and rotationally about at least two spatial axes, and/or the angle of attack (a) of the processing optics (3) is between 0 and 60° and/or the partial laser beams (200) of the laser beam (20) at a maximum angle of incidence of 80 ° to the surface normal (N) of the workpiece (1) meet the workpiece (1) and/or to align the long axis (A) of the non-radially symmetrical transverse intensity distribution (220) along the feed direction (V), the axis system (62) is adjusted , and/or the workpiece holder (62) has a surface which does not reflect and/or scatter the laser beam (20).

12. Device according to one of claims 7 to 11, characterized in that polarization optics (32), preferably comprising a polarizer and a wave plate, are set up to adjust the polarization of the laser beam (20) relative to the plane of incidence of the laser beam (20), preferably parallel to the plane of incidence. Device according to one of claims 7 to 12, characterized in that a beam guiding device (38) is set up to guide the laser beam (20) to the material (1), the beam guiding via a mirror system and / or an optical fiber, preferably one Hollow core fiber takes place. Device according to one of Claims 7 to 13, characterized in that control electronics (64) are set up to trigger a laser pulse emission of the ultrashort pulse laser (2) on the basis of the relative positions of the laser beam (20) and material (1).