WO2022238215A1

WO2022238215A1 - Apparatus and method for determining beam quality

Info

Publication number: WO2022238215A1
Application number: PCT/EP2022/062073
Authority: WO
Inventors: Daniel FLAMM; Jonas Kleiner
Original assignee: Trumpf Laser- Und Systemtechnik Gmbh
Priority date: 2021-05-11
Filing date: 2022-05-04
Publication date: 2022-11-17
Also published as: DE102021112271A1

Abstract

The present invention relates to a method and an apparatus (7) for separating a material (50) of a workpiece (5), wherein material modifications (6) are introduced into the transparent material (50) of the workpiece (5) along a separation line (60) by means of a non-diffractive machining laser beam (22), and the material (50) of the workpiece (5) is then separated along the resulting material modification surface (62) by means of a separation step, wherein the non-diffractive machining laser beam (22) maximally reduced by a phase conicity has a PV value of less than 10λ, and wherein λ is a wavelength of the machining laser beam (22).

Description

1

Device and method for determining the beam quality

technical field

The present invention relates to a device and a method for determining the beam quality of a non-diffracting machining laser beam and a device and a method for cutting a material.

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 100 pJ can lead to non-linear absorption of the pulse energy in the material of a workpiece, 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, a non-diffracting processing laser beam is preferably introduced into the material with perpendicular incidence, as a result of which material modifications are produced in the material, which damage the material in a targeted manner. This creates a kind of perforation along which the material can be separated.

The non-diffracting processing laser beam is generated by various processing optics, which include, for example, axicons or axicon-like elements. However, the beam quality of these processing laser beams is sensitive to the optical adjustment and the optical quality of the processing optics. A processing laser beam with low beam quality can easily introduce material modifications that result in poor separability or produce a low-quality, high-roughness parting surface. 2

Presentation of the invention

Proceeding from the known prior art, it is an object of the present invention to provide an improved device for determining the beam quality of a non-diffracting processing laser beam, and a corresponding method.

The object is achieved by a device for determining the beam quality of a non-diffracting processing laser beam, comprising a processing laser beam configuration that is set up to ferm an incident laser beam of a laser into a non-diffracting processing laser beam and an analyzer with a detector, where the analyzer does this is set up to determine, as the beam quality, a measure of the deviation of the non-diffracting processing laser beam impinging on the detector and provided by the processing laser beam shape from an ideal non-diffracting reference laser beam.

A laser can be a continuous wave laser or a pulsed laser, in particular an ultra-short pulse laser. The laser light or the laser pulses move in the direction of beam propagation along the direction laser beam formed by the laser.

The red laser beam has a transverse intensity distribution that is specific to the laser and given to it. A transversal intensity distribution is to be understood as meaning an intensity distribution which lies in a plane oriented perpendicularly to the beam propagation direction. To a certain extent, a laser beam can be understood as a laser beam composed of a large number of partial laser beams.

For example, a raw laser beam may have a rectangular transverse intensity distribution, like a stripe emitter. However, it can also be the case that the raw laser beam has a Gaussian transverse intensity distribution.

In order to form a non-linear processing laser beam from the raw laser beam, the raw laser beam passes through processing laser beam shaping optics. The processing laser beam shaping optics deflects the partial laser beams of the raw laser beam, so that the partial laser beams are converted into a different transverse intensity distribution that is suitable for processing a material. The laser beam that is used to process a material is referred to here as a processing laser beam. 3

The processing laser beam can be a non-diffractive processing 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-diffractive beams and/or Bessel-type beams, a transverse intensity distribution is essentially constant along the beam propagation direction.

In addition, the focal zone of the processing laser beam is always understood to mean that part of the intensity distribution of the processing laser beam that is greater than the modification threshold of the material. The word focal zone makes 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 a focal zone that is elongated in the direction of beam propagation and that is significantly larger than the transverse dimensions of the focal zone. In particular, a material removal or material modification that is elongated in the beam propagation direction can thereby be generated in order to ensure, for example, a simple separation of a workpiece.

In particular, non-diffracting beams can be used to generate elliptical non-diffracting beams that have a non-radially symmetrical transverse focal zone. For example, elliptical quasi-non-diffracting rays have a main maximum that coincides with the center of the ray. The center of the ray is given by the place where the main axes of the ellipse intersect. In particular, elliptical, quasi non-diffracting beams can result from the superimposition of several 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.

For example, a non-diffracting beam can be generated from a plane wave field or from parallel partial laser beams if all partial laser beams are refracted at the same angle β to the optical axis of the laser beam. This has the consequence that 4 Partial laser beams close to the axis already overlap on the optical axis shortly after the processing laser beam shaping optics and thus form an increased laser intensity, while off-axis beams only overlap later after the processing laser beam shaping optics and form an increased laser beam intensity. A substantially constant laser intensity can thus be generated over a longitudinal length parallel to the beam propagation direction. A laser beam in which all partial laser beams are refracted at the same angle ß to the optical axis is called an ideal non-diffracting reference beam.

However, the non-diffractive machining laser beam is replaced by a real one

Machining laser beam shaping optics shaped so that not all partial laser beams are refracted at the same angle ß to the optical axis as described above. The real processing beam shaping optics can have optical aberrations. In addition, an optical adjustment can be faulty, so that the partial laser beams are refracted at different angles to the optical axis. This can lead to a systematic deviation of the angle of refraction ß. Accordingly, the intensity distribution in the focal zone - where the different partial laser beams overlap - can deviate from that of an ideal non-diffracting reference laser beam.

In order to determine the deviations of the non-diffracting processing laser beam from the ideal non-diffracting reference laser beam, the non-diffracting processing laser beam is detected by a detector of an analyzer and a beam quality is determined, which is a measure of the deviation of the processing laser beam shape optics impinging on the detector provided non-diffractive machining laser beam from a reference non-diffractive laser beam.

This has the advantage that a measure of the beam quality is determined, so that the quality of the processing laser beam is known. In particular, this dimension can also be used for adjustment or quality control of processing optics.

The detector can be arranged and set up in such a way that it detects the phase distribution of the non-diffracting processing laser beam provided by the processing laser beam shaping optics, and the analyzer comprises a calculation unit that is set up to calculate the measure of the deviation from the detected phase curve of the non-diffracting processing laser beam of the non-diffractive machining laser beam from an ideal reference non-diffractive laser beam. 5

The phase curve of a non-diffracting processing laser beam, also known as a wavefront, results mainly from the distances covered by the partial laser beams from the processing beam shaping optics to the detector: f = k * r, where k is the wave vector of the partial laser beam and r is the observation vector.

For example, the partial laser beams of an ideal, non-diffracting reference laser beam, in which all partial laser beams are refracted at an angle β to the optical axis, travel a well-defined distance to the detector. Accordingly, after subtracting the linear, radially symmetrical part, an ideal non-diffracting beam has an ideal plane wavefront.

However, if the laser beam diverges or converges, for example, then the distance for the partial laser beams close to the axis is shorter than for the beams far from the axis, so that a phase profile that deviates from the ideal form is generated. Optical aberrations also produce a phase curve that deviates from the ideal form. In particular, astigmatism in the beam path can result in the partial laser beams being refracted more strongly along a vertical axis than along a horizontal axis. It is also possible that an asymmetric intensity distribution is generated on the detector from an originally symmetric intensity distribution due to asymmetry in the beam path, also known as coma.

The last two aberrations mentioned ensure an asymmetrical phase distribution of the processing laser beam on the detector, while the focus-dependent phase distributions produce a radially symmetrical, conical phase distribution on the detector. In general, the aforementioned image errors and defocusing can overlap.

For this reason, the analyzer can have a calculation unit. The calculation unit is therefore set up to calculate the measure of the deviation of the non-diffracting processing laser beam from an ideal non-diffracting reference laser beam from the detected phase profile of the non-diffracting processing laser beam.

So-called tilt and/or tip aberrations, in which the laser beam propagates at an angle to the optical axis, are preferably not taken into account in the quality analysis of the phase distribution. In particular, the analyzer can detect such a pseudo-aberration and eliminate it numerically.

In addition, the beam quality of non-diffracting vector beams can also be determined. Non-diffractive vector rays are non-diffractive rays in which the polarization has a transverse 6 spatial property is. For this purpose, a polarizer can be fitted in front of the detector, for example a Shack-Hartmann detector, which analyzes the two perpendicular polarization projections and determines the deviations from the reference laser beam, for example for s- and p-polarized light.

To determine the beam quality, the deviation can also be determined for just a single polarization.

The size of the deviation determines the beam quality.

Although the design of the laser amplitude and phase determine the overall beam quality of the non-diffracting laser beam, the phase distribution often plays a more important role when using non-diffracting laser beams in material processing. The amplitude is already predetermined by the laser, for example in the form of a Gaussian intensity distribution. The decisive factor for the shape of the non-diffracting laser beam on the beam axis is the phase. The exact phase distribution is responsible for the alignment and shape of the focal zone perpendicular to the beam propagation direction and thus for the material processing.

The calculation unit can be set up to reduce the phase curve of the non-diffracting machining laser beam detected by the detector by the conical phase component of the non-diffracting machining laser beam by calculation, preferably to remove the conical phase component; and the calculation unit can be set up to calculate the measure for the deviation of the non-diffracting processing laser beam from an ideal non-diffracting reference laser beam from the remaining phase profile of the non-diffracting processing laser beam.

This means that a conical component is subtracted from a detected phase distribution in such a way that, in the best case, there is no longer a conical component in the phase profile reduced as a result.

A conical phase component, i.e. a radially symmetrical phase curve that only depends on the distance from the optical axis, has no negative influence on the beam quality, but is based on the phase f = k * r.

A conical phase progression occurs with the ideal non-diffracting reference laser beam. In particular, the conical phase progression is the basic requirement for a non-diffracting one 7

Laser beam. The reduced phase profile therefore only contains information about the deviation from an ideal beam shape.

A computational minimization of the conical beam component can consist in using the calculation unit to adapt an increasing phase curve that is linearly dependent on the distance from the optical axis to the actually measured phase curve. To a certain extent, the opening angle of the cone is numerically adapted to the measurement. The opening angle of the cone can be achieved, for example, by maximizing a coefficient of determination.

The conical phase profile found in this way can be subtracted numerically from the measured phase distribution using the calculation unit, so that only those phase components that are not determined by a conical phase profile remain.

The measure of the deviation of the non-diffracting processing laser beam from an ideal non-diffracting reference laser beam can be the wave front curvature, preferably the PV value of the non-diffracting processing laser beam reduced at most by the conical phase component.

The wave front indicates the shape of a surface on which partial laser beams of the same phase lie. For example, in a spherical wave, the wavefront is spherical. In a plane wave, the wavefront is plane. For an ideally non-diffracting reference laser beam, the wavefront is conical.

For example, the PV value can be the peak valley value of the reduced phase distribution, ie the difference between the maximum measured phase and the minimum value of the measured phase of the reduced phase distribution.

However, detectors have hitherto had the problem of being able to resolve only a small phase curve. Therefore, the analyzer can comprise an optical phase conicity reducer, wherein the phase conicity reducer can be configured to maximally reduce, preferably remove, the conic phase portion of the non-diffractive processing laser beam provided by the processing laser beam shaping optics; and the phase taper reducer may be arranged such that a non-diffractive processing laser beam shaped by the processing beam shaping optics is directed through the phase taper reducer onto the detector.

An optical phase conicity reducer can impose a further conical phase on the processing laser beam, which is preferably opposite to the conical phase profile of the processing laser beam. As a result, the conical phase component can be reduced. 8th

Ideally, the phase conicity reducer is adapted to the conicity of the non-diffracting processing laser beam in such a way that no conical phase curve is detected by the detector. In this way, in particular, the conical phase component can be reduced in such a way that the detector of the analyzer can resolve the phase curve and can finally determine a beam quality.

The phase taper reducer may be inverse reference laser beam shaping optics configured to shape an ideal non-diffractive reference beam into an ideal diffractive laser beam.

Reference laser beam shaping optics are laser beam shaping optics that form an ideal non-diffracting reference laser beam from an ideal diffracting laser beam, for example an ideal Gaussian laser beam, in that the ideal diffracting laser beam first passes through the entrance side and then through the exit side. Conversely, an inverse reference laser beam shaping optic generates an ideal diffracting laser beam from an ideal non-diffracting reference laser beam. The reference laser beam shaping optics thus has known optical properties, so that the resulting laser beams can be used as a reference for processing laser beams.

In particular, an inverse reference laser beam shape optics is also a real optics in reality, which can have optical errors. However, the optical errors of the reference laser beam shaping optics can be determined by a particularly intensive characterization and calibration, so that they are known. In this respect, the influence of the inverse reference laser beam shape optics on the phase distribution of the processing laser beam is then also known, so that this can be taken into account when determining the degree of deviation. In addition or as an alternative to this, the reference laser beam shaping optics can include very high-quality components that have a particularly high surface quality and that have been adjusted particularly precisely to one another, so that the associated optical errors can be neglected or are at least known to be reliably reproducible.

The ideal non-diffracting reference laser beam is therefore the laser beam that can be generated by the real configuration of the reference laser beam shaping optics.

The inverse reference laser beam shaping optics can be arranged between the processing laser beam shaping optics and the focal zone of the processing laser beam or can be arranged after the focal zone of the processing laser beam. 9

It can thereby be achieved that the beam quality of the processing laser beam can be determined without the intensity increase of the processing laser beam coinciding with the inverse reference laser beam shaping optics and possibly damaging them.

As already described above, the angle of refraction at which the partial laser beams of the processing laser beam are refracted relative to the optical axis is determined by the processing laser beam shaping optics. However, the angle of refraction is constant after the partial laser beams have passed through the processing laser beam shaping optics. Accordingly, the wave field of the processing laser beam already has all the beam quality information before there is an increase in intensity in the focal zone.

The inverse reference laser beam-shaping optics can be an inverse beam-shaping element, or can comprise an inverse beam-shaping element and inverse imaging optics.

The processing laser beam shaping optics can be a beam-shaping element or can comprise a beam-shaping element and imaging optics, with the non-diffracting processing laser beam being generated after the imaging optics.

An imaging optics can be an optical imaging system, for example. For example, imaging 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 location of the focus zone of the laser beam can be determined by the imaging optics. To a certain extent, the placement of the focal zone in the direction of beam propagation can be adjusted.

If the beam-shaping element forms a non-diffracting processing laser beam from the laser beam, then the depth of penetration of the intensity distribution into the material can be determined via the focusing of the imaging optics, for example during material processing.

The beam shaping optics can also be designed in such a way that the non-diffracting processing laser beam is only generated by imaging with the imaging optics.

Inverse imaging optics have the opposite effect of imaging optics. An inverse beam-shaping element also has the inverse effect of a beam-shaping element. 10

The beam-shaping element and/or the inverse beam-shaping element can be an axicon or a diffractive optical element or a free-form surface.

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 a specific non-diffractive 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 that is calculated from the beam entry surface to the lateral surface of the cone. As a result, the marginal rays of the Gaussian laser beam are refracted to a different focal point than rays close to the axis. This results in particular in a focus zone that is elongated in the beam propagation direction.

For example, the cone angle in the approximation for thin optical elements is responsible for a phase conicity β = 2 pl(h - 1 )α, where l is the wavelength of the laser beam, n is the refractive index of the axicon, and α is the cone angle.

A free-form surface is generally a light-refracting surface with which a laser beam can be converted from a first intensity distribution into a second intensity distribution. The shape of the free-form surface allows the phase distribution and intensity distribution of the laser beam to be adjusted in a targeted manner.

In particular, the above optical elements can also be combined with one another in order to produce a beam quality of the processing laser beam that is as ideal as possible, or a phase curve that is as conical as possible.

A beam splitter configured to direct a portion of the incoming raw laser beam to the processing laser beam optics can be arranged in front of the processing laser beam shaping optics and the inverse reference laser beam shaping optics can be a reflective beam-shaping element, the reflective beam-shaping element directing the non-diffractive processing laser beam back through the processing laser beam shaping optics and the beam splitter directs to the detector. 11

In contrast to the beam-shaping elements described above, a reflective beam-shaping element is not based on the refraction and/or diffraction of light, but on the reflection of light. For example, a reflective beam-shaping element can be a reflective optical element that has a cone-shaped cavity.

This has the advantage that the direction of propagation of the partial laser beams of the processing laser beam is reversed by the reflective beam-shaping element, so that the beams pass through the optics used a second time and thus collect the phase curve twice through the processing laser beam-shaping optics.

Finally, the beam splitter makes it possible to decouple part of the processing laser beam and analyze it with the analyzer and detector.

The analyzer can be designed to be separable from the processing laser beam shaping optics.

In particular, different optimal geometric arrangements can be used for the respective application. As a result, the device can in particular be used more flexibly.

In particular, an analyzer can be used for different processing optics, for example in production. However, it is also possible for the analyzer to first determine the beam quality of the processing laser beam and then to use the same processing laser beam shaping optics when processing a material.

The detector can be a Shack-Hartmann sensor or an interferometer or a caustic measuring device or a modal analysis device.

In particular, the detector can detect the phase as a function of location, for example using a pixel-based design.

This has the advantage that well-known and established methods can be used to analyze the beam quality. This ensures that the device can be used quickly.

The above object is also achieved by a method for determining the beam quality of a non-diffracting processing laser beam, with processing laser beam shaping optics shaping an incident raw laser beam into a non-diffracting processing laser beam, and an analyzer downstream of the processing laser beam shaping optics providing a measure of the deviation of the 12 non-diffractive machining laser beam from an ideal non-diffractive reference laser beam.

The beam quality can be specified as a PV value of the phase distribution.

A phase conicity reducer of the analyzer can maximally reduce the conical phase component of the non-diffracting processing laser beam between the processing laser beam shaping optics and the focal zone.

A ring-shaped intensity distribution or a partially ring-shaped intensity distribution or a rotationally symmetrical intensity distribution can be generated behind the phase conicity reducer, which is correlated with the optical aberrations in the beam path.

An annular or rotationally symmetrical intensity distribution is generated in particular if the analyzer with phase conicity reducer analyzes the processing laser beam in front of its focal zone. Since the partial laser beams of the processing laser beam do not yet form a coherent zone, an annular intensity distribution is created.

In particular, information about possible imaging errors can also be drawn from the intensity distribution. For example, an intensity distribution that is only partially annular can indicate that an optical element is tilted in the beam path, so that a beam quality is already reduced by the intensity distribution.

In particular, it can also be the case that the intensity distribution is incorrect, but the measured phase distribution corresponds to that of an (almost) ideal, non-diffracting reference laser beam. By analyzing the intensity distribution and phase distribution, a holistic view of the beam quality is possible.

The beam quality can also be specified as the RMS value (Root Mean Squared) of the phase distribution, with the RMS value often being around a factor of 2 smaller than the PV value.

The phase taper reducer can collimate the non-diffractive machining laser beam.

In particular, this can mean that the phase conicity reducer has a shape that essentially corresponds to the conical phase distribution of the processing laser beam. If the processing laser beam is collimated after the phase conicity reducer, that means 13 in particular that the conicity of the phase conicity reducer was chosen to match the conicity of the processing laser beam.

For example, this can be achieved by each of the beam-shaping element and the inverse beam-shaping element being axicons that have the same cone angle. As a result, the beam shaping of the beam-shaping axicon can be reversed to a certain extent.

Proceeding from the known prior art, it is a further object of the present invention to provide an improved method for separating a material of a workpiece and a corresponding device.

The object is achieved by a method for separating a material of a workpiece with the features of claim 1. Advantageous developments result from the dependent claims, the description and the figures.

Accordingly, a method for separating a material of a workpiece is proposed, wherein material modifications are introduced into the transparent material of the workpiece along a separating line by means of a non-diffractive processing laser beam and the material of the workpiece is then separated along the resulting material modification surface in a separating step. According to the invention, the phase distribution of the non-diffracting processing laser beam that has been maximally reduced by a phase conicity has a PV value of less than 10 l, in particular less than 5 l. Here, l is a wavelength of the processing laser beam.

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 volume of the material by nonlinear absorption, 14 these structural changes are 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. For example, this can mean glasses with different thicknesses from 10 pm to 10 mm.

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. Here, the formation of the voids becomes explosive 15

Attributed to 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 microblast 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 a feed, for example, the laser beam and the workpiece relative to each other with a 16

The feed rate is shifted 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. While the workpiece and laser beam are moved relative to each other, 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.

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 which the non-diffractive processing laser beam has a PV value of less than 5 l, it is possible to produce parting surfaces with a particularly high quality with the parting step. In particular, with such a PV value, crack propagation in the material can be controlled very well, so that the separation step is simplified.

In other words, the partial laser beams of the non-diffracting processing laser beam can converge parallel to a cone surface to the optical axis in the focal zone of the non-diffracting processing laser beam, the opening angle of the cone being determined by the processing laser beam shaping optics and the tip of the cone coinciding with the optical axis.

The opening angle is well defined here, so that an almost ideal, non-diffracting processing laser beam with a PV value of less than 5 l is formed. 17

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 by means of a continuous wave CO 2 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 18

Crack formation 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.

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.

The pulse energy of the laser pulses is between 10pJ and 50mJ, and/or the average laser power is between 1W and 1 kW, and/or the laser pulses are individual laser pulses or part of a laser burst, with a laser burst comprising 2 to 20 laser pulses, with the laser pulses of the Laser bursts have 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.

This means that the method can be used with as many different materials as possible.

The object set above is also achieved by a device for separating a material of a workpiece. Advantageous developments of the device result from the dependent claims and the present description and the figures.

Accordingly, a device for separating a material of a workpiece is proposed, comprising a laser that is set up to provide a raw laser beam, processing laser beam shaping optics that are set up to form a non-diffracting processing laser beam from the raw laser beam, imaging optics that are set up to introducing a non-diffracting machining laser beam into the transparent material of the workpiece and thereby introducing material modifications into the material of the workpiece, and a feed device which is set up to move and/or adjust the non-diffracting machining laser beam and the workpiece relative to one another along the parting line with a feed . According to the invention, the processing beam shaping optics is designed such that 19 the non-diffractive machining laser beam maximally reduced by the phase conicity has a PV value of less than 5 l. Here, l is a wavelength of the processing laser beam.

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, in particular, the laser beam can also be introduced at an angle of incidence along the dividing line.

In particular, an angle of attack is the angle between the optical axis of the laser beam and the surface normal of the material of the workpiece. The setting angle of the optical axis of the processing optics and the surface normal can be between 0 and 60°, for example.

The processing laser beam shaping optics can be or comprise a beam-shaping element and/or the imaging optics can comprise a telescope system which is set up to introduce the non-diffracting processing laser beam into the workpiece in reduced and/or enlarged form and/or.

Enlarging and/or reducing the non-diffracting processing 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, an increased or reduced removal of material can also be realized by increasing or reducing the non-radially symmetrical transverse intensity distribution. In addition, the optical system can be adapted to the given processing conditions by enlarging or reducing it, so that the device can be used more flexibly. 20

The feed device can comprise an axis device and a workpiece holder, which is set up to move the non-diffractive machining laser beam and the workpiece along at least two spatial axes in a translatory manner, preferably along three spatial axes and in a rotary manner relative to 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.

Such an axis device also makes it possible 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 promotes 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.

A beam guidance device can be set up to guide the non-diffracting machining laser beam to the workpiece, with the beam guidance being effected via a mirror system and/or an optical fiber, preferably a hollow-core fiber.

A so-called free beam guide uses a mirror system to guide the raw laser beam of a stationary ultrashort pulse laser in different spatial dimensions to the processing 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 processing beam shaping optics. The hollow-core fiber eliminates the need to adjust mirror optics.

After the processing beam shaping optics, the shaped, non-diffractive processing laser beam is guided to the material, so that overall the beam guiding device guides the processing laser beam to the material. 21

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 parting surface 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: 22

Figure 1 is a schematic representation of the inventive device for

determination of beam quality;

FIG. 2A, B, C shows a schematic representation of the partial laser beams and the phase curve;

FIG. 3 shows a further schematic illustration of the device according to the invention for determining the beam quality;

Figure 4 shows a further schematic representation of the device according to the invention

determination of beam quality;

Figure 5 shows a further schematic representation of the device according to the invention

determination of beam quality; Figure 6 shows a further schematic representation of the device according to the invention

determination of beam quality;

Figure 7 is a further schematic representation of the device according to the invention

determination of beam quality;

FIG. 8 shows the intensity curve and the phase curve of an ideal non-diffracting reference laser beam;

FIG. 9 shows the intensity profile and the reduced phase profile of an ideal, non-diffracting reference laser beam;

FIG. 10A, B shows the intensity curve and the phase curve of a non-diffracting processing laser beam with a defocus aberration; FIG. 11 A, B shows the intensity profile and the phase profile of a non-diffracting processing laser beam with an astigmatism aberration;

FIG. 12A, B shows the intensity curve and the phase curve of a non-diffracting processing laser beam with a trefoil aberration;

FIG. 13 shows an asymmetrical course of intensity due to an adjustment error;

FIG. 14A, B shows a schematic representation of the method for separating a material; 23

Figure 15A, B, C is a schematic representation of a separation step; and

FIG. 16A, B shows a schematic representation of the device for separating a material.

Detailed description of preferred exemplary 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.

A device 1 for determining the beam quality of a non-diffracting machining laser beam 22 is shown schematically in FIG. The device 1 in this case includes a processing laser beam shaping optics 3, which forms the raw laser beam 20 of the laser 2 into a non-diffracting processing laser beam. In addition, the device 1 includes an analyzer 4 with a detector 40. The analyzer 4 is set up to measure the deviation of the non-diffractive processing laser beam 22 that strikes the detector 40 and is provided by the processing laser beam shaping optics 3 from an ideal non-diffractive beam quality Reference laser beam 24 to determine.

The detail enlargement shows that the non-diffracting processing laser beam 22 is composed of partial laser beams 2200 that run as parallel as possible, which converge in the focal zone 220 and cause an increase in intensity there. In addition, the detector plane 400 is shown, which is arranged in front of the focal zone 220 of the non-diffracting processing laser beam 22 .

The parallelism of the partial laser beams 2200 is ultimately responsible for the quality of the non-diffracting processing laser beam 22 . This parallelism is determined by the processing laser beam shaping optics 3 . The partial laser beams 2200 propagate to one another in the entire area between the processing laser beam shaping optics with the respectively impressed angle of refraction β. Accordingly, the beam quality can also already be determined before the focal zone 220 .

In comparison to a determination of the beam quality in the focal zone 220, overexposure and possible damage to the detector 40 due to the excess intensity can be avoided. Accordingly, it is also possible to arrange the detector plane 400 behind the focal zone 220 . 24

The detector 40 is arranged and set up overall in such a way that it detects the phase distribution of the non-diffractive processing laser beam 22 provided by the processing laser beam shaping optics 3 . The detector 40 can be, for example, a Shack-Hartmann sensor or an interferometer or a caustic measuring device or a mode analysis device.

The analyzer 4 also includes a calculation unit 42 which can evaluate the detected phase curve of the non-diffracting processing laser beam 22 . In particular, a measure for the deviation of the non-diffracting processing laser beam 22 from an ideal non-diffracting reference laser beam 24 can be calculated in this way.

For this purpose, an ideal, non-diffracting reference laser beam 24 is shown in FIG. 2A, in which all partial laser beams 2200 are oriented at the same angle β to the optical axis. The reference laser beam 24 would produce a phase curve in the detector plane 400, as shown in FIG. 2B. The phase f of the reference laser beam 24 varies from a minimum phase cpmin to a maximum phase cpmax. In particular, the phase distribution on the optical axis has a minimum, or the phase there corresponds to cpmin. The phase increases approximately linearly as the distance from the optical axis increases radially. A phase cone is thus formed. The rise in phase f is shown in Figure 2C along the dashed line of Figure 2B.

In contrast to an ideal, non-diffracting reference laser beam 24, not all partial laser beams 2200 are aligned parallel to one another in the case of a processing laser beam 22, which is generated by processing laser beam shaping optics 3. This can be due to an optical aberration of the processing laser beam shaping optics 3, for example.

A more detailed analysis of the phase progression f as a function of the distance from the optical axis then reveals systematic deviations of the processing laser beam 22 from an exact linear phase increase or from the radial symmetry of an ideal reference laser beam 24 . These systematic deviations are introduced by the actually existing processing laser beam shaping optics 3 and are therefore almost unavoidable.

The linear phase increase corresponds to that of an ideal non-diffracting reference laser beam 24. The beam quality of the processing laser beam 22 can thus be characterized by the deviations from an ideal reference laser beam 24. 25

The calculation unit 42 is set up to maximally reduce the phase profile of the non-diffracting machining laser beam 22 detected by the detector 40 by the conical phase component of the non-diffracting machining laser beam 22, preferably to remove the conical phase component.

This is based on the fact that the conical phase component of the processing laser beam 22 corresponds to that of an ideal reference laser beam 24, so that the reduced phase distribution only shows the deviations from the ideal phase distribution.

In order to reduce the conical phase component, a cone function can be adapted to the phase distribution, for example. For example, a function (p(r)=a*r+(pmin can be adjusted to the phase distribution. The parameter a indicates the radial increase in the phase distribution and r indicates the distance to the optical axis. Then the adjusted phase distribution can be taken from the measured phase distribution conical phase distribution can be subtracted, so that the deviation of the measured phase distribution from the ideal (purely conical phase distribution) remains.

The calculation unit 42 can determine a measure for the deviation of the non-diffracting processing laser beam 22 from the ideal reference laser beam 24 from the reduced phase profile.

FIG. 3 shows the device 1 in which the analyzer comprises an optical phase conicity reducer 44 . The phase conicity reducer 44 is designed here in the form of an axicon, which is aligned with the axicon tip counter to the beam propagation direction of the non-diffracting processing laser beam 22 . The conical shape of the axicon in turn makes it suitable for reducing the conical phase component of the non-diffracting processing laser beam 22 . The optical phase conicity reducer 44 is arranged between the processing beam shaping optics 3 and the detector 40, in particular arranged after the focal zone 220 of the non-diffracting processing laser beam 22, so that the detector is provided with a phase curve of the non-diffracting processing laser beam 22 that is reduced by the phase conicity of the phase conicity reducer 44.

The phase conicity reducer 44 can in particular also have an inverse

be reference laser beam shaping optics. If a laser beam were to pass through the phase taper reducer 44 from the detector side, an ideal non-diffracting reference laser beam 24 would be formed. Accordingly, with the inverse 26

Reference laser beam shaping optics traversed in the direction of the detector, the phase conicity of the ideal non-diffractive reference laser beam will be subtracted. The detector 44 thus only detects the reduced phase curve of the non-diffracting processing laser beam 22.

The phase conicity reducer 44 can in particular also be arranged between the processing laser beam shaping optics 3 and the focal zone 220 of the non-diffracting processing laser beam 22, as shown in FIG. In this case, however, the inverse reference laser beam shaping optics 440 are aligned in such a way that the laser beam falls on the detector 40 in a collimated manner.

The inverse reference laser beam shaping optics 440 can be an inverse beam shaping element 442, such as shown in FIGS. However, it can also be the case that the inverse reference laser beam shaping optics 440 includes an inverse beam-shaping element 442 and inverse imaging optics 444 . It can also be the case that the processing laser beam shaping optics 3 is a beam-shaping element 30 or comprises a beam-shaping element 30 and imaging optics 32 , with the non-diffracting processing laser beam 22 being generated after the imaging optics 32 .

Such a situation is shown in FIG. The raw laser beam 20 of the laser 2 is guided through the processing laser beam shaping optics 3 . In the processing laser beam shaping optics 3 , the raw laser beam 20 is processed by various lenses and optical elements together with the beam-shaping element 30 to form a beam bundle, which becomes a non-diffracting processing laser beam 22 as a result of imaging with the imaging optics 32 . The non-diffracting processing laser beam 22 is in turn processed by the inverse imaging optics 444 in such a way that the subsequent inverse reference laser beam shaping element 442 and the optical elements and lenses collimate the laser beam and guide it to the detector 40 . In particular, the beam-shaping element 30 and the inverse beam-shaping element 442 can be axicons with the same cone angle.

The inverse reference laser beam shaping optics 440 have known optical properties that have been thoroughly determined through previous characterization. In particular, it is thus known which phase cone the non-diffracting processing laser beam 22 subtracts from passing through the inverse reference laser beam shaping optics 440 . It is thus possible to reduce the conicity of the processing laser beam 22, so that the detector 40 only has to be able to resolve the reduced phase curve. 27

A further device 1 is shown in FIG. As a result, the optical structure in particular can be shortened, which leads to increased adjustment stability.

FIG. 7 shows a further device 1 for determining the beam quality. The raw laser beam 20 of the laser 2 is guided through a beam splitter 46 and through processing laser beam shaping optics 3 and is shaped into a non-diffracting processing laser beam 22 . The non-diffracting processing laser beam 22 is then guided back through the processing laser beam shaping optics 3 by a reflective beam-shaping element 4420 and directed by the beam splitter 46 in the direction of the detector 40 . Because the laser beam passes through the processing laser beam shaping optics 3 twice, the optical error is, so to speak, collected twice. As a result, the parallelism of the partial laser beams and thus the beam quality can be detected in a particularly simple manner.

The devices 1 described above can be used to determine the beam quality. The measure of the deviation of the non-diffracting processing laser beam 22 from an ideal non-diffracting reference laser beam 24 is preferably the wave front curvature, particularly preferably the PV value of the non-diffracting processing laser beam 22 reduced at most by the conical phase component.

The method for determining the beam quality consists of the

To compare processing laser beam shaping optics 3 shaped processing laser beam 22 with a reference beam 24 and to translate the deviations of both beams into a beam quality measure.

An example of a possible detected intensity and phase distribution is shown in FIG.

In the present case, the intensity measured by the detector 40 has a ring-shaped intensity distribution. The phase distribution is shown for the intensity distribution. The representation of the phase distribution is a "modulo 2TT" representation. This means that the conical phase increase is not directly visible here. Instead, the jumps in the color coding indicate when the phase has again increased by a multiple of 2p.

In a subsequent step, a range of the intensity distribution is selected that is above a certain intensity threshold. For example, the intensity threshold can be 20% or 30% or 40% of the maximum value of the measured intensity distribution. All detector pixels that are above the intensity threshold are used together with the associated phase values for a phase cone adjustment. The areas above the intensity threshold are in 28

Figure 8 between the dashed circles. Restricting the selection to the pixels with the greatest intensity can be particularly advantageous, as this is where the best signal-to-noise ratio is found.

FIG. 9 shows the part of the intensity distribution that lies above the specific threshold value, for example above 10% of the maximum intensity. In addition, the adjusted phase cone has already been subtracted from the phase distribution shown. If the result is a phase distribution that is as flat as possible, as shown in FIG. 9, then the partial laser beams 2200 of the non-diffracting processing laser beam 22 are parallel to one another. This ensures that the non-diffracting processing laser beam 22 has a high beam quality.

However, there are also various cases in which the phase distribution is not flat, but where there is a certain residual course of the phase.

FIG. 10A shows the phase distribution for a defocused, non-diffracting machining laser beam 22 . While the defocus is not visible in the intensity display, the phase display shows that a residual phase run remains despite the conical phase distribution being subtracted. The residual phase progression comes about because the partial laser beams 2200 of the non-diffracting machining laser beam 22 diverge or converge. Accordingly, a phase progression results that cannot be explained with a purely conical phase progression.

In particular, the defocus does not mean that the detector plane 440 is not arranged in the focal zone 220 of the processing laser beam 22 . Rather, the defocus originates from an, for example, non-planar optical surface in the processing laser beam shaping optics 3, which breaks or deflects adjacent partial laser beams at different angles.

The representation also corresponds in particular to the measured phase if the inverse reference laser beam shape optics is not adapted to the processing laser beam shape optics and a conical residual phase profile is therefore always visible for the detector 40 .

Defocus present in the machining laser beam shaping optics can cause the diameter of the principal lobe of the non-diffracting machining beam 22 to vary, as shown in Figure 10B. Shown here are the transverse beam cross sections in a first position along the beam propagation direction in a second position of the beam propagation direction. In addition, a cross section is shown in which the beam propagation direction - the z-direction - lies. A 29 Such an intensity behavior would lead to an inferior, since uneven, material processing process

FIG. 11A shows the intensity distribution and the phase distribution when there is astigmatism. Astigmatism causes the phase cone to have a smaller opening angle in one direction than in a direction perpendicular to it. In a sense, the base of the phase cone is an oval. Accordingly, with the maximum phase reduction, only a central phase cone (with a round base) can be subtracted. What remains in the reduced phase representation is a non-radially symmetrical phase distribution.

The influence of the astigmatism on the intensity distribution of the non-diffracting processing laser beam 22 is shown in FIG. 11B. The partial laser beams 2200 that are refracted to different degrees result in a non-uniform superimposition of the partial laser beams 2200 in the focal zone 220 . This has adverse effects on the material processing.

FIG. 12A shows the intensity distribution and the reduced phase distribution when a trefoil is present. A trefoil is a non-radially symmetrical image defect that is related to astigmatism. Such a trefoil causes the intensity distribution of the non-diffractive machining laser beam 22 in the focal zone to be highly dependent on the position within the focal zone, as shown in Figure 12B. In particular, the transversal intensity distribution has three secondary maxima adjacent to the main maximum, which can lead to uncontrolled crack formation during material processing.

In addition to the pure phase errors, it is also possible to use the method to determine an asymmetry in the intensity distribution. Such an intensity modulation is shown in FIG. The intensity distribution of the non-diffractive machining laser beam 22 is not radially symmetrical. Rather, the intensity maximum does not appear to be on the optical axis (in the middle of the illustration). This can lead to an elliptical shape of the transverse intensity distribution in the focal zone of the non-diffracting machining laser beam 22 . As a result, undesired cracking can occur during material processing, particularly along the long axis of the elliptical transverse intensity distribution.

The above phase distributions can be determined by the calculation unit to determine the PV value of the processing laser beam 22 . The lower the PV value, the The partial laser beams 2200 on which the processing laser beam 22 is based are 30 more parallel. The more parallel the partial laser beams 2200 are, the higher the beam quality.

In Figure 14A, B, the method for separating a material 50 of a workpiece 5 is shown. In this case, a non-diffracting processing beam 22 introduces material modifications 6 into the transparent material 50 along a dividing line 60 . The phase conicity of the processing laser beam 22 is smaller than PV=5 l. The material 50 is then separated along the material modification surface 62 created by the material modifications. Due to the high parallelism of the partial laser beams and the beam quality, a high quality of the parting surfaces can be generated

FIG. 14B shows that the material 50 is acted upon by the processing laser beam 22 along the parting line 60 . For this purpose, the workpiece 5 and the processing laser beam 22 can be moved relative to one another with a feed rate V, for example between V=0.05 m/s and V=5 m/s. Because the material 50 of the workpiece 5 is weakened in a targeted manner along the dividing line 60, a predetermined breaking point is formed along the dividing line 60, along which the workpiece 5 can be separated in a subsequent separating step.

In particular, the laser 2 can be an ultra-short pulse laser. The pulse duration of the ultra-short laser pulses is between 100 fs and 100 ns, preferably between 100 fs and 10 ps and/or the average laser power is between 1 W and 1 kW, preferably 50 W and/or the wavelength can be between 300 nm and 1500 nm, preferably 1030 nm and /or the laser pulses can be individual laser pulses or part of a laser burst, with a laser burst comprising between 2 and 20, preferably between 2 and 4 laser pulses and/or the time interval between the laser pulses of the laser burst can be between 10 ns and 40 ns, preferably 20 ns and/ or the pulse or burst energy can be between 10pJ and 50mJ.

The non-diffracting processing laser beam 22 can have a focal zone 220, the diameter of which is smaller than 5 pm perpendicular to the direction of beam propagation. This allows the material modification to be accurately oriented along the parting line 60 by the non-diffractive machining laser beam 22 . In addition, the different laser pulses can be superimposed or spatially overlap, so that there is an accumulation of heat in the material 50 of the workpiece 5, as a result of which the material 50 of the workpiece 5 is weakened. On the other hand, however, it is also possible for the laser pulses to be separated so far from one another that the material 50 of the workpiece 5 is perforated along the dividing line 60 only on the surface. 31

FIG. 14A also shows that the length of the focal zone 220 of the processing laser beam 22, which is elongated in the beam propagation direction, can be greater than the material thickness D. The result of this is that the processing laser beam 22 in conjunction with the feed V can produce material modifications 6 both on the upper side and on the underside of the material 50 of the workpiece 5 . In particular, this ensures that the elongated focal zone 220 penetrates the upper side 52 and the lower side 54 . Alternatively, the focal zone 220 may merely coincide with the top 52 or bottom 54 of the material.

A possible separation step is shown in FIG. 15, which includes the application of a mechanical load to the material 50 of the workpiece 5. In particular, it is shown in FIG.

A bending stress, for example, can be applied as a mechanical force to the parts 500, 502 of the workpiece 5 to be separated. A bending stress can cause the material of the workpiece 5 to be compressed on the upper side 52 towards the material modification 6 , while the material 50 of the workpiece 5 on the lower side 54 is stretched away from the material modification 6 . This creates a voltage gradient which is directed from the bottom 54 to the top 52 . As soon as the material stresses along the stress gradient are greater than the binding forces of the material of the workpiece 5, the material of the workpiece 5 relaxes with the formation of a crack which runs vertically through the material 50, for example. Here, this state of the material of the workpiece 1 is shown in FIG. 15B. FIG. 15C shows the subsequent state in which the parts 500, 502 of the workpiece 5 are isolated and separated. The workpiece 5 was accordingly separated along the dividing line 60 .

Such a separation step can in particular also be implemented by applying a thermal gradient, for example by irradiating the material modifications 6 with a CO 2 continuous-wave laser. Alternatively, it is also possible to etch the material 50 of the workpiece 5 in a chemical bath along the material modifications 6, with the targeted weakening of the material making the material 50 of the workpiece 5 selectively etchable. Another possibility is that through the targeted material weakening with type III modifications, the material tension exceeds the binding forces, so that a self-separation process occurs 32

Workpiece 1 comes. In any case, however, the weakening of the material along the parting line 60 determines the direction of the parting process.

FIG. 16A shows a device 7 for separating a material. In particular, a feed device 9 is shown, which is set up to move the processing laser beam shaping optics 3 and the material 50 of the workpiece 5 in a translatory manner along three spatial axes XYZ. The raw laser beam 20 of the ultra-short pulse laser 2 is directed onto the workpiece 5 by a processing laser beam shaping optics 3 . The workpiece 5 is here arranged on a support surface of a workpiece holder 92 of the feed device 9 , the workpiece holder 92 preferably neither reflecting nor absorbing the laser energy that the material does not absorb nor strongly scattering it back into the material 1 .

In particular, the raw laser beam 20 can be coupled into the processing laser beam shaping optics 3 by a beam guiding device 94 . Here, the beam guiding device 94 can be a free-space line with a lens and mirror system, as shown in FIG. 16A. However, the beam guidance device 56 can also be a hollow-core fiber with coupling-in and coupling-out optics, as shown in FIG. 16B.

In the present example in FIG. 169A, the raw laser beam 20 is directed towards the material 50 by a mirror construction and introduced into the material 50 by the processing laser beam shaping optics 3 . For this purpose, the processing laser beam shaping optics preferably has imaging optics. In the material 50, the non-diffractive machining laser beam 22 causes material modification. The processing laser beam shaping optics 3 can be moved and adjusted with the feed device 9 relative to the material 50, so that, for example, a preferred direction or an axis of symmetry of the transverse intensity distribution of the non-diffracting processing laser beam 22 can be adapted to the feed trajectory and thus the dividing line 60.

In this case, the feed device 9 can move the material 50 under the non-diffractive machining laser beam 22 with a feed V, so that the non-diffractive machining laser beam 22 modifies the workpiece 5 along the desired parting line 60 . In particular, in the shown FIG. 16A, the feed device 9 has a first axis system 90, with which the material 50 can be moved along the XYZ axes and, if necessary, rotated. In particular, the feed device 9 can also have a workpiece holder 92 which is set up to hold the material 50 . 33

The feed device 90 can in particular also be connected to control electronics 96 , the control electronics 96 converting the user commands of a user of the device 7 into control commands for the feed device 9 . In particular, predefined cutting patterns can be stored in a memory of the control electronics 96 and the processes can be automatically controlled by the control electronics 96 .

The control electronics 96 can in particular also be connected to the ultrashort pulse laser 2 . The control electronics 96 can request or trigger the output of a laser pulse or laser pulse train. The control electronics 96 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 900 of the feed device 9 being read out, for example, and the axis encoder signal being able to be interpreted by the control electronics 96 as location information. It is thus possible for the control electronics 96 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 it has been reached. For example, a laser pulse or laser pulse train can be emitted automatically into the material 50 at regular intervals.

Since the feed speed V and the feed direction and thus the dividing line 60 can also be processed in the control electronics 96, the laser pulses or laser pulse trains can be emitted automatically.

The control electronics 96 can also use the measured speed and the fundamental frequency made available by the ultrashort pulse 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 6 in the material 50 do not overlap or that the laser energy is emitted uniformly along the dividing line 60 .

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. 34

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.

35

Reference character list

1 device

2 lasers

20 raw laser beam 22 non-diffractive processing laser beam

2200 partial laser beam

220 focus zone

24 ideal non-diffractive reference laser beam

3 processing laser beam shaping optics 30 beam shaping element

32 imaging optics

4 analyzer

40 detector

400 detector level 42 calculation unit

44 phase taper reducer

440 inverse reference laser beam shaping optics

442 inverse beam-shaping element

444 inverse imaging optics 46 beam splitter

5 workpiece

50 materials

52 top

54 subpage 6 material modification

60 dividing line

62 material modification surface

7 Separating device

9 feed device 90 axis device

900 axis encoder

92 workpiece holder

94 beam guiding device

96 control electronics

Claims

36 claims

1. A method for separating a material (50) of a workpiece (5), wherein material modifications (6) are introduced into the transparent material (50) of the workpiece (5) along a separating line (60) by means of a non-diffracting processing laser beam (22). and the material (50) of the workpiece (5) is then separated along the resulting material modification surface (62) in a separating step, characterized in that the phase distribution of the non-diffracting machining laser beam (22), which is maximally reduced by a phase conicity, has a PV value of less than 10 l, in particular less than 5 l, where l is a wavelength of the processing laser beam (22).

2. The method according to claim 1, characterized in that the partial laser beams (2200) of the non-diffractive processing laser beam (22) converge parallel to a cone surface to the optical axis in the focal zone (220) of the non-diffractive processing laser beam (22), the opening angle of the cone is determined by the processing laser beam shaping optics (3) and the tip of the cone coincides with the optical axis.

3. The method according to any one of claims 1 or 2, characterized in that the separating step comprises a mechanical separation and/or an etching process and/or a thermal treatment and/or a self-separation step.

4. The method according to any one of claims 1 to 3, characterized in that the pulse energy of the laser pulses is between 10pJ and 50mJ, and/or the average laser power is between 1W and 1kW, and/or the laser pulses are individual laser pulses or part of a laser burst, wherein a laser burst comprises 2 to 20 laser pulses, wherein the laser pulses of the laser burst have 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.

5. Device (7) for separating a material (50) of a workpiece (5), comprising -a laser (2) which is set up to provide a raw laser beam (20),

- processing laser beam shaping optics (3) which are set up to form a non-diffracting processing laser beam (22) from the raw laser beam (20), 37

- imaging optics (32) which are set up to introduce the non-diffracting processing laser beam (22) into the transparent material (50) of the workpiece (5) and thereby material modifications (6) into the material (50) of the workpiece (5) to bring in, and

- a feed device (9) which is set up to move and/or adjust the non-diffractive machining laser beam (22) and the workpiece (5) relative to one another along the parting line (60) with a feed (V), characterized in that the machining beam shaping optics (3) is designed in such a way that the non-diffracting processing laser beam (22) reduced to the maximum by the phase conicity has a PV value of less than 10 l, in particular less than 5 l, where l is a wavelength of the processing laser beam (22). Device (7) according to claim 5, characterized in that

- the processing laser beam shaping optics (3) is or comprises a beam-shaping element (30) and/or

- The imaging optics (32) comprises a telescope system which is set up to bring the non-diffracting machining laser beam (22) into the workpiece in a reduced and/or enlarged manner (5) and/or

- the feed device (9) comprises an axis device (90) and a workpiece holder (92), which are set up to move the non-diffracting machining laser beam (22) and the workpiece (5) translationally along at least two spatial axes, preferably along three spatial axes and to move at least two spatial axes rotationally relative. Device (7) according to one of claims 5 or 6, characterized in that

- a beam guidance device (94) is set up to guide the non-diffractive processing laser beam (22) to the workpiece, the beam guidance device (94) being implemented via a mirror system and/or an optical fiber, preferably a hollow-core fiber and/or

- An electronic control system is set up to trigger a laser pulse emission of the ultra-short pulse laser (2) based on the relative positions of the non-diffracting processing laser beam (22) and the workpiece (5) and/or

- The workpiece holder (92) has a surface that does not reflect and/or does not scatter the non-diffracting machining laser beam (22).