EP4196312A1

EP4196312A1 - Laser processing of a workpiece with a curved surface

Info

Publication number: EP4196312A1
Application number: EP21758351.7A
Authority: EP
Inventors: Daniel FLAMM; Jonas Kleiner
Original assignee: Trumpf Laser und Systemtechnik GmbH
Current assignee: Trumpf Laser und Systemtechnik GmbH
Priority date: 2020-08-13
Filing date: 2021-08-05
Publication date: 2023-06-21
Also published as: WO2022033958A1; DE102020121283A1; US20230166352A1; CN116033994A; KR20230031955A

Abstract

A method is disclosed for processing the material of a workpiece (9) using a laser beam (3), wherein the workpiece (9) comprises a material which is largely transparent to the laser beam (3) and which has a curved surface (9A). The method comprises the steps of: beam shaping (step 101) the laser beam (3) to form an elongate focal zone (7) in the material of the workpiece (9), the beam shaping being carried out using an arrangement of diffractive and/or refractive optical units and comprising: - focus-forming beam shaping (step 101A), which brings about an arrival of beam components (3A) at an arrival angle (δ') at a beam axis (5) of the laser beam (3) to form the elongate focal zone (7) along the beam axis (5) in the workpiece (9) by interference, and - phase-correcting beam shaping (step 101B), which counteracts influencing of the interference by an entry of the laser beam (3) into the workpiece (9), and adjusting (step 105) beam parameters of the laser beam (3) in such a way that the material of the workpiece (9) is modified in the elongate focal zone (7).

Description

LASER MACHINING OF A WORKPIECE WITH A CURVED SURFACE

The present invention relates to a method for material processing of a workpiece with a curved surface, such as a glass tube or a glass cylinder, using a laser beam. Furthermore, the invention relates to an optical system and a laser processing system with an optical system.

When laser processing a material that is essentially transparent to the laser radiation, referred to herein as a transparent material, modifications can be produced in the material with laser radiation. An absorption occurring in the volume of the material (volume absorption for short) of the laser radiation can cause a long-drawn-out modification of the structure of the material in the case of transparent materials. Modifications in the structure of the material can be used, for example, for drilling, separating by induced stresses, effecting a modification of the refractive behavior or for selective laser etching. See for example the applications WO 2016/079062 A1, WO 2016/079063 A1 and WO 2016/079275 A1 of the applicant.

For example, ultra-short pulse laser-based glass modification processes for cutting glass are often carried out with elongated focus distributions, such as those found with non-diffracting beams. Such elongated focus distributions are formed, for example, due to interference from beam components arriving from outside and can form elongated modifications in the material, as is the case, for example, with Bessel-like beams.

Beam-shaping elements and optics structures with which long, slim beam profiles with a high aspect ratio can be provided for laser processing in the direction of beam propagation are described, for example, in the cited WO 2016/079275 A1.

One aspect of this disclosure is based on the object of enabling laser processing of a workpiece with a curved surface, such as laser processing of a glass tube or a glass cylinder with an elongated focal zone. In particular, beam shaping approaches, such as those developed for the laser processing of flat workpieces, should also be applicable to workpieces with curved surfaces. one Another aspect of this disclosure is based on the object of specifying a method with which a laser-machined body/hollow body can be separated into two sections.

At least one of these objects is achieved by a method for material processing of a workpiece according to claim 1, an optical system according to claim 16 and by a laser processing system according to claim 21. Further developments are specified in the dependent claims.

In one aspect, methods for material processing of a workpiece with a pulsed laser beam, in particular with ultra-short laser pulses, are disclosed, the workpiece having a material with a curved surface that is largely transparent to the laser beam. The procedures include the steps:

Beam shaping of the laser beam to form an elongated focal zone (in particular in the direction of propagation/along a beam axis) in the material of the workpiece, the beam shaping being carried out with an arrangement of diffractive, reflective and/or refractive optics. Beam shaping includes:

- Focus-forming beam shaping, which causes beam components to run in at an angle of incidence onto a beam axis of the laser beam for forming the elongated focus zone along the beam axis in the workpiece by interference, and

- a phase-correcting beam shaping, which counteracts an influence on the interference by an entry of the laser beam into the workpiece, and

Setting beam parameters of the laser beam in such a way that the material of the workpiece is modified in the elongated focal zone.

Another aspect discloses optical systems for beam shaping of a pulsed laser beam, in particular ultra-short laser pulses, for forming a focal zone in a workpiece with a curved surface, the focal zone being elongated along a beam axis of the laser beam. The optical system includes focus-forming optics, which causes beam components to arrive at an angle of incidence onto a beam axis of the laser beam for formation of the elongated focus zone along the beam axis in the workpiece through interference. A phase correction, which counteracts the interference caused by the laser beam entering the workpiece, is provided with phase-correcting optics or is integrated into the focus-forming optics. In other words, the optical systems include a phase correcting Optics that provide phase correction to counteract the interference caused by entry of the laser beam into the workpiece, or such phase correction is incorporated into the focus-forming optics.

In a further aspect, laser processing systems for processing a workpiece with a pulsed laser beam, in particular with ultra-short laser pulses, are disclosed by modifying a material of the workpiece in a focal zone of the laser beam, the focal zone being elongated along a beam axis of the laser beam and the workpiece largely material transparent to the laser beam with a curved surface. The laser processing equipment includes a laser beam source that emits a laser beam, an optical system as described above, and a workpiece holder for supporting the workpiece.

In some developments of the method, the curved surface can be curved in one direction, and the beam shaping of the laser beam can include impressing at least one two-dimensional phase distribution on the laser beam to form an elongated focal zone in the material of the workpiece, the at least one phase distribution

- for the focus-forming beam formation, first phase contributions, which cause the arrival of beam components at the angle of arrival (and in particular generate a non-diffracting beam for the formation of the elongated focal zone along the beam axis in the workpiece), and

- Second phase contributions for the phase-correcting beam formation, which cancel out an entry phase locally accumulated by the laser beam when entering the workpiece.

In some developments of the method, the locally accumulated entry phase for an alignment of the beam axis along a normal direction of the surface at a point of impact of the beam axis on the surface can be determined and take into account the angle of arrival, a radius of curvature of the surface at the point of impact and a refractive index of the workpiece.

In general, the point of impact is understood here as the point of intersection of the optical axis of the laser beam with the workpiece (for example the substrate to be processed). In some developments of the method, the second phase contributions can form a phase distribution that is axisymmetric to an axis of symmetry, the second phase contributions being constant parallel to the axis of symmetry and changing perpendicularly to the axis of symmetry. The methods may further include the step:

aligning the axisymmetric phase distribution and the workpiece to each other such that the axis of symmetry is orthogonal to a plane in which a radius of curvature of the surface is defined, taking into account an optical path between a place of impressing the axisymmetric phase distribution and the workpiece.

In some developments of the method, the first phase contributions and/or the second phase contributions can be impressed onto a transverse beam profile of the laser beam using a diffractive optical beam-shaping element, with the diffractive optical beam-shaping element having surface elements that adjoin one another and build up a surface grating structure in which each surface element has a phase shift value is assigned, and wherein the phase shift values bring about the first phase contributions and/or the second phase contributions.

In some developments, the methods can also include the steps: irradiating the laser beam onto the surface along a beam path of an optical system that images the laser beam into the material of the workpiece to form the elongated focal zone, and/or

Aligning the beam axis of the laser beam to a normal direction of the surface in such a way that the beam axis impinges on the surface in an angular range of 5° around the normal direction.

In some developments of the method, the phase-correcting beam shaping can be generated by a cylindrical lens, which is positioned in a beam path of the laser beam before or after an optical system that effects the focus-forming beam shaping. The cylindrical lens can have a radius of curvature that is adapted to a radius of curvature of the surface of the workpiece.

If you take into account that when carrying out the material processing method, the elongated focal zone begins before the entry surface of the workpiece (Az larger 0) or the beginning of the elongated focus zone falls into the workpiece (Az less than 0), the following approximate definitions of the radius of curvature of the surface of the cylindrical lens result, which corresponds to the following condition for Az = 0:

2 1

Embodiment Az > 0 (with the parameters a = 5060 mm and b = 9645 mm):

Embodiment Az < 0 (with the parameters c = 284 mm'^ and d = 590): each with

Rz radius of curvature/radius of cylinder of cylindrical lens, nz index of refraction of cylindrical lens,

Rw radius of curvature/ outer radius Ra of the surface, nw refractive index of the material of the workpiece and

M Image factor of the beam path between a location of focus-forming beam shaping and the workpiece.

In the special case z=0, the cylindrical lens can have a radius of curvature which is adapted to a radius of curvature of the surface of the workpiece in such a way that: again with

M Image factor of the beam path between a location of focus-forming beam shaping and the workpiece. The preceding description of the radius of curvature Rz of the surface of the cylindrical lens applies to the embodiment in which the beginning of the elongated focal zone coincides with the entry surface of the workpiece when the method for material processing is carried out. That is, there is no shift Az of the beginning of the elongated focal zone to the entrance surface (Az=0). In this special case, the axicon tip (shown) lies virtually on the surface of the workpiece.

However, immediately after the tip, the non-diffracting beam is not yet of high intensity and a continuous processing of the workpiece from the top to the back would not be possible. Instead, one can, for example, place the axicon tip (pictured) 100 pm to 200 pm in front of the surface (Az in the range 100 pm to 200 pm, i.e. Az > 0). Correspondingly, the estimation of the radius of curvature of the cylindrical lens based on the parameters a, b would have to be used.

In some developments of the method, the beam shaping of the laser beam can be carried out by impressing a two-dimensional phase distribution on a transverse beam profile of an output laser beam with:

- a diffractive optical beam-shaping element having fixed or adjustable phase values in a two-dimensional array; or

- a combination of a cylindrical lens with an axicon; or

- a combination of a cylindrical lens with a diffractive optical beam-shaping element, which has fixed or adjustable phase values in a two-dimensional arrangement, which is designed to impress a phase distribution causing a non-diffracting beam, in particular a Bessel beam-like phase distribution, for the formation of the elongated focal zone is.

In some developments of the method, the beam shaping of the laser beam can be carried out with a single optic, which is designed as a refractive free-form optic element or a hybrid optic element, in particular an optic unit consisting of an input-side cylindrical lens and an output-side axicon.

In some developments, the methods can further include the step:

effecting a relative movement between the workpiece and the focal zone, during which the focal zone is positioned along a scanning trajectory in the material of the workpiece, so that a plurality of modifications are written into the material of the workpiece along the scanning trajectory.

In this case, the workpiece can be in the form of a tube, cylinder or section of a tube or cylinder, such as a half-tube or half-cylinder, and the relative movement can comprise a rotational movement of the workpiece. The beam axis of the laser beam can in particular run through a longitudinal axis of the workpiece. Furthermore, in the case of a purely rotational movement about a longitudinal axis of the workpiece, the scanning trajectory of the laser beam can run in a plane of maximum curvature of the surface of the workpiece. As an alternative or in addition, a translational movement in the direction of the longitudinal axis of the workpiece can additionally or partially take place.

In some developments, the scanning trajectory can be an outer contour for dividing the workpiece into two parts along a longitudinal axis of the workpiece. Alternatively, the scanning trajectory can be embodied as an inner contour closed on a surface of the workpiece for triggering a region delimited by the inner contour.

In some developments, the methods can further include the step:

Monitoring and controlling a position of the surface of the workpiece along the beam axis to a target position.

The monitoring and regulation can be carried out in particular if, during a rotational movement, a rotational axis deviates from an axis of rotational symmetry of the surface of the workpiece and/or the surface of the workpiece deviates at least in sections from a rotationally symmetrical surface profile.

In some developments, the methods may further include adjusting the phase-correcting beam shaping to a change in curvature of the curved surface along the scanning trajectory of the laser beam. For example, a control signal for adjusting the phase-correcting beam shaping can be derived based on a pre-measurement of a curvature of the curved surface along the trajectory and/or based on an online measurement of a curvature of the curved surface during a relative movement between the workpiece and the focal zone along the scanning trajectory. The control signal can then be output to an adjustable beam-shaping element, such as a spatial light modulator or deformable mirror, to adjust the second phase contributions for phase-correcting beam-shaping. In some developments, the optical systems can be set up to impress a two-dimensional phase distribution on the laser beam and to output it as a laser beam that forms a non-diffracting beam, in particular a real or virtual Bessel-like one, with the focus-forming optics first phase contributions of the Can generate phase distribution, and the phase-correcting optics or the phase correction can generate second phase contributions to the phase distribution, which cancel an entry phase locally accumulated by the laser beam when entering the workpiece.

In some developments of the optical systems, the focus-forming optics and/or the phase-correcting optics for the phase imposition of a two-dimensional phase distribution can be designed as a diffractive optical beam-shaping element that is set up to impress the first phase contributions and/or the second phase contributions on a transverse beam profile of the laser beam . The diffractive optical beam-shaping element can have surface elements adjoining one another, which build up a surface grating structure in which each surface element is assigned a phase shift value, and the phase shift values bring about the first phase contributions and/or the second phase contributions. Alternatively or additionally, the focus-forming optics can be designed as an axicon that generates the focus-forming phase contributions. Furthermore, as an alternative or in addition, the phase-correcting optics can be designed as a cylindrical lens, which generates the second phase contributions and is positioned directly before or after the focus-forming optics in the beam path of the laser beam. Alternatively or additionally, the focus-forming optics can be designed as a refractive free-form element that generates the first phase contributions and the second phase contributions. Alternatively or additionally, the focus-forming optics and the phase-correcting optics can be embodied as hybrid optics that generate the first phase contributions and the second phase contributions and are embodied in particular as a combination of an input-side cylindrical lens and an output-side axicon.

In some developments of the optical systems, the phase-correcting optics for the phase imposition of a two-dimensional phase distribution can be designed as an optical element that can be adjusted in the two-dimensional phase distribution. It can be designed, for example, as a diffractive optical beam-shaping element such as a spatial light modulator or a deformable cylinder mirror. Furthermore, the adjustable optical element for an adaptation of the phase corrections when there is a change in a curvature of the curved surface to be corrected, depending on a control signal.

In some developments, the optical systems can also include: a telescope arrangement for reducing a real or virtual focal zone that is assigned to the focus-forming optics, and/or a distance sensor that is set up to determine a position of a surface of the workpiece along the beam axis.

In some developments of the laser processing systems, the optical system and/or the workpiece holder can be set up to:

- aligning the beam axis of the laser beam to a normal direction of the surface in such a way that the beam axis impinges on the surface in an angular range of 5° around the normal direction, preferably along the normal direction, and/or

- bring about a relative movement between the workpiece and the focal zone, in which the focal zone is positioned along a scanning trajectory in the material of the workpiece, the alignment of the beam axis to the normal direction being adapted to the course of the surface.

In some developments, the laser processing systems also include a distance sensor that is arranged and set up to determine a position of a surface of the workpiece along the beam axis, and a controller that is set up to determine a position of the surface of the workpiece along the beam axis with the distance sensor to monitor and regulate to a target position.

In some developments of the laser processing systems, the optical system can have phase-correcting optics for phase imprinting of a two-dimensional phase distribution, which is designed to be adjustable in the two-dimensional phase distribution. For this purpose, the laser processing system can also include a controller that is set up to output a control signal to the adjustable optical element that adapts the two-dimensional phase distribution to a curvature of the curved surface of the workpiece that is to be corrected. The control signal can in particular based on a pre-measurement of a curvature of the curved surface along a scanning trajectory or based on a Online measurement of a curvature of the curved surface can be provided during a relative movement between the workpiece and the focal zone along a scanning trajectory, in particular derived from the control unit.

In some developments, the laser processing systems can also have a distance sensor that is arranged and set up to determine a position of a surface of the workpiece along the beam axis. Furthermore, the laser processing systems can have a controller that is set up to monitor a position of the surface of the workpiece along the beam axis with the distance sensor and to regulate it to a target position.

In summary, according to the concepts disclosed herein, a process for laser machining transparent materials with curved surfaces can be implemented. The underlying optics concept allows, for example, the processing of glass tubes with radii of less than 15 mm, e.g. with radii of a few millimeters, such as 5 mm in elongated focal zones of a few 10 pm up to a few millimeters.

The concepts on which this is based relate to focus-forming beam shaping, which causes beam components to run in at an angle of incidence onto a beam axis of the laser beam for forming the elongated focus zone along the beam axis in the workpiece by interference. In other words, focus-forming beam shaping relates to beam shaping that generates a non-diffracting beam for forming the elongated focal zone along the beam axis in the workpiece.

Concepts are disclosed herein that allow at least some aspects of the prior art to be improved. In particular, further features and their usefulness result from the following description of embodiments with reference to the figures. From the figures show:

Fig. 1 Figures to clarify non-diffracting beams compared to a Gaussian beam,

2 shows a schematic sketch of a laser processing system for material processing, Fig. 3A and 3B schematic sketches of an optical system for beam shaping for

laser processing,

4A and 4B sketches to clarify the effect of a curved surface on the formation of a Bessel beam focus zone,

5A and 5B intensity distributions of a Bessel beam focal zone which was simulated for entry into a planar workpiece and for correction with regard to a curved surface of a workpiece, respectively

6A and 6B intensity distributions of a Bessel beam focal zone without correction for a curved surface.

7 shows a graphical representation of an exemplary dependence of the radius of curvature of the cylindrical lens on the displacement of the start of the focal zone from the workpiece surface,

8A to 8F phase distributions for focus-forming beam formations and phase-correcting beam formations and phase distributions combining these,

Fig. 9 is a flow chart to illustrate an exemplary method for

material processing of a workpiece with a curved surface,

10 shows a flowchart to illustrate an exemplary method of separating a modified workpiece,

11 shows a flowchart to clarify an example of a method for separating a workpiece that has been modified with asymmetrical modifications, and

12A and 12B exemplary workpieces with inner contours cut out.

The aspects described herein relate in particular to the use of non-diffractive radiation in material processing. Non-diffractive beams can be formed by wave fields that correspond to the Helmholtz equation

V ² L7 (r) + k ² U

'' ( 'r) ^z = 0 (equation 1) and a clear separability into a transversal (ie, in the x- and y-direction) dependency and a longitudinal (ie, in the z-direction/propagation direction) dependency of the

shape exhibit. k — c

Here ' is the wave vector with its longitudinal/axial and transversal components k ² = k _z ² + kl _unc j U x,y) _{ejne Ge} ii _eG ig _e complex-valued function that depends only on the transversal coordinates x and y. Since the z-dependence in Equation 2 exhibits pure phase modulation, is an intensity ^z ) ^> a function solving equation 2 is propagation-invariant and is called “non-diffractive”:

This approach provides different solution classes of the Helmholtz equation in different coordinate systems, such as so-called Mathieu rays in elliptic-cylindrical coordinates or so-called Bessel rays in circular-cylindrical coordinates.

See also J. Turunen and AT Friberg, "Propagation-invariant optical fields'", in Progress in optics, 54, 1-88, Elsevier (2010) and M. Woerdemann, "Structured Light Fields: Applications in Optical Trapping, Manipulation , and Organization”, Springer Science & Business Media (2012).

A large number of types of non-diffracting beams can be realized to a good approximation. These realized non-diffractive beams will continue to be referred to herein as "finitely limited non-diffractive beams", "non-diffractive beams", or also as "quasi-non-diffractive beams" for the sake of simplicity. In contrast to the theoretical construct, they lead to a finite performance. A length L of a propagation invariance assigned to them is also finite.

In comparison with intensity representations of a conventional Gaussian focus (see the propagation behavior of a Gaussian focus in figure (a) of Fig. 1), Fig. 1 shows the propagation behavior of non-diffracting rays using intensity representations in figures (b) and (c) . Figures (a), (b) and (c) each show a longitudinal section (xz-plane) and a transverse section (xy-plane) through the focus of a Gaussian beam and non-diffracting rays, respectively, directed in the z-direction propagate.

Figure (b) refers to a rotationally symmetrical, non-diffracting beam, in this case a Bessel-Gaussian beam. Figure (c) refers to a non-asymmetric non-diffracting beam as an example. For a Bessel-Gaussian beam, the Figures (d) and (e) of Figure 1 also show details of a central intensity maximum. Thus, image (d) of FIG. 1 shows an intensity curve in a transverse sectional plane (X-Y plane) and a transverse intensity curve in the X direction. The image (e) of Fig.

1 shows details of the central intensity maximum in a section in the direction of propagation. d rui uen vergieicn wuu em roKusuurcnmessei 0 The Gaussian focus is defined, with the Gaussian focus being defined via the second moments. Furthermore, an associated character- • • < , <• „ , • , _T , ™ nistic length defined in terms of the Rayleigh length, which is defined as a distance from the focal position at which the beam cross-section has increased by a factor of 2. Furthermore, for a quasi-non-diffracting beam, a transverse JND

Focus diameter “0 _a l _s defines the transverse dimension of a local intensity maximum JND, with the transverse focus diameter ^u,) being given by the shortest distance of directly adjacent, opposite intensity minima (eg intensity drop to 25%). See, for example, Figures (b) and (d) in FIG. 1. The longitudinal extension of the almost propagation-invariant intensity maximum can be viewed as a characteristic length L of the quasi-non-diffracting beam. It is defined by an intensity drop to 50%, starting from the local intensity maximum, in the positive and negative z-direction, see images (c) and (e) of Fig. 1.

A quasi-non-diffracting ray is assumed here if, for similar transverse dimensions, e.g , the characteristic length L of the non-diffracting

beam clearly exceeds the Rayleigh length of the associated Gaussian focus, especially when L > IOZR

(Quasi) Bessel rays, also known as Bessel-like rays, are examples of a class of (quasi) non-diffracting rays. In such beams, the transverse field distribution ( ' near the optical axis obeys in good approximation a Bessel function of the first kind of order n. A subset of this class of beams are the so-called Bessel-Gauss beams, which due to their simple A Bessel-Gaussian beam can be formed, for example, by illuminating an axicon of refractive, diffractive or reflective design with a collimated Gaussian beam.

An associated transverse field distribution near the optical axis in the region of a The associated elongated focus zone obeys, in good approximation, a Bessel function of the first kind of order 0 (in a good approximation), which is enveloped by a Gaussian distribution, see Figures (d) and (e) of Fig. 1, the intensity distribution shown correspond to the square of the absolute value of a Bessel function (in a good approximation).

Typical Bessel-Gauss beams, which can be used to process transparent materials, have a diameter of the central intensity maximum on the optical axis of u ₀ . Ü .111 _au p)i _e associated length L can easily exceed 1 mm, see figure (b) of FIG. 1. A focus of a Gaussian beam with ^— 2.5 | m, on the other hand, is characterized by a focal length in air of only '-R ~ at a wavelength λ of 1 pm, see figure (a) of FIG 10-^R, for example 100 times or more or even 500 times or more the Rayleigh length.

Aspects described herein are based in part on the recognition that if a workpiece having a curved surface is to be machined with a non-diffracting beam, such as that formed in an interference-based focal zone of a Bessel-Gaussian beam, the curved surface can affect the formation of the non-diffracting beam (the underlying interference). Accordingly, beam shaping, as used to process flat workpieces, is no longer effective. This is particularly the case when the curvature is not rotationally symmetrical but is one-dimensional, as in the case of a tube or cylinder to be machined made of glass or a transparent ceramic, for example.

It was also recognized that this influence on the non-diffracting beam can be compensated for in one processing step, so that beam shaping concepts or beam shaping components developed for flat workpieces can then also be used to form the non-diffracting beam with, for example, specific phase imprints.

In other words, the inventors have recognized that a curved surface leads to aberrations in the propagation of the laser radiation and spatial properties of a non-diffracting beam, for example a beam profile similar to a Bessel beam, no longer develop. For example, such non-diffracting beams can no longer be used over the full desired length for the formation of material modifications. In order to retain the formation and properties of the non-diffracting beam, for example with a beam profile similar to a Bessel beam, it is proposed here to counteract the aberrations occurring when entering the workpiece with a phase correction. The phase correction in the beam path is preferably carried out in the area in which there is still a Gaussian or almost Gaussian laser beam profile. The phase correction can take place in particular in the area of a phase imprint, such as is used to form the non-diffracting beam, for example a beam profile similar to a Bessel beam, in workpieces. With a square curved surface aligned symmetrically to the pulsed laser beam, the phase correction can be effected with simple optical components. Even with tilted surfaces, the geometries of the optical components required for correction become very complex.

It was thus recognized that, despite aberrations occurring when entering a workpiece, a non-diffracting beam can be generated with an almost undisturbed propagation in the material of a pipe or cylinder. When carrying out the phase correction, elongated modifications can also be inscribed in a workpiece with a curved surface using a pulsed laser beam with appropriately set parameters such as pulse energy, pulse duration and focal zone geometry. Structural modifications created in this way can, as with flat workpieces, enable a cutting process or be used to remove material.

Fig. 2 shows a schematic representation of a laser processing system 1 with a laser beam source 1A and an optical system 1B for beam shaping of a pulsed output laser beam 3' of the beam source 1A. The purpose of beam shaping is to form a pulsed laser beam 3 with a beam profile that can be focused as a non-diffracting beam in a focus zone 7 for material processing. In other words, the focal zone 7 is formed by the non-diffracting beam and the focal zone 7 is elongated along a beam axis 5 of the laser beam 3 .

The focus zone 7 is created in a workpiece to be machined. The workpiece can, for example, consist of a material that is largely transparent (for the laser wavelength of the pulsed laser beam 3 used) in a ceramic or crystalline design such as glass, sapphire, transparent ceramic, glass ceramic. transparency of a material refers herein to the linear absorbance. For example, for light below the threshold fluence/intensity, a “substantially” transparent material may absorb, for example, less than 20% or even less than 10% of the incident light over a length of modification.

In Fig. 2, a (e.g. glass) tube 9 is three-dimensionally indicated as an example of a workpiece with a curved surface 9A. The tube 9 has an outer radius Ra and an inner radius Ri and a wall thickness Ra-Ri. In Fig. 2, the beam axis 5 is directed towards the surface 9A along a normal direction N of the surface 9A and impinges on it at an impingement point P.

In general, the output laser beam 3' and thus the laser beam 3 is determined by beam parameters such as the formation of individual laser pulses or groups of laser pulses, wavelength, spectral width, temporal pulse shape, pulse energy, beam diameter and polarization. For material processing, the laser pulses have e.g. pulse energies that lead to pulse peak intensities that cause volume absorption in the material of the tube wall and thus the formation of a modification in a desired geometry.

Usually, the output laser beam 3' will be a collimated Gaussian beam with a transverse Gaussian intensity profile generated by the laser beam source 1A, for example a high-power USP laser system. The optical system 1B forms a beam profile from the Gaussian beam, which enables the formation of the elongated focal zone 7; For example, a Bessel-Gaussian beam with an ordinary or inverse Bessel-beam-like beam profile is generated with the aid of a beam-shaping element 11 of the optical system 1B. The beam-shaping element 11 is designed to impress a transverse phase curve on the incident output laser beam 3'. The beam shaping element 11 is, for example, a hollow cone axicon, a hollow cone axicon lens/mirror system, a reflective axicon lens/mirror system or a diffractive optical beam shaping element. The diffractive optical beam-shaping element can be a programmable or permanently written diffractive optical beam-shaping element, in particular a spatial light modulator (SLM spatial light modulator). For exemplary configurations of the optical system and in particular of the beam-shaping element 11, reference is made to WO 2016/079275 A1 mentioned at the outset. 2 schematically shows other beam-guiding components 13 as part of the optical system 1B, such as a telescope arrangement 13A, mirrors, lenses, filters and control modules for aligning the various components.

The optical system 1B focuses the pulsed laser beam 3 into the workpiece, here into the wall of the tube 9, so that the elongated focus zone 7 is formed there. The elongated focus zone 7 refers here to a three-dimensional intensity distribution that determines the spatial extent of the interaction and thus the modification of the material with the laser pulse/laser pulse group in the workpiece to be processed. The elongated focus zone 7 defines an elongated volume area in the workpiece to be machined, in which there is a fluence/intensity. If the fluence/intensity is above the threshold fluence/intensity relevant for the processing/modification, an elongated modification 15 is inscribed into the workpiece along the elongated focus zone 7 .

With regard to laser processing, one speaks of elongated focal zones when a three-dimensional intensity distribution with regard to a target threshold intensity is characterized by an aspect ratio (expansion in the direction of propagation in relation to the lateral extent transverse to the axis of the focal zone (diameter of the on-axis maximum)) of at least 10: 1, for example 20:1 and more, or 30:1 and more, or 1000:1 and more. Such an elongated focal zone can lead to modification 15 in material with a similar aspect ratio. In general, with such aspect ratios, a maximum change in the lateral extension of the intensity distribution, which the modification 15 brings about, over the focal zone 7 can be in the range of 50% and less, for example 20% and less, for example in the range of 10% and less. The same applies to a maximum change in the lateral extent of modification 15.

In general, when processing transparent materials by means of elongated volume absorption, it applies that as soon as absorption takes place, this absorption itself or the resulting change in material properties can influence the propagation of laser radiation. It is therefore advantageous to feed the beam components used for modification further down the beam at an angle to the focal zone axis of the interaction zone. An example of such an energy supply is the non-diffracting beam, for example a (conventional) Bessel-Gaussian beam (see FIG. 1), in which there is an annular far-field distribution whose ring width is typically small compared to the radius. At a In the rotationally symmetrical Bessel-Gaussian beam, the interaction zone/focus zone axis is supplied with radial beam components essentially with this angle in a rotationally symmetrical manner. The same applies to the inverse Bessel-Gauss beam and to modifications such as homogenized, asymmetric or modulated (inverse) Bessel beams.

An example of beam shaping that leads to such an elongated focal zone is illustrated in FIGS. 3A to 6B. The figures show, by way of example, in a sectional plane through the beam path, the arrival of (radial) beam components 3A (see in particular Fig. 4B) at an angle of arrival 6 in air or 6 'in the material on the beam axis 5 of the laser beam 3 Focus zone 7 along the beam axis 5 in the workpiece by interference of the beam components 3 A (over a length /., see Fig. 1) are formed.

The formation of an elongated (e.g. Bessel beam-based) focal zone presupposes that energy can be supplied laterally over the entire length L of the focal zone and that the conditions for constructive interference are present.

For the machining of the workpiece, a relative movement takes place between the optical system 1B and the workpiece, so that the focus zone 7 can be radiated into the workpiece at different positions with a pulsed laser beam in order to form an arrangement of modifications 15 . The relative movement is controlled in such a way that the modifications line up along a scanning trajectory T. The arrow illustrating the scanning trajectory T in FIG. 2 represents a movement of the impact point P over the surface of the workpiece (example in FIG. 1 in the plane of the drawing, i.e. the section plane of the tube 9). In particular, a relative movement is effected between the workpiece and the focal zone 7, in which the focal zone 7 is repeatedly positioned along the scanning trajectory T (at least partially) in the material of the workpiece. Accordingly, a plurality of modifications can be written into the material of the workpiece along the scanning trajectory T .

For a circumferential machining of the tube 9 (circular scanning trajectory T), a workpiece holder 19 is shown in FIG. Support rollers 19A are indicated as an example. Furthermore, a base unit 19B of the workpiece holder 19 can allow the tube 9 to be displaced along the longitudinal axis A or can adjust the distance from the optical system 1B. Alternatively or additionally, a relative movement between the workpiece and the optical system 1B can be brought about by moving the optical system 1B (or components thereof). FIG. 2 shows an example of a linear displacement unit 21 of the optical system 1B, with which the focal zone can be positioned along the beam axis. Further processing axes can be provided, which allow the exiting laser beam 3 and thus the axis of the focal zone to be spatially aligned.

Depending on the scanning trajectory T, a piece of pipe can be cut off or structures can be cut out of the piece of pipe. As explained in connection with Figures 10 and 11, this can be done using a heat source 203 and a cooling source 205, for example.

The laser processing system 1 also has a control unit 23 which, in particular, has an interface for a user to input operating parameters. In general, the control unit 23 includes electronic control components such as a processor for controlling electrical, mechanical and optical components of the laser processing system 1. For example, operating parameters of the laser beam source IA such as pump laser power, parameters for setting an optical element (e.g. an SLM) and parameters for spatial alignment an optical element of the optical system 1B and parameters of the workpiece holder 19 (for traversing the scanning trajectory T) are set (illustrated by double arrows 23A).

A distance sensor 25 is also indicated schematically in FIG. 2, which is arranged, for example, on the optical system 1B. The distance sensor 25 is set up to detect the distance between the workpiece and the optical system. In particular, the distance sensor 25 can determine a position of a surface 9A of the workpiece 9 along the beam axis 5 in relation to a target position with regard to the elongated focal zone. The target position is defined for the specific material processing situation of the respective workpiece and for the respective beam formation. For example, the target position can be specified by a desired displacement Az (in or against the propagation direction of the laser beam) between the start of the elongated focus zone and the surface of the workpiece/tube 9 . For example, the beginning of the elongated focal zone can be at the location in the Z-direction at which the intensity has increased to 50% of the maximum intensity. In addition to the coincidence of the beginning of the elongated focus zone with the surface of the workpiece, a displacement Az>0 can be set as the target position, in which the elongated focus zone is already formed in front of the tube 9 and then extends into the material of the tube 9. Likewise, a displacement Az<0 can be set, in which case the elongated focal zone is formed only in the material of the tube or at least beginning in the material of the tube 9 .

The distance sensor 25 outputs status data to the control unit 23, which can regulate the distance, for example, via the workpiece holder 19 or the linear displacement unit 21 in relation to a predetermined target position. Distance sensors can be designed, for example, as confocal white-light sensors, white-light interferometers (such as optical coherence tomographs) or capacitive sensors.

In particular, the distance sensor 25 can be used to measure the position of a workpiece with respect to processing optics and/or the geometry of the workpiece in a pre-measurement step or during processing. For example, it can happen that the rotating work piece (to be positioned) is mounted in the work piece holder 19 with a slight wobbling, in particular a strong wobbling during a rotation. In such a case, the distance between the surface and the specified target position can be measured before the actual processing and the position data of the surface can be saved. For this purpose, the control unit 23 can cause the workpiece to be traversed once along the trajectory to be machined without the laser beam 3 being irradiated. During this pre-measurement, the distance sensor 25 detects the distance data and outputs it to the control unit 23 in which the distance data is stored.

Furthermore, the distance sensor 25 can be designed to measure a curvature of the surface of the workpiece in a pre-measurement step or during processing. The curvature can be calculated from the distance data, for example. For example, the curvature of the surface of the workpiece can vary along the scanning trajectory, so that the scanning trajectory is traversed in a pre-measurement in order to save data about the curvature of the surface along the scanning trajectory and use it for later adjustment of the phase-correcting beam shaping. A corresponding preliminary measurement can in turn be controlled by the control unit 23 and the recorded curvature data can be stored in the control unit 23 . Furthermore, the control unit 23 can set parameters of the laser beam 3 .

Exemplary parameters of the laser beam 3, which can be used within the scope of this disclosure, in particular in the various aspects, embodiments and developments disclosed herein, which preferably use pulsed laser radiation, and in particular ultra-short laser pulses, for material processing, are:

Laser pulse energies/energy of a laser pulse group (burst): e.g. in the mJ range and more, for example in the range between 20 pj and 5 mJ (e.g. 1200 pj), typically between 100 pj and 1 mJ

Wavelength ranges: IR, VIS, UV (e.g. 2 pm > Z. > 200 nm; e.g. 1550 nm, 1064 nm, 1030 nm, 515 nm, 343 nm)

Pulse duration (FWHM): a few picoseconds (for example 3 ps) and shorter, for example a few hundred or a few (tens) of femtoseconds, in particular ultra-short laser pulses/laser pulse groups

Number of laser pulses in a burst: e.g. 2 to 4 pulses (or more) per burst with a time interval in the burst of a few nanoseconds (e.g. 40 ns)

Number of laser pulses per modification: one laser pulse or one burst for a modification Repetition rate: usually greater than 0.1 kHz, e.g. 10 kHz Length of the focal zone in the material: greater than 20 pm, up to a few millimeters

Diameter of the focal zone in the material: greater than 1 pm, up to 20 pm and more

(Resulting lateral expansion of the modification in the material: greater than 100 nm, e.g. 300 nm or 1 pm, up to 20 pm and more)

Feed d between two adjacent modifications: at least the lateral extent of the modification in the feed direction (usually at least twice the extent, for example four or ten times (or more) the extent)

The pulse duration refers to a single laser pulse. Similarly, an exposure time refers to a group/burst of laser pulses that result in the formation of a single modification at a location in the material of the workpiece. If the exposure time, like the pulse duration, is short with respect to a given feed rate, one laser pulse and all laser pulses of a group of laser pulses contribute to a single modification at one location. At lower feed rates, continuous Modification zones, which include modifications that adjoin one another and merge into one another, arise.

The aforementioned parameter ranges can allow the processing of volumes that protrude up to, for example, 20 mm and more (typically 100 μm to 10 mm) into a workpiece. Volumes of this type are used, for example, when processing pipes with internal radii of 100 μm and larger and external radii of, for example, in the range of 10 mm.

The beam shaping is implemented in FIG. 2 with a flat diffractive optical beam shaping element 27 .

The phase correction concepts disclosed herein with regard to the curved surface 9A of the workpiece is implemented in FIG. 2 by a cylindrical lens 29 . A cylinder axis assigned to the cylinder lens extends in Fig. 2 along the axis A of the tube 9. It is also indicated schematically in Fig. 2 that the cylinder lens 29 can be designed as a phase distribution of an (adjustably deformable) cylinder mirror or a diffractive optical beam-shaping element 29' . In this case, the diffractive optical beam-shaping element 29' can be embodied as a permanently inscribed diffractive optical beam-shaping element. Furthermore, the diffractive optical beam-shaping element 29' can be used as an adjustable diffractive optical beam-shaping element. Furthermore, the diffractive optical beam-shaping element 27 and the diffractive optical beam-shaping element 29' can be combined in one diffractive optical beam-shaping element. An adjustable diffractive optical beam-shaping element or a deformable cylinder mirror can be controlled and adjusted by the control unit 23 with regard to the phase-correcting beam shaping to be carried out (see connecting line 23A in FIG. 2).

In general, a diffractive optical beam-shaping element is designed to impose a phase contribution on a transverse beam profile of the output laser beam 3′, the diffractive optical beam-shaping element having surface elements that adjoin one another (see surface elements 27A indicated as an example for the beam-shaping element 27 in FIG. 2). The surface elements 27A can build up a surface lattice structure in which a phase shift value is assigned to each surface element 27A. With the help of specially selected phase shift values, an axicon or an inverse axicon, for example, but also a cylindrical lens can be diffractively simulated. Here, diffractive optical beam-shaping elements and corresponding refractive optics as well as reflective optics implementations are regarded as essentially equivalent optical means with regard to the phase correction to be carried out.

FIGS. 3A and 3B show orthogonal sectional views of the beam path (only schematically, not physically) in an optical system to clarify the beam shaping. Fig. 3A shows a sectional view on a Z-Y plane, and Fig. 3B shows a sectional view on a Z-X plane.

The processing optics are used for (Gaussian) Bessel beam generation and include an axicon 31 with a cone angle y, so that radial beam components each run towards the beam axis 5 at an angle 6 and a first real Bessel beam focus zone (interference zone 33 over form a length 10). The Axicon 31 is embedded in two telescopes. A telescope (not shown) positioned upstream adjusts the beam diameter of the output laser beam 3' onto the axicon 31, generally the beam shaping element. Figures 3A and 3B explicitly show the telescope arrangement 13A positioned downstream with telescope lenses LI and L2 and focal lengths fl and f2, with which the axicon tip 31_S is imaged reduced in relation to the curved surface of the workpiece (reduction factor M=fl/f2). will. The general aim of the imaging is that the interference zone 33 is imaged in the workpiece in a reduced manner to form the elongated focal zone 7 (of the non-diffracting laser beam). The non-diffractive laser beam strikes the workpiece surface at an impact point P. In general, the point of impact is understood here as the point of intersection of the optical axis of the laser beam with the workpiece (for example the substrate to be processed). When the axicon tip 31_S is imaged onto the curved surface, there is no shift Az of the beginning of the non-diffractive laser beam to the entrance surface (i.e., Az = 0). In the example of Fig. 3 A, the beginning of the non-diffracting laser beam is an amount Az > 0 in front of the surface of the workpiece, for example Az is in the range of 100 pm to 200 pm, so that there is already sufficient intensity on the workpiece surface for processing the material is available. With reference to FIG. 5A, the start of the non-diffracting laser beam can also only take place in the workpiece (Az<0).

After imaging and entering the workpiece, the radial beam components in the ZY plane in the material run towards the beam axis 5 at an angle 6', for example. This is shown in FIG. 4A (ideal propagation; without aberrations) for a flat surface 37. FIG. The interference of the radial beam components 3 A takes place over the entire length.

An exemplary intensity profile I(x, z) is shown along the beam axis 5 (in the Z direction) in FIG. 5A, as can be generated with a Bessel beam. An associated transverse intensity profile I(x, y) is shown in FIG. 5B. The intensity curves correspond to those in image (b) of Fig. 1.

The aim is to achieve such an intensity curve for a workpiece with a curved surface 9A. However, this is not possible without correcting the optical path in the plane of curvature.

4B (disturbed propagation; with aberrations) illustrates the problem of a Bessel beam-shaped laser beam entering a material through a curved surface 39. Due to the curvature (ie, a locally inclined incidence), the radial beam components run under the material varying angles 6(r) towards the beam axis 5. In the case of the Bessel beam, the interference conditions are only given at the beginning (in the case of the inverse Bessel beam only at the end) due to the still approximately flat surface in the central area around the beam axis. For example, this is the situation for a surface with a radius of curvature R of 5 mm and a diameter D of the impinging laser beam 3 of, for example, 250 μm to 2 mm.

An exemplary intensity curve I(x,z) is shown in Figures 6A and 6B for this curved surface entry situation. 6A shows an intensity profile I(x, z). It can be seen that high intensities are only present over a limited area along the beam axis 5 (in the Z-direction), zones of somewhat higher intensity then form at a distance from the beam axis 5 . In the associated transversal intensity profile I(x, y) in FIG. 6B, it can be seen that these off-axis zones are arranged in the X and Y directions.

The wavefront aberrations when passing through the curved surface 39 thus result in a focus distribution with a significant loss of intensity in the direction of propagation, so that an optical processing of deep-lying areas in particular is no longer possible.

Coming back to FIG. 3B, due to the surface 9A of the tube 9 being curved in the ZX plane, a non-diffracting beam extending over the entire intended length is formed (ie, constructive interference in particularly deeper lying areas) without compensation in the ZX - level is no longer given, since the conditions regarding the interference in the workpiece differ from those in the interference zone 33. The desired intensity distribution is therefore no longer generated in the workpiece without compensation.

Provided that the phase compensation concept proposed here has been implemented, the correction phase influences the course of the laser beam in the material in such a way that the radial beam components also in the Z-X plane also essentially run towards the beam axis 5 at the angle 6′.

For phase compensation, a cylindrical lens 35 is positioned in front of the axicon 31 in the structure of FIGS. 3A and 3B, the refractive effect of which is in the cross-sectional plane of the tube 9 . To illustrate an alternative arrangement, a cylindrical lens 35' is indicated in dashed lines in FIG. 3B, which is positioned directly downstream of the axicon 31 in the beam path in the processing optics. The cylindrical lens 35, 35' represents the place where an axisymmetric phase distribution is imposed.

The cylindrical lens has a refractive index nz, a cylinder radius Rz and a focal length fz to compensate for aberrations of the workpiece with a radius of curvature Ra of the surfaces and a refractive index nw.

Except for the cylindrical lens 35, the optics in the structure of FIGS. 3A and 3B are to be understood as rotationally symmetrical about the beam axis 5 in the case of a rotationally symmetrical axicon 31.

Because of the cylindrical lens 35, the interference will no longer develop rotationally symmetrically following the axicon 31 since, for example, the conditions in the interference zone 33 in the ZY plane differ from those in the YX plane. The optical systems shown in Figure 2 and in Figures 3A and 3B are examples of an optical system for beam shaping a laser beam for forming a focal zone in a workpiece having a curved surface, the focal zone being elongated along a beam axis of the laser beam. On the one hand, the optical systems have focus-forming optics that allow beam components to enter the beam axis of the laser beam at an angle of incidence for forming the elongated focus zone along the beam axis (ie, for forming a non-diffracting beam) in the workpiece by interference causes. On the other hand, a phase correction is provided in the optical system, which counteracts the interference being influenced by the laser beam entering the workpiece. The phase correction can generally be implemented as diffractive, refractive and/or reflective. It can, for example, be provided as phase-correcting (separate) optics or be integrated into the focus-forming optics.

For the use of a cylindrical lens 35, 35' as compensation optics, the cylindrical lens 35, 35' should be as close as possible in the plane of the axicon or the diffractive optical element (beam shaping element 27) (if possible directly in front of or behind it).

The selection of the radius of curvature Rz of the surface of the cylindrical lens depends on the relative location of the non-diffracting beam with respect to the workpiece, particularly the beginning of the elongated focal zone with respect to the entrance surface of the workpiece.

In the event that there is no shift Az of the beginning of the elongated focal zone to the entrance surface (Az = 0), the radius of curvature Rz of the cylindrical lens is calculated

2 in good approximation from fz » Rw M / (n-1) and fz » Rz / (nz-1)

Rz: radius of curvature of the cylindrical lens, nz: refractive index of the cylindrical lens,

Rw: radius of curvature of the surface of the workpiece, nw: refractive index of the material of the workpiece and

M: M = fl / f2 - imaging factor of the beam path between a location where the phase distribution is impressed and the workpiece. If one considers that the elongated focal zone begins in front of the entry surface of the workpiece (Az greater than 0) or falls into the workpiece (Az less than 0), the following approximate definitions of the radius of curvature R _z of the surface of the cylindrical lens result, which for Az = 0 are the meets the above condition.

2 1

Az > 0 (with the additional parameters a = 5060 mm and b = 9645 mm):

Az < 0 (with the additional parameters c = 284 mm'^ and d = 590):

The graph shown in FIG. 7 shows an exemplary function (composed of the above definitions) of the radius of curvature R _z as a function of the displacement Az, assuming the following parameters:

- imaging factor of the optical system M = 10,

- refractive index of the material of the workpiece n _w = 1.5,

- radius of curvature of the surface of the workpiece R _w = 3.5mm,

- Refractive index of the cylindrical lens n _z = 1.5.

You can see the approximate linear progression for Az < 0 and the approximately quadratic progression for Az > 0.

As indicated in FIG. 2, a “negative” cylindrical lens curvature (concave) is to be provided for a “positive” curved glass tube (convex in the cutting plane). In other words, a phase distribution caused by the cylindrical lens has a scattering effect (and not a collecting effect as occurs when entering the glass tube). Those skilled in the art will appreciate that the concepts disclosed herein can also be used for workpieces with a concavely curved surface (e.g. for laser processing along a rod having a trough) can be machined by providing a "positive" cylindrical lens curvature (convex).

Radii of curvature are generally considered herein to be in a cutting plane transverse to the longitudinal axis of the workpiece/pipe section to be cut. A radius of curvature is inverse to a concave shape for a workpiece having a convex shape (round tube surface) in the cutting plane. The curvature of the correcting optics (or a “curvature” that can be assigned to the corresponding phase curves) is inverted in accordance with the curvature of the workpiece. This is indicated in the above formula for by the factor (-1). A radius of curvature R _z of less than zero/negative cylindrical lens for a concave shape of the workpiece can be seen in FIG. Accordingly, a radius of curvature R _z greater than zero/positive cylindrical lens results for a convex shape of the workpiece. The person skilled in the art will recognize that in addition to plano-convex or plano-concave cylindrical lenses (see FIG. 2), corresponding lenses curved on both sides with the corresponding refractive behavior can be used.

As will be further appreciated by those skilled in the art, diffractive optical beam shaping elements and/or refractive and/or reflective optics may be employed for the phase correction to be performed. Embodiments with diffractive optical beam-shaping elements are explained below with reference to FIGS. 8A to 8F.

Exemplary phase distributions are shown in Figures 8A through 8C for central sections of e.g. Since the phase distribution for the 2° axicon dominates the combined phase distribution, for clarification, FIGS. 8D to 8F show an exemplary case based on phase curves as can be assigned to a 0.5° axicon and a 200 mm cylindrical lens.

FIG. 8A shows a two-dimensional phase distribution PHI_BESSEL(x, y) [in rad] for a diffractive optical element that brings about focus-forming beam shaping. In particular, the phase distribution PHI_BESSEL(x,y) can impose a symmetrical Bessel beam phase distribution on an incident Gaussian beam (to produce a Bessel-Gaussian beam). In the phase distribution PHI_BESSEL(x, y) you can see rings running constant phase shift values radially ramping in a sawtooth shape between -PI and +PI. The phase shift values represent first phase contributions 25 A of the beam formation and cause beam components to arrive at a beam axis of the laser beam at an angle of incidence for formation of an elongated focus zone along the beam axis in the workpiece through interference. The elongated focal zone roughly corresponds to the focal zone created with a 2° axicon (y = 2°).

FIG. 8B shows a two-dimensional phase distribution PHI_ZYL(x, y) for a diffractive optical element, which causes a phase-correcting beam shaping, as is the case when processing a pipe with an outer radius of 5 mm with an elongated focal zone, as is the case with the phase distribution PHI_BESSEL( x, y) is generated can be used. The phase curve roughly corresponds to that of a 1000 mm cylindrical lens with a cylinder radius of "Rz » -500 mm".

One recognizes constant phase shift values in the Y direction, which run (increase) squarely in the X direction in a sawtooth-like form between −PI and +PI in the X direction and represent second phase contributions 25B of the beam shaping. The second phase contributions 25B form a phase distribution that is symmetrical to an axis of symmetry S, the second phase contributions 25B being constant parallel to the axis of symmetry S (in the y-direction) and changing perpendicularly to the axis of symmetry S.

Assuming that there is an imaging factor M = 10 and correspondingly usual refractive indices for the cylindrical lens and the tube, the second phase contributions 25B can cancel out the entry phase that occurs locally, ie, when a laser beam enters the tube with the outer radius of 5 mm on a surface element on the curved surface.

The two-dimensional phase distribution PHI_BESSEL(x, y) and the phase distribution PHI_ZYL(x, y) can be generated together with a diffractive optical element. 8C shows a corresponding superimposed two-dimensional phase distribution PHI total (x, y), in which the two-dimensional phase distribution PHI_BESSEL(x, y) dominates in appearance. To clarify the appearance of a superimposition of a point-symmetrical phase curve for Bessel beam generation of an axisymmetric phase curve for phase correction, Fig. 8D shows a phase distribution PHI_BESSEL(x, y) for generating an elongated focal zone, which is approximately that of a 0.5° axicon generated focus zone corresponds. FIG. 8E shows a two-dimensional phase distribution PHI_ZYL(x, y) whose phase profile corresponds approximately to that of a 200 mm cylindrical lens with a cylinder radius of approximately −100 mm.

In FIG. 8F, a corresponding deformation of the phase distribution PHI_BESSEL(x, y) can now be seen in the superimposed two-dimensional phase distribution PHI total(x, y). With the phase distribution PHI_BESSEL(x,y) of Figure 8F, a tube with an outside radius of 1mm (at M=10) could be machined. It is noted once again that the parameters on which FIGS. 8D to 8F are based serve purely to clarify the phase curves and are not intended to represent a realistic example.

FIG. 9 shows a flow chart of a method for laser machining a workpiece with a curved surface.

In a step 101, a laser beam is shaped to form an elongated focus zone in the material of the workpiece. Beam shaping is performed with an array of diffractive and/or refractive and/or reflective optics. Step 101 includes the sub-steps of focus-forming beam shaping 101A and phase-correcting beam shaping 101B.

The focus-forming beam shaping 101 A causes beam components to run in at an angle of incidence onto a beam axis of the laser beam for forming the elongated focus zone along the beam axis in the workpiece by interference.

The phase-correcting beam shaper 101B counteracts the interference caused by the laser beam entering the workpiece.

Steps 101A and 101B can also be carried out in combination in a common phase imprinting step. In step 101, a two-dimensional phase distribution can be applied to the laser beam to form the elongated focal zone. wherein the phase distribution for the focus-forming beam shaping includes first phase contributions, which cause beam components to arrive at the angle of arrival, and/or for the phase-correcting beam shaping, second phase contributions, which cancel out an entry phase locally accumulated by the laser beam when it enters the workpiece. The accumulated entry phase is determined for an alignment of the beam axis along a normal direction of the surface at a point of impact of the beam axis on the surface. It takes into account the angle of arrival (θ'), the radius of curvature Rw of the surface of the workpiece at the point of impingement and the refractive index nw of the workpiece (particularly of the material in the area where the beam enters the workpiece).

In a step 103, the symmetrical phase distribution and the workpiece can be aligned in such a way that an axis of symmetry of the phase distribution of the second phase contributions, taking into account the beam path, runs orthogonally to a plane between a location where this axisymmetric phase distribution is impressed and the workpiece, in which a (maximum ) radius of curvature of the surface is defined.

In a step 105, beam parameters of the laser beam are set in such a way that the material of the workpiece is structurally modified in the elongated focal zone.

In a step 107, the laser beam is radiated onto the surface of the workpiece along a beam path that images the laser beam into the material of the workpiece to form the elongated focal zone. The beam axis of the laser beam can be aligned to a normal direction of the surface (step 107A) such that the beam axis impinges on the surface in an angular range of 5° around the normal direction and preferably along the normal direction.

With regard to steps 103 and 107, an adjustment process can be carried out, for example with the arrangement described in German patent application 10 2020 103 884.4, “Adjustment device for a Bessel beam processing optics and method”, with the application date February 14, 2020 of the applicant.

For laser processing, for example, the axicon tip 31_S (see FIG. 2) can be imaged virtually on the surface of the tube 9 (Az=0) as the beginning of the elongated focal zone. Alternatively, the beginning of the elongated focal zone in front of the surface of the tube 9 (Az > 0) or only in tube 9 (Az <0). Assuming an appropriately adapted selection of the radius of curvature, the positioning of the optical system relative to the workpiece, preferably in the direction of beam propagation (along the beam axis), can have a z-position tolerance of a few 100 micrometers, eg ±200 pm.

For adjustment, an adjustment cylinder lens can be used as a substitute for the workpiece (front curved like the tube to be processed, back flat). A correspondingly precise exchange must be made possible for laser processing. A marking can be applied to the front of the cylindrical lens, for example metal can be vapor-deposited or a character can be painted on. A telescope is arranged downstream of the adjustment cylinder lens, the focal plane of which is recorded with a camera for imaging the surface.

In a first step of the adjustment process, the camera is adjusted to the surface of the adjustment cylinder lens so that the marking is sharply imaged.

In a second step of the adjustment process, the processing optics are aligned with the surface of the adjustment cylinder lens. Here, both a transversal position (in the X/Y direction) and a longitudinal position (in the Z direction) have to be adjusted.

For transversal positioning, the tube is shifted out of the beam path in opposite directions, with the edges of the lens on both sides being easily detectable and the mean value giving the transversal position.

The virtual plane of the Gaussian envelope of the raw beam on the axicon is searched for the longitudinal positioning. If the test cylinder lens is too close, the camera recognizes the Bessel beam focus zone, if the test cylinder lens is too far away, the camera already recognizes the ring distribution. The largely correct position in the Z-direction is given when the envelope of the beam profile is as circular as possible and not elliptical. The flat back of the test cylindrical lens almost does not aberrate the camera image.

In a second step of the adjustment process, the cylindrical lens is replaced by the workpiece, eg a glass tube, using a reference in the Z position. In a step 109, a relative movement is effected between the workpiece and the focal zone, during which the focal zone is positioned along a scanning trajectory in the material of the workpiece. Accordingly, a plurality of modifications can be written into the material of the workpiece along the scanning trajectory.

The relative movement can be controlled in step 109 as a rotational movement of the workpiece, in which the beam axis of the laser beam runs in particular through a longitudinal axis of the workpiece. In the case of a purely rotational movement about a longitudinal axis of the workpiece, the scanning trajectory of the laser beam can run in a plane of maximum curvature of the surface of the workpiece. Alternatively or additionally, a translational movement in the direction of the longitudinal axis of the workpiece can be controlled in order to traverse any scanning trajectories on the surface of the workpiece. For example, an outer contour for dividing the workpiece 9 into two parts along a longitudinal axis of the workpiece 9 (see the example in Fig. 2) or an inner contour closed on a surface of the workpiece 9 for triggering an area delimited by the inner contour can be traced (see the Example of Figure 12A). Furthermore, the scanning trajectory can run in one or more areas with (substantially) the same curvature in the surface and/or in one or more areas with varying curvature of the surface.

In a step 111, a position of the surface of the workpiece along the beam axis is monitored and regulated to a target position (target distance from the optical system). Monitoring and regulation is carried out in particular when a rotational axis of the rotational movement deviates from an axis of rotational symmetry of the surface of the workpiece and/or the surface of the workpiece deviates at least in sections from a rotationally symmetrical surface profile.

If the trajectory runs in a region with varying curvature, in a step 113 a phase-correcting beam shaping 101B′ can be adapted in its compensation effect to the curvature of the surface that is present in each case. Thus, for the curvature of the surface that is present in each case, an influence on the interference by the entry of the laser beam into the workpiece can be counteracted. The phase-correcting beam shaping is adapted, for example, by taking into account the curvature that is present in each case in the two-dimensional phase distribution of the beam-shaping element. For example, see the workpiece shown in Figure 12B with a tapered end Workpiece surface in which a sequence of modifications is to be inscribed along a closed inner contour. For example, the second phase contributions 25B provided for such a phase correction can be adjusted accordingly in an adjustable SLM. Alternatively, for example, the curvature of a deformable mirror can be adjusted.

The adjustment can be based, for example, on measurements that are carried out during the beam processing. A correspondingly fast analysis unit for the geometry of the workpiece must be provided. As an alternative or in addition, a preliminary measurement of the geometry of the workpiece along the scanning trajectory can be carried out in a step 115 . For the preliminary measurement, the laser processing system can, for example, traverse the scanning trajectory to be traversed for the material processing without activating the laser beam source 1A for measuring the geometry of the workpiece.

In the examples discussed above, separate optics for beam shaping and phase compensation are shown as examples. However, these optics can also be implemented in a single optic (e.g. as a refractive/reflective free-form element or as a diffractive optical element) or in a hybrid optical element (cylindrical lens on the input side, axicon on the output side; "Zaxicon").

Furthermore, for example, the long focal length lens f1 of the telescope 13 A can be included in a hybrid axicon or in a diffractive optical element. As an alternative to imaging a real focal zone (such as a Bessel ray-like focal zone), a virtual focal zone (such as an inverse Bessel ray-like focal zone) can be imaged with the telescope 13A.

Workpieces such as tubes, cylinders or sections of a tube or cylinder, such as a half-tube or half-cylinder, can be machined with the machining methods described herein.

The result of the laser-based workpiece processing is a workpiece into which a plurality of spaced modifications or modifications that merge into one another have been introduced. In the case of a pipe, for example, these are introduced all around (see FIG. 2) in order to divide the pipe into 2 sections (scanning along a circumferential outer contour). Furthermore, modifications can be introduced into a curved surface along an inner contour (see FIGS. 12A and 12B). The modifications may additionally form cracks in the material extending between adjacent modifications or generally randomly from one of the modifications into the material of the workpiece.

The previously explained methods for material processing of a workpiece with a laser beam can represent a first part of a process for separating a workpiece with a curved surface into two parts. After completion of the material processing with the laser beam, the workpiece has many modifications in the material, but there is often still a sufficient connection of unmodified material between the two parts. Correspondingly, a second part of the separation process is necessary, in which these remaining connections are broken, in order to achieve the complete separation of the workpiece into two parts.

With regard to the second separation process, it is added that a modification within the scope of this disclosure represents a structural change in the material of the workpiece, which converts the material, for example, from a non-etchable state of the unmodified material to an etchable state of the modified material. Accordingly, modifications can be characterized in particular by an increase in wet-chemical etchability compared to the unmodified material. Accordingly, the glass tube can be separated into two parts within the scope of a wet-thermal etching process. Such wet-chemical etching processes can be used in particular to remove material areas that have been cut out along an inner contour.

Another approach to separating a workpiece into two parts can be based on the fact that a modification of the material can be accompanied by the formation of a likewise elongated cavity. If this is the case and if a sufficient number of cavities have been formed circumferentially in the glass tube, the glass tube can break (in particular spontaneously) along a weakening line formed by the sequence of cavities.

Another approach to parting a workpiece with a sequence of modifications uses thermally induced, thermally assisted, and/or thermally advanced cracking. In connection with Figures 10 and 11, such an exemplary thermal separation process of machined workpieces is shown using the example of a glass tube 201 1, where the glass tube 201 has been modified using a non-diffracting beam along a circumferential trajectory, for example, at equally spaced positions.

The laser processing system shown in FIG. 2 can additionally include a heat source 203 and/or a cooling source 205 for a thermally supported cutting process. Alternatively, the heat source 203 and/or the cooling source 205 can be provided as part of an independent separating device with the correspondingly required degrees of freedom. The heat source 203 and the cooling source 205 are designed to heat or cool the glass tube 201, in particular in the area of the modifications. For this purpose, local heating/cooling can be carried out in combination with a rotation of the glass tube (indicated by the arrow 206 in FIG. 10). Localized heating can be effected, for example, with a localized flame directed at the work piece or a CO2 laser beam directed at the work piece. A (local or large-area) cooling can be effected, for example, with a water-gas mixture that is sprayed onto the workpiece or, for example, flows through a cavity in the workpiece.

The separation process can include three sub-steps 207A, 207B, 207C. These are illustrated schematically in FIGS. 10 and 11 for the case of a subdivision of a glass tube 201 into glass tube parts 201A, 21B. In the separating process, the glass tube 201 is thermally influenced in such a way that the glass tube 201 separates into the two glass tube parts 201A, 201B.

In step 207A in FIG. 10 one can see the glass tube 201 (shown in perspective) with an arrangement of symmetrical modifications 209. The modifications 209 extend, for example, from the surface of the glass tube 201 radially into the latter. The modifications 209 are present in a zone 209A which extends around the glass tube, for example in a circular manner. In other words, the arrangement of modifications 209 extends once around the glass tube 201, as can be seen from the enlarged (unrolled) section 211 of the surface of the glass tube 201. In the example of Fig. 10, each of the modifications 209 has been written rotationally symmetrically into the material of the glass tube 201, for example with the help of a symmetrical Bessel-Gaussian beam, which, as a non-diffracting beam, covers the elongated focal zone in the material of the glass tube 201 to produce the modifications 209 trains. In a further enlargement 211 A of the unrolled section 211, it was indicated schematically that cracks 213 emanate from the modifications 209. the Cracks 213 are randomly oriented and/or increasingly run (at least partially) between the modifications 209.

In sub-step 207A, the glass tube 201 is held in such a way that it can be continuously rotated by means of a rotation axis, for example around the cylinder axis. The modified zone 209A of the glass tube 201 is continuously heated. This can be done, for example, by a flame 203 A or a CO2 laser beam. The rotation speed can be selected in such a way that no significant cooling occurs during one revolution of the glass tube 201 . In this way, the glass tube 201 can be heated over the entire material thickness, so that the material of the glass tube 201 expands in this area.

In partial step 207B, the surface of the glass tube 201 is now cooled as abruptly as possible. This can be done, for example, by cooling using a water-gas mixture 205A, which is sprayed onto a large area of the glass tube 201 while it continues to rotate.

Thus, in the outer/near-surface area of the material of the glass tube 201, the temperature has cooled down considerably and a large temperature gradient forms with a minimum temperature on the surface of the glass tube 201 and a maximum temperature, for example in the area of zone 209A of the modifications 209 on the Inner wall of the glass tube 201 from. Due to the large temperature gradient, there is a tensile stress (arrow 215) on the surface of the glass tube 201, which causes an initial crack 217 to form on the surface of the glass tube 201 that runs as completely as possible. The initial crack 217 runs along the introduced modifications 209 and can partially/in sections be based on the cracks 213 that have already arisen when the modifications 209 were introduced.

In step 207C, the glass tube 201 is heated from the outside (flame 203B) and optionally cooled from the inside by a water-gas mixture 205B' from a cooling source 205'. A temperature gradient now develops over the entire material thickness of the glass tube 201. The temperature gradient means that the initial crack 217 can propagate through the wall of the glass tube 201.

In Fig. 10, the sub-step 207C is additionally illustrated schematically on a sectioned pipe with regard to the forces acting (arrows 219 for clarification of the tension due to cooling in the interior of the glass tube 201; Arrows 219B to illustrate the stress due to the heating of the outer area of the glass tube 201).

The initial crack 217 transitions into a separating crack 221 which extends completely through the wall of the glass tube 201 . If the separation crack 221 runs completely around the glass tube 201, the glass tube has been completely separated into the parts 201A and 201B.

For the sake of completeness, it is pointed out that, in addition to an intensity distribution in a focal zone that causes a single symmetrical modification, a phase imprint can be carried out, e.g. with a diffractive optical element, which leads to an intensity distribution in the focal zone that has an asymmetric (e.g. in one direction flattened) modification or several modifications running parallel to each other (see image (c) of FIG. 1). The modification or the arrangement of modifications can be generated with a laser pulse or a group of laser pulses. Exemplary phase imprints and intensity distributions are, for example, in the German patent application 10 2019 128 362.0, "Segmented beam shaping element and laser processing system", with the application date October 21, 2019 by the applicant, and in K. Chen et al., "Generalized axicon-based generation of nondiffracting beams", arXiv: 1911.03103vl [physics. optics] 8 Nov 2019 revealed.

Such asymmetric modifications or arrays of modifications may also be utilized with the concepts disclosed herein for processing materials having curved surfaces. In other words, beam shaping, which is to be carried out for such asymmetrical modifications, can also be combined with phase correction, which can correct the influence on the phase distribution when entering the material.

FIG. 11 illustrates a thermal separation process similar to the separation process described in connection with FIG. 10 for such asymmetric modifications using the example of an elliptically flattened modification, with three corresponding partial steps 307A, 307B, 307C being carried out. For details of the three partial steps, reference is made to the preceding description of FIG. Furthermore, the corresponding reference numbers are used in FIG. 11, with the exception of asymmetric modifications 309, a modification zone 309A extending along the modifications 309 and cracks 313 (see sub-step 207A in Fig. 11).

Because of the asymmetrical modifications 309, the cracks 313 can form to a greater extent along the array of asymmetrical modifications 309. Compared to randomly distributed cracks, the cracks 313 may partially overlap or at least protrude closer together (as illustrated in Figure 11).

In partial step 207B, an initial crack 317 is shown—similar to the initial crack 217 of FIG. Due to the preferred direction of the cracks 313, the formation of the initial crack 317 in the partial step 207B and the formation of a separating crack 321 in the partial step 207C can be simplified.

FIGS. 12A, 12B illustrate schematically machined workpieces in which a sequence of modifications was introduced into a pipe wall along an inner contour as a scanning trajectory.

As an example of a workpiece with a constant curvature, FIG. 12A shows a tube section 51 extending in a longitudinal direction (y-direction) with a constant outer radius and a wall thickness in the range of 1 mm. A substantially circular opening 53 was produced in the pipe section 51 on a lateral surface (the outer surface of the pipe section 51 ) by inscribing a row of modifications along a closed inner contour 55 . Due to the constant curvature, a phase-correcting beam shaping, once set, could be retained unchanged during the writing process. After the inscription process, a wet etching process was carried out so that the area of the tube section 51 inside the inner contour 53 was completely separated from the surrounding material and could be removed accordingly. The ends 51A, 51B of the pipe section 51 shown in FIG. 12A can each be the result of a circumferential contour cut.

As an example of a workpiece with varying curvature, FIG. 12B shows a conically tapering hollow body 57, in which the radius of curvature of an outside of the wall increases in the y-direction; ie, the hollow body 57 reduces in radius along the y Direction example linear with a substantially constant wall thickness of 1 mm. Correspondingly, when the surface of the hollow body 57 is being machined, the curvature to be corrected varies as a function of the y position.

As in FIG. 12A, an essentially circular opening 53' was produced in the hollow body 57 by inscribing a row of modifications in the wall along a closed inner contour 55'. Due to the varying curvature, the phase-correcting beamforming was used along the scanning trajectory.

For example, based on the known geometry of the hollow body 57, a y-dependent adaptation of the phase-correcting beam formation can be undertaken. Alternatively, the variation in curvature can be detected during processing along the scanning trajectory and the phase-correcting beam shaping can be adjusted accordingly. Additionally or alternatively, to detect the curvature, the closed inner contour 55' can be traversed separately before the laser processing in order to store the corresponding curvature data in the control unit and to set the phase-correcting beam shaping accordingly.

The ends 57A, 57B of the hollow body 57 can also represent, for example, the result of circumferential contour cuts, it being possible for each of the contour cuts to be carried out with its own phase-correcting beam shaping, adapted to the curvature present in each case.

It is explicitly emphasized that all features disclosed in the description and/or the claims are to be regarded as separate and independent from each other for the purpose of original disclosure as well as for the purpose of limiting the claimed invention independently of the combinations of features in the embodiments and/or the claims should. It is explicitly stated that all indications of ranges or groups of units disclose every possible intermediate value or subgroup of units for the purpose of original disclosure as well as for the purpose of limiting the claimed invention, in particular also as a limit of a range indication.

Claims

patent claims

1. A method for material processing of a workpiece (9) with a pulsed laser beam (3), wherein the workpiece (9) has a largely transparent for the laser beam (3) material with a curved surface (9A), with the steps:

Beam shaping (step 101) of the laser beam (3) to form an elongated focus zone (7) in the material of the workpiece (9), the beam shaping being carried out with an arrangement of diffractive, reflective and/or refractive optics and comprising:

- Focus-forming beam shaping (step 101 A), which involves beam components (3A) entering at an angle of incidence (6') onto a beam axis (5) of the laser beam (3) for forming the elongated focus zone (7) along the beam axis (5 ) in the workpiece (9) caused by interference, and

- a phase-correcting beam shaping (step 101B), which counteracts an influence on the interference by an entry of the laser beam (3) into the workpiece (9), and

Adjusting (step 105) the beam parameters of the laser beam (3) in such a way that the material of the workpiece (9) is modified in the elongated focal zone (7).

2. The method according to claim 1, wherein the curved surface (9A) is curved in one direction, and the beam shaping of the laser beam (3) involves impressing at least one two-dimensional phase distribution (PHI BESSEL, PHI ZYL, PHY total) on the laser beam (3) for forming an elongated focal zone (7) in the material of the workpiece (9), the at least one phase distribution (PHI BESSEL, PHI ZYL, PHY total) comprising:

- for the focus-forming beam formation, first phase contributions (25 A), which bring about the arrival of beam components (3A) at the arrival angle (6') and, in particular, generate a non-diffracting beam for the formation of the elongated focus zone along the beam axis in the workpiece, and

- second phase contributions (25B) for the phase-correcting beam formation, which cancel out an entry phase locally accumulated by the laser beam (3) when entering the workpiece (9).

3. The method according to claim 2, wherein the locally accumulated entry phase is determined for an alignment of the beam axis (5) along a normal direction (N) of the surface (9A) at a point of impact (P) of the beam axis (5) on the surface (9A). and takes into account:

- the infeed angle (6'),

- a radius of curvature (Rw) of the surface (9A) at the impact point (P) and

- a refractive index (nw) of the workpiece (9).

4. The method according to claim 2 or 3, wherein the second phase contributions (25B) form a phase distribution that is axisymmetric to an axis of symmetry (S), the second phase contributions being constant parallel to the axis of symmetry (S) and changing perpendicularly to the axis of symmetry (S). with the step:

Alignment (step 103) of the axisymmetric phase distribution and the workpiece (9) to one another in such a way that the axis of symmetry (S) runs orthogonally to a plane, taking into account a beam path (13) between a location where the axisymmetric phase distribution is impressed and the workpiece (9), in which a radius of curvature of the surface (9A) is defined.

5. The method according to any one of claims 2 to 4, wherein the first phase contributions (25 A) and/or the second phase contributions (25B) are impressed onto a transverse beam profile of the laser beam (3) using a diffractive optical beam-shaping element (15), the diffractive optical beam-shaping element (15) has surface elements (15A) adjoining one another, which build up a surface grating structure in which each surface element (15A) is assigned a phase shift value, and wherein the phase shift values represent the first phase contributions (25 A) and/or the second phase contributions ( 25B).

6. The method according to any one of the preceding claims, further comprising:

Radiation (step 107A) of the laser beam (3) onto the surface (9A) along a beam path (13) of an optical system that images the laser beam (3) in the material of the workpiece (9) to form the elongated focus zone (7), and or

Aligning (step 107B) the beam axis (5) of the laser beam (3) to a normal direction (N) of the surface (9A) such that the beam axis (5) is in an angular range of 5° around the normal direction (N) on the surface (9A) occurs.

7. The method according to any one of the preceding claims, wherein the phase-correcting beam shaping is generated by a cylindrical lens (35, 35'), which is positioned in a beam path of the laser beam (3) before or after an optical system (27, 31) that brings about the focus-forming beam shaping .

8. The method according to claim 7, wherein the cylindrical lens (35, 35') has a radius of curvature which is adapted to a radius of curvature of the surface (9A) of the workpiece (9), so that for the radius of curvature Rz of the cylindrical lens (35, 35') is applicable:

- when positioning the beginning of the elongated focal zone (7) in front of the curved surface (9A) using the parameters a = 5060 mm and b = 9645 mm and the displacement Az of the beginning of the elongated focal zone (7) in the propagation direction in front of the curved one Surface (9A):

- when positioning the beginning of the elongated focal zone (7) in the direction of propagation behind the curved surface (9A) using the parameters c = 284 mm' ¹ and d = 590 and the displacement Az of the beginning of the elongated focal zone (7) in front of the curved surface (9A):

- when positioning the beginning of the elongated focal zone (7) on the curved surface (9A):

Rz (-1) Rw M ² (nz-l)/(nw-l) with nz : refractive index of the cylindrical lens (35, 35 '),

Rw: radius of curvature Ra of the surface (9A), nw: refractive index of the material of the workpiece (9) and

M: imaging factor of the beam path between a location of the focus-forming

Beam shaping and the workpiece (9).

9. The method according to any one of the preceding claims, wherein the beam shaping of the laser beam (3) is carried out with an imprint of a two-dimensional phase distribution on a transverse beam profile of an output laser beam (3') with:

- a diffractive optical beam-shaping element (27) having fixed or adjustable phase values in a two-dimensional array; or

- A combination of a, in particular deformable, cylindrical mirror with an axicon (31); or

- a combination of a cylindrical lens (35, 35') with an axicon (31); or

- a combination of a cylinder lens (35, 35') or a cylinder mirror, in particular a deformable one, with a diffractive optical beam-shaping element (27), which has fixed or adjustable phase values in a two-dimensional arrangement, which is used to impress a phase distribution, in particular a Bessel beam Like phase distribution, is designed for the formation of the elongated focus zone (7).

10. The method according to any one of the preceding claims, wherein the beam shaping of the laser beam (3) is carried out with individual optics, which are designed as a refractive free-form optics element or a hybrid optics element, in particular an optics unit consisting of an input-side cylindrical lens and an output-side axicon.

11. The method according to any one of the preceding claims, further comprising:

Effecting (step 109) a relative movement between the workpiece (9) and the focal zone (7), in which the focal zone (7) is positioned along a scanning trajectory (T) in the material of the workpiece (9), so that a plurality of modifications in the Material of the workpiece (9) along the scanning trajectory (T) are inscribed, in particular the scanning trajectory (T) an outer contour for dividing the workpiece (9) into two parts along a longitudinal axis of the workpiece (9) or on a surface of the workpiece ( 9) closed inner contour for triggering an area delimited by the inner contour.

12. The method according to claim 11, wherein the workpiece (9) is designed as a tube, cylinder or section of a tube or cylinder, such as a half-tube or half-cylinder, and the relative movement comprises a rotational movement of the workpiece (9), and wherein the Beam axis (5) of the laser beam (3) in particular through a longitudinal axis (A) of the workpiece (9).

13. The method according to claim 11 or 12, wherein in the case of a purely rotational movement about a longitudinal axis of the workpiece (9), the scanning trajectory (T) of the laser beam (3) runs in a plane of the maximum curvature of the surface (9A) of the workpiece (9), and/or wherein a translational movement in the direction of the longitudinal axis of the workpiece (9) takes place additionally or in sections.

14. The method according to any one of claims 11 to 13, further comprising:

Monitoring and controlling (step 111) a position of the surface (9A) of the workpiece (9) along the beam axis (5) to a target position, and wherein the monitoring and controlling is carried out in particular if, in the case of a rotational movement, a rotational axis differs from an axis of rotational symmetry the surface (9A) of the workpiece (9) deviates and/or the surface (9A) of the workpiece (9) deviates at least in sections from a rotationally symmetrical surface profile.

15. The method according to any one of claims 11 to 14, further comprising:

Adjusting the phase-correcting beam shaping to a change in a curvature of the curved surface along the scanning trajectory (T) of the laser beam (3), a control signal for adjusting the phase-correcting beam shaping, in particular based on a pre-measurement of a curvature of the curved surface (9A) along the trajectory (T) and/or is derived from an online measurement of a curvature of the curved surface (9A) during a relative movement between the workpiece (9) and the focal zone (7) along the scanning trajectory (T).

16. Optical system (1B) for beam shaping of a pulsed laser beam (3) for forming a focus zone (7) in a workpiece (9) with a curved surface (9A), wherein the focus zone (7) along a beam axis (5) of the Laser beam (3) is formed elongated, with: a focus-forming optics, the arrival of beam portions (3 A) at an angle of incidence (6 ') on a beam axis (5) of the laser beam (3) for a formation of the elongated focus zone (7) caused by interference along the beam axis (5) in the workpiece (9), wherein a phase correction, which counteracts the interference being influenced by the laser beam (3) entering the workpiece (9), is provided with phase-correcting optics or is integrated into the focus-forming optics.

17. Optical system (1B) according to claim 16, wherein the optical system (1B) is set up to impress a two-dimensional phase distribution on the laser beam (3') and to output it as a real or virtual Bessel-like laser beam (3). , the focus-forming optics generating first phase contributions (25 A) of the phase distribution, which in particular generate a non-diffracting beam for the formation of the elongated focus zone along the beam axis in the workpiece, and the phase-correcting optics or the phase correction generating second phase contributions (25B) of the phase distribution , which cancel a locally accumulated entry phase from the laser beam (3) when entering the workpiece (9).

18. Optical system (1B) according to claim 16 or 17, wherein the focus-forming optics and/or the phase-correcting optics for the phase imposition of a two-dimensional phase distribution are designed as a diffractive optical beam-shaping element (27) which is set up to convert the first phase contributions (25 A ) and/or to impress the second phase contributions (25B) on a transverse beam profile of the laser beam (3), wherein the diffractive optical beam-shaping element (27) has surface elements (27 A) adjoining one another, which build up a surface lattice structure in which each surface element (27 A) a phase shift value is associated, and wherein the phase shift values cause the first phase contributions (25A) and/or the second phase contributions (25B); and/or the focus-forming optical system is designed as an axicon (31) which generates the focus-forming phase contributions (25A); and/or the phase-correcting optics are designed as a cylindrical lens (21) which generates the second phase contributions (25B) and is positioned directly before or after the focus-forming optics in the beam path of the laser beam (3); and/or the focus-forming optics are designed as a refractive free-form element which generates the first phase contributions (25 A) and the second phase contributions (25B); and/or the focus-forming optics and the phase-correcting optics are designed as hybrid optics that have the first phase contributions (25A) and the second phase contributions (25B) is generated and formed in particular as a combination of an input-side cylindrical lens and an output-side axicon.

19. Optical system (1B) according to one of claims 16 to 18, wherein the phase-correcting optics for the phase imposition of a two-dimensional phase distribution are designed as an optical element that can be set in the two-dimensional phase distribution, in particular as a diffractive optical beam-shaping element (27) such as a spatial light modulator or a deformable cylinder mirror is formed, and the adjustable optical element is formed for an adjustment of the phase corrections when there is a change in a curvature of the curved surface (9A) to be corrected in dependence on a control signal.

20. Optical system (1B) according to any one of claims 16 to 19, further comprising: a telescope arrangement (13A) for reducing a real or virtual focal zone which is assigned to the focus-forming optics, and/or a distance sensor (25) which is connected thereto is set up to determine a position (P) of a surface (9A) of the workpiece (9) along the beam axis (5).

21. Laser processing system (1) for processing a workpiece (9) with a pulsed laser beam (3) by modifying a material of the workpiece (9) in a focal zone (7) of the laser beam (3), the focal zone (7) along a The beam axis (5) of the laser beam (3) is elongated and the workpiece (9) has a material that is largely transparent to the laser beam (3) and has a curved surface (9A), with: a laser beam source (1A) that emits a laser beam (3 ') outputs, an optical system (1B) according to any one of claims 16 to 20 and a workpiece holder (19) for supporting the workpiece (9).

22. Laser processing system (1) according to claim 21, wherein the optical system (1B) and/or the workpiece holder (19) are set up to:

- to align the beam axis (5) of the laser beam (3) to a normal direction (N) of the surface (9A) in such a way that the beam axis (5) is in an angular range of 5° around the normal direction (N), preferably along the normal direction (N ), impinging on the surface (9A), and/or - to bring about a relative movement between the workpiece (9) and the focal zone (7), in which the focal zone (7) is positioned along a scanning trajectory (T) in the material of the workpiece (9), the alignment of the beam axis (5) to the Normal direction (N) is adapted to the course of the surface (9A).

23. Laser processing system (1) according to claim 21 or 22, further comprising: a distance sensor (25) which is arranged and set up to a position (P) of a surface (9A) of the workpiece (9) along the beam axis (5). determine, and a controller (23) which is set up to monitor a position of the surface (9A) of the workpiece (9) along the beam axis (5) with the distance sensor (25) and to regulate it to a target position.

24. Laser processing system (1) according to one of claims 21 to 23, wherein the optical system (1B) has phase-correcting optics for the phase imposition of a two-dimensional phase distribution, which is designed to be adjustable in the two-dimensional phase distribution, and in particular as a diffractive optical beam shaping element (27) as a spatial light modulator or as a deformable cylinder mirror, further comprising: a controller (23) which is set up to output to the adjustable optical element a control signal which matches the two-dimensional phase distribution to a curvature of the curved surface (9A) to be corrected of the workpiece (9), the control signal being based in particular on a pre-measurement of a curvature of the curved surface (9A) along a trajectory (T) or on the basis of an online measurement of a curvature of the curved surface (9A) during a relative movement between the workpiece (9) and en r focal zone (7) along a scanning trajectory (T) is derived.

25. Laser processing system (1) according to one of Claims 21 to 24, further comprising: a distance sensor (25) which is arranged and set up to detect a position (P) of a surface (9A) of the workpiece (9) along the beam axis (5 ) to determine, and a controller (23) which is set up to monitor a position of the surface (9A) of the workpiece (9) along the beam axis (5) with the distance sensor (25) and to regulate it to a target position .