EP4168207A1

EP4168207A1 - Machining optical system, laser machining device, and method for laser machining

Info

Publication number: EP4168207A1
Application number: EP21730843.6A
Authority: EP
Inventors: Daniel FLAMM; Julian Hellstern; Jonas Kleiner; Malte Kumkar; Marcel Schaefer
Original assignee: Trumpf Laser und Systemtechnik GmbH
Current assignee: Trumpf Laser und Systemtechnik Se
Priority date: 2020-06-22
Filing date: 2021-06-01
Publication date: 2023-04-26
Also published as: KR20230020532A; CN115835934A; US20230182234A1; DE102020207715A1; KR102706742B1; WO2021259597A1

Abstract

The invention relates to a machining optical system (16) for machining workpieces, comprising: a polariser arrangement (7) which comprises a birefringent polariser element (1a, 1c) for splitting at least one in particular pulsed input laser beam (3) into at least two partial beams (5a, 5b) each having one of two different polarisation states; and a focussing optical system (17) which is located in the beam path downstream of the polariser arrangement (7) and is intended for focussing the partial beams (5a, 5b) onto at least two focal zones, characterised in that the polariser arrangement (7) has at least one further optical element (8, 13) which is located in the beam path downstream of the birefringent polariser element (1a, 1c) and is intended for modifying an angle and/or a distance of at least one of the partial beams (5a, 5b) relative to an optical axis (6) of the machining optical system (16). The invention also relates to a laser machining device (14) which has such a machining optical system (16) and a laser source (11) for generating a laser beam (12), and to a method for laser-machining a workpiece (9) by means of a machining optical system (16).

Description

Processing optics, laser processing device and method for

Laser processing

The present invention relates to processing optics for workpiece processing, in particular by means of an ultra-short pulse laser source, comprising: a polarizer arrangement which comprises a birefringent polarizer element for splitting at least one especially pulsed input laser beam into at least two partial beams, each with one of two different polarization states, and a focusing optics arranged in the beam path after the polarizer arrangement for focusing the partial beams on at least two focus zones. The invention also relates to a laser processing device with such processing optics, as well as a method for laser processing a workpiece by means of processing optics, comprising: splitting at least one especially pulsed input laser beam into at least two partial beams, each having one of two different polarization states, on a birefringent polarizer element a polarizer arrangement, as well as focusing the partial beams on focus zones in the area of the workpiece by means of a focusing device of the processing optics. For the purposes of this application, partial beams with different polarization states are understood to be linearly polarized partial beams whose polarization directions are aligned at an angle of 90 ° to one another. However, partial beams with different polarization states are also understood to mean circularly polarized partial beams with opposite directions of rotation, ie two left and right circularly polarized partial beams. The conversion of linearly polarized partial beams with mutually perpendicular directions of polarization into circularly polarized partial beams with opposite directions of rotation can take place, for example, with the aid of a suitably oriented retardation plate (1/4 plate).

When laser processing a workpiece, especially when laser ablation, laser cutting, surface structuring, laser welding, laser drilling, etc., it is beneficial to split an input laser beam into several partial beams that strike or are focused on the workpiece at different locations. The division can take place on a polarizer element, whereby two partial beams, each with one of two different polarization states, e.g. two perpendicularly polarized partial beams, are formed as output laser beams from an input laser beam. It is possible for several input laser beams which are spatially offset or which have an angular offset to impinge on the polarizer element. In this case, each of the input laser beams can be split into a pair of partial beams, each with one of two different polarization states. Whether or with what power proportions the two partial beams are formed depends on the polarization of the input laser beam.

WO2015 / 128833A1 describes a laser cutting head which has a polarizing beam offset element arranged in the beam path of a laser beam for generating two linearly polarized partial beams. The polarizing beam offset element is arranged in a divergent or in a convergent beam path section of the laser beam. The beam displacement element can be formed from a birefringent material. When using focusing, magnifying optics and a beam offset element arranged in the beam path behind the focusing optics, the two partial beams may partially overlap in the focal plane. From WO2015 / 5114032 A1 a laser processing device for workpiece processing has become known which has processing optics in which an input laser beam is divided into two perpendicularly polarized partial beams at a polarizer. The processing optics have a greater path length for the second partial beam than for the first partial beam, as a result of which the second partial beam has a longer transit time than the first partial beam. The second partial beam is changed in at least one geometric beam property compared to the first partial beam. The changed second partial beam is superimposed on the first partial beam in such a way that both partial beams form a common output laser beam.

WO2018 / 020145A1 describes a method for cutting dielectric or semiconductor material by means of a pulsed laser, in which a laser beam is split into two partial beams that hit the material in two spatially separated zones offset from one another by a distance. The distance is set to a value below a threshold value in order to produce a rectilinear micro-fracture in the material which runs in a predetermined direction between the two mutually offset zones. Beam shaping can be carried out on the two partial beams in order to generate a local distribution on the material in the form of a Bessel beam.

WO2016 / 089799A1 describes a system for laser cutting at least one glass article by means of a pulsed laser assembly which comprises a beam-shaping optical element for converting an input beam into a quasi-non-diffractive beam, for example a Bessel beam. The laser assembly also includes a beam transformation element for converting the quasi-non-diffractive beam into a plurality of partial beams spaced between 1 gm and 500 gm apart. The phase of at least one of the quasi-non-diffractive partial beams can be shifted between approximately TT / 4 and approximately 2 p.

DE 102019205394.7 describes processing optics for workpiece processing which have a birefringent polarizer element for dividing at least one input laser beam into a pair of partial beams polarized perpendicular to one another and one in the beam path after the polarizer element having arranged focusing optics for focusing the partial beams on focus zones, the processing optics being designed to generate at least partially overlapping focus zones of the partial beams polarized perpendicular to one another. The processing optics can be designed to generate a plurality of pairs of at least partially overlapping focus zones along a predetermined contour in a focal plane, wherein focus zones of two perpendicularly polarized partial beams from directly adjacent pairs at least partially overlap.

Object of the invention

The invention is based on the object of providing processing optics, a laser processing device with them and a method for laser processing which make it possible to align the partial beams in the focus zones at defined angles and / or positions with respect to the optical axis of the processing optics.

Subject of the invention

This object is achieved according to the invention by processing optics of the type mentioned at the outset, in which the polarizer arrangement has at least one further optical element arranged in the beam path after the birefringent polarizer element for changing an angle and / or a distance of at least one of the partial beams relative to an optical one Has axis of the processing optics.

When dividing the input laser beam onto the at least two partial beams on the or on a single birefringent polarizer element, the distance and / or that alignment of the partial beams relative to the optical axis of the processing optics may not be able to be generated that was used when the Partial beams should be generated on the focus zones. This is due to the fact that by means of one and the same polarizer element, as a rule, a predetermined spatial and / or angular offset of the two partial beams relative to one another and a desired angle and / or a desired position in relation to the optical axis of the processing optics can be generated. In order to achieve both, it is proposed to arrange at least one further optical element in the beam path after the birefringent polarizer element.

As a rule, the input laser beam strikes the birefringent polarizer element parallel to the optical axis, in particular along the optical axis of the processing optics. In principle, however, it is also possible to use one or more optical elements that are arranged in the beam path in front of the polarizer element to set or specify the alignment and / or the position of the input laser beam relative to the optical axis.

Even if only one polarizer arrangement with a birefringent polarizer element for splitting into two partial beams is described in the following description, two or more birefringent polarizer elements can in principle also be provided in the processing optics. For example, the laser beam generated by a laser source and entering the processing optics can be split into two or more partial beams, each of which represents an input laser beam for an associated birefringent polarizer element, or the laser beams from several laser sources can be used as input laser beams.

In one embodiment, the polarizer element is designed to generate a spatial offset and / or an angular offset between the partial beams with the different polarization states. As a rule, when the input beam is split into the at least two partial beams at a birefringent polarizer element, a lateral offset (spatial offset) and / or an angular offset is generated between the two partial beams. The birefringent polarizer element can either be designed to generate a lateral (spatial) offset or to generate an angular offset or to generate a combination of an angular offset and a spatial offset between the two partial beams with the different polarization states. With the help of a birefringent polarizer element, typically in the form of a birefringent crystal, with suitable polarization of the input laser beam, e.g. with an unpolarized input laser beam or with an input laser beam with undefined, elliptical or circular polarization, the targeted spatial division of the input laser beam into its polarization components is made possible . The division of the power of the input laser beam between the two partial beams depends on the polarization of the input laser beam or can be determined by choosing the polarization of the input laser beam: If the polarization of the input laser beam is linear or has some other preferred direction, e.g. elliptical polarization, this is typically done no equal distribution of the power of the input laser beam between the two partial beams.

It can be useful to influence the polarization of the input laser beam with the help of suitable polarization-influencing optical elements, for example in the form of retardation plates, in order to specifically influence the splitting ratio when splitting the input laser beam into the two partial beams and, if necessary, the splitting of the input laser beam between the two switch both partial beams on or off. If the input laser beam is circularly polarized, the power of the input laser beam can be split into two partial beams with comparable power proportions regardless of the angle of any preferred direction during processing (see below).

Depending on the design of the birefringent polarizer element, a well-defined, pure spatial offset, a well-defined, pure angular offset or a combination of a defined spatial offset and a defined angular offset between the two partial beams with the different polarization states can be generated.

To generate the local offset (without angular offset), the birefringent polarizer element can have, for example, generally planar beam entry and exit surfaces that are aligned in parallel. In this case, the optical axis of the birefringent crystal is typically oriented at an angle to the beam entrance surface. If the input laser beam hits the Beam entrance surface, a pure spatial offset is generated at the beam exit surface.

To generate the angular offset (without local offset), the birefringent polarizer element can have a beam exit surface which is inclined at an angle to the beam entry surface. In this case, the optical axis of the birefringent crystal is typically aligned parallel to the beam entrance surface. In this case, the two partial beams emerge from the birefringent crystal at the beam exit surface at the same location and with a defined angular offset.

To generate a spatial and angular offset, the birefringent polarizer element can have a beam exit surface which is inclined at an angle to the beam entry surface. In this case, the optical axis of the birefringent crystal is typically aligned at an angle to the beam entrance surface and to the beam exit surface. A birefringent polarizer element, which generates a pure spatial offset, and a birefringent polarizer element, which generates a pure angular offset, represent special cases of the birefringent polarizer element described here, which generates both an angular offset and a spatial offset.

In a further development, the polarizer element is designed to generate an angular offset between the partial beams with the different polarization states and the further optical element is designed to change the angle of at least one of the two partial beams relative to the optical axis in order to have the at least one partial beam parallel to the optical axis Align the axis. Alignment of (at least) one of the partial beams parallel to the optical axis is particularly advantageous if the polarizer element or the polarizer arrangement is rotated about the optical axis in order to change a preferred direction when machining the workpiece. Such an alignment makes it possible to avoid an undesired offset of this partial beam that is dependent on the angle of rotation of the polarizer element about the axis of rotation or to generate a constant offset about the optical axis when the partial beam is rotated. In a further development, the further optical element is designed to be optically isotropic, the polarizer element preferably being designed to generate an angular offset without generating a spatial offset. In this case, the further optical element is preferably designed as a wedge-shaped optically isotropic element. In this case, the wedge angle of the wedge-shaped further optical element is typically adapted to a wedge angle of the exit surface of the polarizer element in order to compensate for the angular offset of one of the two partial beams or to average out the angular offset for both partial beams relative to the optical axis. In general, by suitably matching the wedge angle of the wedge-shaped further optical element and the wedge angle of the birefringent polarizer element, a desired distance or offset of the parallel partial beam from the optical axis can be specified, which is maintained during rotation about the axis of rotation.

By using a wedge-shaped optical element that has two wedge angles that lie in mutually perpendicular planes, the two focus zones, which are generated after passing through the focusing optics, can also have an angle (identical for both partial beams) in a direction perpendicular to the plane of incidence or to the plane in which the optical axis of the birefringent polarizer element is arranged. After the Fourier transformation by the focusing optics, the impressed angle is converted into a spatial offset in the focal plane. Given a suitable distance between the polarizer arrangement and the focusing optics, the two partial beams in the focal plane can run parallel to the optical axis and be positioned at the same distance from the optical axis.

In a further development, the polarizer arrangement has beam offset optics which include a further birefringent optical element in order to align both partial beams parallel to one another. An additional optical element, which is designed, for example, as a wedge-shaped optical element and which is arranged in the beam path after the further birefringent optical element, can change the beam direction of the two parallel partial beams so that both partial beams are aligned parallel to the optical axis. By adjusting the distance between the further birefringent element and the additional optical element of the beam offset optics in the direction of the optical axis, the distance between the two partial beams and the optical axis can be determined.

In a further development, the polarizer arrangement is designed to position one of the partial beams on the optical axis or to position both partial beams at the same distances from the optical axis. In particular when rotating the polarizer element around the optical axis of the processing optics (Z direction), it has proven to be advantageous if one of the two partial beams is positioned on the optical axis of the processing optics so that its position does not change during the rotation . A symmetrical arrangement of the two partial beams in relation to the optical axis, in which both partial beams are arranged at the same distances from the optical axis, is also possible. There are several options for positioning the partial beam on the optical axis or the two partial beams symmetrically to the optical axis:

One possibility is to specify the distance between the further birefringent optical element and the additional optical element along the optical axis in the above-described beam offset optics or, if necessary, to adjust it by means of a suitable displacement device so that one of the two partial beams along the optical axis the processing optics and the other partial beam is offset from the optical axis or that both partial beams extend at the same distance from the optical axis.

In a further development, the birefringent polarizer element is also designed to generate the angular offset to generate a spatial offset and the further optical element is designed to be birefringent in order to position the partial beam on the optical axis. In this case, the optical axis of the birefringent material of the polarizer element and its beam entrance surface and its beam exit surface are aligned and arranged at such a distance from the further birefringent element that one of the two partial beams is aligned parallel to the optical axis and on the optical axis of the Processing optics is positioned. In a further development, the polarizer arrangement is designed to change the angular offset and / or spatial offset between the two partial beams. The angular offset and / or spatial offset between the two partial beams generated by the polarizer element is typically constant, given the given boundary conditions. In order to change the angular offset and / or spatial offset generated by the polarizer arrangement, the or at least one further, generally birefringent optical element is provided in the polarizer arrangement, which makes it possible to adjust the angular offset and / or the spatial offset between the two partial beams change or adjust. For this purpose, the further, generally birefringent optical element can typically be moved relative to the optical axis of the polarizer arrangement.

In a further development of this embodiment, the further optical element is birefringent and can be displaced along the optical axis of the processing optics and / or rotated about the optical axis of the processing optics to change the angular offset and / or to change the spatial offset between the two partial beams. A translation drive can be used to displace the further birefringent optical element along the optical axis, which can be designed, for example, in the manner of a linear drive or the like. For the rotation of the further optical element about the optical axis of the polarizer arrangement, the polarizer arrangement typically has a rotary drive. To control the translation drive and / or the rotary drive, a control device of the processing optics or a device connected to the latter for signaling purposes, for example a control computer, can be used. When using such a polarizer arrangement, the distance between the focus zones of the two partial beams in the area of the workpiece can be set to a desired value.

In a further embodiment, the further optical element is designed to be birefringent and a polarization-influencing optical element, in particular a 1/4 retardation plate or a 1/2 retardation plate, is arranged in front of the further optical element. By the polarization-influencing optical element, which produces, for example, a delay of 1/4, the two partial beams, which are linearly polarized after exiting the birefringent polarizer element, can be converted into circularly polarized partial beams.

When rotating the further birefringent optical element, it should be noted that in the event that the optical axes of the two birefringent elements do not lie in a common plane (or the planes spanned by the beam axes are not perpendicular to one another), in the general case from the Input laser beam four partial beams or four output laser beams are formed, ie there is a cascaded beam splitting. If a cascaded beam splitting is not desired, it is necessary that the two partial beams entering the further birefringent optical element are aligned perpendicular or parallel to the optical axis of the further birefringent optical element. This can be ensured, for example, by means of a 1/2 retardation plate which is suitably aligned with the two birefringent optical elements and which is rotated accordingly (but at half the angle of rotation) when the further birefringent optical element is rotated, in order to prevent a split into four partial beams.

The polarization-influencing optical element, for example in the form of a 1/4 retardation plate, can also be used to generate four partial beams from the two partial beams. The polarization-influencing optical element can in this case be used to distribute the power of the input laser beam evenly over all four partial beams. In the event that the birefringent polarizer element and the further birefringent optical element are rotated relative to one another, it is not necessary to rotate the polarization-influencing optical element in the form of the λ / 4 retardation plate in order to maintain the effect of uniform division. Depending on the angle of the two birefringent optical elements relative to the optical axis of the processing optics or on the alignment of the optical axes of the birefringent optical elements relative to the optical axis of the processing optics, the four partial beams can again be superimposed collinearly. This can be beneficial if, for example, four or more partial beams are to be arranged on a common line or along a preferred direction. The distance between the partial beams or the focus zones (see below) can also be set by a suitable choice of the relative angle of rotation of the two birefringent optical elements to one another.

The arrangement of the further birefringent optical element and the polarization-influencing optical element arranged in front of the further birefringent optical element, in particular in the form of a 1/4 retardation plate, can be cascaded, that is, this arrangement can be repeated N times in order to produce a Number M of M = 2 ^{N + 1} partial beams to be generated. If all partial beams are to be arranged collinearly and run along a common preferred direction, it is typically necessary to arrange the optical axes of all other birefringent optical elements in a common plane. If circularly polarized partial beams are generated with the aid of a respective 1/4 retardation plate, the power can be evenly distributed to all partial beams in this case.

It goes without saying that instead of a 1/4 retardation plate, another polarization-influencing optical element can also be introduced into the beam path of the partial beams between two consecutive birefringent optical elements in order to suitably set the polarization and thus influence the power distribution. To change the power distribution or to switch the distribution on or off, the polarization-influencing optical element can also be rotated relative to the respective birefringent optical elements.

In a further embodiment, the processing optics include beam-shaping optics for converting an input laser beam with a Gaussian beam profile into an exiting laser beam with a quasi-non-diffractive beam profile, in particular with a Bessel-like beam profile.

A non-diffractive beam represents a solution to the Flelmholtz equation, which can be separated into a longitudinal part and a transverse part. A Such a non-diffractive beam has a transverse beam profile which is invariant to propagation, ie which does not change during the propagation of the non-diffractive beam. Depending on the coordinate system used, different solution classes of non-diffractive rays occur, for example Mathieu rays in elliptical-cylindrical coordinates or Bessel rays in circular-cylindrical coordinates.

A non-diffractive beam is a theoretical construct that can be implemented to a good approximation in the form of so-called quasi-non-diffractive beams. A quasi-non-diffractive beam has the propagation invariance only over a finite length (characteristic length) L. A quasi-non-diffractive beam is present if, with a similar or identical focus diameter, the characteristic length L clearly exceeds the Rayleigh length of the associated Gaussian focus, in particular if: L> ZR, where ZR denotes the Rayleigh length of the Gaussian beam. The characteristic length L can, for example, be in the order of 1 mm or more.

The Bessel-like rays represent a subset of the quasi-non-diffractive rays, in which the transverse ray profile in the vicinity of the optical axis corresponds to a good approximation of a Bessel function of the first type of order n. The Bessel-Gaussian rays represent a subset of the Bessel-like rays, in which the transverse ray profile in the vicinity of the optical axis corresponds to a good approximation of a Bessel function of the first type of the 0th order, which is enveloped by a Gaussian distribution .

The use of a quasi-non-diffractive beam profile has proven to be particularly advantageous when introducing modifications to the material of the workpiece for glass cutting applications or for selective laser etching applications, since with such a beam profile in the longitudinal direction over a comparatively long distance an essentially homogeneous beam profile can be maintained, whereby a modification volume is generated with a preferred direction

A Bessel-like jet has proven to be particularly advantageous here, if necessary, however, other quasi-non-diffractive beam profiles, for example an Airy beam profile, a Weber beam profile or a Mathieu beam profile, can also be generated with the beam-shaping optics. The beam-shaping optics can in particular be designed to generate a quasi-non-diffractive beam profile with a beam cross-section that is rotationally symmetrical to the direction of propagation, as is the case, for example, with a Bessel-Gaussian beam.

In a further development, the beam-shaping optics are designed to generate a quasi-non-diffractive beam profile with a non-rotationally symmetrical beam cross-section, in particular with a preferred direction. It has proven to be advantageous if the beam-shaping optics are designed as diffractive optics in this case. The preferred direction of the non-diffractive beam profile generally coincides with the (preferred) direction or the plane in which the polarizer element of the polarizer arrangement generates the two partial beams. The quasi-non-diffractive beam profile can have a plurality of spaced apart (secondary) maxima along the preferred direction, so that the beam-shaping optics act in the manner of beam splitter optics and, for example, generate a so-called multi-Bessel beam profile. A beam profile with a preferred direction can also be generated with the aid of the cascading described above of birefringent optical elements of the polarizer arrangement with interposed polarization-influencing optical elements.

In a further development, the processing optics are designed to focus the partial beams in at least partially overlapping focus zones of a contiguous interaction area, in particular along the preferred direction, with partial beams each having different polarization states being focused in adjacent focus zones of the contiguous interaction area.

If a laser beam, which is generated, for example, by a single-mode laser and has a Gaussian beam profile, is split into two or more partial beams and the partial beams are at least partially superimposed, this can lead to undesirable interference effects if the partial beams are the same or a similar one Have polarization. It is true that when the partial beams are focused, the focus zones or the focus cross-sections can therefore be as close as desired to one another, but in this case the undesired interference effects occur in the resulting intensity profile. The partial beams are therefore usually focused on the workpiece in focal zones that are spaced apart from one another.

When using partial beams, each of which has one of two different polarization states, in particular in the form of mutually perpendicular polarization states, the (partial) superposition in the intensity profile does not lead to interference effects of the laser radiation from different spatial or angular ranges, provided that the polarization state of the respective partial beams is uniform over the entire relevant beam cross-section or the respective focus zone. The polarization of a respective partial beam should therefore vary as little as possible over the beam cross-section or over the focus zone, depending on the location. In this case, the focus zones can be as close to one another as desired, partially or completely overlap and even form homogeneous focus zones, both transversely, i.e. perpendicular to the direction of propagation of the partial beams, and longitudinally, i.e. in the direction of propagation of the partial beams.

A beam shape or intensity distribution - linear in the case of a preferred direction - is formed along the specified, not necessarily straight interaction area, which usually has a continuous transition, i.e. no zero points in the intensity distribution between the partial beams or between the focus zones. In this case, partial beams of the respective pairs that are polarized perpendicular to one another overlap each other, but only to the extent that they do not overlap with the differently polarized partial beam of a respective pair, so that no overlapping of identically polarized partial beams occurs.

As an alternative to using completely or partially overlapping partial beams that have mutually perpendicular polarization states, completely or partially overlapping partial beams can also be used that have a time offset that is so great that practically no interference effects occur. This is typically the case when the time offset corresponds to at least the order of magnitude of the pulse duration or the order of magnitude of the coherence length. As a rule, a minimum of 50% of the respectively smaller of the two values (pulse duration or coherence length) is selected as the time offset.

The beam-shaping optics described above or the cascading described above can be used to focus the partial beams or a plurality of partial beams, each of which - in particular in pairs - have one of two different polarization states, on partially overlapping focus zones. The gaps between the maxima of the quasi-non-diffractive beam profile can in this case be filled by dividing the input laser beam into the two partial beams on the polarizer element. In this way, two or more at least partially overlapping focus zones can be generated along a predetermined contour, usually along the preferred direction.

The beam-shaping optics can comprise an axicon and / or a diffractive optical element. The generation of a (quasi) non-diffractive beam profile, for example in the form of a Bessel beam, can advantageously be generated by means of an axicon, which typically comprises at least one essentially conical surface. If such an axicon, which has a rotationally symmetrical conical surface, is irradiated with a collimated Gaussian beam, a Bessel-Gaussian beam is typically generated. The axicon can be modified in a suitable manner to generate a preferred direction of the beam profile (e.g. by using a non-rotationally symmetrical conical surface) to generate a flomogenization of the beam profile, etc. Alternatively or additionally, a diffractive optical element can be used to generate the (quasi ) non-diffractive beam profile can be used. By means of such a diffractive optical element, the properties of an axicon can be simulated and expanded. The beam-shaping optics can optionally or additionally be designed to generate an exiting laser beam with a flat-top beam profile from an entering laser beam with a Gaussian beam profile, etc.

In the event that the partial beams have a quasi-non-diffractive beam profile, for example a Bessel-like beam profile, they are focused during focusing by means of the focusing optics on a focus volume (e.g. in the order of millimeters) which is comparatively long compared to the diameter of the focus zone (e.g. in the order of micrometers). Nevertheless, for the sake of simplicity, the following text also speaks of focusing in a focal plane in the case of beam profiles of this type. The focal plane or the planes described below are predetermined by the properties of the respective optics (regardless of the type of beam profile).

The arrangement of the polarizer arrangement or the birefringent polarizer element in the beam path of the processing optics depends, in addition to the type of laser processing, on whether a pure spatial offset, a pure angular offset or a combination of a spatial offset and an angular offset is to be generated.

The birefringent polarizer element of the polarizer arrangement can be designed to generate an angular offset and be arranged in a plane that is optically conjugate to the focal plane. A plane that is optically conjugate to the focal plane is understood to mean a plane which is correlated with the focal plane by a Fourier transformation, that is to say an angle-to-position transformation. Assuming that the focusing optics have an (effective) image-side focal length f2, the conjugate plane with the polarizer element, which is designed to generate an angular offset, is typically arranged at a distance from the object-side focal length fi of the focusing optics. For the special case that fi = f ₂ = f, the birefringent polarizer element is arranged at a distance 2 f (or generally 2 f + N x 4 f, N greater than or equal to 0, N as an integer) from the focal plane. In the following, a 2f setup is used for the sake of simplicity, even if the condition fi = f ₂ = f is not met.

Alternatively, the birefringent polarizer element of the polarizer arrangement can be designed to generate a spatial offset and be arranged in the beam path in front of a further, preferably collimating optic, the processing optics being designed to convert the spatial offset between the partial beams polarized perpendicular to one another on the polarizer element into the Focus plane map. In this case, the birefringent polarizer element can be arranged in front of the further optics in a plane corresponding to the focal plane.

Such a plane is correlated with the focal plane, for example, via two angle-to-position transformations. Assuming that the focusing optics have an (effective) focal length of f, the plane corresponding to the focal plane with the birefringent polarizer element in a special case, in which the same focal lengths are used for collimation and focusing, can be at a distance of 4 f (or generally from 4 f + N x 4 f, N greater than or equal to zero, N as an integer) are arranged from the focal plane. In the following, a 4f setup is referred to for the sake of simplicity, even if the optical elements used do not necessarily have a uniform focal length f. In the event that the birefringent polarizer element is arranged in the (essentially) collimated beam path, the precise arrangement of the polarizer element at a given distance from the focal plane is generally not important, only a (extensive) Place-to-place transformation, ie a mapping between the plane with the polarizer element and the focal plane.

The birefringent polarizer element should, however, be arranged in the beam path in front of the further optics, which can be designed, for example, as collimating optics for generating an angle-to-location transformation. Together with the angle-to-position transformation (or equivalent position-to-angle transformation) generated by the focusing optics, the spatial offset of the partial beams that is generated at the polarizer element is converted into a spatial offset in the focal plane. pictured. The further, e.g. collimating optics, together with the focusing optics, can produce an image of the plane with the birefringent polarizer element on the focal plane, i.e. on a plane linked to the focus zone, with a predetermined, e.g. reducing image scale.

The polarizer arrangement is usually arranged in the beam path of the processing optics clearly in front of the rear focal plane of the focusing optics. This offers two important advantages: On the one hand, the fluences in the rear focal plane are very high, since in the quasi-Bessel case a ring focus is formed there. In conjunction with short pulses with high pulse energy, optics can pass through near this level the laser radiation can be damaged. In addition, the rear focal plane is mechanically not easily accessible, especially with short focal lengths of the focusing optics.

In the case of the processing optics described here, no spatial separation of the beam paths of the partial beams generated by the polarizer arrangement is typically required. In terms of a compact and robust implementation of the processing optics, the partial beams typically largely overlap at least partially over the entire optical path length covered up to the workpiece to be processed. Furthermore, as a rule, all of the partial beams generated by the polarizer arrangement pass through the same optical components.

The processing optics can have a preferably diffractive beam splitter optics for generating a plurality of pairs of partial beams polarized perpendicularly to one another. The beam splitter optics can be designed, for example, in the form of a diffractive optical element, but it can also be a different type of beam splitter optics, for example a geometric beam splitter optics. The beam splitter optics can be arranged in the beam path of the laser beam entering the processing optics in front of the polarizer element or in front of the polarizer arrangement and generate several input laser beams that are each split into a pair of perpendicularly polarized partial beams on the polarizer element. The reverse is also possible, i.e. the beam splitter optics can be arranged in the beam path after the birefringent polarizer element. In this case, a plurality of pairs of partial beams are generated from the pair of partial beams generated by the polarizer element by means of the beam splitter optics, the focus zones of which can partially overlap along a preferred direction, in particular as described above.

The beam splitter optics can be arranged in a plane that is optically conjugate to the focal plane. In the plane conjugate to the focal plane, an angular offset can be generated between the pairs of partial beams, which is transformed by the focusing optics into a spatial offset in the focal plane. In this case, the beam splitter optics can, for example, be in a plane that is optically conjugate to the focal plane be arranged between the further imaging optics described above and the focusing optics in order to generate the plurality of pairs of partial beams from a pair of partial beams generated by the polarizer element.

The preferred diffractive beam splitter optics can also be designed as beam-shaping optics for converting an entering laser beam with a Gaussian beam profile into an exiting laser beam with a flat-top beam profile. Shaping a laser beam with a flat-top beam profile, i.e. with a beam profile that has an essentially homogeneous intensity distribution with steeply sloping edges, enables the intensity distribution to be controlled on an area that is oriented essentially perpendicular to the direction of propagation. For details on the formation of the flat-top beam profile, reference is made to DE 102019205394.7 cited at the beginning, the content of which is made part of this application by reference in its entirety.

In a further embodiment, the processing optics comprise a rotary drive for rotating the polarizer arrangement and / or the beam-shaping optics about a (possibly common) axis of rotation. The axis of rotation of the rotary drive typically coincides with the optical axis of the processing optics. The rotation is particularly useful if partially overlapping focus zones are to be generated along a predetermined interaction area, in particular along a preferred direction.

When rotating, it has a favorable effect that the birefringent polarizer element or the polarizer arrangement as a whole only contains components that are not critical for adjustment, which favors its use in adaptive optics in particular. However, the spatial offset or the angular offset generated by the polarizer element is usually not symmetrical to the direction of propagation of the input beam, ie to the optical axis or to the axis of rotation. When the polarizer element is rotated about an axis of rotation, which usually runs in the longitudinal direction, ie along the direction of propagation of the input beam or the optical axis of the processing optics, an undesirable angle and / or location that is dependent on the angle of rotation may occur -Offset of the partial beams. To this one To compensate for the offset, a suitably designed further optical element can be used in the polarizer arrangement, for example the wedge-shaped optical element described above.

In the case of workpiece processing in the form of a laser cutting process for cutting glass along a processing path, it may be necessary or beneficial to change the preferred direction of the focus zones as a function of a location-dependently variable feed direction when moving relative to the workpiece, in order to prevent cracks from spreading in the glass along the feed direction support financially. The targeted alignment of cracks during glass cutting enables working in a process regime that enables a significantly simplified separation of the glass. In such a glass cutting application, the focus zones of two or more quasi-non-diffractive beams with a comparatively long focus volume, for example in the form of Bessel-like beams, in particular in the form of Bessel-Gaussian beams, are at least partially superimposed spatially, as a rule, as described in more detail above. To change the preferred direction, it is not necessary in this case to rotate optical elements that are critical for adjustment, such as lenses, even if such a rotation is basically also possible.

The invention also relates to a laser processing device, comprising: processing optics, which are designed as described above, and a laser source, in particular an ultrashort pulse laser source, for generating a laser beam, in particular a laser beam with a Gaussian beam profile. The laser source is preferably designed to generate a single-mode laser beam with a Gaussian beam profile, but this is not absolutely necessary. The processing optics can be accommodated, for example, in a laser processing head or in a housing of a laser processing head, in particular in the form of a module or in the form of modules of a modular laser processing head that can be moved relative to the workpiece. The laser processing device can alternatively or additionally comprise a scanner device in order to align the partial beams on the workpiece or on different positions on the workpiece. In addition to the optics described above, the processing optics can also have other optics which, for example, enable spatial filtering or spatial rearrangement of the input laser beam in order to favor beam shaping, e.g. homogenization of a Bessel-like beam profile, mask imaging, etc.

For glass cutting applications or for other applications, the laser source can be designed to supply a laser beam with individual pulses or with burst pulses (e.g. 2-6 pulses in a burst with a burst pulse interval of 2 ns to 150 ns, preferably 13 ns to 40 ns) produce. The individual pulses or the pulses in the burst advantageously have a pulse duration between 200 fs and 20 ps, in particular between 300 fs and 20 ps. The pulse energy (entire burst or as a single pulse) is preferably between 10 pJ and 10 mJ, in particular between 30 pJ and 1 mJ. The spatial pulse spacing or the modification spacing between adjacent focus zones of the interaction area that is generated by the laser processing device is preferably between approx. 0.8 pm and approx.

30 pm.

The invention also relates to a method of the type mentioned at the beginning, further comprising: changing an angle and / or a distance of at least one of the partial beams relative to an optical axis of the processing optics to at least one further optical element of the polarizer arranged in the beam path after the birefringent polarizer element -Arrangement. The method offers the advantages described above in connection with the processing optics. Laser processing or workpiece processing can involve laser ablation, laser cutting, surface structuring, laser welding, laser drilling, ...

Further advantages of the invention emerge from the description and the drawing voltage. The features mentioned above and those listed below can also be used individually or collectively in any combination. The embodiments shown and described are not to be understood as a final enumeration, but rather have an exemplary character for describing the invention. Show it:

Fig. 1a-c schematic representations of three birefringent polarizer

Elements for generating an angular offset without a spatial offset, a spatial offset without an angular offset and a spatial offset and an angular offset between two partial beams with different polarization states,

2a, b are schematic representations of a polarizer arrangement with a birefringent polarizer element and an isotropic optical element for aligning one of the two partial beams parallel to the optical axis,

3a-c schematic representations of a polarizer arrangement with a birefringent polarizer element and with further optical elements for positioning one of the two partial beams on the optical axis or for positioning both partial beams at equal distances from the optical axis,

4 shows a schematic representation of a polarizer arrangement with a birefringent polarizer element and with a further birefringent optical element for the formation of two partial beams which intersect at a predetermined distance from the polarizer arrangement,

5a-c schematic representations of a polarizer arrangement with a birefringent polarizer element and with a further birefringent optical element which can be rotated or displaced along the optical axis for changing a spatial offset or an angular offset between the two partial beams is,

Fig. 6a, b schematic representations of the with the polarizer arrangement of Fig.

5a generated local offset or with the polarizer arrangement of 5b angular offset generated as a function of the angle of rotation of the further birefringent optical element,

7a, b are schematic representations of processing optics with beam-shaping optics for forming two partially overlapping partial beams with a Bessel-shaped beam profile and with a polarizer arrangement according to FIG. 2a for generating an angular offset or with a polarizer element according to FIG. 1b to generate a spatial offset between the two partial beams,

8a-c show a schematic representation of processing optics with beam-shaping optics and with an interaction area with two partially overlapping partial beams that have a spatial offset or processing optics that have a polarizer arrangement according to FIG. 2a or according to FIG. 3c .

In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

1a-c each schematically show a birefringent polarizer element 1a, 1b, 1c in the form of a birefringent crystal. Different birefringent materials can be used as the crystal material for the polarizer element 1a, 1b, 1c, e.g. alpha-BBO (alpha-barium borate), YV04 (yttrium vandanate), crystalline quartz, etc.

The birefringent polarizer element 1a of Fig. 1a is wedge-shaped, i.e. a planar beam entry surface 2a for the entry of an input laser beam 3 and a planar beam exit surface 2b of the polarizer element 1a are aligned at a (wedge) angle to one another. The optical axis or an optical axis 4 of the crystal material is aligned parallel to the beam entrance surface 2a.

The unpolarized, elliptically or circularly polarized input laser beam 3, which enters the birefringent polarizer element 1a shown in FIG 2a inclined beam exit surface 2b divided into two partial beams 5a, 5b which are perpendicular to one another (s- or p-polarized). In Fig. 1a, as is generally customary, the first, p-polarized partial beam 5a is identified by a double arrow, while the second, p-polarized partial beam 5b is identified by a point. The first, p-polarized partial beam 5a is refracted more strongly when exiting the birefringent polarizer element 1a than the second, s-polarized partial beam 5b, so that an angular offset Da occurs between the first and second partial beams 5a, 5b. The first and second partial beams 5a, 5b emerge from the birefringent polarizer element 1a at the same point on the beam exit surface 2b; la generated.

As can also be seen in FIG. 1 a, the first partial beam 5a, which forms the ordinary beam, is _{refracted at a first angle a 0} relative to an optical axis 6, which forms the extension of the direction of propagation of the entrance laser beam 3 (not to be confused with each other) with the optical axis 4 of the birefringent crystal). The second partial beam 5b, which forms the extraordinary beam, is _{refracted at a second, smaller angle a eo} relative to the optical axis 6.

The power components in the division of the entrance laser beam 3 into the first, ordinary partial beam 5a and the second, extraordinary partial beam 5b depend on the polarization of the entrance laser beam 3: If the entrance laser beam 3 is elliptically polarized, the ratio of the flal axes of the entrance laser beam 3 in X- Direction or in the Y direction, the power ratio of the ordinary partial beam 5a and the extraordinary partial beam 5b can be set. In the case of an unpolarized, linearly or circularly polarized entry laser beam 3, the power components can optionally be adjusted by a different alignment relative to the XZ plane. The use of an unpolarized or circularly polarized input laser beam 3 is particularly advantageous if the preferred direction is to be rotated during processing (see below). In the polarizer element 1b shown in FIG. 1b, the beam entrance surface 2a and the beam exit surface 2b are aligned parallel to one another and the optical axis 4 of the birefringent crystal material is aligned at an angle of 45 ° to the beam entrance surface 2a. The input beam 3 impinging perpendicular to the beam entry surface 2a is in this case divided at the beam entry surface 2a into a first, ordinary partial beam 5a and a second, extraordinary partial beam 5b. The two partial beams 5a, 5b emerge parallel to the beam exit surface 2b, that is to say without an angular offset, but with a local offset Dc.

In the polarizer element 1c shown in FIG. 1c, the beam entry surface 2a is oriented at an angle to the optical axis 6 and the beam exit surface 2b is oriented perpendicular to the optical axis 6. In the example shown, the optical axis 4 of the crystal material is oriented at an angle of 45 ° to the beam exit surface 2b, but can also be oriented at a different angle. The input beam 3 impinging perpendicular to the beam exit surface 2b is in this case divided at the beam entry surface 2a into a first, ordinary partial beam 5a and a second, extraordinary partial beam 5b. The two partial beams 5a, 5b emerge at the beam exit surface 2b with an angular offset Da and with a spatial offset Dc.

The birefringent polarizer elements 1a, 1b, 1c shown in FIGS. 1a to 1c thus differ fundamentally in that the polarizer element 1a shown in FIG. 1b shown polarizer element 1b a local offset Dc (without angular offset) and that the polarizer element 1c shown in Fig. 1c generates a local offset Dc and an angular offset Da.

The polarizer elements 1a-c shown in Fig. 1a-c can each form a component of a polarizer arrangement 7, as shown, for example, in Fig.

2a, b is shown. The polarizer arrangement 7 of FIGS. 2a, b each has an additional optical element 8, which is a non-birefringent, optically isotropic optical element. In the case of the polarizer arrangement 7 shown in FIG. 2a, the polarizer element 1a is as in FIG. 1a shown and is used to generate an angular offset Da without generating a local offset. As can be seen in FIG. 2a and in particular in FIG. 1a, the two partial beams 5a, b are refracted to different degrees in the same direction by the birefringent optical element 1a, ie neither of the two partial beams 5a, 5b runs when exiting the birefringent optical element Polarizer element 1a parallel to optical axis 6.

This proves to be unfavorable if the entire polarizer arrangement 7 is rotated around the optical axis 6 by means of a rotary drive 9, as shown in FIG Axis 6 can come. In order to avoid this, the polarizer arrangement 7 shown in FIG. Element 1a matched so that one of the two partial beams 5a, b, in the example shown the second, extraordinary partial beam 5b, is aligned parallel to the optical axis 6.

To achieve this, a wedge angle gk of the wedge-shaped optically isotropic element 8 - taking into account the respective refractive indices of the materials used - is adapted to the wedge angle y of the beam exit surface 2b of the birefringent polarizer element 1a, so that the second partial beam 5b when entering the optically isotropic element 8 is refracted in such a way that it is aligned parallel to the optical axis 6, ie a _e o = 0 °. Due to the small distance between the birefringent polarizer element 1a and the optically isotropic element 8, the second partial beam 5b runs almost exactly along the optical axis 6, ie it is only a very small distance from the optical axis 6, see also the illustration in FIG 2a on the right-hand side, which shows a top view of the two partial beams 5a, b in the XY plane perpendicular to the optical axis 6. The angular offset Da between the two partial beams 5a, b is retained when passing through the optically isotropic element 8. It is possible for the second partial beam 5b to be positioned exactly on the optical axis 6 when the optically isotropic element 8 is rotated or tilted about the Y axis. Similar to a tilted plane-parallel optical element, a additional parallel offset of the two partial beams 5a, 5b, which can be selected so that the first partial beam 5a runs along the optical axis 6.

In general, the axis of rotation Z (of an XYZ coordinate system) coinciding with the optical axis 6 is fixedly predetermined and by the choice of the wedge angle gk of the wedge-shaped optically isotropic element 8, which is in the XZ plane, shown in FIG of the wedge angle g of the birefringent polarizer element 1a, the two partial beams 5a, 5b can be positioned at any distance in the X direction to the axis of rotation Z. The distance Xeo of the second, extraordinary partial beam 5b to the optical axis 6 depends on the wedge angle gk of the wedge-shaped optically isotropic element 8 and, in the example shown, does not depend on the position in the Z direction, since the second partial beam 5b is parallel to the optical axis 6 is aligned. The spatial offset DC between the two partial beams 5a, 5b is _{dependent on the wedge angle g r of} the birefringent polarizer element 1a and on the position in the Z direction.

In addition to the positioning of the two partial beams 5a, 5b in the X direction, in the example shown in FIG. 2a, in which the optically isotropic element 8 has an additional wedge angle gk in the ZY plane (cf.Fig. 2a, bottom), the two partial beams 5a, 5b are also deflected together in the YZ plane. As can be seen at the bottom right in FIG. 2a, in this way the (identical) distance Y ₀ , Yeo of the two partial beams 5a, 5b from the optical axis 6 in the Y direction can be specified, that of the position in the Z direction is dependent.

The polarizer arrangement 7 shown in Fig. 2a, which uses a birefringent polarizer element 1a, which produces only an angular offset Da, but no spatial offset, can be implemented in a compact design and has proven itself in applications in which a rotation of the polarizer -Arrangement 7 around the axis of rotation Z is required, has proven to be particularly favorable. For example, the polarizer arrangement 7 can be integrated particularly easily into a mechanical mount. The use of the polarizer element 1a has also proven to be advantageous compared to the use of the polarizer element 1b shown in FIG. 1b in such applications for other reasons. FIG. 2b shows a polarizer arrangement 7 which has a birefringent polarizer element 1c which, as in FIG. 1c, generates both a spatial offset Dc and an angular offset Da. In the polarizer element 1c shown in FIG. 2b, the optical axis 4 of the birefringent crystal is aligned at 45 ° to the beam entrance surface 2a. The local offset Dc at the beam exit surface 2b depends on the alignment of the optical axis 4 of the birefringent crystal and is at a maximum of less than 45 ° in the shown alignment. In the case of the polarizer arrangement 7 shown in FIG. 2 b, one of the two partial beams 5 a, b is also aligned on the optically isotropic wedge-shaped element 8 parallel to the optical axis 6. In contrast to the example shown in FIG. 2a, this is the first, ordinary partial beam 5a. As can also be seen in FIG. 2b, both partial beams 5a, 5b are refracted at the optically isotropic element 8 towards the optical axis 6. The first, ordinary partial beam 5a runs after the optically isotropic element 8 parallel to the optical axis 6, while the second, extraordinary partial beam 5b, after passing through the optically isotropic element 8, approaches the optical axis 6 and _{intersects it at an angle a e} o.

3a, b each show a polarizer arrangement 7 which is designed to align the two partial beams 5a, b parallel to one another. For this purpose, the polarizer arrangement 7 shown in FIGS. 3a, b has the arrangement shown in FIG has another birefringent optical element 11 and a further optically isotropic element 12 following in the beam path 10. The further birefringent optical element 11 of the beam offset optics 9 serves to align the two partial beams 5a, 5b parallel to one another when they exit the further birefringent optical element 11. The two partial beams 5a, b aligned parallel to one another are refracted at a beam entrance surface of the further optically isotropic element 12 and aligned parallel to the optical axis 6 so that both partial beams 5a, 5b make an angle a ₀ and a _e o of 0 ° to the optical Have axis 6.

The distance between the further birefringent optical element 11 and the further optically isotropic element 12 along the optical axis 6 is at The example shown in FIG. 3 a is selected such that the second partial beam 5 b is positioned exactly on the optical axis 6. With the help of the polarizer arrangement 7 shown in Fig. 3a, both partial beams 5a, b can also be aligned parallel to one another, so that they have a beam offset Dc 'but no angular offset to one another when they exit the polarizer arrangement 7, without this for this purpose a birefringent polarizer element 1b must be used, which generates a spatial offset Dc without an angular offset Da.

By changing the distance along the optical axis 6 (in the Z direction) between the optically isotropic element 8 and the beam offset optics 11, the beam offset Dc 'when exiting the polarizer arrangement 7 can be set. If the distance in the Z direction between the further birefringent optical element 11 and the further optically isotropic element 12 of the beam offset optics 11 is also suitably adapted, the second partial beam 5b can always be positioned on the optical axis 6.

As an alternative to positioning the second partial beam 5b on the optical axis 6, as shown in FIG. 3a, both partial beams 5a, 5b can be positioned at the same distance X ₀ , Xeo from the optical axis 6, as shown in FIG. 3b . For this purpose it is necessary to suitably select or adapt the distance in the Z direction between the further birefringent optical element 11 and the further optically isotropic element 12. In this case too, the beam offset Dc 'of the two partial beams 5a, 5b when exiting the polarizer arrangement 7 and thus their distance from the optical axis 6, as described above, can be achieved by changing the distance between the optically isotropic element 8 and the beam displacement optics 11 can be adjusted along the optical axis 6 (ie in the Z direction).

3c shows a polarizer arrangement 7 which has a birefringent polarizer element 1c which is additionally designed to generate an angular offset Da to generate a spatial offset Dc. The polarizer arrangement 7 comprises a further optical element 13 which is designed to be birefringent in order to align the first partial beam 5a parallel to the optical axis 6 (a ₀ = 0 °) and to position it on the optical axis 6. the The second, extraordinary partial beam 5b is refracted at the further birefringent optical element 13 towards the optical axis 6 and forms an angle a _e o with it.

The polarizer arrangement 7 shown in FIG. 4 has a birefringent polarizer element 1b which is designed as in FIG. 1b and which generates a spatial offset Dc without an angular offset Da. A further birefringent optical element 13 is arranged in the beam path 10 after the birefringent polarizer element 1b, which _{refracts the two partial beams 5a, b aligned at an angle a 0} and a _e o of 0 ° to the optical axis 6 to different degrees, so that after passing through the further birefringent optical element 13, these each have an angle a ₀ or a _e o to the optical axis 6. The angle a _e o at which the second, extraordinary partial beam 5b extends to the optical axis 6 is smaller than the angle a ₀ at which the first partial beam 5a extends to the optical axis 6. Due to the spatial offset Dc between the two partial beams 5a, 5b, they intersect at a predetermined distance behind the polarizer arrangement 7, as can also be seen in FIG. 4. The polarizer arrangement 7 shown in FIG. 4 has similar properties to the polarizer arrangement 7 shown in FIG. 3c. In the polarizer arrangement 7 shown in FIG. 4, however, the distance between the birefringent polarizer element 1b and the further birefringent optical element 13 in the Z direction can be freely selected, so that this polarizer arrangement 7 is less sensitive to tolerances.

In contrast to what is shown in Fig. 3c and in Fig. 4, the mean angle 1/2 (a ₀ + aeo), at which the two partial beams 5a, 5b are aligned with the optical axis 6, can also be 0 ° ( a ₀ = - a _e o). In this case, the two partial beams 5a, 5b run mirror-symmetrically to the ZY plane.

5a-c each show a polarizer arrangement 7 which is designed to change the constant angular offset Da or constant spatial offset Dc predetermined by a respective birefringent polarizer element 1a, 1b. For this purpose, the polarizer arrangement 7 of FIGS. 5a-c each has a further birefringent optical element 13. In the polarizer arrangement 7 shown in FIG. 5a, the birefringent polarizer element 1b is designed to generate a constant spatial offset Dc (without angular offset) between the two partial beams 5a, 5b, and the further birefringent optical element 13 is also designed to generate a spatial offset ( without angular offset). The polarizer arrangement has a rotary drive 14a, which is designed to rotate the further optical element 13 about an axis of rotation Z which coincides with the optical axis 6. By rotating the further birefringent optical element 13 about the axis of rotation Z at a respective adjustable angle of rotation cp, a spatial offset Dc 'generated by the polarizer arrangement 7 between the two partial beams 5a, 5b can be set, as can be seen in FIG. 6a .

In the example shown in Fig. 5a, a polarization-influencing optical element 15, for example in the form of a suitably aligned 1/2 retardation plate, is arranged in front of the further birefringent optical element 13. This is favorable because if the optical axes 4 of the birefringent polarizer element 1b and of the birefringent further optical element 13 do not lie in one plane, in the general case not two but four partial beams 5a-d are formed, as in this case is indicated by dashed lines in Figure 5a. If the 1/2 retardation plate 15 is rotated accordingly (with half the angle of rotation) when the further birefringent optical element 13 is rotated, it can be achieved that the power of the input laser beam is only split into two when the further birefringent optical element 13 is rotated Partial beams 5a, 5b takes place.

In the event that the polarization-influencing optical element 15 is designed as a 1/4 retardation plate, the two partial beams 5a, 5b, which are linearly polarized after exiting the birefringent polarizer element 1b, can be converted into circularly polarized partial beams. With the help of the 1/4 retardation plate 15 or with the help of other polarization-influencing optical elements, the power of the input laser beam can be divided into the two partial beams 5a, 5b. It is also possible, with the aid of the 1/4 retardation plate 15, to undertake a cascaded beam splitting in a targeted manner in order, for example, to generate four partial beams 5a-d, as indicated in FIG. 5a. With a suitable alignment of the 1/4 retardation plate 15 to the further birefringent optical element 13, a uniform distribution of the power of the input laser beam to the four partial beams 5a-d can also take place in this case. In the event that, with such a division, the polarization-influencing optical element 13 is rotated with the aid of the rotary drive 14a in order to set the distance or the beam offset DC between the partial beams 5a-d in the X direction, it is typically not necessary to change the first / 4-retardation plate 15 should be rotated accordingly in order to maintain the effect of the even distribution.

The arrangement of the further birefringent optical element 13 and the polarization-influencing optical element 15 arranged in front of it, for example in the form of the 1/4 retardation plate, can be cascaded, ie the arrangement surrounded by a dashed frame in FIG. 5a can be repeated N times be arranged in the beam path in order ^{to generate a number M of M = 2 N + 1} partial beams from an input laser beam.

Depending on the angle of rotation cp of the two birefringent optical elements 7, 13 relative to one another or on the alignment of the optical axes 4 of the birefringent optical elements 7, 13 relative to one another, the four partial beams 5a-d can again be superimposed collinearly, as shown in FIG. 5a is indicated. If all four or more partial beams 5a-d are to be arranged collinearly and run along a common preferred direction, eg the X direction, it is typically necessary to arrange the optical axes 4 of all further birefringent optical elements 13 in a common plane when cascading. If circularly polarized partial beams are generated with the aid of a respective 1/4 retardation plate 15, even with such a cascading, an even distribution of power can take place over all M = 2 ^{N + 1} partial beams.

In the polarizer arrangement 7 shown in FIG. 5b, the further birefringent optical element 13 can also be rotated by means of a rotary drive 14 relative to the birefringent polarizer element 1a about the optical axis 6 to set or change an angular offset Da 'generated by the polarizer arrangement 7. In the polarizer arrangement 7 shown in FIG. 5b, the birefringent polarizer element 1a is designed to generate a constant angular offset Da and the angular offset Da 'generated by the polarizer arrangement 7 can be set as a function of the rotation angle cp of the further birefringent optical element 13 as shown in Fig. 6b. In order to avoid splitting into four partial beams 5a-d during rotation, a polarization-influencing optical element 15 can also be arranged in front of the further birefringent optical element 13 in the example shown in FIG. 5b.

In the case of the polarizer arrangement 7 shown in FIG. 5c, the further birefringent optical element 13 can be displaced along the optical axis 6 with the aid of a translational drive 14b. The birefringent polarizer element 1a is designed as in FIG. 5b to generate a constant angular offset Da (without local offset). With the help of the further wedge-shaped birefringent optical element 13, the (constant) angular offset Da is converted into a spatial offset Dc ', the amount of which depends on the distance between the birefringent polarizer element 1a and the further birefringent optical element 13, which is determined with the aid of the translational drive 15 is changed.

In the examples shown in FIGS. 5a-c, in the simplest case the respective birefringent polarizer element 1a, 1b and the further birefringent optical element 13 can be of identical construction.

All of the polarizer arrangements 7 shown above can form a component of processing optics 16, which can be designed, for example, as shown in FIGS. 7a, b. The processing optics 16 shown in FIGS. 7a, b have focusing optics 17 which are used to focus the two partial beams 5a, 5b in the area of a focal plane 18 which, in FIGS. 2a, b, lies on the upper side of a workpiece 19 to be processed. In contrast to what is shown in FIGS. 7 a, b, the focal plane 18 can also be in the beam path 10 of the processing optics 16 shortly before the workpiece 19, in a plane within the workpiece 19 or shortly after Workpiece 19 lie. The input laser beam 3, which strikes the birefringent polarizer element 1a-c of the polarizer arrangement 7, corresponds to a laser beam 21 generated by a laser source 20 and entering the processing optics 16. The processing optics 16 shown in FIGS. 7a, b are designed, to focus the two partial beams 5a, 5b on two focus zones 22a, 22b in or in the vicinity of the focal plane 18, which partially overlap and which are shown in Fig. 7a, b by a black and a white circle. The processing optics 16 shown in FIG. 7a, together with the laser source 11, form a laser processing device 23 for processing the workpiece 19, for example in the form of an abrasive laser processing. For this purpose, the processing optics 16 can be moved relative to the workpiece 19 and / or have a scanner device for aligning the partial beams 5a, 5b at different locations in the area of the focal plane 18.

In the processing optics 6 shown in FIG. 7a, the polarizer arrangement 7 with the birefringent polarizer element 1a and the further optically isotropic element 8 from FIG. 2a are arranged in or near a plane 24 that is optically conjugate to the focal plane 18. The optically conjugate plane 24 is linked to the focal plane 18 by an angle-to-position transformation (Fourier transformation) which is generated by the focusing optics 17. Angles in the optically conjugate plane 24 correspond to locations in the focal plane 18 and vice versa. The two partial beams 5a, 5b emerging from the polarizer element 1a with the angular offset Da are therefore focused in the focal plane 18 with a spatial offset DC "of the two centers of the focus zones 22a, b, which is smaller than the diameter of the focus zones 22a, b, so that the two focus zones 22a, b overlap one another. Due to the non-existent spatial offset of the two partial beams 5a, 5b emerging from the polarizer element 1a, the two partial beams 5a, 5b are aligned parallel and perpendicular to the focal plane 18 after passing through the focusing optics 17. The distance between the focal plane 18 and the optically conjugate plane 24 is 2 f in the example shown in FIG.

The processing optics 16 shown in FIG. 7 b have a further imaging optics 25 which are arranged in the beam path 10 in front of the focusing optics 17. The other The imaging optics 25 together with the focusing optics 17 form the two partial beams 5a, which are arranged in the beam path 10 in front of the further imaging or collimating optics 25, of the polarizer arrangement 7 from FIG. 5a with a variable spatial offset Dc ', 5b into the focal plane 18. The imaging scale for imaging in the focal plane 18 is selected in such a way that the diameter of the two partial beams 5a, b and the distance Ax ″ between the two partial beams 5a, b in the focal plane 8 are reduced. In the example shown in FIG. 7b, the polarizer element 1b is arranged for simplicity at a distance of 4 f from the focal plane 18 in a further plane 24 corresponding to the focal plane 18. As a rule, the further optics 25 and the focusing optics 17 have different focal lengths fi, f2, ie the further plane 24 is arranged at a distance 2 (fi + f2). By selecting suitable different focal lengths fi, f2, the image scale can be set, for example in order to bring about the reduction described above.

The local distribution in the further level 24 corresponds to the local distribution in the focal plane 18 (with an adaptation of the scale). Since the polarizer element 1b is arranged in the collimated beam path 10 of the laser beam 21 entering the processing optics 16, it is not absolutely necessary that it is positioned in the further plane 24, but can also be positioned in the beam path 10 before or after the further plane 24 be arranged.

The processing optics 16 of Fig. 7a, b also have a beam-shaping optics 26 for converting a laser beam entering the processing optics 16, which in the example shown corresponds to the laser beam 21 with a Gaussian beam profile generated by the laser source 20, into an input laser beam 3 a quasi-non-diffractive beam profile, more precisely with a Bessel-like beam profile, which strikes the polarizer arrangement 7.

The Bessel-like beam profile can be rotationally symmetrical to the direction of propagation, but it is also possible for the beam-shaping optics 26 to generate a non-rotationally symmetrical beam profile which has a preferred direction, ie the beam-shaping optics 26 act in the manner of a beam splitter optics. Others too or more complex beam profiles, for example non-diffractive beam profiles such as Airy beam profiles, Mathieu beam profiles, beam homogenization, the generation of a vortex, a bottle, ... can be generated with the aid of the beam-shaping optics 26. The beam-shaping optics 26 can be designed as a diffractive optical element, as an axicon, ... or a combination of these elements. The beam-shaping optics 26 can also be designed as a diffractive optical element which has the function of an axicon.

After the beam-shaping optics 26, in the present example there is a beam profile which corresponds to an essentially rotationally symmetrical Bessel beam, i.e. a radial intensity profile in the transverse direction in the form of a Bessel function.

The processing optics 16 shown in FIG. 7a additionally have an imaging or collimating optics 25, which are arranged in the beam path 10 between the beam-shaping optics 26 and the polarizer element 1a of the polarizer arrangement 7 and which are used for reduced imaging. At the location of the polarizer element 1a, the far field of the Bessel-like beam profile is present in FIG. 7a. The generation of a beam profile in the form of a Bessel-like beam has proven to be advantageous for separating a workpiece 19 which is made of a transparent material, for example glass, and in which separation and possibly crack guidance along a predetermined direction is beneficial that of the in Fig.

7a, b can correspond to the preferred direction X shown, but which can also be aligned at a predetermined angle to the preferred direction X or possibly forms a predetermined contour deviating from a line. The fact that the longitudinal beam profile of the partial beams 5a, 5b that penetrate the workpiece 19 runs almost homogeneously over a comparatively great length also facilitates the separation, possibly with crack formation, and thus the separating processing of the glass material.

A plurality of pairs of focus zones 22a, 22b can be generated in the area of the focal plane 18, which are arranged next to one another along the preferred direction X, with focus zones 22a, 22b of partially overlap adjacent partial beams 5a, 5b and form a coherent interaction region 27, which extends along the preferred direction X in the example shown. As has been described above, the interaction area 27 can also extend along a non-linear contour, which can also extend into the volume of the workpiece 19 in particular in the Z direction. For details of the beam splitting with the aid of the beam splitter optics and for details of the transverse or longitudinal beam profiles that are generated with the aid of the beam-shaping optics 26, reference is made to DE 102019205394.7 cited at the beginning.

The beam path 10 of the processing optics 16 shown schematically in FIGS. 7a, b is shown in a more realistic manner in FIGS. 8a-c. 8a shows the beam path 10 without the polarizer device 7, i.e. only the beam-shaping optics 26, which generate a Bessel-like beam profile from the laser beam 12 entering the processing optics 16. For this purpose, the beam-shaping optics 26 can have a refractive optical element in the form of an axicon, but a diffractive optical element can also be used as the beam-shaping optics 26 instead of the axicon. In particular when using a diffractive optical element, a Bessel-like beam profile with a preferred direction (X direction) with a plurality of partial beams 5a, b overlapping in pairs can also be generated (cf. FIGS. 7a, b), ie the beam-shaping optics 26 acts like a beam splitter optic.

FIG. 8b shows the processing optics 16 from FIG. 7a, which additionally have the polarizer arrangement 7 from FIG. 2a with the polarizer element 1a and the further optically isotropic element 8, which is arranged in the beam path 10 behind the beam-shaping optics 26 and which splits the input laser beam 3 into two partial beams 5a, 5b polarized perpendicularly to one another, in order to generate the interaction region 27 which is shown in FIG. 8a and is extended in the longitudinal direction Z. As can be seen in FIG. 8a, the interaction region 27 has a preferred direction X, along which the two partial beams 5a, 5b or the two focus zones 22a, 22b have a spatial offset Ax ″ to one another. The processing optics 16 shown in FIG. 8c differ from the processing optics 16 shown in FIG. 8b by the polarizer arrangement 7, which is designed as shown in FIG. 3c. The polarizer arrangement 7 comprises a birefringent polarizer element 1c, which generates both a spatial offset Dc and an angular offset Da, as well as a further birefringent optical element 13.

The focusing optics 17 are shown in FIGS. 8b, c only by way of example as a lens and, as a rule, have several optical elements which together form an objective. In addition to the front focal plane 18 facing the workpiece 19, the focusing optics 17 also have a rear focal plane 18a which faces the polarizer arrangement 7.

The respective polarizer arrangement 7 of the processing optics 16 shown in FIGS. 8b, c makes it possible to position one of the two partial beams 5a, 5b on the optical axis 6, but this is not absolutely necessary. As described above, this is beneficial in order to prevent beam wobbling when the polarizer arrangement 7 - typically together with the beam-shaping optics 26 - is rotated by means of the rotary drive 9 around the optical axis 6 of the processing optics 16 in order to adjust the position of the To change the preferred direction in the XY plane during the machining of the workpiece 19 (to rotate).

With the aid of the processing optics 16 shown in FIGS. 8a-c, a glass cutting or glass cutting application, among other things, can be carried out in a particularly advantageous manner, which as a rule requires high fluences. In such an application, a laser beam 21 with individual pulses or with burst pulses (for example 2-6 pulses in burst with a burst pulse interval of 2 ns to 150 ns, preferably 13 ns to 40 ns) is typically used. The individual pulses or the pulses in the burst advantageously have a pulse duration between 200 fs and 20 ps, in particular between 300 fs and 20 ps, ie the laser source 20 is designed as an ultra-short pulse laser source. The pulse energy (entire burst or as a single pulse) is preferably between 10 pJ and 10 mJ, in particular between 30 pJ and 1 mJ. The spatial pulse spacing or the modification spacing between adjacent focus zones 22a, 22b of the Interaction area 27 is typically between approx. 0.8 gm and approx. 30 gm.

An essential advantage of the processing optics 16 shown in FIGS. 8a-c is that the polarizer arrangement 7 can be arranged comparatively far from the rear focal plane 18a of the focusing optics 17. In the rear focal plane 18a of the focusing optics 17, the fluences that occur are very large, especially in the quasi-Bessel case, since a ring focus is formed there in this case. The comparatively large distance of the polarizer arrangement 7, more precisely the last optical element 8, 13 of the polarizer arrangement 7, from the rear focal plane 18a, which is typically at least as large as the rear focal length of the focusing optics 17, can damage the polarizer -Arrangement 7 can usually be avoided by too high fluences. In addition, the rear focal plane 18a is mechanically not easily accessible, particularly in the case of short focal lengths of the focusing optics 17.

Depending on the application, it can be useful to generate circularly polarized partial beams 5a, 5b on the left or right in the focal plane 18 instead of linearly polarized partial beams 5a, 5b. For this purpose, a delay element, e.g. in the form of a 1/4 plate, can be arranged at a suitable point in the beam path 10 after the polarizer arrangement 7.

Claims

1. Processing optics (16) for workpiece processing, comprising: a polarizer arrangement (7) which has a birefringent polarizer element (1a, 1b, 1c) for splitting at least one especially pulsed input laser beam (3) into at least two partial beams (5a, 5b ) each with one of two different polarization states (s, p), as well as focusing optics (17) arranged in the beam path (10) after the polarizer arrangement (7) for focusing the partial beams (5a, 5b) on at least two focus zones (22a) , 22b), characterized in that the polarizer arrangement (7) has at least one further optical element (8, 11 to 13) arranged in the beam path (10) after the birefringent polarizer element (1a, 1b, 1c) for changing an angle (a ₀ , a _e o) and / or a distance (x ₀ , Xeo) at least one of the partial beams (5a, 5b) relative to an optical axis (6) of the processing optics (16).

2. Processing optics according to claim 1, in which the polarizer element (1 ac) is designed to generate a spatial offset (Dc) and / or an angular offset (Da) between the partial beams (5a, 5b) with the different polarization states (s, p) is.

3. Processing optics according to claim 2, in which the polarizer element (1 a, 1 c) is designed to generate an angular offset (Da) between the partial beams (5a, 5b) with the different polarization states (s, p) and in which the Another optical element (8, 11 to 13) is designed to change the angle (a _qo , a ₀ ) of one of the two partial beams (5a; 5b) relative to the optical axis (6) to make the partial beam (5a; 5b) parallel to align to the optical axis (6).

4. Processing optics according to claim 3, in which the further optical element (8) is designed to be optically isotropic, the polarizer element (1 a) preferably for Generation of an angular offset (Da) is formed without generating a local offset (Dc).

5. Processing optics according to claim 3 or 4, in which the polarizer arrangement (7) has a beam offset optics (9) which has a further birefringent element (11) in order to align both partial beams (5a, 5b) parallel to one another.

6. Processing optics according to one of claims 3 to 5, in which the polarizer arrangement (7) is designed to position one of the partial beams (5a; 5b) on the optical axis (6) or to position both partial beams (5a, 5b) in the same way To position distances (xo, Xeo) from the optical axis (6).

7. Processing optics according to claim 6, in which the birefringent polarizer element (1c) in addition to generating the angular offset (Da) is designed to generate a spatial offset (Dc) and in which the further optical element (13) is designed to be birefringent To position the partial beam (5a) on the optical axis (6).

8. Processing optics according to one of claims 2 to 7, in which the polarizer arrangement (7) is designed to change the angular offset (Da ') and / or spatial offset (Dc') between the two partial beams (5a, 5b).

9. Processing optics according to claim 8, in which the further optical element (13) is designed to be birefringent and to change the angular offset (Da) and / or to change the spatial offset (Dc) between the two partial beams (5a, 5b) along the optical axis (6) the processing optics (16) is displaceable and / or rotatable about the optical axis (6) of the processing optics (16).

10. Processing optics according to one of the preceding claims, in which the further optical element (13) is designed to be birefringent and in which in front of the further optical element (13) a polarization-influencing optical element (15), in particular a 1/4 retardation plate or a l / 2- retardation plate, is arranged.

11. Processing optics according to one of the preceding claims, further comprising: a beam-shaping optics (26) for converting an incoming laser beam (21) with a Gaussian beam profile into an exiting laser beam (3) with a quasi-non-diffractive beam profile, in particular with a Bessel beam. similar beam profile.

12. Processing optics according to claim 11, in which the beam-shaping optics (26) are designed to generate a non-rotationally symmetrical, quasi-non-diffractive beam profile, which preferably has a preferred direction (X).

13. Processing optics according to one of the preceding claims, which are designed to focus the partial beams (5a, 5b) in at least partially overlapping focus zones (22a, 22b) of a contiguous interaction area (27), with partial beams (5a, 5b) each having different polarization states in adjacent focus zones (22a, 22b) of the contiguous interaction area (27), in particular along the preferred direction (X).

14. Processing optics according to one of the preceding claims, further comprising: a rotary drive (9) for rotating the polarizer arrangement (7) and / or the beam-shaping optics (26) about an axis of rotation (Z).

15. Laser processing device (23), comprising: processing optics (16) according to one of the preceding claims, and a laser source (20), in particular an ultrashort pulse laser source (20), for generating a laser beam (21), in particular a laser beam (21) with a Gaussian beam profile.

16. A method for laser processing a workpiece (19) by means of processing optics (16), comprising:

Splitting at least one, in particular pulsed, input laser beam (21) into at least two partial beams (5a, 5b), each of which has one of two different polarization states (s, p), at one birefringent polarizer element (1a, 1b, 1c) of a polarizer arrangement (7), as well as

Focusing the partial beams (5a, 5b) on focus zones (22a, 22b) in the area of the workpiece (9) by means of a focusing device (17) of the processing optics (16), characterized by

Changing an angle (a ₀ , a _e o) and / or a distance (x ₀ , Xeo) of at least one of the partial beams (5a, 5b) relative to an optical axis (6) of the processing optics (16) to at least one in the beam path ( 10) after the birefringent polarizer element (1a, 1b, 1c) arranged further optical element (8, 11 to 13) of the polarizer arrangement (7).