Method and apparatus for embedding hollow channel-like filaments into brittle fracture workpieces and use thereof

Abstract

The invention relates to a device for embedding a hollow channel-like filament (1) into a brittle fracture workpiece (2), wherein a focused laser beam (4) of a pulsed laser (3) having a wavelength lambda is directed to the workpiece for machining. The workpiece is transparent to the laser wavelength Lambda, and the filament (1) is produced by the incidence of at least one burst pulse packet of laser, where the burst pulse packet has a burst duration Tb and comprises a series of ultrashort laser pulses having a monopulse energy Ep and a burst internal delay Ti. The monopulse energy Ep0 of the laser pulse at the beginning of the burst duration Tb is greater than the monopulse energy Epx of the laser pulse at the end of the burst duration Tb. The subject matter of the invention also relates to some advantageous applications.

Description

Technical Field

[0001] This invention relates to a method for embedding hollow channel-shaped filaments into brittle fracture workpieces. The subject matter of this invention also relates to an apparatus for generating hollow channel-shaped filaments in such workpieces, and the method and / or application of the apparatus. Background Technology

[0002] Therefore, this invention employs a laser-assisted method. Brittle fracture workpieces generally include those made of brittle fracture materials, or at least those whose filamentary regions are made of brittle fracture materials. In the context of this invention, such materials particularly refer to glass, glass-ceramics, silicon, etc.

[0003] In laser processing, filament generally refers to the thin, filamentous damage caused by laser radiation to the workpiece material.

[0004] One known application of filamentation is laser cutting. Here, damage is introduced into the glass. If multiple damages are placed side-by-side, a separation line is obtained, and the glass can be separated at this line by introducing stress.

[0005] The basic mechanism is that microcracks originating from fine filaments weaken the material. When multiple damages are placed side by side, the cracks will connect to form a line, making separation along this line possible.

[0006] Patent document WO2012 / 006736A2 describes a laser cutting method based on the nonlinear optical Kerr effect. This method relies on two nonlinear effects: pulse self-focusing caused by the optical Kerr effect; and defocusing caused by plasma generated by the laser in the material. It is noted that self-focusing is maintained over a focusing length of approximately 500 μm to 1000 μm, and the self-focusing becomes spatially dispersed when the pulse energy is insufficient to refocus and regenerate the plasma channel.

[0007] EP3169635A1 describes the use of a Bessel beam with an axial pyramidal optics to extend the laser focal line in laser cutting. The inventors of this document point out that, unlike methods based on the Kerr effect (such as WO2012 / 006736A2), laser beam refocusing as proposed in WO2012 / 006736A2 requires changing the refractive index of the workpiece material (in this case, glass). This inevitably leads to different damage morphologies, which may be undesirable.

[0008] The WO2018 / 189080A1 uses a biaxial conical lens to focus a Bessel beam with a long laser focal length onto the workpiece. Based on this optical element, high-energy laser beams can be used.

[0009] WO2018 / 210746A1 describes a laser cutting method in which a laser focal line of an ultrashort pulse laser system is generated by means of an optical arrangement with chromatic aberration.

[0010] The common feature of the aforementioned prior art is that the resulting microcracks around the filament extend radially around the filament, and some cracks also penetrate into the workpiece volume perpendicular to the predetermined separation line. These microcracks reduce the strength of the cut edge. Summary of the Invention

[0011] In view of the above, the object of the present invention is to control the formation of microcracks during the filamentation process. The solution of the present invention to achieve the above object is the method and apparatus of the present invention as described in the independent claims. Preferred embodiments of the present invention are given in the dependent claims.

[0012] The inventors have recognized that the method for embedding hollow channel-shaped filaments into brittle fracture workpieces involves directing a focused laser beam of a pulsed laser with wavelength λ onto the workpiece for processing. The workpiece is transparent to the laser wavelength λ. The filament is generated by incident with at least one burst pulse packet of the laser pulse, wherein the at least one burst pulse packet has a burst duration Tb and comprises a series of ultrashort laser pulses with single-pulse energy Ep and an internal burst delay Ti, wherein the single-pulse energy of the laser pulses at the beginning of the burst duration Tb is greater than the single-pulse energy of the laser pulses at the end of the burst duration. Hollow channel-shaped filaments can be generated by applying an array of burst pulse packets. Advantageously, each hollow channel-shaped filament is generated by a single set of burst pulse packets. If several burst pulse packets are used to generate the hollow channel-shaped filament, then for the purposes of this specification, it is sufficient that a single burst pulse packet (especially the first set of burst pulse packets) possesses the stated characteristic, i.e., the first laser pulse in the burst pulse packet has a higher energy than the last laser pulse. This is particularly advantageous for all corresponding burst pulse packets. What is particularly advantageous is that, within the burst pulse packet, the energy of each single pulse is lower than that of the previous single pulse.

[0013] The characteristic of hollow channel-shaped filaments is the cavity along the filament axis. This hollow channel is not limited to material damage and / or refractive index changes, but also enables reasonable subsequent processing of the workpiece, such as separating or further expanding the filament.

[0014] A filament is generally understood as a long, thin, thread-like structure whose diameter is significantly smaller than its length.

[0015] In the context of this invention, a brittle fracture workpiece comprises or is made of a brittle material, at least within the filament region. Brittle materials can only undergo a very small degree of plastic deformation, thus characterized by low ductility. Brittle fracture occurs with low elongation and is typically close to the yield point. In the context of this invention, brittle materials and / or brittle fracture workpieces particularly include glass, glass-ceramics, and / or silicon.

[0016] To embed the hollow channel-shaped filament into the workpiece, a focused laser beam from a pulsed laser is directed onto the workpiece. The laser emits a laser beam of wavelength λ, wherein the workpiece is transparent to the laser wavelength λ, at least within the region where the laser beam is incident. This should be understood as the workpiece having a transmittance of greater than 85%, preferably greater than 90%, and particularly preferably greater than 95% at wavelength λ in that location.

[0017] In order to still achieve the interaction between the laser beam and the workpiece material, an ultrashort pulse laser is employed according to the present invention. In this case, the pulse width is very short, i.e., in the range of less than 1 ns, especially a few ps to a few fs, especially 100 ps or 10 ps to 100 fs or 10 fs, and particularly advantageously, the range is 10 ps to 200 fs.

[0018] To efficiently provide sufficient energy for filament generation using industrially available laser sources, filaments are generated by incident with at least one laser burst pulse packet. The burst pulse packet consists of a series of ultrashort laser pulses, hereinafter referred to as single pulses. One burst pulse packet contains at least two single pulses. Typically, 2 to 20 pulses are used, preferably 3 to 10 pulses, but up to approximately 100 single pulses can also be used.

[0019] The pulse duration of a single pulse corresponds to the pulse duration of the laser, i.e., the duration of the burst pulse packet (called the burst duration Tb). It depends on the pulse duration of the single pulse, the number of single pulses in the corresponding burst pulse packet, and the time interval between single pulses (called the burst delay Ti), all of which are measured at the moment of maximum single pulse intensity. Each single pulse has a single pulse energy Ep, which corresponds to the integral of the single pulse intensity distribution over the single pulse duration. When the single pulse duration is constant, this single pulse energy is related to the maximum intensity of the single pulse in the burst pulse packet.

[0020] According to the present invention, the single pulse energy of the laser pulse at the beginning of the burst duration Tb is greater than the single pulse energy of the laser pulse at the end of the burst duration.

[0021] Until now, it has been generally believed that as much energy as possible should be accumulated in the workpiece through a single pulse in a burst pulse packet. The inventors realized that it is not necessary to use as much energy as possible, but rather to control the amount of energy input over time, which on the one hand can effectively generate hollow channel-like filaments, and on the other hand can control their interaction with the surrounding materials of the workpiece, especially mechanical interaction.

[0022] An advantageous design of this method proposes that the burst pulse packet has a burst attenuation rate of 40% to 90%, more preferably 50% to 70%, and particularly preferably 60% to 70%.

[0023] Burst decay rate (BG) is expressed as a percentage representing the single-pulse energy (Ep) of the last single pulse in the burst packet at the end of the burst duration. x The burst decay rate BG is the ratio of the single-pulse energy Ep0 of the first single pulse in the burst pulse packet at the start of the burst duration. Therefore, the burst decay rate BG is equal to the single-pulse energy Ep0. x The quotient of Ep0 is preferably expressed as a percentage. Accordingly, the following formula applies: .

[0024] For example, if Ep0 is 100 units, Ep x If the value is 60 units, then BG = 0.6 = 60%.

[0025] The energy of a single pulse is significantly reduced relative to the first pulse at the end of the burst pulse packet. As a result, fewer and / or shorter microcracks extend from the filament into the workpiece surrounding the filament, which helps to avoid unintentionally weakening the filamentated workpiece.

[0026] What has proven particularly advantageous is that the method is designed so that, starting from the second single pulse in the burst pulse packet, the energy of the laser pulse is lower than that of the preceding single pulse.

[0027] This applies from the second single pulse onwards. It can also be equivalently stated as: the energy of each laser pulse in a burst pulse packet is greater than the energy of its subsequent single pulse.

[0028] In other words, this means that the energy of a single pulse in a burst pulse packet decays over time. Although this significantly reduces the energy accumulated in the workpiece and / or filament by a burst pulse packet made from a single pulse, it still effectively produces hollow channel-like filaments. This is particularly surprising, as it is generally believed that as much energy as possible should be applied.

[0029] It has been proven advantageous that the energy of a single pulse within the burst pulse packet decays linearly, or particularly advantageous that the energy of a single pulse decays exponentially over the burst duration.

[0030] Of particular advantage is that the single-pulse energy exhibiting exponential decay satisfies the following equation: Where E(t) represents the single pulse intensity at time t in the burst pulse packet, E0 represents the single pulse energy of the first single pulse in the burst pulse packet, and AF represents the attenuation factor of the entire burst pulse packet, that is, the attenuation of the single pulse energy of the last pulse in the burst pulse packet relative to the first pulse. In the above advantageous embodiment, when the last single pulse has, for example, 60% of the single pulse energy, the attenuation is 40%.

[0031] The design scheme of the method described in this invention proposes to generate a filamentary initial channel, particularly an initial hollow channel, during the first single pulse in the burst pulse packet, which expands through subsequent single pulses in the burst pulse packet.

[0032] This is presumably explained by the filamentation mechanism described in this paper. The first single pulse generates an initial filamentary channel, which is likely already hollow. Subsequent laser single pulses in the burst pulse packet further expand the initial channel, which essentially means expanding the channel diameter. Ultimately, a hollow channel-like filament is formed in the workpiece.

[0033] Although this document mentions the diameter of the hollow channel, it should be noted that in reality, filaments generated by lasers in a workpiece rarely correspond to uniform channels. This viewpoint is merely an idealized and simplified description. Local diameter variations are entirely possible along the filament axis (i.e., the axis in the longitudinal direction of the filament). This invention also covers situations where the diameter of the filament at its beginning and / or end can differ from the diameter of its intermediate portion.

[0034] Another design of the method of the present invention includes: generating a region (also called a compression zone or compression area) around a hollow channel-shaped filament that compresses the workpiece material, which in particular has a higher density than the starting material.

[0035] The densification of the surrounding material appears to be a result of the laser pulse expanding the initial channel. In short, a cylindrical, dense workpiece material region exists around the hollow channel-like filament, where the filament axis substantially coincides with the cylinder axis. The advantage of this compressed material region is that it allows the hollow channel-like filament (especially its filament walls) to acquire mechanical stability. This effectively hardens the filament walls.

[0036] Surprisingly, firstly, the first single pulse in the burst pulse packet is sufficient to generate an initial channel without energy accumulation, and secondly, the energy decay of the single pulse in the burst pulse packet still causes compression of the material around the workpiece.

[0037] A particularly advantageous method proposes that, during the initial channel expansion, a single pulse in a burst pulse packet presses the workpiece material, especially in a direction perpendicular to the channel axis, into the workpiece.

[0038] The described compression also results in the workpiece material not being removed from the workpiece due to interaction with the laser pulse, but rather being so-called pressed into the filament wall and thus into the workpiece. The advantage of the described method is that, generally, far less material is removed by embedding the hollow channel-like filament than is pressed into it; otherwise, the removed material (i.e., the so-called ablated material) would be released as dust into the production facility. This dust not only contaminates the photosensitive devices used for beam shaping, but also absorbs incident laser radiation if it floats in the beam path and / or initial channel, especially since the ablated material corresponds at least substantially to the material processed by interacting with the laser radiation. Such parasitic absorption negatively impacts the efficiency of the method.

[0039] In particular, it is believed that the reduction in single-pulse energy in the burst pulse packet helps to reduce the amount of ablated material, which is beneficial for compressing the material.

[0040] The compression phenomenon described in this paper occurs based on measurement experiments, which first weigh the workpiece to be filamentized. Then, the workpiece is filamentized using the described method, i.e., hollow channel-shaped filaments are embedded into the workpiece as described. The diameter and length of the hollow channels are measured, and their volume is determined accordingly. Correlating the measured volume of the hollow channels with the specific gravity of the workpiece material reveals that the weight removed from the workpiece by filamentization (i.e., the material removed) is significantly less than the weight expected from the embedded hollow channel volume. Therefore, the material must still remain in the workpiece, and it is reasonable to infer that it is the compressed material as described above.

[0041] In the described method, the relative weight loss per filament is less than 10%.

[0042] The method for determining that the relative weight loss of each hollow channel filament is less than 10% is as follows (taking 2mm thick soda-lime glass as an example, which is manually scribed and cut into 150 x 250mm pieces using a commercially available glass cutter). 2(Dimensions): The sample is cleaned on both sides manually or automatically using glass cleaner, ethanol, and compressed air (using a cleaning machine) to remove particles, fingerprints, and other contaminants. The prepared sample is then weighed on a precision balance (Mettler Toledo AB204-S). During this process, the entire structure is enclosed in a transparent plastic case to improve measurement accuracy. The sample is then fixed on the stage of the XY-axis system (Aerotech Inc., 3D Micromac microSTRUCT). During this process, the sample is aligned with two limiting blocks to prevent slippage. Laser processing is performed as previously described, using an ultrashort pulse laser with a pulse width of 10 ps, ​​a wavelength of 1064 nm, a burst pulse energy of 400 µJ, and specifically containing 3 to 7 single pulses, to produce a size of 90 x 160 mm. 2 A two-dimensional hollow channel-shaped filament mesh was constructed. The sample was then weighed again. To eliminate potential measurement distortions caused by particle deposition during laser processing, the aforementioned cleaning steps (glass cleaner, ethanol, compressed air) or an automated cleaning method were performed again, and the sample was weighed again. The relative weight loss per filament was calculated using the following rules.

[0043] If the intact material of the hollow channel is removed from the sample, the theoretical weight loss per hollow channel filament is m. theo The calculation is as follows: ; in: d: Diameter of the cylindrical hollow filament, determined by SEM images of the fractured edge along the filamentation direction; h: Glass thickness; ρ: Sample density, from the material data sheet.

[0044] The actual weight loss per pre-damage m actual The self-measured weight loss m mess Divide by the number of pre-damage units N: .

[0045] The relative quality loss can be determined by taking the quotient: .

[0046] Here, we take a 2mm thick glass sample as an example: the sample thickness is h=2mm, and the density is ρ = 2.5g / cm³. 3 Given that the diameter of the filament is d = 600 ± 60 nm, the theoretical mass loss per filament is calculated to be m. theo =1413±60pg.

[0047] The actual (average) weight loss is derived from: when m mess =6±1mg and N=5.8∙10 7 At that time, m actual =104±17 pg / filament. The relative weight loss is calculated to be 7.4±2.7%. Error propagation is included in all calculations.

[0048] Therefore, an advantageous method proposes that the relative weight loss m of each hollow channel-like filament is... rel Less than 10%, it is measured by the following formula: And / or particularly advantageously, when measured within a 3µm radius around the longitudinal axis of the corresponding hollow channel-shaped filament, the material compaction of the workpiece is at least 1% higher than the intrinsic material density.

[0049] The compaction of glass or glass-ceramic within a 3µm radius of the longitudinal axis of the corresponding cylindrical symmetrical pre-damage was determined using the following measurement method to be at least 1% higher than the intrinsic material density: Lena Bressel, Dominique deLigny, Camille Sonneville et al., “Femtosecond laser-induced density changes in GeO2 and SiO2 glasses: Fictive temperature effect [Invited]”, *Optical Materials Express*, Vol. 1, No. 4, pp. 605-613 (August 1, 2011), DOI: 10.1364 / OME.1.000605. Material densification was indirectly demonstrated by the spectral shift of the Nd peak in the Raman spectrum. For this purpose, a Raman microscope with a 10000 cm⁻¹ aperture was required. -1 The spectral range is required to measure Nd glow discharge at approximately 890 nm under 488 nm excitation, and a suitable electric XYZ stepper motor shaft and a suitable microscope objective (NA>0.7) are needed to achieve a spatial resolution of less than 1 micrometer. According to the invention, a grating scan of the component within the measurement area is performed using a stepper motor. The Raman spectrum of the Nd peak is recorded at each point. Its spectral position is recorded, and pressure and density are inversely derived using standard spectra. These standard spectra are taken from glass or glass-ceramic bodies compacted using a belt press. Further verification can be performed using spatially resolved Brillouin spectroscopy. A 3 µm radius around the longitudinal axis or filament axis represents the measurement area of ​​compaction or compression, hereinafter also referred to as the compression measurement line. The compaction zone can further extend around the filament into the workpiece material.

[0050] In the context of this specification, the diameter of a hollow channel-shaped filament refers to the distance perpendicular to the filament axis from one channel wall to another. For cylindrical channels, the diameter is essentially the same throughout. However, a hollow channel-shaped filament can taper towards a specific surface of the workpiece, or widen depending on the viewing angle. This is called a V-shaped filament. Similarly, a hollow channel-shaped filament can also be locally narrowed, forming what are known as an hourglass or X-shape. The filament shape can be influenced by the formation and position of the focal wire.

[0051] In the context of this invention, an advantageous method is proposed where the diameter of the hollow channel-like filament is from 100 nm to 3 µm. Particularly advantageously, this range is from 250 nm to 1.5 µm or from 500 nm to 1 µm.

[0052] If the filament is not a hollow cylinder or a hollow cylinder with significant local deviations, but rather a V-shape or X-shape, then the aforementioned diameter refers to the diameter at the maximum value, or in other words, the diameter at the widest point. In this specification, the filament diameter is measured at the workpiece surface, especially on the laser-facing surface. This side can also be clearly determined on the workpiece during machining.

[0053] As previously described, the present invention strikes a balance between the need for efficient production and the production of filaments that are as large as possible (especially filaments with the largest diameter). However, such large filaments can adversely weaken the workpiece due to undesirable crack formation around the filaments. The present invention controls the energy input and thus controls crack formation. As previously described, it is particularly advantageous that the workpiece material is compacted around the filament axis.

[0054] This process is particularly preferably achieved by the following method: a focused laser beam generates plasma in the workpiece, which forms hollow channel-like filaments.

[0055] It is believed that the burst pulse packet of an ultrashort laser pulse ignites plasma, particularly within the slender laser focal line of the workpiece. As previously described, the plasma explosion can press material perpendicular to the filament axis into the workpiece, thus forming hollow channels and / or hollow channel-shaped filaments with the aforementioned geometry.

[0056] It has proven particularly advantageous that the method is designed such that the first single pulse in the burst pulse packet generates an initial plasma, which is powered and sustained by subsequent single pulses in the burst pulse packet.

[0057] The burst pulse packet continuously replenishes the plasma and sustains its combustion, following the first single pulse. However, because the single pulse energies of the subsequent pulses following the first single pulse are relatively low, the plasma explosion appears to be controllable.

[0058] According to an advantageous design of the method of the present invention, microcracks extending from hollow channel-like filaments into the workpiece volume are generated by plasma.

[0059] This crack formation can serve as a basis for separating workpieces using the described method. In principle, the cracks form perpendicular to the filament axis and extend from the filament into the workpiece volume. The cracks are typically uniformly distributed around the filament axis. This means that, when viewed from the perspective of the filament and / or its axis, the crack density is substantially the same across a 360° range around the filament. It has been demonstrated that, compared to methods that do not reduce the single-pulse energy in the burst pulse packet, the method of this invention achieves lower crack numbers, crack density, and average crack length.

[0060] A particularly advantageous design of this method proposes that at least 90% of the microcracks terminate within the aforementioned compression zone, and particularly advantageously within a radius of 3µm around the longitudinal axis of the hollow channel-like filament.

[0061] This involves statistical observation. The number and length of microcracks are observed, and the extent to which microcracks terminate within the compression zone and how many extend beyond it is assessed. Advantageously, at least 10% of the microcracks terminate within the compression zone. As previously described, the degree of compression is measured within a 3µm radius around the longitudinal axis of the hollow channel-like filament. This means that, particularly advantageously, 90% of the microcracks terminate within this 3µm radius. This compression zone thus advantageously confines what is considered the vast majority of microcracks.

[0062] In order to provide a particularly efficient separation method, another advantageous design of the method is proposed, in which the slender focal wire expands in a direction perpendicular to the axis of the filament, and the length and / or number of microcracks in the direction of focal wire expansion is greater than the length and / or number of microcracks perpendicular to the direction of expansion.

[0063] It should be noted that, surprisingly, by making the single-pulse energy Ep0 of the laser pulse at the start of the burst duration Tb greater than the single-pulse energy Ep of the laser pulse at the end of the burst duration... x It can effectively limit the crack length to the compression region.

[0064] The direction of expansion of the focal line perpendicular to the filament axis is also referred to below as the preferred direction. Expansion of the focal line in one direction will also cause the plasma to expand in that direction. The plasma explosion may be stronger in the direction of expansion. In any case, the number of microcracks in the preferred direction is greater than the number of microcracks perpendicular to the preferred direction, and / or the average length of microcracks in the preferred direction is greater than the average length of microcracks perpendicular to the preferred direction.

[0065] In particular, the preferred direction can be selected to be consistent with and / or at least substantially coincide with the predetermined workpiece separation line direction. This means that the expansion of the laser focus is controlled accordingly relative to the workpiece. This can be achieved by movable optical devices and / or movable workpiece fixtures, especially by microcontrollers and / or data processing devices. Accordingly, in the sense of the present invention, the invention encompasses the ability to individually set the preferred direction at any location on the workpiece, i.e., the preferred direction is variable and, in particular, adjustable according to the positioning of the focal line on the workpiece.

[0066] In the context of this invention, the expansion shape of the focal line can be arbitrarily chosen. Elliptical laser focal points are particularly common. The principal axis of the ellipse corresponds to the preferred direction. This invention also covers linear shapes, asymmetrical shapes, and any other suitable expansion shape.

[0067] The described method can be designed to cause the plasma to emit X-rays, which are attenuated and / or shielded by at least one shielding element.

[0068] The inventors recognized that it is perhaps the aforementioned plasma explosion that causes the emission of X-rays. In particular, these are in the range of 4 keV to 20 keV, and are therefore remarkably intense. This can be used, for example, to specifically inspect materials and / or workpieces and / or workpieces to be processed, especially during laser processing. It has also been demonstrated that, according to the invention, the attenuation of the single-pulse energy within the burst pulse packet also contributes to reducing the emitted X-ray radiation.

[0069] However, it is advantageous to confine the generated X-ray radiation to a specific spatial area. In particular, the production environment should be protected from the emitted X-ray radiation. Therefore, at least one shielding element should be provided, which at least attenuates and / or shields the X-ray radiation emitted from the plasma.

[0070] The shielding element can be designed, in particular, to at least partially surround the space surrounding the workpiece. Specifically, an entrance port for the laser beam that must irradiate the workpiece is provided, and / or an inlet and / or outlet port is provided for feeding the workpiece before processing and removing it after processing. In a simplified case, the shielding element forms a cavity surrounding the workpiece, particularly having a so-called passageway. In this case, the shielding element can be constructed, in particular, as a single piece or in multiple pieces.

[0071] One advantageous method involves attaching a shielding element such that it at least partially surrounds the workpiece, wherein the shielding element comprises or is made of an X-ray absorbing material, preferably selected from the group of metals including iron, steel, stainless steel, and tungsten, or from the group of composite plastics including metal-filled composite plastics and tungsten-filled composite plastics.

[0072] Generally, shielding elements should possess the highest possible shielding efficiency. However, they should also be manufactured and operated in a reasonable manner. In principle, shielding performance is related to the nuclear charge number of the atoms in the material contained within the shielding element. This, along with the thickness of the shielding element, determines whether the shielding element can at least reduce and / or shield X-ray radiation.

[0073] Metals are particularly well-suited to satisfy the aforementioned trade-offs. For example, lead is a well-known good X-ray absorber, but it is not the most advantageous material in practical applications. For the purposes of this invention, ferrous materials are preferred, especially steel and / or stainless steel, particularly conforming to standard EN 10020:2000 (published July 2000), including both non-alloy and alloy stainless steels. Tungsten has also proven to be an advantageous material. Metal-filled composite plastics, especially tungsten-filled composite plastics, can also be used.

[0074] As described above, it is advantageous to direct the laser beam onto the workpiece in the form of a long focal line. Accordingly, an advantageous method includes directing the focused laser beam onto the workpiece in the form of a long focal line. Particularly advantageously, the long focal line is generated by beam-shaping optics selected from the group consisting of: SLMs (spatial light modulators), axial cones, truncated cones, biaxial cones, spherical aberration lenses, and / or chromatic aberration lenses.

[0075] Ideally, spatial confinement of laser radiation through the focal line can be achieved using so-called Bessel beams. These beams are made from a centrally bright maximum value surrounded by a weaker ring of light and are characterized by a constant radius relative to the laser emission direction. These beams not only allow for a greater range of machining depths but also allow for larger tolerances when aligning workpieces. Furthermore, these beams exhibit virtually no diffraction.

[0076] The primary method for generating Bessel beams and expanding linear focal lengths is by using so-called axicones as beam-shaping lenses. As an optical element, the axicon was introduced by McLeod in 1954 (John H. McLeod, “The Axicon: A New Type of Optical Element,” *Journal of the Optical Society of America*, Vol. 44, No. 8, August 1954). In this sense, an axicon is an optical element that images light from a small point source into a straight, continuous focal line. McLeod described various forms of axicones but emphasized that glass axicones are the most important.

[0077] The truncated conical mirror has a flat surface at the tip of the cone along the laser beam axis. The central beam is not refracted by the truncated conical mirror. This makes the tunability of the optical system easier to achieve, since it is usually difficult to precisely align the central beam with the tip of the axial conical mirror. Similarly, the tilt of the axial conical mirror and / or its manufacturing precision (i.e., especially the sharpness and symmetry of the tip) are less critical.

[0078] The incident surface of a biaxial conical mirror is designed to shape the laser beam into a ring beam within the mirror. The advantage of a biaxial conical mirror is that, by selecting the laser energy, the refractive index of the mirror, and the axial-cone angle of the incident surface, the intensity of the laser beam within the mirror can be set below the threshold intensity of the mirror material, ensuring that the beam does not damage the mirror material as it passes through.

[0079] Equally advantageous is the ability to generate elongated laser focal points and / or line focal points using Gaussian optics.

[0080] Therefore, beam extension can be achieved by the spherical aberration of a Gaussian lens. In this case, spherical and / or cylindrical lenses, each with aspherical portions, can be used.

[0081] When utilizing spherical aberration, it is particularly important to note that the laser beam is not aligned with the geometric center of the lens and / or the lens is tilted. This can also be implemented dynamically, i.e., the orientation of the lens relative to the laser beam can be controlled by actuators, microcontrollers, and / or data processing devices.

[0082] In addition to monochromatic lasers, pulsed multicolor laser beams with specific pulse durations and wavelengths can also be used. Wavelength-dependent focusing of the laser beam is achieved through an optical arrangement with chromatic aberration, and preferably, wavelength-dependent filtering of the laser beam is achieved using at least one filter. A focal line can be generated along the laser beam direction, thereby selectively and precisely setting the processing depth of the workpiece. In particular, the length of the focal line can be set by generating different focal points.

[0083] In some cases, the presence or absence of a narrow laser focal point is irrelevant. Therefore, conventional Gaussian optics are often sufficient. This invention naturally covers these situations as well.

[0084] The method is advantageously designed such that the filament forms a channel connecting one surface of the workpiece to another and thus completely penetrates the workpiece, i.e., a through channel, or a channel terminating in the workpiece volume as a blind hole.

[0085] As described above, the shape of the hollow channel can be cylindrical, V-shaped, and / or X-shaped. This can be specifically set by the focusing position of the focal line relative to the workpiece in the beam direction and the intensity distribution of the focal line perpendicular to the beam direction.

[0086] In one advantageous method, the laser wavelength is 500 nm to 1100 nm, preferably 1020 nm to 1080 nm, and / or the pulse duration of a single pulse is 200 fs to 11 ps, and / or the burst duration is 1 ps to 500 ns, and / or the single pulse energy of the first single pulse at the start of the burst duration is 100 µJ to 1000 µJ, preferably 200 µJ to 500 µJ, and / or the workpiece comprises or is made of glass and / or glass ceramic and / or silicon and / or ceramic.

[0087] The workpiece, especially in the region where it interacts with the laser beam, i.e., in the location of the hollow channel-like filament, contains the aforementioned materials, particularly glass and / or glass ceramics and / or silicon and / or ceramics.

[0088] The laser wavelength is determined by the laser used, and its bandwidth is typically strictly limited. The aforementioned wavelength range is intended to indicate the lasers that can be used within the described wavelength range. As previously described, the laser wavelength is chosen so that the workpiece is substantially transparent within that wavelength range.

[0089] As explained in the preceding paragraphs, by reducing the single-pulse energy in the burst pulse packet, the microcrack density and / or microcrack length around the hollow channel-like element can be controlled.

[0090] To enable efficient separation of workpieces via filamentation, the spacing between two adjacent filaments can be appropriately set. Advantageously, the spacing between two adjacent filaments is 3µm to 20µm, especially 3µm to 10µm or 4µm to 8µm. For glass with a thickness exceeding 0.5mm, an empirical formula for filament spacing is advantageously applicable: The factor Z can take values ​​from 3 to 7. This empirical formula for spacing selection has been proven particularly suitable for glass and / or glass-ceramic workpieces with thicknesses or material thicknesses ranging from 0.5 mm to 30 mm. For example, applying this formula, a favorable filament spacing of 3 µm to 7 µm is suitable for a workpiece with a thickness of 1 mm.

[0091] Compared to the conventional burst pulse packet method (where the single pulse energy remains constant and should be chosen to be as large as possible), this interval is significantly smaller.

[0092] Particularly advantageously, the burst attenuation rate is 90% to 70%, especially for burst packets of 2 to 7 single pulses and burst packets of 3 to 5 single pulses.

[0093] The above parameters are particularly applicable to silicon- and boron-containing glasses.

[0094] The above parameter combination allows for the use of particularly appropriate methods to process the workpiece.

[0095] In addition to the methods described above, the present invention also covers the following apparatus. This apparatus is particularly suitable for performing and / or applying the described methods. The aspects described with respect to the methods also apply to the apparatus. Similarly, the aspects of the apparatus described below also apply to the methods.

[0096] Accordingly, the present invention also relates to an apparatus for embedding a hollow channel-shaped filament into a brittle fracture workpiece under laser assistance, particularly an apparatus for applying the above-described method, the apparatus comprising: an ultrashort pulse laser having a wavelength λ, wherein the workpiece is transparent to the incident wavelength; and a beam-shaping optics configured such that the laser beam is directed toward the workpiece along a focal line, and the focal line is at least partially located within the workpiece, wherein the laser is configured to emit at least one burst pulse packet of laser pulses, wherein the at least one burst pulse packet has a burst duration Tb and comprises a series of ultrashort laser pulses having a single pulse energy Ep and a burst internal delay Ti, and wherein the single pulse energy of the laser pulse at the beginning of the burst duration Tb is greater than the single pulse energy of the laser pulse at the end of the burst duration.

[0097] This equipment can be integrated into a production environment that enables efficient workpiece processing.

[0098] The advantage of the aforementioned device lies in its inclusion of a regulating mechanism, thereby controlling the single-pulse energy Ep of the last single pulse at the end of the burst duration Tb. x The energy decrease of the single pulse Ep0 compared to the energy of the first single pulse at the start of the burst duration is adjustable, and particularly preferably the energy decrease of the single pulse during the burst duration is adjustable, especially exhibiting linear or exponential decay behavior. These decay behaviors naturally also apply to the methods described above.

[0099] Advantageous designs of the device include means for moving the laser and / or optical device relative to the workpiece, particularly including a movable workpiece fixture and / or means for moving the laser and / or optical device; and a control unit for controlling the relative movement.

[0100] The control device can be configured in particular to allow the filament to be embedded in the workpiece in a predetermined pattern, particularly adjacent to a predetermined separation line.

[0101] This structure and / or separation line can be created in the workpiece by moving it relative to the laser, especially the focal line, and repeatedly impacting different locations on the workpiece with burst pulses, at least as a precursor to a separation line along which the workpiece can be separated. In the case of a separation line precursor, the workpiece remains in a continuous state and is later separated by applying mechanical fracture force or thermal stress. This has advantages in mass production of workpieces, especially in terms of workpiece transport and / or subsequent reprocessing.

[0102] In order to generate the aforementioned preferred direction, the beam shaping optics of the device includes an optical element that expands the focal line in a direction perpendicular to the filament axis (i.e., the so-called preferred direction), preferably in a direction toward the adjacent filament on a predetermined separation line.

[0103] The device may include a control unit, thereby enabling the setting of a position in a preferred direction, particularly through positioning optical elements. As previously described, this positioning can be achieved using a microcontroller and / or a data processing system.

[0104] As previously described, the device includes a shielding element for shielding against X-ray radiation, which at least partially surrounds the workpiece.

[0105] Advantageously, the shielding element is constructed as a single piece. Of course, multiple shielding elements may also exist, even located in different positions on the equipment.

[0106] The materials suitable for shielding elements have been mentioned above. An advantageous device is one in which the shielding element comprises, or is made of, a material selected from, in particular, the group of metals including iron, steel, stainless steel, and tungsten, or a material selected from, in particular, the group of composite plastics including, in particular, tungsten-filled composite plastics.

[0107] The subject matter of this invention also relates to the application of methods and / or apparatus. Advantageously, the methods and / or apparatus can be used to separate, structure, or prepare etched glass elements and / or glass-ceramic elements and / or silicon elements.

[0108] When structuring a workpiece, hollow channel-shaped filaments are embedded into the workpiece according to a predetermined pattern. The diameter of the hollow channel-shaped filaments can be increased by etching. It has been proven advantageous that etching removes material from the channel wall region much faster than removing material from the workpiece surface. It is speculated that the microcracks surrounding the filaments present stronger erosion points for the etching medium. Suitable etching media include, in particular, HF, HCl, NaOH, and / or KOH. Attached Figure Description

[0109] The invention will now be described in detail with reference to the accompanying drawings. All drawings are schematic diagrams and need not be drawn to scale. Each drawing also illustrates an embodiment, and the same reference numerals in different drawings have the same meaning. In the drawings: Figure 1 The device is shown schematically; Figure 2 The diagram illustrates a device for processing workpiece strips; Figure 3 The burst pulse packet of the laser pulse is shown; Figures 4a to 4d An example of a laser pulse energy distribution curve within a burst pulse packet is shown; Figures 5a to 5cAn example of the filament shape in the workpiece is shown; Figure 6 A top view of the filamentized workpiece is shown; Figure 7 A top view shows a filament with microcracks in a workpiece according to the prior art; Figure 8 A top view shows a filament with microcracks according to this specification; Figure 9 A top view shows a filament with shortened microcracks; Figure 10 A filament with microcracks distributed along a preferred direction is shown in a top view; Figure 11 The correlation between microcrack length and preferred direction is shown; Figure 12 An example of the focus area in the preferred direction is shown in a top view. Detailed Implementation

[0110] Figure 1 An apparatus schematically illustrated according to this specification is shown. This apparatus (100) is particularly suitable for applying this method. The apparatus (100) is used to embed at least one hollow channel-shaped filament (1) into a workpiece (2). The apparatus includes an ultrashort pulse laser (3) and beam-shaping optics (30). This focuses a laser beam (4) having a wavelength λ onto the workpiece (2) with a narrow focal line. At least a portion of this focal line is located within the workpiece, where the filament (1) is generated by interaction with an ultrashort pulse of a burst pulse packet.

[0111] The workpiece (2) is placed on a workpiece fixture. The incident point of the laser beam (4) of the ultrashort pulse laser (3) can be laterally positioned on the surface of the workpiece (2) using a positioning device (200). As previously described, the workpiece (2) is a brittle fracture workpiece, particularly containing glass, glass ceramics and / or silicon. As previously described, the wavelength λ of the laser (3) is selected such that the workpiece (2) is transparent to that wavelength.

[0112] As previously described, the beam-shaping optics (30) can also be configured such that the focal line expands perpendicular to the filament axis to provide a preferred direction (VR). Similarly, an aperture can be introduced in the beam path to produce a correspondingly shaped focal point.

[0113] In the example shown, the positioning device (200) includes an xy stage on which the workpiece (2) rests with its underside. Alternatively or additionally, the laser (3) and / or beam-shaping optics (30) may also be configured to be movable so as to move the laser beam (4), thereby allowing the incident point of the laser beam 4 to be movable even when the glass element (1) remains fixed. These two modes of movement may also be combined.

[0114] The ultrashort pulse laser (3), positioning device (200) and / or beam shaping optics (30) are connected to a control device (210), such as a microcontroller and / or a data processing device.

[0115] As previously described, plasma generated by an ultrashort laser pulse beam can emit X-rays, which then produce filaments. A shielding element (300) is also shown in the figure to protect the environment from this radiation. For this purpose, the shielding element comprises a material of moderate thickness that at least partially absorbs the X-ray radiation. As shown, the shielding element (300) is made of stainless steel plate, which at least surrounds the area where the laser is focused. As an optional element, a sensor device (310) is provided, which can, for example, detect the reflection of the incident laser beam, or in particular, detect the emitted X-ray radiation. Other measurement variables are also conceivable, especially those related to the energy of the incident laser power. In the present case, the energy of the emitted laser power can be used as a control variable for the laser (3) and / or the positioning device (200), for which it is connected to the control unit (210). In this way, for example, X-ray emission is used as a measure of the incident laser power, and the laser (3) is controlled using these measurement variables to maintain the desired processing parameters, thereby enabling high process stability.

[0116] Figure 2An apparatus (100) for performing the laser filamentation described herein on a workpiece (2) as a strip is shown. In this example, ultrathin glass is obtained from a drawing groove (250) in particular by a pull-down method. The method of the present invention can also be applied accordingly to other ultrathin glass manufacturing methods, such as overflow melting. Here, the material thickness of the ultrathin glass is about 100 µm at most, and in this example, the material thickness is particularly 20 µm to 50 µm. The strip is deflected toward a laser processing apparatus with a laser (3) by means of a deflection device (251). The filamentation process is completed in the cold zone of the system due to the distance from the drawing groove. However, laser processing can also be performed in the hot zone (220) closer to the drawing groove (250). For example, the strip can be stored and / or rolled up on a spool, here a glass spool (221). For this purpose, the spool is rotated according to the pulling speed of the glass strip. The figure also shows a shielding element (300) that at least partially surrounds the filamentation region and, as previously described, shields the surrounding environment from emitted X-ray radiation. In the present case, a shielding element (300) is also provided below the workpiece.

[0117] Figure 3 Three sets of laser burst packets are shown as graphs of laser pulse intensity I versus time t. As previously described, the energy of a single laser pulse corresponds to the integral of intensity over time, and therefore the laser pulse energy E is related to its intensity. Accordingly, this graph also corresponds to a schematic graph of laser pulse energy versus time. Each of the three sets of burst packets shown in the figure contains four laser pulses, with a burst duration of Tb. Tb is defined as the time from the highest intensity of the first laser pulse (41) in the burst packet to the highest intensity of the last pulse in the burst packet.

[0118] In the example shown, the number of pulses in the burst pulse packet is 4. Advantageously, the burst pulse packet contains, for example, 2 to 20 pulses and / or 2 to 10 pulses. Advantageously, the pulse width is 300 fs to 11 ps. Advantageously, Tb is in the range of 1 ps to 500 ns, while Ti is in the range of 400 fs to 400 ns. To generate the hollow channel-like filament (1), only a single burst pulse packet needs to be incident on the workpiece. However, it may also be advantageous to use 2 to 10 burst pulse packets, especially 2 to 5 burst pulse packets. The time interval between the individual burst pulse packets is called the inter-burst delay (Td). Advantageously, 1 / Td can be from 1 kHz to 1000 kHz.

[0119] The selection of the above parameters depends on the workpiece material, the expected filament geometry, and the spacing between the filaments.

[0120] In the context of this invention, the energy Ep0 of the first laser pulse (41) in the burst pulse packet is greater than the energy Ep of the last laser pulse (42) in the same burst pulse packet. x .

[0121] Figures 4a to 4d Exemplary energy distribution curves of each laser pulse in a single burst pulse packet over time t are shown. For simplicity, these distribution curves are shown as continuous curves rather than as discrete points. The number of pulses in the burst pulse packet is arbitrary, but it is advantageous to select the range described above. The simplest energy distribution curve is a linear distribution, such as... Figure 4a As shown. In this case, the energy of each pulse within the burst pulse packet decays at least substantially the same amount. It is also possible that the first or first few pulses in the burst pulse packet have at least substantially the same energy, while subsequent pulses have lower, and especially equally constant, energy. This corresponds to... Figure 4b The two-stage energy distribution curves are shown.

[0122] It can also be a non-linear distribution curve, for example Figure 4c As shown, the energy of a single pulse in a burst pulse packet decays exponentially. It can also be proposed that the energy of a single pulse in a burst pulse packet first increases and then decreases; as mentioned earlier, the energy of the first single pulse is higher than that of the last single pulse. Subsequent laser pulses following the first single pulse have even higher energies, and then the energy decreases again towards the last single pulse. This distribution curve is shown in the figure. Figure 4d As shown.

[0123] Figures 5a to 5c A cross-section of a filamented workpiece is shown to schematically illustrate the feasible shapes of hollow channel-like filaments. Figure 5a A simplified case is shown where a cylindrical hollow channel is introduced into the workpiece as a filament (1). The axis A of the filament passes through the center point of the filament. The filament walls are axially symmetric. In the example shown, the filament (1) connects the upper side (O) of the workpiece (2) to its lower side (U). The hollow channel-shaped filament (1) represents a through channel or through hole. As previously described, the filament can also terminate inside the workpiece. In this case (not shown in the figure), the filament represents a blind hole. The workpiece has a workpiece thickness (s). The present invention is applicable to workpieces of almost any thickness. Therefore, the workpiece thickness (s) covers a range from thin glass a few micrometers thick to ordinary glass a few centimeters thick. In particular, the range of 10µm to 200µm (i.e., the thin glass range) and the range of 0.5mm to 3mm (i.e., the substrate glass or flat glass range) are applied.

[0124] Figure 5a The compression region (22) surrounding the filament is also shown. The compression region (or compression zone) and its development process have been described in detail above. This compression region extends substantially perpendicular to the filament axis into the workpiece material (21).

[0125] like Figure 5b As shown, a truncated conical filament (1), also known as a V-shaped filament, can also be used. This shape can also be called a hollow channel. The truncated conical filament is particularly axially symmetric about the filament axis (A). In this figure, the filament is open towards the lower side of the workpiece. This means that the diameter (dU) of the filament (1) on the lower side of the workpiece (2) is greater than its diameter (dO) on the upper side. Although not shown in the figure, it can also be designed as a blind hole. In particular, the filament can be expanded towards the workpiece side by setting the focusing position of the beam shaping optics, especially by setting the convergence of the laser beam and the distance from the workpiece. Common channel angles α are from 0.1° to about 30°, especially 0.1° to 10° or 0.2° to 3°. This channel angle is measured between the workpiece normal and the inner wall of the filament, and is thus equivalent to a half-angle.

[0126] Figure 5c A filament 1, also known as an X-shape, is shown, formed as a continuous hollow channel. This embodiment is particularly created by placing the area where the laser is most tightly focused within the workpiece volume. It is advantageous that the range of the channel angle and / or the angle α is the same as that of the so-called range for a V-shaped filament. The X-shaped filament is characterized by a contraction in the filament diameter within a certain region along the filament axis (A). In the example shown, the contraction is located at the center of the workpiece (2), i.e., at a distance equal to that from the workpiece surface. In some embodiments, the contraction is arranged closer to one surface of the workpiece (2) (compared to its opposite surface).

[0127] For clarity, Figure 5b and Figure 5c The compression region (22) is not shown. Of course, a compression region may also exist in V-shaped and / or X-shaped filaments (1), especially with the corresponding channel walls.

[0128] Figure 6 A top view of the filamentized workpiece (2) is shown. Hollow channel-shaped filaments (1) are arranged in a predetermined pattern within the workpiece (2), also referred to as the structured workpiece (2). The filaments (1) are surrounded by a compression zone (21), in which the workpiece material is compacted by ultrashort laser pulse irradiation, as previously described. Also as previously described, at least 1% compression exists within a 3µm radius around the filament axis, the so-called compression measurement line (23). This means that the degree of compaction, also referred to as the degree of compressibility, can be determined on this compression measurement line (23).

[0129] Figure 7The diagram schematically illustrates the mechanism of workpiece separation using laser filamentation according to existing technology. The figure shows a top view of the workpiece. A filament (1) is surrounded by microcracks (50) of length RL. According to a common interpretation, these microcracks are initiated in the workpiece material (21) by shock waves generated by plasma explosions within the focusing region of an ultrashort laser pulse. If the microcracks (50) connect with interconnected microcracks (51) of adjacent filaments, these interconnected microcracks (51) can form a continuous crack line along which the workpiece can be separated.

[0130] In comparison, Figure 8 A schematic top view of a wire-fusing workpiece according to the present invention is shown. The energy of the last single pulse in the burst pulse packet is less than the energy of the first single pulse in the burst pulse packet used to generate the filament (1), and therefore the crack length RL is shorter than in the prior art. It is presumed that the reduction in laser pulse energy in the burst pulse packet can at least reduce the uncontrolled energy input to the workpiece material (21). This is unexpected because it is generally considered more advantageous to concentrate as much laser energy as possible into the workpiece material during the wire-fusing process.

[0131] Viewed from above, microcracks (50) generally extend radially into the workpiece material from the filament (1) as the center point. Here, microcracks of adjacent filaments can connect to form one or more interconnected microcracks (51), thus forming a separation line.

[0132] While shortening the crack length RL has drawbacks, namely that the filaments (1) must be arranged more closely to form connected filaments (51) and thus constitute a separation line, it still achieves a balance with its advantages, namely that the microcracks extending into the workpiece material (21) beyond the separation line are shortened and / or reduced. Otherwise, these microcracks might weaken the edges of the separated workpiece, resulting in poor edge strength. High edge strength is more advantageous because it allows for more efficient processing and / or application of filamentized workpieces, especially reducing scrap.

[0133] exist Figure 8 The example also shows a compression region (22) surrounding the filament (21). In this embodiment, the crack length RL is greater than the thickness of the compression region. This means that most microcracks extend beyond the compression region, especially beyond the compression measurement line. It should be noted that these embodiments are based on statistical observations. This paper explores the characteristics of most microcracks. Therefore, the crack length RL should refer to the average crack length, determined by taking the arithmetic mean of all measured crack lengths. This, of course, also means that in actual embodiments, there may be microcracks that are significantly longer or shorter than those described herein. Such microcracks are only a minority, especially a very small minority.

[0134] Figure 9It shows something similar to Figures 7 to 8 An advantageous implementation method is described. Accordingly, the microcrack (50) extends into the compression zone (22). The crack length RL is less than the width of the compression ring around the filament (1). In order to form a coherent separation line with the connecting microcrack (51), the compression zones (22) must be at least adjacent to each other and / or overlap each other. This is particularly applicable to compression measurement lines. If the distance between the filaments (1) is too great, a microcrack (52) cannot be formed, and thus the separation line is interrupted at this point. This is particularly advantageous for setting the fracture force required to actually separate the parts of the workpiece along the separation line. In many cases, it is advantageous that the filamented workpiece does not separate or separate on its own, but requires additional mechanical force (i.e., separation force), which simplifies the reprocessing of the filamented workpiece, especially transportation.

[0135] exist Figure 9 In the example, it is hypothesized that the microcrack (50) in the compression region (22) will so-called spontaneously cease propagation. In the compacted material, crack propagation appears to be suppressed, thus allowing for particularly good setting of the laser pulse energy attenuation in the burst pulse packet, as previously described, so that the microcrack (50) terminates within the compression region (22), particularly within the compression measurement line. For clarity, this compression measurement line is not shown in this figure.

[0136] Figure 10 This indicates a particularly advantageous implementation method, which, in its form, resembles... Figures 7 to 9 In the top view, the laser focus expands along the separation line direction, especially along the predetermined separation line direction, thereby generating the preferred direction as described above. As a result, the crack length RL of the microcrack (50) in the preferred direction is greater than the crack length of the microcrack (50) in the non-preferred direction. This allows the filaments (1) to be arranged further apart in the preferred direction, the microcracks to form connected microcracks (51) in the preferred direction and thus generate a separation line, while only fewer and / or shorter microcracks extend into the workpiece material (21), and thus reduce edge strength weakening. Through the single-pulse energy attenuation in the aforementioned burst pulse packet, microcracks outside the preferred direction can be confined to the compression region (22), especially within the compression measurement line, while microcracks (50) in the preferred direction propagate outside the compression region. This achieves an excellent trade-off between processing efficiency and edge stability.

[0137] Figure 11 The diagram schematically illustrates the relationship between the crack length RL of each microcrack and the angle Ω between its orientation and the preferred direction. From Figure 11 The results are qualitative. This figure shows the variation of the average crack length RL with the angle Ω. As described earlier, the angle Ω represents the angle between the microcrack propagation direction and the axis of the preferred direction. This figure uses elliptical focused propagation as an example, where the principal axis of the ellipse is located in the preferred direction.

[0138] The crack length RL exhibits a highly nonlinear relationship with the angle Ω. Perpendicular to the preferred direction, the crack length is shortest and the RL value is smallest when Ω is 90°. Within the preferred direction, the crack length is largest when Ω is 0°. This demonstrates that effectively orienting the preferred direction towards the separation line direction can significantly improve method efficiency and edge strength.

[0139] The focal expansion shape in the preferred direction is not limited to the ellipse shown in the aforementioned top view. In principle, the invention covers all applicable shapes. Figure 12 An exemplary top view of some feasible expansion focal points in the preferred direction is shown. VR represents the preferred direction as a vector, which lies on a predetermined separation line (53). The first example is an elliptical expansion with the principal axis located on the separation line (53). There may also be teardrop-shaped expansions, heart-shaped expansions, and / or triangular expansions with the separation line (53) as the axis of symmetry.

[0140] As previously described, the overall advantage of this invention is that microcrack propagation is controlled and the degree of propagation within the workpiece material (21) is reduced, which improves the material strength of the structured workpiece, thereby aiding subsequent processing and avoiding scrap. In summary, the filaments (1) can also be arranged more closely without unduly compromising material strength, which not only allows for miniaturization of components but also helps avoid scrap. In particular, in the case of separating brittle fracture workpieces (2), the following conflicting objectives are resolved: on the one hand, the processing time for the reasonable separation of brittle fracture workpieces should be minimized as much as possible, thereby maximizing the spacing between the filaments (1) on the separation line; on the other hand, the processed workpiece should be ensured to have high edge strength.

[0141] List of reference numerals 1. Fine filament 2. Workpiece 3. Laser 4. Laser beam 21. Workpiece Material 22 Compression Area 23 Compression Measurement Line 30-beam shaping optics 41 The first pulse in a burst pulse packet 42 The last pulse in a burst pulse packet 50 microcracks 51 Connected microcracks 52 No microcracks 53 Separation line 100 devices 200 Positioning Device 210 Control device 220 Hot Zone 221 Roller 250 pull groove 300 shielding element 310 Sensor Device Tb burst duration Ti instantaneous delay Td burst delay BG burst decay rate The pulse energy of the first pulse in the Ep0 burst pulse packet. Ep x Pulse energy of the last pulse in a burst pulse packet A. Wire axis O upper side U bottom side dO upper filament diameter dU lower filament diameter s Workpiece thickness α channel angle RL Crack Length VR priority Ω is the angle toward the preferred direction.

Claims

1. A method for embedding a hollow channel-shaped filament (1) into a brittle fracture workpiece (2), wherein a focused laser beam (4) of a pulsed laser (3) having a wavelength λ is directed onto the workpiece (2) for processing, wherein the workpiece (2) is transparent to the wavelength λ of the laser, and wherein the filament (1) is generated by incident with at least one burst pulse packet of the laser pulse. The at least one burst pulse packet has a burst duration Tb and comprises a series of ultrashort laser pulses with a single pulse energy Ep and a burst internal delay Ti. The single-pulse energy Ep0 of the laser pulse at the start of the burst duration Tb is greater than the single-pulse energy Ep of the laser pulse at the end of the burst duration. x .

2. The method according to the preceding claim, wherein, The burst pulse packet has a burst attenuation rate BG of 40% to 90%, preferably 50% to 80%, and more preferably 60% to 70%, wherein the burst attenuation BG is calculated as a percentage of the single-pulse energy Ep of the last single pulse in the burst pulse packet at the end of the burst duration Tb. x The ratio of the single-pulse energy Ep0 of the first single pulse in the burst pulse packet at the start of the burst duration.

3. The method according to at least one of the preceding claims, wherein starting from the second single pulse in the burst pulse packet, the single pulse energy of the laser pulse is lower than the single pulse energy of the previous single pulse; preferably, the single pulse energy decreases exponentially over the burst duration Tb.

4. The method according to at least one of the preceding claims, wherein a filamentary initial channel, particularly an initial hollow channel, is generated during the first single pulse of the burst pulse packet, the initial channel expanding through subsequent single pulses of the burst pulse packet.

5. The method according to at least one of the preceding claims, wherein a compression region (22) for compressing workpiece material is generated around the hollow channel filament (1), the compression region having a higher density, in particular, compared to the starting material.

6. The method according to at least one of claims 4 to 5, wherein the relative weight loss m of each hollow channel filament (1) rel Less than 10%, it passes through m rel = m actual / m theo It was found, particularly preferably, that when measured within a 3µm radius (23) around the longitudinal axis of the corresponding hollow channel filament (1), the material compaction of the workpiece was at least 1% higher than the original material density.

7. The method according to at least one of the preceding claims, wherein the diameter of the hollow channel filament (1) is 100 nm to 3 μm.

8. The method according to at least one of the preceding claims, wherein the focused laser beam (4) generates plasma in the workpiece (2), the plasma forming the hollow channel filament (1); preferably, the first single pulse in the burst pulse packet generates the initial plasma, the initial plasma being powered and sustained by subsequent single pulses in the burst pulse packet.

9. The method according to claim 8, wherein, The plasma generates microcracks (50) in the workpiece (2) that extend from the hollow channel filament (1) into the volume of the workpiece.

10. The method according to claim 9, wherein the focused laser beam (4) expands in a direction perpendicular to the filament axis (VR), and the length and / or number of the microcracks (50) in the focal line expansion direction is greater than the length and / or number perpendicular to the expansion direction.

11. The method according to at least one of claims 5 to 10, wherein at least 90% of the microcracks (50) terminate within the compression region (22), preferably within a radius (23) of 3µm around the longitudinal axis of the hollow channel filament (1).

12. The method according to at least one of claims 8 to 11, wherein the plasma emits X-rays, the X-rays being attenuated and / or shielded by at least one shielding element (300); preferably, the shielding element (3) is attached such that it at least partially surrounds the workpiece (2), and wherein the shielding element comprises or is made of an X-ray absorbing material; particularly preferably, the material is selected from the group consisting of metals including iron, steel, stainless steel, and tungsten, or from the group consisting of composite plastics including metal-filled composite plastics and tungsten-filled composite plastics.

13. The method according to at least one of the preceding claims, wherein the hollow channel-shaped filament (1) is a channel connecting one surface (O, U) of the workpiece to another surface (O, U) and penetrating the workpiece (2), or a channel terminating as a blind hole within the volume of the workpiece (2).

14. The method according to at least one of the preceding claims, wherein the laser wavelength λ is 500 nm to 1100 nm, and / or the burst duration of a single pulse is 200 fs to 11 ps, and / or the burst duration is 1 ps to 500 ns, and / or the single pulse energy of the first single pulse at the start of the burst duration is 100 µJ to 1000 µJ; and / or wherein the workpiece is made of or contains glass and / or glass ceramic and / or silicon and / or ceramic; preferably, the spacing between two adjacent filaments is 3 µm to 10 µm.

15. An apparatus for embedding a hollow channel-shaped filament (1) into a brittle fracture workpiece (2) under laser assistance, particularly an apparatus for applying the method according to claims 1 to 14, the apparatus comprising: An ultrashort pulse laser (3) having a wavelength λ, wherein the workpiece (2) is transparent to the incident wavelength; And a beam-shaping optics (30) configured such that the laser beam (4) is directed toward the workpiece along a focal line, and the focal line is at least partially located within the workpiece (2), wherein the laser (3) is configured to emit at least one burst pulse packet of laser pulses, wherein the at least one burst pulse packet has a burst duration Tb and comprises a series of ultrashort laser pulses having a single pulse energy Ep and a burst internal delay Ti, and wherein the single pulse energy Ep0 of the laser pulse at the start of the burst duration Tb is greater than the single pulse energy Ep0 of the laser pulse at the end of the burst duration Tb. x .

16. The device of claim 15, further comprising an adjustment mechanism, wherein the single-pulse energy Ep of the last single pulse at the end of the burst duration Tb is... x The energy decrease of the single pulse Ep0 compared to the energy of the first single pulse at the start of the burst duration is adjustable; preferably, the energy decrease of the single pulse during the burst duration is adjustable, especially exhibiting linear or exponential decay behavior.

17. The apparatus according to at least one of claims 15 to 16, comprising a shielding element for shielding X-rays, the shielding element at least partially surrounding the workpiece; preferably, the shielding element comprises, or is made of, a material selected from, in particular, the group consisting of metals including iron, steel, stainless steel, and tungsten, or a material selected from, in particular, the group consisting of composite plastics including, in particular, tungsten-filled composite plastics.

18. Use of the method or apparatus according to at least one of claims 15 to 17 for separating and / or structuring and / or preparing etched glass and / or glass ceramics and / or silicon elements.

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