Method and device for welding a transparent workpiece to another workpiece, with a modulation of the energy of the laser beam in the welding zone

Description

Technical area

[0001] The present invention relates to a method and a device for welding a transparent workpiece to another workpiece according to the preamble of claims 1 and 11 (see e.g. DE 10 2010 038554 A1). State of the art

[0002] For machining workpieces and in particular for welding two workpieces together, it is known to subject the respective workpieces in a process zone to a laser beam in order to generate a melt by energy absorption in the process zone exposed to the laser beam, which melt forms a weld seam between the two workpieces after solidification.

[0003] In particular, it is known to place the process zone between the two workpieces to weld a transparent workpiece to a non-transparent workpiece or to weld two transparent workpieces. This is achieved by focusing the processing laser beam into the process zone such that the energy input is highest in the process zone area, in order to create a melt between the two workpieces in the process zone and then, after the melt has solidified, a weld seam. The processing laser beam passes through one of the transparent workpieces and is only focused into the process zone on the side of the workpiece opposite the entry area.

[0004] The laser beam being processed is focused by appropriate optics and the associated beam shaping into the material of one of the workpieces, into both workpieces and / or into the area of ​​an interface between the two adjacent workpieces in order to then form the respective process zone in this area.

[0005] When machining workpieces, and especially when welding two workpieces together, the strong local energy input from the focused laser beam in the process zone leads to high temperatures that are not present in the surrounding material areas. Accordingly, the heat required for machining in the process zone—for example, for producing a weld—leads to thermal stresses in the surrounding material areas. This can lead to stresses and / or cracks in the material in the weld area, which can reduce the quality of the joined materials.

[0006] This also applies to other local machining processes that involve local volume or surface modifications. In these other machining processes, the shape and size of the local volume or surface modifications are also limited by the permissible thermal stresses in the surrounding material areas.

[0007] The thermal stresses that occur, especially during the actual heat input, limit the size and shape of the modifications that can be introduced into the process zone. In other words, existing welding processes are limited by the fact that the thermal stresses introduced through local heat input should not exceed a certain level, which could lead to structural changes in the material, cracks, or poor quality of the weld seam or the joined workpieces.

[0008] US 2008 / 0080570 A1 discloses a method and system for a pulsed laser source for providing shaped optical wavefronts.

[0009] US 5 073 687 A discloses a method and apparatus for processing a print board with a laser beam.

[0010] DE 10 2009 049 750 A1 discloses a method and a device for cutting material by means of a modulated laser beam.

[0011] DE 10 2007 063 456 A1 discloses a method for welding workpieces made of a metallic material using a laser beam. Description of the invention

[0012] Based on the known prior art, it is an object of the present invention to further develop the known machining methods for machining workpieces carried out with pulsed laser beams.

[0013] This object is achieved by a method for welding a transparent workpiece to another workpiece according to claim 1, and a device for welding a transparent workpiece to another workpiece according to claim 11. Advantageous further developments emerge from the dependent claims, the present description and the attached figures.

[0014] By temporally modulating the energy injected into the process zone by the laser beam, the thermal stresses generated in the material can be reduced compared to processing carried out without this modulation. Both so-called transient stresses, which occur during and shortly after the actual processing when the material is still heated, and permanent stresses can be reduced. By temporally modulating the energy injected into the process zone by the laser beam, the local heat accumulation can be modulated in such a way that a more homogeneous coupling of energy into the process zone is achieved. This can, among other things, increase the average energy with which welding can be carried out without the occurrence of unwanted cracks in the material, thus resulting in improved processing efficiency.This also allows the limitations regarding the size and shape of the modification introduced into the material, by means of which it can be machined without cracks, to be shifted.

[0015] By modulating the energy coupled into the process zone, it is possible to better utilize the heat diffusion processes taking place in the material of the workpiece to simultaneously achieve a more efficient energy input and thus a shortening of the processing time, as well as a reduction of stresses in the material.

[0016] Depending on the selected modulation frequency, a more homogeneous energy coupling into the process zone can be achieved compared to modulation-free processing.

[0017] When using ultrashort laser pulses, the modification introduced into the material is generated either by an overlap of the respective laser pulses in the material or by a spatially separated impact of the laser pulses in the material.

[0018] When the material is exposed to a high overlap of laser pulses, a temporal modulation of the energy coupled into the process zone achieves a corresponding modulation of the degree of heat accumulation in the material. The modulations to be used depend, in particular, on the material's typical heat diffusion time. If the time until the next laser pulse at the same or overlapping location is insufficient to sufficiently diffuse the heat introduced by the laser pulse within the material, a strong local heat accumulation occurs when the next laser pulse occurs in the overlap area.By temporally modulating the coupled energy, the material's typical thermal diffusion time can be applied in such a way that the occurrence of transient and permanent stresses in the material is reduced, since the diffusion of heat to other areas can be advantageously used to reduce stresses. In other words, the heat is distributed advantageously within the workpiece, thus reducing the unfavorable occurrence of high temperature gradients in the workpiece material and thus simultaneously reducing the occurrence of thermal stresses.

[0019] When using an overlapping introduction of the laser pulses into the material, an improvement in the processing result is achieved by the temporal modulation of the coupled energy.

[0020] If, however, the respective laser pulses are introduced into the workpiece as spatially separated spots, a defined crack guidance can be achieved by appropriate temporal modulation of the coupled energy, which may be desirable for separating a workpiece, for example for separating glass.

[0021] Preferably, the energy coupled into the process zone by the laser beam is temporally modulated by modulating the time interval between the laser pulses and / or between the pulse trains, preferably with constant energy per laser pulse and / or pulse train, wherein the repetition rate is preferably modulated between 10 kHz and 1 GHz.

[0022] Preferably, the energy coupled into the process zone by the laser beam is temporally modulated by modulating the pulse duration of the laser pulses, wherein the pulse duration is preferably modulated between 0.1ps and 20ps.

[0023] Preferably, the energy coupled into the process zone by the laser beam is temporally modulated by modulating the average energy and / or the energy distribution of successive pulses and / or pulse trains, preferably with a constant time interval between the successive laser pulses and / or pulse trains.

[0024] Preferably, the energy coupled into the process zone by the laser beam is temporally modulated by a pulse pause, preferably by a pulse pause of 0.05 ms to 5 ms.

[0025] Preferably, the pulse energy and / or the pulse duration and / or the length of a pulse train is temporally modulated by a control unit of a laser beam source generating the pulsed laser beam, wherein the modulation is preferably controlled via an external signal generator.

[0026] Preferably, the energy coupled into the process zone by the pulsed laser beam is modulated by a shutter and / or an acousto-optic modulator and / or deflected by an acousto-optic deflector (AOD), thus modulating the energy introduced into the process zone. Deflection and modulation by an AOD preferably involve modulation frequencies greater than 1 MHz.

[0027] Preferably, the energy coupled into the process zone by the pulsed laser beam is generated by temporal modulation of aberrations, preferably by means of a deformable mirror and / or a TAG lens ("tunable acoustic gradient" lens). A TAG lens contains a liquid that exhibits a temporally modulated refractive index distribution through acousto-optical modulation, thereby temporally modulating the focal length of the lens.

[0028] Preferably, a laser beam with a Bessel beam shape is used to process the at least one workpiece.

[0029] For processing the at least one workpiece, a pulsed laser beam is preferably used which has at least two beam profiles offset longitudinally and / or laterally relative to one another in a process zone, preferably at least two Gaussian profiles offset longitudinally and / or laterally relative to one another.

[0030] Preferably, an axicon and / or a diffractive optical element and / or a spatial light modulator is arranged between the laser source and the process zone. Short description of the characters

[0031] Preferred further embodiments of the invention are explained in more detail in the following description of the figures. In the figures: Figure 1: a schematic representation of a pulsed laser beam with temporal energy modulation, wherein the energy of the individual laser pulses is temporally modulated in the form of a sawtooth compared to the following laser pulses; Figure 2: a further schematic representation of a pulsed laser beam with temporal energy modulation, wherein the energy of the individual laser pulses is sinusoidal (orsin 2n< with n = natural number) is modulated in time; Figure 3 is a further schematic representation of a pulsed laser beam with temporally modulated energy, wherein the energy of the individual laser pulses is temporally modulated in a rectangular manner compared to the following laser pulses; Figure 4 is a schematic representation of a pulsed laser beam with temporally modulated energy at a high frequency (in the kHz range), wherein the individual laser pulses with their energy modulated are subject to a superimposed modulation of the average energy of the individual pulse trains, as well as a microscope image of a workpiece machined with such a laser beam; Figure 5 is a schematic representation of a laser beam with its average energy modulated with a slow modulation of the pulse trains but without the modulation of the pulse trains shown in . Figure 4present energy modulation carried out at a high frequency in the kHz range, as well as a microscope image of a workpiece machined with such a laser beam; Figure 6 shows a schematic representation of a top view of the spots of a pulsed laser beam introduced into a workpiece and, below that, a schematic representation of the time-modulated energy of the respective laser pulses, wherein the energy of the entire pulse train is sinusoidally time-modulated; Figure 7 shows a schematic representation of the modulation of the time interval between the laser pulses of a pulsed laser beam; Figure 8 shows a schematic representation of the modulation of the time interval between laser pulses of a pulsed laser with simultaneous time modulation of the energy of the pulsed laser beam, wherein the energy of the entire pulse train is time-modulated in the form of a sawtooth;Figure 9 shows a schematic representation of the temporal modulation of the pulse durations of the laser pulses with simultaneous temporal modulation of the energy of the individual laser pulses; Figure 10 shows a schematic representation of the temporal modulation of the pulse durations of the laser pulses with simultaneous temporal modulation of the energy of the individual laser pulses in a further variant; Figure 11 shows a schematic representation of the spots introduced into a workpiece by the individual laser pulses and, below this, a schematic representation of a modulation of the temporal interval between the laser pulses of the pulsed laser beam; Figure 12 shows a schematic representation of the spots introduced into a workpiece via the laser pulses and, below this, a schematic representation of a modulation of the temporal interval between the laser pulses of the pulsed laser beam and, below this, a schematic representation of the relative feed rate between the workpiece and the focus of the laser beam.Figure 13 shows a schematic representation of a pulsed laser beam with temporal energy modulation, wherein the energy of the laser pulses is sinusoidally modulated and a pulse pause is included in the modulation; Figure 14 shows a schematic representation of the structure of a device for welding two workpieces using a pulsed laser beam. Detailed description of preferred embodiments

[0032] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are provided with identical reference numerals, and a repeated description of these elements is partially omitted to avoid redundancies.

[0033] For welding a transparent workpiece to another workpiece, in particular for welding two transparent workpieces, the invention uses an ultrashort pulsed laser beam, which is applied to a process zone of the workpiece or both workpieces. For this purpose, the pulsed laser beam is typically focused into the process zone using an optical system in order to achieve a particularly high energy density in the process zone while simultaneously minimizing the energy input into the surrounding material areas.

[0034] The energy of the laser pulses of the pulsed laser beam is partially absorbed by the material in the process zone, resulting in a corresponding increase in temperature there. With each laser pulse, new energy is supplied to the process zone, causing the temperature of the material in the process zone to rise again. At the same time, the heat from the process zone is dissipated to surrounding volume regions of the material through thermal diffusion processes. Taking into account the typical thermal diffusion coefficient of the workpiece material, successive laser pulses impinging on the process zone can result in either a temperature increase, a constant temperature in the process zone, or a temperature decrease at an already high temperature.This depends on whether the temperature can be raised by the laser pulses faster than it diffuses out of the process zone through the heat diffusion processes in the material.

[0035] Whether heat accumulation or heat diffusion occurs in the process zone is therefore essentially determined by the frequency of the successive laser pulses and the energy introduced into the material by the laser pulses. In machining operations involving a relative velocity between the workpiece and the laser beam being processed, a spatial overlap (N>1) of the laser spots must also be present, with the focus size (D), repetition rate (R), and feed rate (V) defining the pulse overlap (N=D*R / V).

[0036] In order to reduce the formation of transient or permanent stresses within the workpiece, it is now proposed to temporally modulate the energy coupled into the process zone by the laser beam.

[0037] In Figure 1 A schematic diagram of a variant of the temporal modulation of the energy of the individual laser pulses or pulse groups of the pulsed laser beam applied to the process zone is shown. The laser energy (E) is plotted against time (t). The individual laser pulses 10 or pulse groups are schematically indicated by the lines and are bounded by an envelope 12.

[0038] The laser pulses 10 represented as lines can, in principle, also represent groups of laser pulses. The temporal modulation of the energy of the successive laser pulses or laser pulse groups is important here. In other words, this represents an inter-pulse modulation of the energy of the laser pulses or laser pulse groups.

[0039] In Figure 1Accordingly, a temporal modulation of the energy of the individual laser pulses 10 relative to the following laser pulses is shown in the form of a sawtooth function, which is represented by the envelope 12.

[0040] The temporal modulation of the energy of the individual laser pulses 10 relative to the following laser pulses can be achieved either by the laser source itself or by an optical element connected between the laser source and the process zone, which causes a temporal modulation of the energy of the pulsed laser beam. This applies to all embodiments and modulation patterns disclosed here.

[0041] In Figure 2 is a schematic representation of a temporal modulation of the laser energy E of the individual laser pulses 10 over time, in which the envelope 12 of the energies of successive laser pulses or laser pulse groups shows a quasi-sinusoidal modulation.

[0042] In Figure 3 a temporal modulation of the laser pulses 10 is shown schematically, in which the envelope 12 of the energies of successive laser pulses shows a quasi-rectangular modulation. Figure 4 The upper part of the figure shows a temporal modulation of the laser energy E of the laser pulses 10 with a fast, sinusoidal envelope 12, which can be provided, for example, with a modulation frequency between 10 Hz and 10 GHz. The envelope 12 is superimposed by a modulation 14, which is also sinusoidal. The frequency of the superimposed modulation 14 is constant in this embodiment and can, for example, be in a range from 0.01 Hz to 2.5 kHz.

[0043] The frequency of the slow modulation can be adjusted to the length of the line being processed. For example, a 10 mm line length can be welded at 10 mm / s using a slow 1 Hz modulation.

[0044] In an alternative embodiment, the modulation 14 may also have a varying frequency.

[0045] Through the Figure 4 The corresponding form of the superimposed modulation 14 shown varies the average energy and / or the energy distribution of successive laser pulses 10 or of successive laser pulse groups, which is shown by the envelope 12.

[0046] Below the laser energy versus time diagram, a microscope image of a cross-section (in this image, the laser beam was irradiated from above and the resulting process zone moved from left to right) of the material modification inscribed in a workpiece by this modulation 14 superimposed on the envelope 12 is shown. It can be seen that the material modification follows the temporally modulated energy of the laser pulses.

[0047] In the Figure 5For comparison, a diagram of laser pulses 10 is shown, which are only changed in their energy via a slow modulation 14, but not via the fast modulation as in Figure 4 Below, the material modification inscribed into a workpiece via a slow modulation 14 can be seen in a cross-sectional microscope image, which shows that the material modification does not follow the temporally modulated energy of the laser pulses particularly precisely. The resulting material modification is relatively inhomogeneous.

[0048] In Figure 6The upper illustration schematically shows a workpiece 20 in which laser spots 30 are drawn that overlap slightly. Below this, a schematic representation of the individual laser pulses 10 is shown, the energy of which is temporally modulated such that, in each adjacent laser spot 30 in the material 20, a different energy can be coupled into the workpiece and thus also into the process zone 4 in the workpiece.

[0049] In Figure 7A modulation of the time interval between the individual laser pulses 10 is shown schematically. For example, a time t1 is provided between the first and second laser pulses, a longer time t2 between the second and third laser pulses, and an even longer time t3 between the third and fourth laser pulses. The same time t3 is then used again until the following laser pulse, then time t2 again, and then time t1, etc. Accordingly, a modulation of the time interval between the respective laser pulses 10 takes place here.

[0050] In Figure 8A further schematic representation of the modulation of the time interval between the individual laser pulses 10 is shown, wherein at the same time, a temporal modulation of the laser energy E is performed, which follows the envelope 12. The laser energy E of the laser pulses 10 decreases towards the shorter time intervals between the laser pulses 10 and increases again towards the longer time intervals.

[0051] In Figure 9 An embodiment is shown in which the pulse duration d1, d2, d3, d4 of the laser pulses 10 is temporally modulated—for example, between 0.1 and 20 ps. Here, the pulse duration of the laser pulses increases within a pulse train.

[0052] At the same time, the repetition frequency can be modulated between 10 kHz and 1 GHz. The energy of the respective laser pulses can also be temporally modulated to produce the envelope 12, which exhibits a quasi-sinusoidal function.

[0053] In Figure 10 is one of the Figure 9 A similar embodiment is shown, but the pulse duration d1, d2, d3 initially increases towards the center of the envelope 12 and then decreases again. It does not go beyond the scope of the present invention if the pulse duration deviates from Fig. 9 and Fig. 10 is modulated.

[0054] In Figure 11 a further schematic representation of a workpiece 20 is shown, in which again 4 laser spots 30 are shown in a process zone, which here, however, have different distances from one another, wherein there are laser spots 30 which overlap one another and wherein there are laser spots 30 which are separated from one another.

[0055] From the schematic representation of the individual laser pulses 10 over time below, it can be seen that the time interval between each two laser pulses is modulated, with four different time intervals being provided between the respective laser pulses 10. In this way, the energy coupled into the process zone 4 by means of the laser beam in the respective laser spots 30 can be temporally modulated, which simultaneously also leads to a spatial modification of the energy coupled into the process zone 4.

[0056] In this embodiment, both the feed rate V between the laser beam and the workpiece and the energy coupled by each laser pulse 10 into the workpiece 20 or into the process zone 4 of the workpiece 20 are the same.

[0057] In Figure 12A further illustration of a schematically indicated workpiece 20 is shown, in which individual laser spots 30 are introduced into a process zone 4. The laser spots 30 are equally spaced from one another in the workpiece 20. In the diagram below, the individual laser pulses 10 are shown again in their temporal sequence, with the interval between two consecutive laser pulses 10 being temporally modulated. Three different time intervals between the laser pulses, t1, t2, t3, are shown schematically here.

[0058] Shown below is a variable relative feed rate V between the laser beam and the workpiece 20, with the feed rate being lower in the areas where a longer time interval is provided between two consecutive laser pulses 10. This accordingly results in the fact that, despite the different time intervals between the individual laser pulses 10, the laser spots 30 in the workpiece 20 are nevertheless arranged at equal distances from one another.

[0059] The energy coupled into process zone 4 via the laser beam is temporally modulated such that, in areas where the interval between successive laser pulses is greater, the workpiece 20 has a correspondingly longer time to dissipate the heat from process zone 4 into the surrounding material. Accordingly, a temporal modulation of the energy coupled into the process zone takes place by utilizing the heat diffusion time of material 20.

[0060] In Figure 13 a further schematic representation of a pulsed laser beam to be coupled into the process zone is shown, in which the individual laser pulses 10 are temporally modulated with respect to their laser energy E, wherein the modulation forms an envelope 12 which describes a quasi-sinusoidal function, wherein the sinusoidal function has a fixed modulation frequency F. A pulse pause P is provided between each individual pulse group.

[0061] The pulse pause P can be between 0.05 ms and 5 ms long. The pulse pause P is included in the temporal modulation of the energy of the laser pulses.

[0062] When ultrashort laser pulses are focused into the volume or onto the surface of transparent materials, such as quartz glass, the high intensity at the focus leads to nonlinear absorption processes, which can induce various material modifications depending on the laser parameters. By moving the focus position (scanning the laser focus or the sample), extended areas can be modified, with focus size (D), repetition rate (R), and feed rate (V) defining the pulse overlap (N=D*R / V). This addresses both process regimes with spatially separated (N<1) and overlapping (N>1) pulses or pulse trains (so-called bursts). Under high overlap conditions, heat accumulation may occur if the pulse interval is shorter than the typical heat diffusion time of theThis causes the temperature in the focal area to increase from pulse to pulse, which can lead to local melting of the glass. If the modification is placed at the interface between two glasses, the cooling melt generates a stable bond between the two samples.

[0063] Both during feed-feed machining and during stationary machining, temporal modulation (e.g., sawtooth, sinusoidal, or rectangular) of the coupled pulse energy can reduce the (transient and permanent) stresses induced in the material. Under heat accumulation and high pulse overlap, this increases the average power (and thus the magnitude of the introduced modification) at which crack-free welding can be achieved. Depending on the modulation frequency, it is possible to generate a more homogeneous energy coupling (typically at modulation frequencies from 100 Hz to approximately 5 kHz) compared to modulation-free machining, or to impose a dynamic effect on the modification process (typically at modulation frequencies > 5 kHz).

[0064] Likewise, in a process regime of spatially separated spots, an energy modulation of successive pulses (or pulse trains) can promote a defined crack path, which is desired, for example, for glass cutting.

[0065] The modulation can exhibit various temporally periodic profiles, particularly modulation amplitudes, slopes, or even positive and negative attenuation. The modulation is independent of the beam shape used; in particular, non-Gaussian beam shapes (e.g., Bessel) or beam shapes consisting of multiple (longitudinally and / or laterally) offset Gaussian profiles can be used or subjected to modulation. The modulation parameters (e.g., shape, frequency, amplitude, etc.) can also be changed during the process.

[0066] In addition, other approaches to modulate the coupled energy are conceivable. These include rapidly changing the laser repetition rate, which can, for example, alter the degree of heat accumulation (in the high overlap regime). Likewise, the pulse duration could be changed periodically, e.g., from 1 ps to 50 ps and back. This could cause the pulse intensity to drop below the modification threshold (assuming otherwise identical parameters), which also results in a modulation of the coupled energy.

[0067] Figure 14is a schematic representation of a device 100 for machining a workpiece, wherein a first workpiece 20 and a second workpiece 22 are provided here, wherein the first workpiece 20 has a bottom side 200 and the second workpiece 22 has a top side 220, which directly adjoin one another. The bottom side 200 of the upper workpiece 20 and the top side 220 of the lower workpiece 22 form a plane in which a process zone 4 is to be formed.

[0068] A pulsed laser beam 110 is provided in a laser source 114, which is focused into the process zone 4 via an optics 112. The two workpieces 20, 22 are moved in a feed direction X relative to the laser beam 110.

[0069] The laser beam 110 is already modulated in the laser source 114 with respect to the time interval between the laser pulses and / or between the pulse trains. At the laser source 114, the laser beam 110 can also be temporally modulated with respect to the respective pulse energy of each reader pulse 10. For this purpose, an internal or external signal generator 118 can preferably be provided, by means of which the modulation of the pulse energy is controlled.

[0070] The modulation of the energy coupled into the process zone 4 by the pulsed laser beam 110 can also be achieved by means of a shutter and / or an acousto-optical modulator and / or an acousto-optical deflector, which is then also preferably controlled by an internal or external signal generator.

[0071] In a further development, the energy coupled into the process zone 4 by the pulsed laser beam 110 can be modulated by means of a temporal modulation of aberrations, preferably by means of a deformable mirror and / or by means of a TAG lens.

[0072] To generate a Bessel beam, an axicon 116 and / or a diffractive optical element (DOE) and / or a spatial light modulator (SLM) can be provided in the beam path. The methods described herein for processing at least one workpiece can all preferably be performed using a Gaussian beam or a Bessel beam.

[0073] For processing the at least one workpiece 20, 22, a pulsed laser beam 110 can also be used, which has at least two beam profiles offset longitudinally and / or laterally relative to one another in the process zone 4, preferably at least two Gaussian profiles offset longitudinally and / or laterally relative to one another.

[0074] The self-healing properties of Bessel beams are advantageous in this regard. They allow the beam to regain its original shape in the event of a partial disruption or blockage at one point along the propagation axis, for example, by a scattering center. This makes Bessel beams particularly suitable for processing transparent workpieces, where material processing is to take place in a process zone that only occurs after the laser beam has passed through the transparent material, on a side of the transparent workpiece opposite the entrance side. Due to the self-healing properties of Bessel beams, any disruptions in the workpiece material have little or no influence on the processing result.Accordingly, the device comprises, for example, an ultrashort pulse laser, optionally additional beam-shaping elements (SLM / DOE) and / or scanners (especially micro-scanners), focusing optics (e.g., microscope objective), and sample and / or beam positioning (e.g., positioning system for sample movement). The temporal modulation of the coupled energy can be realized using various techniques: For example, the pulse energy can be temporally modulated directly by the laser control unit. The temporal modulation of the pulse energy can also be specified via an external signal generator (e.g., function generator) of the laser control unit or realized by an external device (e.g., shutter, electro / acousto-optical modulator).

[0075] The temporal modulation can be generated indirectly by temporally periodic aberrations, e.g. by means of a deformable mirror or TAG lens.

[0076] Furthermore, the modulation of the repetition rate can be realized, for example, using acousto-optical modulators.

[0077] Alternatively, the laser pulse duration can also be modulated internally / externally. List of reference symbols

[0078] 10Laser pulse 12Envelope 14Superimposed modulation 100Device for processing at least one workpiece 110Laser beam 112Optics 114Laser source 116Axicon 118External signal generator 20Workpiece 22Second workpiece 200Underside of workpiece 220Top of second workpiece 30Laser spot 4Process zone EEnergy tTime t1Time interval t2Time interval t3Time interval t4Time interval d1Pulse duration d2Pulse duration d3Pulse duration d4Pulse duration VFeed rate PPulse pause FModulation frequency XFeed direction

Claims

1. A method for welding a transparent workpiece (20) to another workpiece (22), comprising applying an ultrashort pulse laser beam (110) to a process zone (4) of the workpieces (20, 22), characterized in that the energy coupled into the process zone (4) by the ultrashort pulse laser beam (110) is temporally modulated, wherein the ultrashort pulse laser beam (110) is displaced relative to the workpieces (22, 20), wherein the laser pulses are emitted into the process zone with a spatial overlap, whereby a modulation of the degree of heat accumulation in the workpieces (20, 22) is achieved, and wherein the temperature stresses generated in the material of the workpieces (20, 22) are reduced compared to a machining operation carried out without this modulation, by the temporal modulation of the energy coupled into the process zone by the ultrashort pulse laser beam (110).

2. The method in accordance with claim 1, characterized in that the energy coupled into the process zone (4) by the ultrashort pulse laser beam (110) is temporally modulated by modulating the time interval (t1, t2, t3, t4) between the laser pulses (10) and / or between the pulse trains, preferably with a constant energy per laser pulse and / or pulse train, wherein the repetition rate is preferably modulated between 10kHz and 1GHz.

3. The method in accordance with claim 1 or 2, characterized in that the energy coupled into the process zone (4) by the ultrashort pulse laser beam (110) is temporally modulated by modulating the pulse duration (d1, d2, d3) of the laser pulses (10), wherein the pulse duration is preferably modulated between 0.1 ps and 20 ps.

4. The method in accordance with one of the preceding claims, characterized in that the energy coupled into the process zone (4) by the ultrashort pulse laser beam (110) is temporally modulated by a modulation, preferably at 0.01 Hz to 2.5 kHz, of the energy distribution and / or the energy of consecutive pulses (10) and / or the pulse trains, preferably with a constant time interval between the consecutive laser pulses (10) and / or pulse trains.

5. The method in accordance with one of the preceding claims, characterized in that the energy coupled into the process zone by the ultrashort pulse laser beam (110) is temporally modulated by a pulse pause (P), preferably by a pulse pause of 0.05 ms to 5 ms.

6. The method according to one of the preceding claims, characterized in that the pulse energy and / or the pulse duration (d1, d2, d3) and / or the length of a pulse train is / are temporally modulated by a control unit of a laser beam source (114) generating the ultrashort pulse laser beam (110), wherein the modulation is preferably controlled via an internal and / or external signal generator (118).

7. The method according to one of the preceding claims, characterized in that the energy coupled into the process zone (4) by the pulsed ultrashort pulse laser beam (110) is modulated by means of a shutter and / or an acousto-optical modulator and / or an acousto-optical deflector.

8. The method according to one of the preceding claims, characterized in that the energy coupled into the process zone by the pulsed ultrashort pulse laser beam is generated by means of a temporal modulation of aberrations, preferably by means of a deformable mirror and / or by means of a TAG lens.

9. The method in accordance with one of the preceding claims, characterized in that an ultrashort pulse laser beam (110) with a Bessel beam shape is used to process the workpieces.

10. The method in accordance with one of the preceding claims, characterized in that a pulsed ultrashort pulse laser beam (110) is used to process the workpieces (20, 22), which has at least two beam profiles that are longitudinally and / or laterally offset with respect to one another in the process zone (4), preferably at least two Gaussian profiles that are longitudinally and / or laterally offset with respect to one another.

11. An apparatus (100) for welding a transparent workpiece (20) to another workpiece (22), comprising a laser source (114) for generating an ultrashort pulse laser beam (110) and an optical system for applying the ultrashort pulse laser beam (110) to a process zone (4) in the workpieces (20, 22), characterized in that the laser source (114) is configured to temporally modulate the ultrashort pulse laser beam (110), wherein the apparatus (100) is configured to displace the ultrashort pulse laser beam (110) relative to the workpieces (22, 20), so that the laser pulses are emitted into the process zone with a spatial overlap, whereby a modulation of the degree of heat accumulation in the workpieces (20, 22) is achieved, and so that the temperature stresses generated in the material of the workpieces (20, 22) are reduced compared to a machining operation carried out without this modulation, by the temporal modulation of the energy coupled into the process zone by the ultrashort pulse laser beam (110).

12. The apparatus (100) in accordance with claim 11, characterized in that the laser source (114) is temporally modulated by means of an internal and / or external signal generator (118).

13. The apparatus (100) in accordance with claim 11 or 12, characterized in that an axicon (116) and / or a diffractive optical element and / or an acousto-optical modulator and / or an acousto-optical deflector is arranged between the laser source (114) and the process zone (4).