CN116547100A

CN116547100A - Apparatus and method for determining the position of the beam waist of a focused beam relative to a reference surface

Info

Publication number: CN116547100A
Application number: CN202180074248.0A
Authority: CN
Inventors: R·高奇; M·克劳斯; D·特维勒; M·波利
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-11-04
Filing date: 2021-11-02
Publication date: 2023-08-04
Also published as: WO2022096443A1; DE102020213858A1

Abstract

The invention relates to a device for determining the position of the beam waist of a focused beam (10) relative to a reference surface (12) by means of a controller (30), the controller (30) being programmed and/or designed to operate a focusing device (32) to focus the beam (10) in such a way that the beam waist (F) is successively adjusted to a plurality of positions, at least one measurement profile being determined on the basis of the values of the intensity I and/or of a parameter of a process radiation (16) which is measured for these positions by means of a detection device (38), wherein the process radiation is generated by means of the focused electromagnetic beam (10) or a particle beam, and the local maximum, local minimum or symmetry axis of the at least one determined measurement profile being determined, in which case the beam waist (F) of the focused beam (10) is located on the reference surface (12). The invention also relates to a corresponding method for determining the position of the beam waist of a focused beam (10) relative to a reference surface (12).

Description

Apparatus and method for determining the position of the beam waist of a focused beam relative to a reference surface

Technical Field

The invention relates to a device for determining the position of the beam waist of a focused beam relative to a reference surface. Furthermore, the invention relates to a method for determining the position of the beam waist of a focused beam relative to a reference surface.

Background

A method for determining the focal position of a laser beam is described in EP 1 565 288 B1. In carrying out the method, the laser beam is deflected onto the substrate to be processed by means of a deflection unit and an imaging unit, wherein the focal position of the laser beam changes relative to the substrate surface during firing of the line onto the substrate surface by means of the laser beam. The line width of the lines burned into the substrate surface in this way should correspond to the focal position of the laser beam. By determining the line with the smallest line width, the focus of the laser beam should then be adjusted directly on the substrate surface.

Disclosure of Invention

The present invention provides an apparatus for determining the position of the beam waist of a focused beam relative to a reference surface having the features of claim 1 and a method for determining the position of the beam waist of a focused beam relative to a reference surface having the features of claim 5.

The laser focus of a focused beam can also be interpreted as a beam waist. It is explicitly stated that the beam to be focused can be understood to be not only an electromagnetic beam but also a particle beam, respectively.

THE ADVANTAGES OF THE PRESENT INVENTION

The invention creates the possibility to determine the position of the beam waist of the focused beam with respect to the reference surface without generating a series of test structures at different focus positions and without subsequently measuring these structures. The invention thus enables the position of the beam waist of the respective focused beam relative to the reference surface to be determined with less effort and in a material-saving manner than in the prior art described above. Advantageously, the invention enables a fast, high-precision and fully automatic measurement of the beam waist position (focal position) of a focused beam, respectively, for a fast initial start-up of a laser process and for ensuring said process by cyclically checking the beam waist position of said focused beam. Furthermore, the present invention enables a beam waist position of a focused beam to be determined much more accurately and reliably than if a diameter of a material processed by means of the focused beam was observed in a conventional manner using a camera. Additionally, the application of the present invention does not require expensive and bulky beam focus measuring equipment. Conversely, the present invention may be practiced without expensive and large hardware.

In particular for laser material processing, the focal position, i.e. the position of the beam waist of the focused laser beam relative to the component surface as reference surface, must be set correctly in order to be able to perform the corresponding process while maintaining the desired accuracy. In this connection, the invention can be used in particular to support processes for laser material processing in this connection. However, it is pointed out here that the usability of the invention is not limited to laser beams nor to laser material processing. Instead, the invention is applicable to all high energy radiation types that cause process irradiation proportional to the focal position, and to all processes that use these radiation types. The invention can thus be used in a variety of ways.

The potential of the invention lies on the one hand in ensuring the quality of the process in production. On the other hand, the invention enables an improved throughput, since undesired deviations/drifts of the position of the beam waist of the focused beam with respect to the reference surface can be recognized early and the error effects thereof can be suppressed early by correction. Furthermore, the invention enables high precision in the implementation of the process that would otherwise not be possible due to the high demands placed on the precision of the focal position setting.

It is also noted that the present invention can be used for most of all laser processing facilities in mass production, as well as in the laboratory field.

In an advantageous embodiment of the apparatus, the detection device of the apparatus comprises an event camera. This Camera type is also called Event-based Camera (Event Camera) or neuromorphic Camera (Neuromorphic Camera). In the case of this camera type, each pixel within the corresponding camera operates independently and only an increase in intensity is detected. Thus, this type of camera, which is often advantageously used, can also be used to implement the present invention.

Alternatively or additionally, a filter device may be provided upstream of the detection device of the apparatus, by means of which the spectrum of the electromagnetic beam may be at least partially filtered out. The focused beam process illumination used to implement the invention can thus be easily verified as process illumination by means of a filtering device.

For example, the focusing apparatus of the device may comprise a telecentric f-Theta objective lens. The telecentric f-Theta objective is a low cost optic used to produce the desired function of the focusing apparatus when practicing the present invention.

In an advantageous embodiment of the method, the intensity values of the process radiation measured at these positions are determined by means of at least one event camera. As will become apparent from the following description, the position determination of the beam portion can be implemented more quickly by means of an event camera.

For example, as an electromagnetic beam, an electromagnetic beam having a continuous waveform may be focused, and then a beam waist position of the electromagnetic beam may be determined with respect to a reference surface. Such electromagnetic beams are also commonly referred to as cw (continuous wave) beams. The invention can thus also be used for radiation with high beam quality, such as that produced by a single mode laser (Single Mode Laser).

Alternatively, as an electromagnetic beam, a pulsed electromagnetic beam may also be focused, and then the beam waist position of the electromagnetic beam may be determined with respect to a reference surface. In principle, the invention can be applied in all pulse duration ranges of femtoseconds, picoseconds, nanoseconds, microseconds and milliseconds. The present invention can be used in a variety of ways.

Furthermore, as a particle beam, an electron beam can also be focused, and in this case the position of its beam waist relative to the reference surface can be determined. Thus, the usability of the invention is not limited to electromagnetic radiation.

In a further advantageous embodiment of the method, the modified electromagnetic beam or particle beam whose intensity distribution differs from the gaussian distribution by beam shaping is focused and then the position of its beam waist relative to the reference surface is determined. Thus, the invention can also be used for optically modulated radiation.

Drawings

Further features and advantages of the invention are explained below with reference to the drawings. Wherein:

FIGS. 1a to 1e show a plurality of schematic diagrams and a coordinate system for explaining an embodiment of a method for determining the position of the beam waist of a focused beam relative to a reference surface;

fig. 2 and 3 show coordinate systems for explaining further embodiments of a method for determining the position of the beam waist of a focused beam relative to a reference surface;

fig. 4 shows a schematic view of a first embodiment of an apparatus for determining the position of the beam waist of a focused beam relative to a reference surface;

fig. 5 shows a schematic view of a second embodiment of an apparatus for determining the position of the beam waist of a focused beam relative to a reference surface; and

fig. 6a to 6d show a schematic view of a third embodiment of the device for determining the position of the beam waist of the focused beam relative to the reference surface and a coordinate system for explaining the way it works.

Detailed Description

Fig. 1a to 1e show a plurality of schematic diagrams and a coordinate system for explaining an embodiment of a method for determining the position of the beam waist of a focused beam relative to a reference surface.

In the implementation of the method schematically represented by means of fig. 1a to 1e, the beam 10 is focused in such a way that the beam waist F of the focused beam 10 is successively adjusted in a predefined spatial reference system to a plurality of positions P1 to P3 along an axis 14, wherein said axis 14 is aligned obliquely with the respective reference surface 12. The focused beam 10 may be alternatively understood as an electromagnetic beam 10, such as a laser beam or a particle beam. The focal point F of the focused beam 10 can also be interpreted as a beam waist F. Thus, determining the position of the beam waist F of the focused beam 10 relative to the reference surface 12 may also mean determining the focal position, i.e. the position of the focal spot F of the focused beam 10 relative to the reference surface 12.

The reference surface 12 may be, for example, a surface to be processed later by means of the focused beam 10, such as in particular a workpiece surface. The axis 14 may be aligned in particular perpendicular to the reference surface 12. However, the examples presented herein with respect to the reference surface 12 and the axis 14 aligned perpendicular thereto should not be construed in a limiting manner.

Fig. 1a shows a focused beam 10 having a beam waist F at a first position P1 on a first side of a reference surface 12, which position is at a distance from the intersection of the axis 14 with the reference surface 12 that is not equal to zero. In contrast, in fig. 1b, the beam waist F of the focused beam 10 is located at a second position P2 within the reference surface 12. On the other hand, fig. 1c shows the focused beam 10 with its beam waist F in a third position P3, which is at a distance from the intersection of the axis 14 with the reference surface 12 different from zero and which is located on a second side of the reference surface 12 facing away from the first side. Fig. 1a to 1c thus reproduce a procedure in which the beam waist F of the focused beam 10 is adjusted relative to the reference surface 12 from the first position P1 through at least the second position P2 to the third position P3.

For the positions P1 to P3 in the spatial reference system, the intensity I/brightness of the process radiation 16 generated by the focused beam 10 and/or parameters relating to the intensity distribution of the process radiation 16 are measured, respectively. The process radiation 16 is sometimes referred to in the literature as thermal radiation. The process illumination 16 is understood to be an optical process emission which is generated by the interaction of the focused beam 10 with the reference surface 12 and the atmosphere adjacent to the reference surface 12 and whose intensity I/brightness is in particular related to the power density of the focused beam 10 effective on/at the reference surface 12. Accordingly, the intensity distribution of the process illumination 16 is also related to the intensity distribution of the focused beam 10 on the reference surface 12. As a parameter concerning the intensity distribution of the process radiation 16, for example, the standard deviation σ of the intensity distribution of the process radiation 16 can be measured. However, the examples mentioned here for the parameters of the intensity distribution of the process illumination 16 should not be interpreted as limiting. The process illumination 16 is generated by excitation or heating of the reference surface 12 and may thus comprise thermal radiation and/or an emission spectrum, which is generated in particular due to plasma relaxation. Since the spectrum of the process illumination 16 differs from the spectrum of the focused beam 10, the spectrum 12 of the focused beam 10 can be at least partly filtered out from the emission originating from the reference surface 12 and comprising said process illumination 16, e.g. by using at least one filter. The intensity I/brightness of the process illumination 16 caused by the focused beam 10 and/or parameters concerning the intensity distribution of the process illumination 16 can be determined, for example, using photodiodes and/or by evaluating/reading out the image of the camera.

In the embodiment described here, for example, for the positions P1 to P3 of the focused beam 10 adjusted relative to the reference surface 12, only the intensity I of the process illumination 16 is measured. Fig. 1d shows the process illumination 16 at different positions, for example at positions P1 to P3. It can be seen that in a process in which the brightness of the process illumination 16 decreases as the distance from the beam waist F of the focused beam 10 to the intersection of the axis 14 and the reference surface 12 increases, the process illumination 16 "brightest" when the beam waist F of the focused beam 10 is located in the reference surface 12. Accordingly, when the beam waist F of the focused beam 10 is located in the reference surface 12, the intensity I of the process illumination 16 has its maximum value.

In a further method step of the method explained with reference to fig. 1a to 1e, at least one measurement curve is determined in the coordinate system from the values measured at the positions P1 to P3 of the intensity I of the process radiation 16 (and/or the parameters of the intensity distribution of the process radiation 16). Fig. 1e shows a coordinate system with a corresponding measurement curve. The abscissa (as the first axis) of the coordinate system of fig. 1e shows the positions P1 to P3 in the spatial reference system, while the ordinate (as the second axis) of the coordinate system of fig. 1e shows the corresponding values of the intensity I of the process illumination 16 (or of the parameters of the intensity distribution with respect to the process illumination 16). In the method schematically illustrated by fig. 1a to 1e, as electromagnetic beam 10, a pulsed electromagnetic beam 10 is focused. For example, the reference surface 12 can be irradiated with a sequence of ultrashort or short laser pulses as the beam 10. Thus, the measurement curve of the coordinate system in fig. 1e shows an exemplary brightness variation of the process illumination 16 under pulsed radiation.

In a further method step, a local maximum, a local minimum or an axis of symmetry of at least one of the determined measurement curves is determined. The determination can also be understood as a drawing of a local maximum, a local minimum or an axis of symmetry into the at least one determined measurement curve. Subsequently, the coordinate of the local maximum or local minimum on the abscissa/first axis or the coordinate of the intersection of the symmetry axis and the abscissa/first axis is determined as a position in the spatial reference system (e.g. position P2) in which the beam waist F of the focused beam 10 lies on/in the reference plane 12. The beam waist/focus offset deltas (in μm) for positions P1 to P3 can then also be determined on the abscissa if desired.

By way of example only, the reference surface 12 depicted in fig. 1a-1c is the outer surface 12 of the sample 18 on a work plane 20, wherein the reference surface 12 faces away from the work plane 20. However, it is noted that the method described herein is not limited in its performability to such a reference surface 12. In particular, the reference surface 12 may also be an interface within a compact body or an outer surface of the sample that is aligned with the working plane 20. The method described herein also does not require the construction of the remainder of the sample 18 or the reference surface 12, which is composed of a particular material.

Using the methods described herein, the position of the beam waist/focus F of the focused beam 10 relative to the reference surface 12 can be quickly and reliably determined and at the same time adjusted/set to a desired position relative to the reference surface 12. As can be seen from fig. 1a to 1c, this adjustment of the beam waist/focus F of the focused beam 10 can be made with respect to the reference surface 12 during the time that the sample 18 to be processed by the focused beam 10 is already located on the working plane 20. It is explicitly pointed out here that the determination of the position of the beam waist/focus F of the focused beam 10 and the adjustment of the beam waist/focus F of the focused beam 10 with respect to the reference surface 12 can be achieved with a high accuracy even if the method is performed on a sample 18 already located on the working surface 20. Furthermore, the methods described herein may also be readily automated.

As an advantageous development of the method described here, the image recorded by the camera can also additionally be digitally processed by means of optional method steps. In this way, spatter (from the liquid/luminescent metal) occurring in particular during welding can be "filtered out" from the image. For example, spatter is more frequent in the welding of copper or aluminum using infrared laser radiation. These splashes can be distinguished from the process illumination 16 due to their own spectrum being offset from the spectrum of the process illumination 16 and/or due to their own light distribution not being rotationally symmetrical about the beam axis of the beam 10. In particular, these splashes can generally be reliably detected as "elongated" light distributions due to their directional ("flying-out") movement from the center. In particular, the light distribution of the splatter may be automatically identified (by using preprogrammed or learning image detection software), be "filtered out" and thus not used to calculate the intensity I or intensity distribution utilized for focus position identification. Thus, even in the case where spatter is more frequent, the position of the beam waist F of the focused beam 10 with respect to the reference surface 12 can be accurately and reliably determined.

Fig. 2 and 3 show coordinate systems for explaining further embodiments of a method for determining the position of the beam waist of a focused beam relative to a reference surface.

In the method schematically illustrated by fig. 2 and 3, the focused electromagnetic beam 10 is also used to illuminate the respective sample 18 at different focus positions, but wherein an electromagnetic beam 10 having a continuous waveform is used. Such electromagnetic beams are also commonly referred to as cw (continuous wave) beams. In this case too, an optical process emission is produced by the interaction of the focused beam 10 with the reference surface 12 and the atmosphere, the intensity I of which is in particular related to the power density of the focused beam 10 effective on the reference surface 12 and the intensity distribution of which is related to the intensity distribution of the focused beam 10 on the reference surface 12. The power density of the focused beam 10 on the reference surface 12, or the intensity distribution of the focused beam 10 on the reference surface 12, in turn, varies depending on the relative position of the beam waist/focus F of the focused beam 10 with respect to the reference surface 12.

Thus, the coordinate systems of fig. 2 and 3 show an exemplary brightness variation process of the optical process emission in the case of continuous radiation. The abscissa (as the first axis) of the coordinate systems of fig. 2 and 3 shows the position in the spatial reference system, or beam waist offset/focus offset deltas (in millimeters), while the ordinate (as the second axis) of the coordinate systems of fig. 2 and 3 shows the corresponding value of the intensity I of the process illumination 16. With such a measurement profile, it is also possible to determine the position in the spatial reference system at which the beam waist/focus F of the focused beam 10 lies on/in the reference plane 12 by determining the local maximum, local minimum or symmetry axis of the respective measurement profile.

With regard to the further method steps of the method illustrated by means of fig. 2 and 3 and their advantages, reference is made to the description of fig. 1.

The method described herein may also be implemented for a particle beam as the focused beam 10. In particular, the electron beam or ion beam may be focused as a particle beam and its position of the beam waist F relative to the reference surface 12 may then be determined using the above-described method steps. The above advantages are also ensured in this application.

It is also pointed out here that the beams 10 respectively used for carrying out the method described here can optionally have an intensity distribution according to a gaussian distribution or an intensity distribution deviating from a gaussian distribution. The method may thus also advantageously be performed after the intensity distribution of the beam 10 has been changed from a gaussian distribution by beam shaping. The beam 10 modulated by beam shaping may also optionally be an electromagnetic beam 10 or a particle beam.

Fig. 4 shows a schematic view of a first embodiment of an apparatus for determining the position of the beam waist of a focused beam relative to a reference surface.

The apparatus schematically shown in fig. 4 has at least one controller 30 which is programmed and/or designed to use at least one first control signal S1 to operate a focusing device 32 of the apparatus itself or outside the apparatus to focus the focused beam 10 by means of said focusing device 32 in such a way that the beam waist F of the focused beam 10 is successively adjusted in a predetermined spatial reference frame to a plurality of positions along an axis 14 aligned obliquely to the reference surface 12. In this case, the focused beam 10 may also be optionally an electromagnetic beam or a particle beam. The apparatus may have, for example, a telecentric f-theta objective lens 32 as the focusing device 32. However, instead of a purely optical focusing device 32, a focusing device with wedge-shaped components may also be used to successively adjust the beam waist F of the focused beam 10 in the spatial reference frame to a plurality of positions along an axis 14 aligned obliquely to the reference surface 12. Optionally, the controllable telescope 34 can also be manipulated by at least one second control signal S2 of the controller 30. Alternatively or additionally, the beam deflection system 36, for example a 2D beam deflection system or a scanner system, can also be actuated by at least one third control signal S3 of the controller 30 in such a way that the focused beam 10 can be adjusted in at least one direction aligned parallel to the reference surface 12.

The controller 30 is furthermore programmed/designed to determine at least one measurement curve in the coordinate system as a function of the value I measured for the position in the spatial reference system by means of the device-specific or device-external detection device 38 and sigma of the intensity I of the process radiation 16 generated by means of the focused beam 10 and/or a parameter sigma of the intensity distribution of the process radiation 16. For this purpose, the values I and σ respectively measured by the detection device 38 are supplied to the controller 30. In the coordinate system of the at least one measurement curve, the first axis of the coordinate system shows the position in the spatial reference system, while the second axis of the coordinate system shows the corresponding value I of the intensity I of the process radiation 16 or the corresponding value σ of the parameter σ of the intensity distribution of the process radiation 16. The respective value I of the intensities I may be, for example, the peak intensities measured by the detection device 38 for the respective positions or the sum of the intensities I measured by the detection device 38 for the respective positions.

The detection device 38 may comprise, for example, a camera 38a, such as in particular a coaxial camera 38a or an event camera. Instead of the camera 38a or in addition to the camera 38a, a photodiode 38b or another optical sensor may also be used as (at least part of) the detection device 38. Preferably, a filter device 40 is arranged upstream of the detection device 38, by means of which filter device 40 the frequency spectrum of the focused beam 10 can be filtered out at least in part. In particular, a dichroic mirror/beam splitter 40 may be used as the filtering device 40. The filtering device 40 may be arranged upstream of the detection device 38 by a camera adapter 42.

Furthermore, the controller 30 is programmed/designed for determining a local maximum, local minimum or symmetry axis of at least one of the determined measurement curves and for determining the coordinates of the local maximum or local minimum on the first axis or the coordinates of the intersection of the symmetry axis with the first axis as a position in the spatial reference system in which the beam waist F of the focused beam 10 lies on/in the reference plane 12. In this way, the position of the beam waist/focus F may be automatically calculated by the controller 30 of the apparatus, for example using a fitting function.

Fig. 5 shows a schematic view of a second embodiment of an apparatus for determining the position of the beam waist of a focused beam relative to a reference surface.

In the arrangement of fig. 5, the industrial PC 30 serves as a controller 30 for operating the focusing device 32 using at least one first control signal S1, the controllable telescope 34 using at least one second control signal S2, the beam deflection system 36 using at least one third control signal S3 and the light source 44, e.g. the laser 44, using at least one fourth control signal S4. The camera 38a is also read by the industrial PC 30 and can also be manipulated. Steering can also be understood as the cooperation of the focusing device 32, the controllable telescope 34, the beam deflection system 36 and the camera 38 a. Various software packages for process management, image processing, and data analysis may be stored on the industrial PC 30. The light source 44 may be triggered by these software packages, recording the optical process emissions, evaluating the image from the camera 38a and determining the position of the beam waist F. On the basis of determining the position of the beam waist F, the position of the beam waist F may be set or adjusted according to a predetermined target position of the beam waist F.

Fig. 6a to 6d show a third embodiment of the device and a coordinate system for explaining the operation thereof.

The apparatus schematically shown in fig. 6a has an event camera 38c as a detection device 38. This Camera type is also called Event Camera (Event Camera) or neuromorphic Camera (Neuromorphic Camera). Thus, event-based camera technology may also be used to determine the location of the focal point F/waist of the focused beam 10. As explained in more detail below, the position of the beam waist/focus F may be determined even faster using the event camera 38 a.

Fig. 6b shows a detection surface 46 of the event camera 38c with a plurality of pixels/detection pixels 48, which observe the interaction area of the focused beam 10 with the reference surface 12. According to the standard deviation sigma of the intensity distribution of the process illumination 16, the standard deviation sigma of the intensity distribution of the process illumination 16 mapped onto the detection surface 46 of the event camera 38c ₄₆ And also changes. Different standard deviations sigma of the process illumination 16 mapped onto the detection surface 46 ₄₆ In these pixels 48, there are generated: a different number of events E related to the position of the beam waist/focus F of the focused beam 10 with respect to the reference surface 12.

The coordinate system of fig. 6c shows the total number E of events E detected by means of all pixels 48 of the detection surface 46 depending on the position of the beam waist/focus F _total Where its abscissa represents the beam waist offset/focus offset deltas. For better understanding, the beam caustic 50 is also drawn into the coordinate system of fig. 6 c.

The coordinate system of fig. 6d represents the number N (t) of events E detected by only one central pixel X1 of the pixels 48 of the detection surface 46 during the intensity I/power variation of the focused beam 10, wherein its abscissa represents the time axis t and its ordinate represents the number N (t) of events E detected by only the pixel X1. Graph F1 shows the number N (t) of events E detected only by pixel X1 when beam waist/focus F is present on reference surface 12, while graphs F2 and F3 show the number N (t) of events E detected only by pixel X1 when the distance of beam waist/focus F from reference surface 12 is not equal to zero, respectively. It can be seen that the number N (t) of events E detected by only pixel X1 is maximum when the beam waist/focus F is located on/in the reference surface 12.

The association between the number N (t) of events E detected only by pixel X1 and the position of beam waist/focus F as described in the previous paragraph can be used to determine the position of beam waist/focus F faster. To this end, during the intensity I/power variation of the focused beam 10, the beam waist F of the focused electromagnetic beam 10 is successively adjusted in a predetermined spatial reference frame to a plurality of positions along the axis 14, wherein said axis 14 is obliquely aligned with said reference surface 12, wherein for these positions a respective number N (t) of events E detected by only a single pixel X1 of the event camera 38c is determined.

Thus, the use of event based camera techniques as shown according to fig. 6a to 6d is a more robust technique for determining the focus position than the use of photodiodes. In the case of the event based recording technique, the recording rate is comparable to that of a high speed camera > 10kHz and is therefore orders of magnitude faster than other conventional camera based systems. Dynamic ranges exceeding 120dB allow recording over a large range of focal positions, enabling very stable measurements. (other conventional cameras are typically less than 60 dB.) additionally, more information can be determined from the camera image of the event camera 38c, whereby, for example, the position of the beam waist/focal length F with respect to the reference surface 12 can be determined even during spot welding where process stability is critical. It is also noted herein that the event camera 38c is relatively low cost compared to beam focus measurement devices. Furthermore, event-based camera techniques may also be implemented in a cycle time in many cases.

The position of the beam waist/focus F with respect to the reference surface 12 may be determined in any laser-based process by means of event-based camera technology. This is also achieved: the position of the beam waist/focus F is continuously monitored and corrected if necessary during the respective procedure. In particular, the position of the beam waist/focus F with respect to the reference surface 12 can be continuously monitored and corrected if necessary in all processes without interrupting production. This achieves a new, larger tolerance band in the separately manufactured products and thus a correspondingly large saving in their component costs. The 10 times higher speed of the event camera 38c compared to the other camera type also makes a new process possible.

Another advantage of using the event camera 38c over another camera type is that a single cw welding process can be recorded multiple times due to the very fast image sequence of images generated by the event camera 38c. Therefore, splatter and spray can be better identified based on these images and "filtered out" before determining the position of the beam waist F of the focused beam 10 relative to the reference surface 12. Thus, even in the case where spatter is more frequent, the position of the beam waist F of the focused beam 10 relative to the reference surface 12 can be accurately and reliably determined by using the event camera 38c.

It is pointed out again here that all the above-mentioned methods and devices are able to guarantee an important basic premise with respect to laser material processing in such a way that they are able to guarantee: the beam waist/focus F is always set correctly with respect to the position of the reference surface 12 without the need to implement a work-intensive process.

Claims

1. An apparatus for determining the position of a beam waist (F) of a focused beam (10) relative to a reference surface (12), the apparatus having:

-a controller (30) programmed and/or designed for:

-manipulating a focusing device (32) of the device itself or external to the device, by means of which focusing device (32) the electromagnetic beam (10) or the particle beam is focused such that the beam waist (F) of the focused electromagnetic beam (10) or particle beam is successively adjusted in a predetermined spatial reference frame to a plurality of positions (P1, P2, P3) along an axis (14) aligned obliquely to the reference surface (12);

-determining at least one measurement curve in a coordinate system from values (I, σ) of the intensity (I) of the process illumination (16) and/or of a parameter (σ) of the intensity distribution of the process illumination (16) measured for a position (P1, P2, P3) in a spatial reference system by means of a detection device (38) of the device itself or external to the device, wherein the process illumination is generated by means of a focused electromagnetic beam (10) or a particle beam, wherein a first axis of the coordinate system shows the position (P1, P2, P3) in the spatial reference system and a second axis of the coordinate system shows the respective value (I) of the intensity (I) of the process illumination or the respective value (σ) of the parameter (σ) of the intensity distribution of the process illumination (16); and

-determining a local maximum, local minimum or symmetry axis of at least one of the determined measurement curves and determining the coordinates of the local maximum or local minimum on the first axis or of the intersection of the symmetry axis with the first axis as a position in the spatial reference system in which the beam waist (F) of the focused electromagnetic beam (10) or particle beam lies on the reference plane (12).

2. The apparatus of claim 1, wherein the detection device (38) of the apparatus comprises an event camera (38 c).

3. The apparatus according to claim 1 or 2, wherein a filter device (40) is provided upstream of the detection device (38) of the apparatus, by means of which the spectrum of the electromagnetic beam (10) can be filtered out at least in part.

4. The apparatus according to any of the preceding claims, wherein the focusing device (32) of the apparatus comprises a telecentric f-Theta objective lens (32).

5. A method for determining the position of a beam waist (F) of a focused beam (10) relative to a reference surface (12), the method having the steps of:

focusing the electromagnetic beam (10) or the particle beam in such a way that the beam waist (F) of the focused electromagnetic beam (10) or the particle beam is successively adjusted in a predetermined spatial reference system to a plurality of positions (P1, P2, P3) along an axis (14) aligned obliquely to the reference surface (12), wherein for the positions (P1, P2, P3) in the spatial reference system the intensity (I) of a process illumination (16) generated by the focused electromagnetic beam (10) or the particle beam and/or a parameter (sigma) relating to the intensity distribution of the process illumination (16) are measured, respectively;

determining at least one measurement curve in a coordinate system from the values (I, σ) measured at the positions (P1, P2, P3) of the intensity (I) of the process illumination (16) and/or the parameters (σ) about the intensity distribution of the process illumination (16), wherein a first axis of the coordinate system shows the positions (P1, P2, P3) in the spatial reference system and a second axis of the coordinate system shows the respective values (I) of the intensity (I) of the process illumination (16) or the respective values (σ) of the parameters (σ) about the intensity distribution of the process illumination (16); and

-determining a local maximum, a local minimum or an axis of symmetry of at least one determined measurement curve, wherein the coordinates of the local maximum or the local minimum on a first axis or of an intersection of the axis of symmetry with the first axis are determined as a position in a spatial reference system in which the beam waist (F) of the focused electromagnetic beam (10) or particle beam lies on the reference plane (12).

6. The method according to claim 5, wherein the value (I) of the intensity (I) of the process illumination (16) measured at the position (P1, P2, P3) is determined by at least one event camera (38 c).

7. The method according to claim 5 or 6, wherein as an electromagnetic beam (10), an electromagnetic beam having a continuous waveform is focused and the position of the beam waist (F) of the electromagnetic beam relative to the reference surface (12) is determined.

8. The method according to claim 5 or 6, wherein as an electromagnetic beam (10), a pulsed electromagnetic beam (10) is focused and the position of the beam waist (F) of the electromagnetic beam relative to the reference surface (12) is determined.

9. The method according to claim 5 or 6, wherein an electron beam is focused as a particle beam and the position of the beam waist (F) of the electron beam relative to the reference surface (12) is determined.

10. The method according to any of claims 5 to 9, wherein a modified electromagnetic beam (10) or particle beam having its own intensity distribution different from a gaussian distribution by beam shaping is focused and the position of the beam's beam waist (F) relative to a reference surface (12) is determined.