An apparatus and method for determining a focal position

Abstract

The invention relates to a light beam analysis device (10) for determining an axial position of a focal point (71) of an energy beam or a sample beam (70) separated from the energy beam, comprising a beam shaping device (12), a detector (40) and an analysis device (45). The beam shaping device (12) is configured to modulate an intensity distribution (81) of the energy beam (77) or the separated sample beam (70) on a modulation plane (19) with a two-dimensional transmission function in order to form a modulated sample beam (79). The transmission function has at least two contrast steps (32, 33) in the form of a transition between at least one blocking region (25) and at least one passage region (21), which are at a distance a from each other. The beam shaping device (12) is configured to direct the modulated sample beam (79) onto the detector (40) along a propagation path in order to form an intensity distribution (83) having at least two contrast features (92, 93) on the detector (40) along a first lateral direction (31). The analysis device (45) is configured to determine the distance a between the contrast features (92, 93) on the detector (40) along the first lateral direction (31) and to determine the axial position of the beam focal point (71) based on the distance a and / or a change in the axial position of the beam focal point (71) based on a change in the distance a. The invention also relates to a corresponding method for determining an axial position of a beam focal point (71).

Description

An apparatus and method for determining the position of a focal point Technical Field

[0001] This invention relates to an apparatus and method for determining the axial position of the focal point of an electromagnetic radiation energy beam, and more particularly to an apparatus and method for determining the axial position of the focal point of a processing optics beam. Specifically, the energy beam may be a laser beam. The invention also provides an apparatus and method capable of determining the focal point position of a processing optics beam during laser processing operations. Background Technology

[0002] The central task of laser material processing is to adjust and control the axial focal position of the laser beam relative to the material or workpiece being processed. Through optimized process control, the laser beam focal point does not necessarily lie directly on the workpiece surface. Instead, the optimal positioning of the laser beam focal point relative to the workpiece depends on several factors. For example, the focal point can be located within the workpiece, that is, below the workpiece surface, especially when processing workpieces with high material thickness. Typically, the processing outcome is sensitively dependent on the accurate focal position of the laser beam, which is why it is desirable or necessary for the laser beam focal point positioning relative to the workpiece to remain unchanged during processing.

[0003] In laser cutting, it is also important to keep the distance between the workpiece and the cutting nozzle as constant as possible during processing, because the flow dynamics of the cutting gas have a significant impact on the cutting results. This problem can be solved using existing technologies, such as capacitive distance measurement and closed-loop control.

[0004] Typically, the problem of changing the position of the beam focus relative to the workpiece is not detecting or tracking the workpiece position or the distance of the workpiece relative to the machining optics, but rather detecting the position of the actual beam focus relative to the machining optics.

[0005] Modern laser processing systems use lasers with high brightness and power, typically in the kilowatt range. Due to the material properties of the optical components, high laser power causes the components to heat up. This creates a radial temperature gradient within the optical component, leading to changes in the refractive power of the optics due to the temperature dependence of material parameters such as refractive index. This effect is called thermal focus shift. Although this thermal focus shift can be minimized by selecting appropriate optical component materials, such as using high-purity, low-absorption type quartz glass, it is always present in practice. Reaction products and particles of various sizes generated during laser material processing enhance this effect; these can deposit on the processed optics or the protective glass of the processed optics, leading to increased absorption. Therefore, in particular, the protective glass often helps to alter the beam focus position of the processed optics.

[0006] Devices for determining workpiece distance or workpiece surface position are known in the prior art; they operate based on fundamental principles, such as optical triangulation.

[0007] For example, patent application EP0248479A1 discloses an apparatus for optically measuring the distance between a surface and a reference surface. To this end, after reflected radiation passes through a screen having two off-axis openings, the surface is illuminated by a radiation source, and the reflected radiation is guided to a detector by an optical system. The range of the light spot pattern produced by the screen is a measure of the distance between the surface and the reference surface.

[0008] The distance measurement method disclosed in patent number DE4206499C2 works in a very similar manner. Here, light emitted by the object is also guided through a screen with an off-axis opening and directed to the measuring head. The feature here is that, in order to avoid speckle patterns that would affect the accuracy of the measurement, only a small fraction of the incoherent radiation of the light spot is used; the object is excited to emit this radiation by being irradiated by electromagnetic radiation.

[0009] The apparatus and method for determining the focal position of a high-energy beam are known technologies from patent application DE102013210078A1. Among other things, the apparatus includes an image acquisition device for forming at least two observation beams, and imaging optics for generating at least two images or reference profiles of the area to be monitored. On one hand, changes in the lateral distance between the two images of the area to be monitored on the workpiece surface can be used to infer the deviation of the focal position relative to the workpiece. On the other hand, changes in the focal length of the focusing element, which can be formed by, for example, the inner profile of a laser processing nozzle, can be determined based on changes in the lateral distance between the two images of the reference structure, thus allowing the inference of changes in the focal position. Since light emitted or reflected by the workpiece or reference structure is also used by the apparatus to generate images, the focal position of the high-energy beam cannot be measured strictly. Changes in the beam focal position are not caused by the focusing element, but by, for example, collimating optics, which cannot be determined by the disclosed apparatus.

[0010] Patent application EP2886239A1 discloses a method and apparatus for monitoring and controlling the processing path during a laser joining process. Among other things, the processing head described in this disclosure has a distance sensor in the form of a dual-slit sensor including imaging optics and a dual-slit screen. The distance sensor can be used to determine the distance between the processing head and the workpiece surface.

[0011] In all the disclosures cited above, the position or distance to the workpiece surface is ultimately determined optically. On the other hand, the aforementioned apparatus and methods cannot determine the focal position of the light beam pointing onto the workpiece surface, or can only determine it with low precision. To determine the actual focal position of the processed light beam, it is necessary to directly measure the processed light beam, or to separate the sample beam from the processed beam and measure the sample beam.

[0012] Patent application DE102017215973A1 describes an apparatus and method for determining the beam position of a laser beam. For this purpose, a secondary beam is separated from the laser beam by a beam splitter and guided to a position sensor. A beam shaper is disposed in the optical path of the secondary beam or in front of the beam splitter. The apparatus is intended to determine the beam position of the laser beam based on the intensity distribution of the shaped secondary beam detected by the optical position sensor, or based on the position of the focal point of the shaped secondary beam. The apparatus is used to detect beam position errors of the laser beam. Similarly, deviations in the laser beam diameter can be detected. Therefore, the apparatus is intended to detect beam position errors and deviations that are transverse, that is, radial or lateral variations. Determining the axial focal point position of the laser beam is not contemplated.

[0013] An apparatus and method for processing materials using electromagnetic radiation is disclosed in WO2012 / 041351A1, which discloses the known technology. It is conceivable that a device for pattern generation (e.g., a shadow mask) is rotated into an electromagnetic beam focused on the material. A partially reflective surface is positioned in front of the focal point, such that an image of a pattern generated by a pattern generator is reflected back onto the partially reflective surface and reaches a detector via a beam splitter. The image on the detector is processed by a computer, generating an electrical signal related to the focal point position. The disclosed method is intended for use in ophthalmic surgery. However, this method is unsuitable or less suitable for general applications in laser material processing because it is generally not possible to permanently position the partially reflective surface in front of the beam focal point, and setting a shadow mask in a high-power laser beam is also disadvantageous.

[0014] In the apparatus for monitoring a laser beam disclosed in WO2015 / 185152A1, radiation is reflected back by means of a plate positioned at an angle within the laser beam and detected by a spatially resolved detector. Changes in laser beam divergence can be determined by detecting the shift in the focal position of the sub-beam imaged onto the detector. This apparatus is particularly useful for analyzing and monitoring driving lasers used to generate EUV radiation.

[0015] Patent application DE102011007176A1 describes an apparatus for focusing a laser beam and a method for monitoring laser processing. For this purpose, laser radiation is reflected back from a transmission optical element, particularly from a protective glass, and the back-reflected radiation is detected by a detector to determine the focal position. Here, the protective glass is set at an angle such that the back-reflected radiation is directly deflected to the side, and no further beam separation is required. A screen is provided to block the back-reflected radiation from one side of the protective glass. The focal position of the laser beam is determined by estimating the size (i.e., diameter) of the area irradiated by the back-reflected laser radiation on the detector.

[0016] Patent DE102013227031A1 discloses an apparatus and method for analyzing a light beam incident on a substrate and for correcting focal length shift. In the illustrated apparatus, for beam analysis, a portion of the light beam reflected by a protective glass is deflected into the measurement optical path on a sensor. The portion reflected from the protective glass is guided through a screen in the measurement optical path, thus blocking the interference beam reflected from other parts of the apparatus. To achieve the desired interference beam blocking, tilting the protective glass and / or using a wedge to deflect the reflected beam are envisioned. As the sensor, the disclosure indicates the use of a CCD camera or a CMOS camera, which enables measurements conforming to DIN ISO 11146. Furthermore, it is envisioned that the actual focal length is determined by calculation using an ABCD matrix.

[0017] Patent application DE102018105364A1 discloses an apparatus and method for determining the focal position of a laser beam in a laser processing system, which is very similar to the apparatus from DE102011007176A1. In the method of DE102018105364A1, calibration data including measurements of the laser power's beam diameter are envisioned for determining the focal position. Therefore, in the method described here, the determination of the focal position is also based on the determination of the diameter of the intensity distribution on the detector.

[0018] In recently cited publications, the focal position is typically determined by measuring the size or diameter of the spot on the detector. While this method can theoretically determine the focal position if the beam parameters are known, it is disadvantageous for several reasons: firstly, the detected beam diameter changes with the divergence and / or diameter of the processed laser beam; secondly, especially in the beam waist region, the change in diameter with changing focal position is minimal. Both contribute to considerable uncertainty in determining the axial focal position. Finally, based on measurements of the optimal focal position, it is impossible to detect in which direction the beam focus has moved, since the diameter increases in both directions.

[0019] Brief Description of the Invention

[0020] Therefore, the present invention aims to advantageously improve the principle of optical triangulation, and in particular, to enable it to measure the focal position of a laser beam guided in laser processing optics without relying on radiation emitted or reflected by the workpiece, thereby enabling particularly precise determination of the focal position. Another aspect of the invention aims to provide particularly robust, accurate, versatile, and compact apparatus and methods for determining the focal position, and, where applicable, for determining further beam parameters.

[0021] This task can be accomplished by a beam analysis apparatus having the features of claim 1.

[0022] The beam analysis apparatus according to the invention is used to determine the axial position of a beam focal point, wherein the beam focal point is the focal point of an energy beam of electromagnetic radiation, or the focal point of a sample beam separated from the energy beam, the apparatus comprising a beam shaping device, a detector, and an evaluation device.

[0023] The beam shaping device is configured to modulate the intensity distribution of an energy beam or a sample beam separated from the energy beam in a modulation plane having a two-dimensional transmission function, thereby forming a modulated sample beam with a modulated intensity distribution, wherein the transmission function has at least one channel region containing a substantially constant first intensity transmission factor and at least one blocking region containing a substantially constant second intensity transmission factor, wherein the second intensity transmission factor is at most 50% of the first intensity transmission factor.

[0024] The transmission function has at least two contrast steps along a first lateral direction, in the form of a transition between at least one blocking region and at least one channel region, wherein the contrast steps have a distance k between each other along the first lateral direction.

[0025] The term "lateral" can refer (at least substantially) to a planar direction perpendicular to the respective local optical axis.

[0026] The beam shaping device is also configured to form an intensity distribution with at least two contrast features along a first transverse direction on the detector and to guide the modulated sample beam to the detector along a propagation path, wherein the contrast features in the intensity distribution on the detector are formed by at least two contrast steps in the modulated intensity distribution through the beam propagation of the modulated sample beam to the detector.

[0027] The detector includes a spatially two-dimensionally resolved optical radiation-sensitive sensor configured to convert the intensity distribution incident on the detector into an electrical signal. The detector (especially its sensor) is positioned at a distance s behind the modulation plane along the propagation path.

[0028] The evaluation device is configured to process electrical signals from the detectors, which represent the intensity distribution on the detectors.

[0029] In addition, the evaluation device is configured to determine the distance 'a' between two contrast features on the detector along a first lateral direction, and to determine the axial position of the beam focus based on the distance 'a', and / or to determine the change in the axial position of the beam focus based on the change in the distance 'a'.

[0030] This beam analyzer is a particularly robust, precise, versatile, and compact device for determining the location of a focal point.

[0031] The term “sample beam” can also be understood as the term “energy beam”, especially if the sample beam is not formed by separating it from the energy beam.

[0032] The beam analysis apparatus according to the invention may optionally be further improved by one or more of the features listed below.

[0033] To receive electrical signals from the detector, the evaluation device can be connected to the detector. For example, the evaluation device can be connected to the detector via at least one data line. Optionally or additionally, to receive electrical signals from the detector, the evaluation device can be wirelessly connected to the detector. According to another aspect of the invention, the evaluation device and the detector can be designed as a common unit.

[0034] In a preferred embodiment, in each of the at least two contrast steps, a portion of the channel region extends beyond width b along a first lateral direction, and a portion of the blocking region extends beyond width p along the first lateral direction.

[0035] Particularly preferably, the width b of the channel region is at least 1.5 times the width p of the blocking region. This achieves highly accurate measurement.

[0036] In another embodiment, the channel region portion and the blocking region portion at the contrast step extend beyond a width h in the second lateral direction. The second lateral direction is perpendicular to the first lateral direction.

[0037] Most preferably, the width h is at least twice the width p.

[0038] In a preferred embodiment, the contrast step is designed as a line whose tangent at the intersection with the first lateral direction is perpendicular to the first lateral direction.

[0039] Preferably, the contrast steps are designed as straight lines perpendicular to the first lateral direction.

[0040] According to another aspect, the beam analyzer is preferably configured to change the first lateral direction and local optical axis between the modulation plane and the detector by beam folding and / or beam redirection. Furthermore, a second lateral direction can also be changed accordingly by beam folding and / or beam redirection. With the aid of beam folding and / or beam redirection, the beam analyzer can, for example, be manufactured to be more compact without compromising measurement accuracy.

[0041] The beam analysis apparatus preferably includes a separation device, which comprises a beam splitter for separating the sample beam from the energy beam. In this way, the beam analysis apparatus can be easily used with existing processing optics. Furthermore, the separation device enables the beam analysis apparatus to perform measurements during the normal operation of the processing optics.

[0042] Particularly preferably, the beam splitter is a beam splitter device configured to separate the radiation component of the energy beam in the range of 0.01% to 5% into a sample beam by reflection and / or transmission. In typical applications, on the one hand, this radiation component is sufficient for accurate measurement, and on the other hand, the energy beam is significantly weakened only by the separation.

[0043] The beam shaping device may include an imaging device with at least one optical lens for guiding the modulated sample beam onto a detector. For example, this allows for the use of a more compact detector. Optionally or additionally, this feature can improve measurement accuracy.

[0044] The modulation plane can be set at the image-side focal point (also known as the second focal point) of the imaging device. This makes estimation particularly easy.

[0045] Preferably, the evaluation device is configured to determine the axial position of the beam focal point based on the distance 'a' between contrast features, using a calculation rule that is linear in at least some parts. Optionally or additionally, the evaluation device is preferably configured to determine the change in the axial position of the beam focal point based on the change in the distance 'a' between contrast features, using a calculation rule that is linear in at least some parts. This allows for simple, accurate, and rapid estimation with minimal computational effort.

[0046] In a further improvement, the evaluation device is configured to determine the axial position of the beam focal point based on the distance 'a' between contrast features using a linear calculation rule. Optionally or additionally, the evaluation device can be configured to determine the change in the axial position of the beam focal point based on the change in the distance 'a' between contrast features using a linear calculation rule. This allows for a particularly simple, accurate, and rapid estimation with minimal computational effort.

[0047] In an advantageous embodiment, the beam analysis apparatus includes a beam folding device comprising a beam splitter and at least one mirror disposed in an optical path in front of a detector. The at least one mirror is configured to reflect radiation components exiting the beam splitter back into the beam splitter, thereby forming a first folded optical path. A modulation plane is disposed in the optical path in front of the beam folding device, or is disposed within the first folded optical path. Beam folding allows for a more compact design of the beam analysis apparatus without compromising measurement accuracy.

[0048] In another improvement to the beam analysis apparatus, the beam folding device may additionally include at least one second mirror, which is configured to reflect another radiation component leaving the beam splitter back into the beam splitter, thereby forming a second folded optical path. This second folded optical path can, for example, enable the measurement of additional parameters.

[0049] In a preferred embodiment, the modulation plane of the beam shaping device is disposed in the first folded optical path, wherein no modulation is disposed in the second folded optical path, so as to guide the radiative component of the sample beam or energy beam as an unmodulated beam onto the detector. The evaluation device can be configured to determine the beam diameter and / or beam profile based on the intensity distribution of the unmodulated beam spot on the detector. This allows the energy beam or sample beam to be characterized more accurately.

[0050] In a further improvement, the mirror is configured to be axially movable within the second folded optical path, and the position of the mirror can be adjusted by a positioning device. The axial displacement of the second mirror can be used, for example, to determine the beam caustics (also known as the beam envelope) of the energy beam or sample beam. An evaluation device can be accordingly configured to determine the beam caustics. Specifically, the evaluation device can be configured to control the axial displacement of the mirror. The evaluation device can be connected to the second mirror, particularly to the positioning device.

[0051] Preferably, the evaluation device is configured to determine the lateral position of the entire intensity distribution on the detector, and is used for:

[0052] - Calculate the lateral position of the sample beam based on the lateral position of the entire intensity distribution, and / or

[0053] -Calculate the change in the lateral position of the sample beam's focal point based on the change in the lateral position of the entire intensity distribution.

[0054] In a preferred embodiment, the beam analysis apparatus includes a beam splitter for separating a sample beam, another imaging device having at least one optical lens, and a second detector. Here, the beam splitter is disposed in the optical path in front of the plane of the modulation plane, and is positioned between the optical lens of the (foreign) imaging device and the modulation plane. Simultaneously, the other imaging device is disposed between the beam splitter and the second detector, and is configured to image a magnified image of the magnified spot or beam focal point onto the second detector. This allows for more accurate characterization of the energy beam or sample beam.

[0055] The evaluation device can be configured to process the electrical signal generated by the second detector, and the evaluation device can be configured to determine the beam diameter and / or focal spot diameter based on the intensity distribution on the second detector.

[0056] To receive electrical signals from the detector, the evaluation device can be connected to the second detector. For example, the evaluation device can be connected to the second detector via at least one data line. Optionally or additionally, to receive electrical signals from the detector, the evaluation device can be wirelessly connected to the second detector. According to another aspect of the invention, the evaluation device and the second detector can be designed as a common unit.

[0057] According to another aspect, the beam analysis apparatus includes a beam splitter for separating a sample beam, another imaging device having at least one optical lens, and a second detector. Here, the beam splitter is positioned in front of the modulation plane in the optical path, between the optical lens of the imaging device (mentioned at the beginning, i.e., the first one mentioned) and the modulation plane. The other imaging device is positioned between the beam splitter and the second detector. The imaging device and the other imaging device together form a combined lens system having an image-side focal plane (also referred to as a second focal plane). The second detector may be positioned in the image-side focal plane of the combined lens system.

[0058] The evaluation device can be configured to process the electrical signal generated by the second detector, and the evaluation device can be configured to determine the divergence angle based on the intensity distribution on the second detector.

[0059] To receive the electrical signal from the detector, the evaluation device can be connected to a second detector. The provisions for the above variations of the second detector apply mutatis mutandis.

[0060] The above objectives are also achieved by a system comprising a beam analysis apparatus according to embodiments of the disclosed form and processing optics for guiding and focusing an energy beam. The beam analysis apparatus can be used to inspect the energy beam.

[0061] The advantages mentioned for the corresponding improvements to the beam analysis device are applicable to this system accordingly.

[0062] The processing optics may include a separation device for separating a sample beam from an energy beam, and a beam analysis device may be connected to the processing optics to receive the separated sample beam. Therefore, the beam analysis device can be used for energy beam inspection in a particularly simple manner.

[0063] The above-mentioned task is further solved by a method for determining the axial position of the beam focal point having the features of claim 25.

[0064] This method is used to determine the axial position of a beam focal point, wherein the beam focal point is the focal point of an energy beam of electromagnetic radiation, or the focal point of a sample beam separated from the energy beam. The method includes at least the following steps:

[0065] - Modulating the intensity distribution of an energy beam or a sample beam separated from the energy beam within a modulation plane having a two-dimensional transmission function, thereby forming a modulated sample beam (in a transverse plane) with a modulated intensity distribution, wherein the transmission function has at least one channel region containing a substantially constant first intensity transmission factor, and at least one blocking region containing a substantially constant second intensity transmission factor, wherein the second intensity transmission factor is at most 50% of the first intensity transmission factor, wherein the transmission function has at least two contrast steps in a transitional form between at least one blocking region and at least one channel region along a first transverse direction, wherein the contrast steps have a distance k between each other along the first transverse direction. The term "transverse" refers to a planar direction perpendicular to its respective local optical axis.

[0066] - A modulated sample beam is guided onto a detector positioned at a distance *s* behind the modulation plane along the propagation path of the modulated sample beam, so as to form an intensity distribution on the detector having at least two contrast features along a first lateral direction, wherein the contrast features in the intensity distribution on the detector are formed by at least two contrast steps in the modulated intensity distribution propagating through the beam from the modulated sample beam to the detector.

[0067] -The intensity distribution incident on the detector is converted into an electrical signal by a spatially two-dimensionally resolved optical radiation-sensitive sensor.

[0068] - Process the electrical signal of the detector, which represents the intensity distribution on the detector.

[0069] - Determine the distance 'a' between contrast features along the first lateral direction.

[0070] - The axial position of the beam focal point can be determined based on the distance a, or the change in the axial position of the beam focal point can be determined based on the change in the distance a.

[0071] The method according to the invention can determine the focal position in a particularly robust, accurate and universal manner.

[0072] In particular, the beam shaping device can be designed according to any of the forms described in the embodiments. The advantages mentioned herein apply accordingly to the beam analysis method.

[0073] In particular, the evaluation apparatus can be designed according to any of the forms described in the embodiments. The advantages mentioned herein apply accordingly to the beam analysis method.

[0074] The beam analysis method according to the present invention can be further improved by one or more of the optional steps listed below.

[0075] In a further step, the sample beam can be separated from the energy beam, for example, by a beam splitter in a separation device.

[0076] As a sample beam, the radiation components of the energy beam in the range of 0.01% to 5% can be separated by reflection and / or transmission, for example by means of a beam splitter.

[0077] Guiding the modulated sample beam onto the detector can be done using an imaging device with at least one optical lens. The imaging device can be located within a beam shaping device.

[0078] The image-side focal point of the imaging device can be located in the modulation plane. Modulation of the intensity distribution can be performed at the image-side focal point of the imaging device.

[0079] Preferably, this is achieved through linear calculation rules in at least some parts:

[0080] - The axial position of the beam focal point is determined based on the distance 'a' between contrast features, or

[0081] - The change in the axial position of the beam focal point is determined based on the change in the distance 'a' between contrast features.

[0082] In further improvements, linear calculation rules are used:

[0083] - The axial position of the beam focal point is determined based on the distance 'a' between contrast features, or

[0084] - The change in the axial position of the beam focal point is determined based on the change in the distance 'a' between contrast features.

[0085] According to another aspect, the first folded optical path is preferably formed by a beam folding device comprising a beam splitter (and at least one reflector). The first folded optical path is disposed in the optical path in front of the detector by reflecting the radiation components leaving the beam splitter back to the beam splitter at the at least one reflector. Here, the modulation of the intensity distribution can be performed in the optical path in front of the beam folding device or in the first folded optical path.

[0086] In another step, a second folded optical path is formed by a beam folding device, which additionally includes at least one second mirror to reflect another beam component leaving the beam splitter back into the beam splitter at the second mirror.

[0087] In a further improvement, intensity distribution modulation occurs in the first folded optical path, while no intensity distribution modulation occurs in the second folded optical path, and the radiation component is guided onto the detector as an unmodulated beam. Here, for example, by an evaluation device, the beam diameter and / or beam profile can be determined based on the intensity distribution of the unmodulated beam spot on the detector.

[0088] Particularly preferably, the axial position of the reflector in the second optical path can be changed by a positioning device, and for each of at least three different positions of the reflector, the intensity distribution of the unmodulated beam spot is recorded on a detector. Optionally, at least one beam parameter of the unmodulated beam is determined by the recorded intensity distribution, for example, by an evaluation device.

[0089] In a further improvement to the method, the method includes the following steps:

[0090] - The sample beam is split by a beam splitter, which is located in the optical path behind the optical lens of the imaging device (described at the beginning) and in front of the modulation plane.

[0091] - The separated sample beam is imaged onto a second detector by means of an additional imaging device including at least one optical lens, the at least one optical lens being disposed between the beam splitter and the second detector for forming an enlarged spot or an enlarged image of the beam focus on the second detector.

[0092] - Determine the beam diameter or focal spot diameter based on the intensity distribution on the second detector.

[0093] According to another aspect, the method preferably includes the following steps:

[0094] - The sample beam is split by a beam splitter located in the optical path behind the optical lens and in front of the modulation plane of the imaging device (described at the beginning).

[0095] - A separated sample beam is guided onto a second detector by another imaging device having at least one optical lens disposed between the beam splitter and the second detector to form a far-field beam distribution on the second detector. Here, the imaging device and the other imaging device together form a combined lens system having an image-side focal plane. The second detector is disposed here in the image-side focal plane of the combined lens system.

[0096] - Determine the far-field beam diameter or divergence angle based on the intensity distribution on the second detector.

[0097] In a further advantageous improvement to the method, the energy beam is focused by processing optical devices.

[0098] Particularly preferably, the determined axial position of the beam focal point, or the change of the determined axial position of the beam focal point, is used to control the laser processing operation. Attached Figure Description

[0099] Brief description of the attached figures

[0100] The invention will be described in more detail with the aid of the following figures, and is not limited to the forms of the embodiments and examples shown. More specifically, as illustrated in the figures, embodiments in which elements and aspects can be combined are also contemplated. Wherein:

[0101] Figure 1 shows a schematic diagram of one embodiment of the beam analysis apparatus according to the present invention.

[0102] Figure 2 shows a schematic diagram of one embodiment of a beam analysis device similar to that in Figure 1, with an additional separation device.

[0103] Figure 3 shows a schematic diagram of the modulation device for the beam analysis apparatus, a schematic diagram of the transmission function of the modulation device, and a schematic diagram of exemplary intensity distributions in front of and behind the modulation device.

[0104] Figure 4 shows a schematic, exemplary representation of the intensity distribution on a detector with contrast characteristics, which also shows how the intensity distribution changes with the focal position.

[0105] Figure 5 shows an exemplary representation of the contour of the simulated intensity distribution on a detector with contrast characteristics, which also shows how the contour of the intensity distribution changes with the focal position.

[0106] Figure 6 shows a schematic diagram of a variation of the beam analysis device, wherein the modulation device is disposed in the focal plane of the imaging device.

[0107] Figure 7 shows a schematic diagram of another embodiment of a beam analysis apparatus with a beam folding device for forming two different optical paths on the detector, wherein the modulation device is only disposed in one optical path.

[0108] Figure 8 shows a schematic diagram of another embodiment of a beam analysis device with two optical paths on the detector, wherein the modulation device is only arranged in one optical path, and wherein the optical path length of the unmodulated beam can be adjusted.

[0109] Figure 9 shows a schematic diagram of another embodiment of the beam analysis device, which has two optical paths similar to those in Figure 7, and additionally separates the beam and images the far-field beam distribution of the sample beam onto a second detector. Detailed Implementation

[0110] Figure 1 illustrates a beam analysis apparatus 10 according to the present invention, which includes a beam shaping device 12, a detector 40, and an evaluation device 45. The beam shaping device 12, the detector 40, and the evaluation device 45 are preferably housed together in a housing. The beam analysis apparatus 10 receives a sample beam 70 propagating along an optical axis 11 with a beam focal point 71. The beam shaping device 12 includes a modulation device 20 and an imaging device 50, which, in this embodiment, are designed as independent devices. The modulation device 20 is used to modulate the intensity distribution of the sample beam 70 in a modulation plane 19. For this purpose, the modulation device 20 has at least two regions of a channel region 21 and at least one region of a blocking region 25. In the channel region 21, radiation further propagates to the detector 40; in the blocking region 25, the propagation of radiation to the detector is impeded. Therefore, the modulation device 20 provides a transmission function by means of which the intensity distribution of the sample beam 70 can be modulated, thereby forming a modulated sample beam 79. Along the first lateral direction 31, the transmission function has two contrast steps 32, 33, presenting a transitional form between the blocking region 25 and the channel region 21. The contrast steps 32, 33 are spaced apart by a distance k along the first lateral direction 31, where the term "lateral" refers to a direction in a plane perpendicular to the optical axis 11. The sample beam 70 or modulated sample beam 79 is guided onto the detector 40 by means of the beam shaping device 12. In doing so, the intensity distribution of the modulated sample beam is reduced in the lateral range by utilizing the imaging characteristics of the imaging device 50. The detector 40 is not positioned at the location of the image at the beam focus 71. In the sensor plane 39, the detector 40 has a spatially two-dimensionally resolved light radiation sensitive sensor that converts the intensity distribution on the detector 40 into an electrical signal, which is received and processed by the evaluation device 45. In this embodiment, the evaluation device 45 is electrically connected to the detector 40 for this purpose. The imaging device 50 includes at least one optical lens 51. By guiding the modulated sample beam 79 onto the detector 40, at least one contrast feature 92, 93 is formed in the intensity distribution on the detector of each contrast step 32, 33. Two contrast features 92, 93 are spaced apart from each other by a distance a in the first lateral direction 31 on the detector 40. Among other things, distance a depends on the distance k between the contrast steps 32, 33, the distance s between the modulation plane 19 and the sensor plane 39, and the axial position of the beam focus 71 and the distance z between the modulation plane 19. sThe distance e between the position of lens 51 (more precisely, the position of the main plane of imaging device 50) and modulation plane 19 is also considered. Therefore, the axial position of beam focus 71 can be determined based on distance a. If the image position of beam focus 71 falls on detector 40 or sensor plane 39, distance a will be zero; furthermore, no contrast features will be formed in the intensity distribution of the image of beam focus 71. Therefore, detector 40 or sensor plane 39 is positioned at an axial distance from the image position of beam focus 71.

[0111] Figure 2 illustrates a beam analysis apparatus 10 similar to the embodiment shown in Figure 1. A variation of the embodiment of the beam analysis apparatus 10 shown in Figure 2 differs from the embodiment according to Figure 1 in that it includes an additional separation device 14. The separation device 14 includes a beam splitter 15. By means of the beam splitter 15, the sample beam 70 is separated from the energy beam 77 of electromagnetic radiation (e.g., a laser beam). In this embodiment, the beam splitter 15 is a flat plate configured as a beam splitter, and at one of its interfaces, a portion of the intensity of the energy beam 77 is reflected as the sample beam 70. To adjust the degree of reflection, the flat plate can be coated, for example, with a reflection reduction layer. Typical antireflective coatings with low residual reflection in the range of about 0.05% to about 1% are sufficient to provide the sample beam 70. Therefore, the separation device 14 simultaneously reduces and / or limits the radiation intensity of the sample beam 70. Beams 72 and 73 are formed at contrast steps 32 and 33; the points on the detector 40 they illuminate represent the locations of contrast features 92 and 93. All other features of the embodiment in FIG2 correspond to the features shown in FIG1, and the same reference numerals correspond to the same features as in FIG1; in this respect, for other features, refer to the description in FIG1.

[0112] Figure 3 illustrates an example of a modulation device 20, which may be used, for example, in the beam analysis device 10 according to Figure 1 or 2. The modulation device 20 has two region portions of a channel region 21, each having a width b on either side of a region portion centrally located in a blocking region 25 having a width p. In each case, the transition between the region portions of the channel region 21 and the blocking region 25 forms one of contrast steps 32, 33. The contrast steps 32, 33 are spaced apart from each other by a distance k in a first lateral direction. No radiation is transmitted in the blocking region 25; the blocking region 25 may be composed of absorbing and / or reflecting materials. An exemplary transmission function 80 formed in this way is schematically shown in the upper right portion of Figure 3. A sample beam 70 is irradiated onto the modulation device 20, having an intensity distribution 81 in front of the modulation device 20, which may, for example, be of Gaussian form. After modulation by the modulation device 20, the sample beam has an intensity distribution 82 on which the transmission function 80 is applied, such that the contrast steps 32, 33 now included in the transmission function 80 are included in the intensity distribution 82. In the lower right part of Figure 3, the intensity distribution in front of (81) and behind (83) of the modulation device is schematically shown for the Gaussian sample beam 70.

[0113] Figure 4 is a schematic, exemplary representation of the intensity distribution 83 on the detector 40 in the beam analysis apparatus 10 according to Figure 1 or Figure 2, which has the modulation device 20 shown in Figure 3. The intensity distribution on the detector 40 consists of two regions with higher intensity, wherein the regions are in the form of a circular cross section. Contrast features 92 and 93 caused by contrast steps 32 and 33 are formed on the inner edge of the circular portion. The intensity distribution 83 on the detector represents the (reduced) shadow projected by the modulation device 20, which is illuminated by the sample beam 70. The contrast features 92 and 93 are separated from each other by a distance a in the first lateral direction 31. The distance a changes when the axial position of the beam focus 71 changes. Figure 4 further shows the change in the distance a between the contrast features 92 and 93 on the detector 40 when the axial position of the beam focus 71 changes. The apostrophe reference symbols in the figure indicate details of the axial displacement change of the beam focus. The amount of change in the beam focus position is Δz = z s -z s The amount that causes the interval of contrast features 92 and 93 to change is Δa = a' - a.

[0114] Figure 5 shows an example of the intensity distribution 83 on the detector 40 of a beam analyzer 10 according to Figure 1 or Figure 2 and having a modulation device 20 according to Figure 3. These two curves show the results of a simulation of the beam analyzer 10 using ray tracing software. Here, an incoherent light with a focal spot diameter of 0.1 mm and a divergence of 67 mrad is assumed. The width p of the central portion of the blocking region is 6 mm, which in this example is the same as the distance k between the contrast steps. The distance z from the beam focus to the modulation device... s The focal length of the lens is 67mm, the distance s from the modulation device to the detector is 180mm, and the solid line represents the intensity distribution when the beam focus 71 is in its original position. The dashed line represents the intensity distribution when the focus position is moved 2mm axially. Due to the propagation path to the detector 40, the contrast steps 32 and 33 are actually "blurred", but the positions of the contrast features 92 and 93 in the intensity distribution 83 can still be clearly and accurately determined.

[0115] Figure 6 shows a variation of the beam analysis device 10, wherein the imaging device 50 is positioned in front of the modulation device 20 in the beam direction. In this case, the distance between the position of the lens 51 (more precisely, the position of the principal plane of the imaging device 50) and the modulation plane 19 is d. A particularly advantageous implementation is provided if the distance d is equal to the focal length f of the imaging device 50, that is, if the modulation plane 19 is positioned at the image-side focal point of the imaging device 50. Various forms of implementation will be explained in more detail in the section containing the detailed description of the invention. All other details shown correspond to the details in Figure 1.

[0116] Figure 7 illustrates one embodiment of the beam analysis apparatus 10, which includes a beam shaping device 12, a beam folding device 60, a detector 40, and an evaluation device 45. The beam shaping device 12, beam folding device 60, detector 40, and evaluation device 45 are preferably housed together in the same housing. The beam shaping device 12 includes an imaging device 50 having at least one optical lens 51 and a modulation device 20. The beam folding device 60 includes a beam splitter 61 and mirrors 64 and 65. The beam folding device 60 is positioned behind the lens 51 of the imaging device 50 in the beam direction. The beam splitter 61 splits the sample beam 70 into two radiation components. The first of the two radiation components passes through the modulation device 20 and illuminates the mirror 64. The intensity distribution of the sample beam 70 is modulated by means of the modulation device 20, and contrast steps 32 and 33 are applied. The contrast steps 32 and 33 are spaced apart by a distance k in the first lateral direction 31. Subsequently, the modulated sample beam 79 formed in this manner is reflected back into the beam splitter 61 by the reflector 64 of the beam folding device 60, thereby forming a first folded optical path. After passing through the beam splitter 61, the second of the two radiation components illuminates the reflector 65 and is reflected back into the beam splitter 61 by the reflector 65, thereby forming a second folded optical path. In the second folded optical path, no modulation of the intensity distribution of the sample beam 70 occurs, thus forming an unmodulated beam 78 in the second optical path. In the beam splitter 61, the two radiation components from the two folded optical paths are superimposed and guided to the detector 40 along a common propagation path having a local optical axis 11. Therefore, the intensity distribution on the detector 40 consists of an intensity distribution 83 with contrast features 92, 93 and a laterally spaced spot 98 formed by the unmodulated beam 78. The lateral spacing between the spot 98 and the intensity distribution 83 can be achieved, for example, by a slight tilt of one of the two reflectors 64, 65. Two contrast features 92 and 93 in intensity distribution 83 are formed by the propagation of the modulated sample beam 79 in the manner described above, applying contrast steps 32 and 33 to the modulated sample beam. Contrast features 92 and 93 are spaced apart by a distance a in the first lateral direction 31 on the detector 40. This distance a changes when the axial position of the beam focus 71 changes. Based on distance a or the change in distance a, the evaluation device 45 determines the axial focal position or change in the axial focal position of the beam focus 71. A third spot 98 is formed on the detector 40 by imaging the unmodulated beam 78 propagating via the second folded optical path. Therefore, the spot 98 of the unmodulated beam represents the original intensity distribution of the sample beam 70 or energy beam 77 from which the sample beam 70 can be separated. In particular, the spot 98 can also be an image of the beam focus 71. The intensity distribution and / or diameter of the beam focus 71 can therefore also be determined by the evaluation device 45 by means of the imaging scale of the imaging device 50.In order to image the image of the beam focus 71 onto the detector 40, the second folded optical path through the reflector 65 can have different, in particular, longer, optical path lengths.

[0117] The variant of the embodiment shown in Figure 8 differs from the embodiment in Figure 7 in that the second folded optical path has a variable and adjustable optical path length. For this purpose, the reflector 64 is configured to be axially movable, for example, via a straight guide rail, and coupled to the positioning device 66. With the aid of the positioning device 66, the reflector 64 can be moved to different axial positions (64, 64'). The positioning device 66 may include, for example, a plunger coil driver, thereby enabling very rapid adjustment, for example, within milliseconds. An evaluation device 45 can be configured to control the positioning device 66. The evaluation device 45 can also be configured to exchange data with the positioning device 66, for example, exchanging information about changes in the reflector position or adjustment path. Therefore, multiple (preferably at least 3, particularly preferably at least 10) reflector positions can be set one after another, and the respective intensity distributions of the light spots 98 on the detector 40 can be recorded. Based on these data, various beam parameters of the sample beam 70, such as focal spot diameter, beam divergence, and / or beam parameter products, can be determined. Therefore, the beam analysis device 10 shown here can determine the axial beam focal point position in near real-time, and measure the beam caustics (also known as the beam envelope of the sample beam 70 or energy beam 77) in almost real-time or at least within a very short time period. This also allows the beam to be measured according to the ISO 11146 standard in a very short time, for example, less than 1 second. Figure 8 shows another aspect. The modulation device 20 in the first folded optical path is here designed, in an exemplary manner, as a switchable and spatially controllable reflector. For this purpose, the modulation device 20 may include, for example, an LCD (liquid crystal display) panel with a mirror disposed at the rear, or an LCOS (liquid crystal on silicon) element. The switchable modulation device 20 is controlled by a control device 46, which can exchange data with the evaluation device 45.

[0118] Figure 9 illustrates an embodiment of the beam analysis device 10, which further includes a far-field analysis device. This far-field analyzer can be combined with any of the aforementioned beam analysis devices 10. The far-field analysis device includes a second beam splitter 62, another imaging device 67, and a second detector 42. The second beam splitter 62 is positioned behind at least one lens 51 of the imaging device 50 along the beam direction, and in front of the modulation device 20, and also in front of the beam folding device 60. Through the second beam splitter 62, the radiation component is separated from the sample beam 70 to form (possibly further) an unmodulated beam 78, which is guided onto the second detector 42 to form a beam intensity distribution 99 on the second detector 42. An additional imaging device 67, comprising at least one optical lens, or possibly a multi-lens objective, is positioned between the second beam splitter 62 and the second detector 42. The additional imaging device 67, together with the imaging device 50 and the lens 51 contained therein, forms a combined lens system. The combined lens system has a combined focal length and an image-side focal plane of the combined lens system. The second detector 42 is precisely positioned in the image-side focal plane of the combined lens system. Since the intensity distribution 99 of the unmodulated beam 78 formed on the second detector 42 is a Fourier transform of the intensity distribution of the sample beam 70, the combined lens system forms a so-called Fourier lens for the second detector 42. Therefore, the intensity distribution 99 on the second detector 42 is a so-called far-field intensity distribution, which is independent of the axial position of the beam focus 71. Therefore, based on this intensity distribution 99, the divergence angle of the sample beam 70 can be determined in particular. In other details, the embodiment corresponds to the apparatus shown in FIG. 7 and is explained in the relevant text.

[0119] Detailed description of the invention

[0120] The present invention envisions a beam analysis apparatus 10 for determining the axial position of a beam focal point 71. Here, the beam focal point 71 is either the focal point 76 of an energy beam 77 of electromagnetic radiation, or the focal point of a sample beam 70 separated from the energy beam 77. The beam analysis apparatus 10 includes a beam shaping device 12, a detector 40, and an evaluation device 45.

[0121] The beam shaping device 12 is configured to modulate the intensity distribution 81 of the energy beam 77 or a sample beam 70 separated from the energy beam 77 in a modulation plane 19 having a two-dimensional transmission function, so as to form a modulated sample beam 79 having a modulated intensity distribution 82. Here, the transmission function has at least one channel region 21 including a substantially constant first intensity transmission factor and at least one blocking region 25 including a substantially constant second intensity transmission factor. The second intensity transmission factor is at most 50% of the first intensity transmission factor. Along a first lateral direction 31, the transmission function has at least two contrast steps 32, 33 in a transitional form between the at least one blocking region 25 and the at least one channel region 21. The contrast steps 32, 33 are spaced apart from each other by a distance k along the first lateral direction 31, wherein the term "lateral" refers to a direction in a plane perpendicular to the respective local optical axis 11.

[0122] The first lateral direction 31 lies in a plane perpendicular to the local optical axis 11. Since the local optical axis 11 in the optical path is always identified by the z-axis of the local coordinate system, the first lateral direction 31 lies in the xy plane.

[0123] The beam shaping device 12 is also configured to guide the modulated sample beam 79 along the propagation path onto the detector 40 to form an intensity distribution 83 on the detector 40, which has at least two contrast features 92, 93 along a first transverse direction 31. The contrast features 92, 93 in the intensity distribution 83 on the detector 40 are formed by at least two contrast steps 32, 33 in the modulated intensity distribution 82 as the beam propagates from the modulated sample beam 79 to the detector 40. The contrast features 92, 93 are spaced apart from each other by a distance a in the first transverse direction 31, a distance particularly influenced by the distance k between the contrast steps of the transmission function.

[0124] In other words, the contrast feature 92 caused by the first of at least two contrast steps on the detector 40 and in the intensity distribution 83, and the contrast feature 93 caused by the second of at least two contrast steps on the detector 40 and in the intensity distribution 83, are at a distance a along the first lateral direction 31 in the intensity distribution 83.

[0125] The transmission function is a function that defines the (position-dependent) magnitude of the intensity transmission factor over a (lateral) two-dimensional region.

[0126] The intensity transmission factor is the ratio of the modulated radiation intensity to the unmodulated radiation intensity at the same lateral position.

[0127] The magnitude of the intensity transmission factor can, in principle, be between 0 and 1.

[0128] The modulation of the intensity distribution 81 of the beam shaping device 12 can be achieved, for example, by a modulation device 20 configured to form at least one channel region 21 and at least one blocking region 25. The channel region 21 and the blocking region 25 can each be a continuous region; however, the channel region 21 and / or the blocking region 25 can also be implemented as multiple parts separated from each other.

[0129] The channel region 21 is characterized in that the transmittance of radiation within channel regions 21 and 22 is significantly greater than the transmittance within blocking region 25. The term transmittance is understood here with respect to the intended propagation direction of the modulated sample beam 79 formed in this manner. Transmittance is specifically defined by the intensity transmission factor. The intensity transmission factor can be determined, for example, by means of radiative transmittance and / or radiative reflectance.

[0130] Specifically, the radiation transmittance (or reflectance) in channel region 21 is at least twice that in blocking region 25. Preferably, the radiation transmittance (or reflectance) in blocking region 25 is at least 10 times smaller than that in channel region 21. Particularly preferably, the radiation transmittance (or reflectance) in blocking region 25 is at least 100 times smaller than that in channel region 21.

[0131] Detector 40 includes a spatially two-dimensionally resolved optical radiation sensitive sensor configured to convert the intensity distribution 83 illuminating detector 40 into an electrical signal. Detector 40 may be a CCD camera, a CMOS camera, or a similar device. Spatially two-dimensionally resolved optical radiation sensitive sensors are typically pixel-based semiconductor sensors. Detector 40 is positioned at a distance s behind modulation plane 19 along the propagation path of the modulated sample beam 79.

[0132] Evaluation device 45 is configured to process an electrical signal from detector 40, representing an intensity distribution 83 on detector 40. Evaluation device 45 is configured to determine a distance 'a' between contrast features 92, 93 on detector 40 along a first lateral direction 31. The positions of the corresponding contrast features 92, 93 are preferably defined by the center of the gradient region and / or by the position of the average intensity value within the gradient region of the intensity distribution 83 of the corresponding contrast features 92, 93 on detector 40. Here, the gradient region is a region within the intensity distribution 83 formed by the propagation of contrast steps 32, 33 in the intensity distribution 82 after modulation device 20.

[0133] Furthermore, the evaluation device 45 is configured to determine the axial position of the beam focus 71 based on distance a, and / or to determine the change in the axial position of the beam focus 71 based on the change in distance a.

[0134] The evaluation device 45 can be implemented, for example, in the form of a software program running on a computer.

[0135] To achieve high accuracy in determining the positions of light spots 92, 93 on detector 40, it is advantageous if the profile of the transmission function between channel region 21 and blocking region 25 (that is, the transition to the formation of contrast edges 32, 33) is as steep as possible, for example, if it changes abruptly. The profiles of the corresponding contrast features 92, 93 in the intensity distribution 83 on the detector are also as narrow or steep as possible. On the other hand, sharp contrast edges promote the formation of diffraction structures, which is why it is also conceivable to advance continuously in the transition between channel region 21 and blocking region 25. If the widths of the regional portions of channel region 21 and blocking region 25 are not the same, the modulation depth of the diffraction structure can be reduced.

[0136] When the axial position of the beam focus 71 changes, the distance 'a' between the contrast features 92 and 93 on the detector 40 changes. That is, the distance 'a' has a functional relationship with the z-position of the beam focus 71. This functional relationship is influenced by and / or defined by the following geometric quantities:

[0137] a is the distance between contrast features 92 and 93 on detector 40;

[0138] a' is the distance between contrast features 92' and 93' on detector 40 when the beam focal position changes;

[0139] Δa is the change in distance between contrast features 32 and 33, Δa = a' - a;

[0140] k is the distance between contrast steps 32 and 33 in the modulation plane 19 on the first lateral direction 31;

[0141] z s The distance between the axial position of the beam focus 71 and the modulation plane 19;

[0142] z s 'is the distance between the axial position of the offset beam focus 71' and the modulation plane 19;

[0143] Δz represents the change in the position of the axial beam focal point, Δz = z s -z s ';

[0144] s is the distance between the modulation plane 19 and the sensor plane 39 of the detector 40;

[0145] e is the distance from the modulation plane 19 to the position of the imaging device 50. More precisely, if the modulation device 20 with the modulation plane 19 is located in front of the imaging device 50, it is the distance to the main plane of the imaging device 50.

[0146] d is the distance from the position of the imaging device 50, or more precisely, from the main plane of the imaging device 50 to the modulation plane 19, if the modulation device 20 having the modulation plane 19 is located behind the imaging device 50.

[0147] In practice, using the modulation plane 19 as a reference point for the distance to the beam focal position 71 is generally not very advantageous. It would be more practical if the reference point could be arbitrarily chosen or calibrated. Therefore, it is advantageous to specify a functional relationship that directly describes the change in focal position. Based on the intercept theorem and the application of known imaging equations, the following functional relationship is obtained for the ray analysis apparatus 10:

[0148] Δz = Δa c1 / (c2 + Δa c3)

[0149] The formula symbols c1, c2, and c3 are coefficients introduced to simplify the representation of the formula.

[0150] For the case where the modulation device 20 is positioned in front of the imaging device 50 (see Figure 1 or 2), the coefficients c1, c2, and c3 are given by the following formula:

[0151] c1 = z s 2

[0152] c2=k{s[1-(e / f)]+(e 2 / f)}

[0153] c3 = z s

[0154] For the case where the modulation device 20 is located behind the imaging device 50 (see Figures 6 to 9), the coefficients c1, c2, and c3 are given by the following formula:

[0155] c1 = [z s (fd)+d 2 ] 2

[0156] c2 = f 2 ks

[0157] c3=(fd)[z s (fd)+d 2 ]

[0158] The coefficients c1, c2, and c3 can be determined by setting at least three different known axial positions of the beam focus 71 and determining the corresponding change Δa in distance a. The coefficients determined in this way can be stored as calibration data in the evaluation device 45, thereby allowing the evaluation device 45 to calculate the change in focus position Δz for any change in distance Δa.

[0159] Optionally or additionally, the coefficients can be calculated directly from the set geometric distance using the formula given above and stored in the evaluation device 45.

[0160] It should be noted here that all axial distances, i.e., z s d, e, and s are all distances along the optical axis 11. Therefore, in the case of beam deflection, the distance z, if necessary, s d, e, and s are composed of segments along the local optical axis 11. It should also be noted that when the beam is partially guided through the optical material, such as when it is guided through the beam splitter cube, the corresponding partial distances must be corrected by a factor that depends on the refractive index of the optical material.

[0161] In a variation of the beam analysis device 10, the modulation device 20 is located behind the imaging device 50, that is, behind at least one optical lens 51 in the beam direction. A particularly interesting special case exists where the distance d from the principal plane of the imaging device 50 to the modulation plane 19 is equal to the focal length f of the imaging device 50. In other words, the modulation plane 19 is located at the image-side focal point of the imaging device 50. For this embodiment of the beam analysis device 10, the coefficients of the functional relationship are given by the following equation:

[0162] c1 = f 4

[0163] c2 = f 2 ks

[0164] c3 = 0

[0165] This leads to a particularly simple functional relationship with a specific feature: the change Δa in the distance a between contrast features 92 and 93 is exactly proportional to the change Δz in the position of the axial beam focal point.

[0166] Δz=Δaf 2 / (ks)

[0167] This linear relationship simplifies equipment calibration and enables high precision in determining the focal position.

[0168] In this setup, a particular advantage is that the calculation of the change in focal position Δz does not require the absolute z-position of the beam focal point (z0). s ).

[0169] This feature or arrangement can be advantageously implemented in a way that, in any case, such as when the modulation device 20 is positioned in a folded optical path, the distance between the imaging device 50 and the modulation device 20 is set. Therefore, this aspect of the invention can also be advantageously combined into an embodiment in which two folded optical paths are implemented, and in one of the folded optical paths, the modulation device is absent, thereby allowing the simultaneous recording and determination of the original beam profile of the sample beam 70 (see Figures 7 and 9). In a further combination with the axially adjustable mirrors 64 or 65 in the optical path of the unmodulated beam 78, it is also possible to record the entire beam caustic and thereby determine all geometric beam parameters (see Figure 8).

[0170] A first lateral direction 31 can be locally defined. In every case (at least substantially), it is perpendicular to the local optical axis 11. In particular, it can be defined as a direction in a plane perpendicular to the local optical axis 11, in which contrast features 92, 93 are spaced apart only along this direction by a distance k between contrast steps 32, 33.

[0171] The sample beam 70 can be the same as the energy beam 77, especially if the sample beam 70 is not formed by separating it from the energy beam.

[0172] In another embodiment of the invention, the modulation device 20 can be switched in order to change the transmission function.

[0173] Particularly preferably, the modulation device 20 can be switched. For example, the beam shaping device 12 can form an LCD screen device for forming contrast edges 32, 33. In this case, the plane of the LCD screen device can define the modulation plane 19.

[0174] To form the contrast steps 32, 33 of the beam shaping device 12, the portion of the channel region 21 and the portion of the blocking region 25 are preferably unchanged. For example, such contrast steps 32, 33 can be designed based on a fixed screen opening and / or the (space-constrained) reflective surface of the mirror. This can be achieved simply, robustly, reliably, and cost-effectively.

[0175] In a preferred embodiment, the contrast steps 32, 33 of the beam shaping device 12 are variable. For example, the variable contrast steps 32, 33 can be implemented according to the multiple pixels of the LCD screen device and / or the mechanically adjustable screen opening. The variable contrast steps 32, 33 can adapt to the current measurement conditions (e.g., light intensity, light distribution in the beam to be measured, wavelength, etc.).

[0176] The beam direction can be defined locally. Globally, the beam direction can be changed, for example, through beam folding and / or beam redirection. For instance, the local beam direction can be defined by the direction of the local Poynting vector of the sample beam 70.

[0177] In the propagation direction of radiation downstream of modulation plane 19, the local beam direction of the modulated sample beam 79 can be defined by the direction of the local Poynting vector of each modulated sample beam 79. Alternatively, the local (collective) beam direction can be defined by the Poynting vector of the virtual profile of the sample beam without modulation.

[0178] The local optical axis 11 can be defined by, for example, the local total beam direction expected during operation.

[0179] The advantage of this invention lies in the fact that the measurement principle of the beam analysis device is based on the determination of the positions of uniquely identifiable features (contrast features) on the detector. The determination of these positions and their distances from each other is largely independent of, for example, the level of a constant signal background, which can be caused by scattered light and / or sensor noise. This makes the measurement principle less prone to error than other methods, such as those based on the determination of the beam diameter, i.e., the second moment of the intensity distribution and its variations, because the determination of the second moment is more sensitive to changes in the background level.

[0180] Another significant advantage of this invention is that the determination of the axial position of the beam focal point is not affected by laser radiation or changes in the beam quality of the sample beam.

[0181] The axial position change of the beam focal point can be determined in near real-time, meaning that this determination requires only a fraction of the typical time constant of the focal position change caused by thermal focal point offset. Therefore, the present invention can also provide signals for controlling the processing of laser materials during laser processing operations.

[0182] The invention can be further modified in various ways without departing from its scope and purpose. Many configurations and possible embodiments are shown in the accompanying drawings and explained in the description of the drawings, but the invention is not limited to the embodiments shown. Various features or forms of the embodiments shown in the drawings can also be combined with each other to obtain further forms of embodiments of the invention.

[0183] For the purposes of this disclosure, the energy beam is preferably an electromagnetic radiation beam with a wavelength in the range of 0.1 micrometers to 10 micrometers, particularly preferably in the range of 0.3 micrometers to 3 micrometers, and even more particularly in the range of 0.3 micrometers to 1.5 micrometers.

[0184] For the purposes of this disclosure, the laser radiation is preferably electromagnetic radiation in the range of 0.3 micrometers to 1.5 micrometers, with a power of at least 1 lmw, and particularly preferably at least 100W.

[0185] Reference Symbol List

[0186] 10-beam analysis device

[0187] 11 optical axes, local optical axes

[0188] 12-beam shaping device

[0189] 14 Separation Device

[0190] 15 beam splitter

[0191] 16 Second beam splitter

[0192] 19 Modulation plane

[0193] 20 Modulation Device

[0194] 21-lane area

[0195] 25 Blocking Zone

[0196] 31 First lateral direction

[0197] 32, 33 Contrast Steps (Transition between the Channel Area and the Blocking Area)

[0198] 37 Second lateral direction

[0199] 39 sensor plane

[0200] 40 detectors

[0201] 42 Second Detector

[0202] 43 Absorption Device

[0203] 44 Absorbers and / or power measuring devices

[0204] 45 Evaluation Device

[0205] 46 control devices

[0206] 49. The position of the imaging device, the main plane of the imaging device

[0207] 50 imaging devices

[0208] 51 Optical Lenses

[0209] 60-beam folding device

[0210] 61 beam splitter

[0211] 62 Second beam splitter

[0212] 63 Another imaging device

[0213] 64 and 65 reflectors

[0214] 66 Positioning Device

[0215] 67 Another imaging device

[0216] 68 deflection mirror

[0217] 70 sample beams

[0218] 71 beam focal points

[0219] The beams formed at the contrast steps of 72 and 73

[0220] 76 Energy Beam Focus

[0221] 77 energy beams

[0222] 78 Unmodulated beams

[0223] 79 Modulated Sample Beam

[0224] 80 transmission function

[0225] Intensity distribution in front of the modulation device 81

[0226] Intensity distribution behind the 82 modulation device

[0227] Intensity distribution on the 83 detector

[0228] 92, 93 Contrast Characteristics

[0229] 98 Unmodulated beam spot

[0230] 99 Far-field intensity distribution

[0231] 100 Processing Optical Components

[0232] 110 fiber optic terminal

[0233] 113 Collimator

[0234] 116 Focusing Optics

[0235] 120 protective glass

Claims

1. A beam analysis device (10) for determining the axial position of a beam focal point (71), characterized in that, The beam focus (71) is the focus (76) of the energy beam (77) of electromagnetic radiation, or the focus of a sample beam (70) separated from the energy beam (77), and includes a beam shaping device (12), a detector (40), and an evaluation device (45); wherein the beam shaping device (12) includes a modulation device (20) and an imaging device (50), wherein the modulation device (20) has at least two regions of a channel region (21) and at least one region of a blocking region (25), and is configured to modulate the energy beam (77) or the sample beam (70) separated from the energy beam (77) in a modulation plane (19) having a two-dimensional transmission function. The intensity distribution (81) of the sample beam (70) separated by the beam (77) forms a modulated sample beam (79) with a modulated intensity distribution (82), wherein the transmission function has at least one channel region (21) having at least two regional portions including a substantially constant first intensity transmission factor, and at least one blocking region (25) having a substantially constant second intensity transmission factor, wherein the second intensity transmission factor is at most 50% of the first intensity transmission factor, wherein the transmission function along the first lateral direction (31) is included in the at least one blocking region. (25) and at least two contrast steps (32, 33) in a transitional form between the at least one channel region (21), wherein the contrast steps (32, 33) are spaced apart by a distance k along the first lateral direction (31), wherein the term "lateral" refers to a direction in a plane perpendicular to the corresponding local optical axis (11), the imaging device (50) is configured to guide the modulated sample beam (79) onto the detector (40) along the propagation path so as to form on the detector (40) at least two contrast features (92, 93) along the first lateral direction (31). The intensity distribution (83), wherein the contrast features (92, 93) in the intensity distribution (83) on the detector (40) are formed by the at least two contrast steps (32, 33) in the modulation intensity distribution (82) by propagating the modulation sample beam (79) to the detector (40); wherein the detector (40) - includes a spatially two-dimensionally resolved light radiation sensitive sensor, configured to convert the intensity distribution (83) illuminating the detector (40) into an electrical signal, and - is disposed at a distance s behind the modulation plane (19) along the propagation path;And, wherein the evaluation device (45) is configured to process electrical signals of the detector (40), the electrical signals representing the intensity distribution (83) on the detector (40), is configured to determine a distance a between two contrast features (92, 93) on the detector (40) along the first lateral direction (31), and is configured to determine the axial position of the beam focus (71) based on the distance a, and / or determine a change in the axial position of the beam focus (71) based on a change in the distance a.

2. The beam analysis device (10) according to claim 1, characterized in that, At each of the at least two contrast steps (32, 33), in each case a portion of the channel region (21) extends beyond width b along the first lateral direction (31), and in each case a portion of the blocking region (25) extends beyond width p along the first lateral direction (31).

3. The beam analysis device (10) according to claim 2, characterized in that, The width b of a portion of the channel region (21) is at least 1.5 times the width p of a portion of the blocking region (25).

4. The beam analysis device (10) according to claim 2, characterized in that, A portion of the channel region (21) and a portion of the blocking region (25) at the contrast steps (32, 33) extend beyond a width h in a second lateral direction (37), which is perpendicular to the first lateral direction (31).

5. The beam analysis device (10) according to claim 4, characterized in that, The width h is at least twice the width p.

6. The beam analysis apparatus (10) according to claim 1 or 2, characterized in that, The contrast steps (32, 33) are designed as lines whose tangents at the intersection with the first lateral direction (31) are perpendicular to the first lateral direction (31).

7. The beam analysis apparatus (10) according to claim 1 or 2, characterized in that, The contrast steps (32, 33) are designed as straight lines arranged at right angles to the first lateral direction (31).

8. The beam analysis device (10) according to claim 1, characterized in that, Includes a separation device (14), wherein the separation device (14) includes a beam splitter (15) for separating the sample beam (70) from the energy beam (77).

9. The beam analysis device (10) according to claim 8, characterized in that, The beam splitter (15) is a beam splitter device configured to split the energy beam (77) into sample beams (70) from radiation components in the range of 0.01% to 5% by reflection and / or transmission.

10. The beam analysis apparatus (10) according to claim 1 or 2, characterized in that, The imaging device (50) has at least one optical lens (51).

11. The beam analysis apparatus (10) according to claim 1 or 2, characterized in that, The modulation plane (19) is located at the image-side focal point of the imaging device (50).

12. The beam analysis apparatus (10) according to claim 1 or 2, characterized in that, The evaluation device (45) is configured to determine the axial position of the beam focus (71) based on the distance a between the contrast features (92, 93) by means of a calculation rule that is linear in at least some parts, and / or to determine the change in the axial position of the beam focus (71) based on the change in the distance a between the contrast features (92, 93).

13. The beam analysis apparatus (10) according to claim 1 or 2, characterized in that, The device includes a beam folding device (60), which includes a beam splitter (61) and at least one reflector (64) and is disposed in the optical path in front of the detector (40). The at least one reflector (64) is configured to reflect radiation components leaving the beam splitter (61) back into the beam splitter (61) in such a way as to form a first folded optical path. The modulation plane (19) is disposed in the optical path in front of the beam folding device (60) or in the first folded optical path.

14. The beam analysis apparatus (10) according to claim 13, characterized in that, The beam folding device (60) further includes at least one second mirror (65), wherein the at least one second mirror (65) is configured to reflect another radiation component leaving the beam splitter (61) back into the beam splitter (61) in such a way as to form a second folded optical path.

15. The beam analysis apparatus (10) according to claim 14, characterized in that, The modulation plane (19) of the beam shaping device (12) is disposed in the first folded optical path, wherein no modulation is configured in the second folded optical path to guide the radiation component of the sample beam (70) or the energy beam (77) as an unmodulated beam (78) onto the detector (40), and wherein the evaluation device (45) is configured to determine the beam diameter and / or beam profile based on the intensity distribution of the spot (98) of the unmodulated beam (78) on the detector (40).

16. The beam analysis apparatus (10) according to claim 15, characterized in that, The at least one reflector (65) is configured to be axially movable in the second folded optical path, and the position of the at least one reflector (65) can be adjusted by the positioning device (66).

17. The beam analysis apparatus (10) according to claim 1 or 2, characterized in that, The evaluation device (45) is further configured to determine the lateral position of the entire intensity distribution (83) on the detector (40), and is configured to calculate the lateral position of the beam focus (71) of the sample beam (70) based on the lateral position of the entire intensity distribution (83), and / or calculate the change in the lateral position of the beam focus (71) of the sample beam (70) based on the change in the lateral position of the entire intensity distribution (83).

18. The beam analysis apparatus (10) according to claim 10, characterized in that, It also includes a beam splitter (62) for separating the sample beam (70), another imaging device having at least one optical lens, and a second detector (42), wherein the beam splitter (62) is disposed in the optical path in front of the modulation plane (19), wherein the beam splitter (62) is disposed between the optical lens (51) of the imaging device (50) and the modulation plane, and wherein the other imaging device is disposed between the beam splitter (62) and the second detector (42) for imaging a magnified spot (98) or a magnified image of the beam focus (71) onto the second detector (42).

19. The beam analysis apparatus (10) according to claim 18, characterized in that, The evaluation device (45) is configured to process the electrical signal generated by the second detector (42), and wherein the evaluation device (45) is configured to determine the beam diameter and / or focal spot diameter based on the intensity distribution on the second detector (42).

20. The beam analysis apparatus (10) according to claim 10, characterized in that, It also includes a beam splitter (62) for separating the sample beam (70), another imaging device (67) having at least one optical lens, and a second detector (42), wherein the beam splitter (62) is disposed in the optical path in front of the modulation plane (19), wherein the beam splitter (62) is disposed between the optical lens (51) of the imaging device (50) and the modulation plane (19), wherein the other imaging device (67) is disposed between the beam splitter (62) and the second detector (42), wherein the imaging device (50) and the other imaging device (67) together form a combined lens system having an image-side focal plane, and wherein the second detector (42) is disposed in the image-side focal plane of the combined lens system.

21. The beam analysis apparatus (10) according to claim 20, characterized in that, The evaluation device (45) is configured to process the electrical signal generated by the second detector (42), and wherein the evaluation device (45) is configured to determine the divergence angle based on the intensity distribution on the second detector (42).

22. A system, characterized in that, The device includes a beam analysis apparatus (10) according to any one of the preceding claims, and a processing optics for guiding and focusing the energy beam (77), wherein the processing optics includes a separation device (14) for separating the sample beam (70) from the energy beam (77), and wherein the beam analysis apparatus (10) can be connected to the processing optics to receive the separated sample beam (70).

23. A method for determining the axial position of a beam focal point (71), characterized in that, The beam focus (71) is the focus (76) of the energy beam (77) of electromagnetic radiation, or the focus of a sample beam (70) separated from the energy beam (77), comprising the following steps: - modulating the intensity distribution (81) of the energy beam (77) or the sample beam (70) separated from the energy beam (77) in a modulation plane (19) having a two-dimensional transmission function, thereby forming a modulated sample beam (79) having a modulation intensity distribution (82), wherein the transmission function has at least one channel region (21) having at least two regional portions including a substantially constant first intensity transmission factor and including a substantially constant first intensity transmission factor. At least one blocking region (25) of a constant second intensity transmission factor, wherein the second intensity transmission factor is at most 50% of the first intensity transmission factor, wherein the transmission function along the first lateral direction (31) includes at least two contrast steps (32, 33) in a transitional form from the at least one blocking region (25) to the at least one channel region (21), wherein the contrast steps (32, 33) are spaced apart from each other by a distance k along the first lateral direction (31), wherein the term "lateral" refers to a direction in a plane perpendicular to the corresponding local optical axis (11), - to the modulated sample beam ( 79) Guided to detector (40), which is positioned at a distance s behind the modulation plane (19) along the propagation path of the modulated sample beam (79) so as to form an intensity distribution (83) on the detector (40) having at least two contrast features (92, 93) along the first lateral direction (31), wherein the contrast features (92, 93) in the intensity distribution (83) on the detector (40) are formed by at least two contrast steps (32, 33) in the modulation intensity distribution (82) by the propagation of the modulated sample beam (79) to the detector. The detector (40) is formed by: - ​​converting the intensity distribution (83) irradiated on the detector (40) into an electrical signal by a spatially two-dimensionally resolved light radiation sensitive sensor of the detector (40); - processing the electrical signal of the detector (40) that represents the intensity distribution (83) on the detector (40); - determining the distance a between the contrast features (92, 93) along the first lateral direction (31); - determining the axial position of the beam focus (71) based on the distance a, or determining the change in the axial position of the beam focus (71) based on the change in the distance a.

24. The method according to claim 23, characterized in that, This includes separating the sample beam (70) from the energy beam (77).

25. The method according to claim 24, characterized in that, Through reflection and / or transmission, the radiation components of the energy beam (77) in the range of 0.01% to 5% are separated as the sample beam (70).

26. The method according to claim 25, characterized in that, The modulated sample beam (79) is directed onto the detector (40) by an imaging device (50) having at least one optical lens (51).

27. The method according to claim 26, characterized in that, The modulation of the intensity distribution (81) occurs at the image-side focal point of the imaging device (50).

28. The method according to claim 23 or 24, characterized in that, The axial position of the beam focus (71) is determined based on the distance a between the contrast features (92, 93) using a calculation rule that is at least linear in some parts, or the change in the axial position of the beam focus (71) is determined based on the change in the distance a between the contrast features (92, 93).

29. The method according to claim 26, characterized in that, By means of a beam folding device (60), which includes a beam splitter (61) and at least one reflector (64) and is disposed in the optical path in front of the detector (40), a first folded optical path is formed by reflecting the radiation component leaving the beam splitter (61) back into the beam splitter (61) at the at least one reflector (64), and wherein the modulation of the intensity distribution (81) in the optical path occurs in front of the beam folding device (60) or in the first folded optical path.

30. The method according to claim 29, characterized in that, The beam folding device (60), which additionally includes at least one second reflector (65), forms a second folded optical path by reflecting another radiation component leaving the beam splitter (61) back into the beam splitter (61) at the at least one second reflector (65).

31. The method according to claim 30, characterized in that, The modulation of the intensity distribution (81) occurs in the first folded optical path, wherein no modulation of the intensity distribution occurs in the second folded optical path, the radiating portion is guided onto the detector (40) as an unmodulated beam (78), and wherein the beam diameter and / or beam profile are determined based on the intensity distribution of the spot (98) of the unmodulated beam (78) on the detector (40).

32. The method according to claim 31, characterized in that, The axial position of the at least one reflector (64) in the second optical path is changed by the positioning device (66), and for at least three different positions of the at least one reflector (64), in each case, the intensity distribution of the spot (98) of the unmodulated beam (78) is recorded on the detector (40), and wherein at least one beam parameter of the sample beam (70) is determined based on the recorded intensity distribution.

33. The method according to claim 23 or 24, characterized in that, This includes determining the lateral position of the entire intensity distribution (83) on the detector (40), calculating the lateral position of the beam focus (71) of the sample beam (70) based on the lateral position of the entire intensity distribution (83), or calculating the change in the lateral position of the beam focus (71) of the sample beam (70) based on the change in the lateral position of the entire intensity distribution (83).

34. The method according to any one of claims 26, 27, 29, 30, 31, and 32, characterized in that, Includes the following steps: - The sample beam (70) is separated by a beam splitter (62) disposed in the optical path behind the optical lens (51) and in front of the modulation plane (19) of the imaging device (50). - The separated sample beam is imaged onto a second detector (42) by another imaging device having at least one optical lens disposed between the beam splitter (62) and the second detector (42) to form an enlarged spot (98) or a magnified image of the beam focus (71) on the second detector (42). - The beam diameter or focal spot diameter is determined according to the intensity distribution on the second detector (42).

35. The method according to any one of claims 26, 27, 29, 30, 31, and 32, characterized in that, Includes the following steps: - The sample beam (70) is separated by a beam splitter (62) disposed in the optical path behind the optical lens (51) and in front of the modulation plane (19) of the imaging device (50). - The separated sample beam is guided to a second detector (42) by another imaging device (67), wherein at least one optical lens is disposed between the beam splitter (62) and the second detector (42) to form a far-field beam distribution (99) on the second detector (42), wherein the imaging device (50) and the other imaging device (67) together form a combined lens system having an image-side focal plane, and wherein the second detector (42) is disposed in the image-side focal plane of the combined lens system, and - the far-field beam diameter or divergence angle is determined according to the intensity distribution on the second detector (42).

36. The method according to claim 23 or 24, characterized in that, The energy beam (77) is focused through processing.

37. The method according to claim 36, characterized in that, The determined axial position of the beam focus (71), or the change in the determined axial position of the beam focus (71), is used to control the laser processing operation.

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