JP2024061609A - Device and method for optical coherence tomography in laser material processing - Patents.com - Google Patents

Abstract

To provide a device for monitoring a process in laser material processing, comprising a laser generating a light beam, where the light beam may impinge on a lens matrix positioned between a light source and a beam splitter.SOLUTION: The lens matrix may comprise microlenses operable to generate a matrix of light beams from an impinging light beam. Part of the matrix of light beams may be directed to a mirror in a reference arm, and part may be directed to an unknown surface in a measuring arm. The reflection of these beams may be used to generate an interference signal to be evaluated.SELECTED DRAWING: Figure 1

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims priority to and the benefit of German patent application DE 10 1022 003 907.9, filed on Oct. 21, 2022 in the Deutsches Patent-und Markenamt. The above-mentioned application is incorporated herein by reference.

[0002] This disclosure relates to devices and methods for optical coherence tomography in laser material processing processes.

[0003] Aspects of the present disclosure relate to devices and methods for optical coherence tomography in laser material processing processes. Various challenges may exist with conventional solutions for optical coherence tomography in laser material processing processes. In this regard, conventional systems and methods for optical coherence tomography may be expensive, cumbersome, and/or inefficient.

[0004] Limitations and drawbacks of conventional systems and methods will become apparent to those skilled in the art through a comparison of such approaches with certain aspects of the present methods and systems described in the remainder of this disclosure with reference to the drawings.

[0006] A device and method for optical coherence tomography is shown in and/or described in connection with at least one of the figures, and more fully described in the claims.

[0007] These and other advantages, aspects, and novel features of the present disclosure, as well as details of illustrated embodiments thereof, will become more fully understood from the following description and drawings.
[0008] The various features and advantages of the present disclosure may be more readily understood by reference to the following detailed description considered in conjunction with the accompanying drawings, in which like reference characters refer to like structural elements and in which:

[0009] FIG. 1 illustrates a setup for OCT measurements. [0010] FIG. 1 illustrates a setup for measurements using OCT.

[0011] The following description provides various examples of semiconductor devices and methods of manufacturing semiconductor devices. Such examples are non-limiting, and the scope of the appended claims should not be limited to the specific examples disclosed. In the following description, the terms "example" and "for example" are non-limiting.

[0012] The figures show schematic aspects of structures, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the present disclosure. In addition, elements in the figures may not be drawn to scale. For example, the dimensions of some elements in the figures may be exaggerated relative to other elements to help improve understanding of the examples described in the present disclosure. The same reference numbers in different figures represent the same elements.

[0013] The term "or" means any one or more of the items in a list linked by "or". As an example, "x or y" means any element of the 3-element set {(x), (y), (x,y)}. As another example, "x, y, or z" means any element of the 7-element set {(x), (y), (z), (x,y), (x,z), (y,z), (x,y,z)}.

[0014] The terms "comprise," "include," "have," and/or "have" are "non-exclusive" terms and specify the presence of stated features but do not exclude the presence or addition of one or more other features.

[0015] Terms such as "first," "second," and the like may be used herein to describe various elements, and these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Thus, for example, a first element discussed in this disclosure could be referred to as a second element without departing from the teachings of this disclosure.

[0016] Unless otherwise specified, the term "coupled" may be used to describe two elements that are in direct contact with each other or two elements that are indirectly connected by one or more other elements. For example, if element A is coupled to element B, element A may be in direct contact with element B or indirectly connected to element B by an intervening element C. Similarly, the terms "above" or "on" may be used to describe two elements that are in direct contact with each other or two elements that are indirectly connected by one or more other elements.

[0017] Optical coherence tomography (OCT) is a technique that can be used for high-resolution cross-sectional imaging. OCT uses light and can be used, for example, to obtain cross-sectional images of tissue structures at the micrometer scale in situ and in real time. The use of OCT combined with catheters and endoscopes can enable high-resolution intraluminal imaging of organ systems.

[0018] OCT can function as a type of optical biopsy and can be a powerful imaging technique for medical diagnostics, for example for use in ophthalmology.
[0019] OCT may also be used for material processing processes. For example, an OCT configuration may use a single low-coherence light source and detector in combination with a deflecting mirror. This technique may generate a single "pixel" swept across a field that may be of interest for process monitoring. However, in some instances, the speed and quality of the measurement data may be limited as advanced optics and electronics may be required for data acquisition and processing. According to various embodiments of the present invention, monitoring of material processing processes using OCT may be improved.

[0020] For example, micro-optical elements can be arranged in the optical path of the OCT between the laser source and the beam splitter such that an M×N matrix of independent sub-elements corresponding to the number of micro-optical elements can be used for measurements instead of one laser source corresponding to, for example, one pixel.

[0021] The sub-elements, in the sense of light beams or pixels, can be combined in a kind of matrix, each of which can be controlled separately. Light can be projected onto the surface to be measured and the reflected light can be collected. The aforementioned matrix can be understood as a grid of many lenslets acting individually. These can be arranged in rows or lines as may be required by the particular application.

[0022] The use of such a matrix may allow M×N measurement points to be taken as snapshots in the sense of capturing an instantaneous state. This may be particularly beneficial for processes that are continuously changing their state, such as the melt zone in a laser welding process.

[0023] Although the size of individual pixels in the matrix may be technically limited, it may also be possible to generate scan programs according to requirements, since individual pixels can be controlled separately or grouped together as needed. One of these scan programs may be a kind of "flash lidar" for the melt pool, i.e. a "photo" that may contain substantially all individual pixels instead of the results of many scans over the entire field of view. This may increase the quality of the results and may result in better quality assurance, for example, when welding critical paths for parts of batteries for electric vehicles.

[0024] Moreover, according to various embodiments of the present invention, a camera may be used to record such an M x N matrix of interference signals.
[0025] Figure 1 shows an exemplary configuration for OCT measurements. A light beam 2 may be generated in a light source 1 with low coherence and may impinge on a beam splitter 5. From the beam splitter 5, an unknown surface 20 of a sample may be illuminated in a measurement arm 75, and the light may be reflected by the unknown surface 20 onto the beam splitter 5. The light transmitted through the beam splitter 5 may hit a mirror 10 in a reference arm 50 and may be reflected back by the mirror 10. The reflected sample beam 76 and reference beam 51 may then be combined in the beam splitter 5 and may interfere when the difference in the paths followed by the two beams 76, 51 may be less than the coherence length. The interference signal 85 may be recorded by a detector 15 and then evaluated. For evaluation, the detector 15 may be coupled to an evaluation unit (not shown). This may be, for example, a data processing unit.

[0026] Moving a mirror in reference arm 50 (double arrow) along the beam axis of light beam 2 emitted by light source 1 while simultaneously measuring interference signal 85 may allow axial scanning of unknown surface 20 of the sample.

[0027] FIG. 2 shows an exemplary configuration according to various embodiments of the present invention. A lens matrix 4 comprising an M×N matrix of microlenses may be disposed between a light source 1 and a beam splitter 5. Thus, multiple light beams 2 may impinge on the beam splitter 5, and thus multiple reference beams 51 may impinge on the mirror 10 in the reference arm 50, and multiple sample beams 76 may impinge on the unknown surface 20 of the sample in the measurement arm 75.

[0028] According to various embodiments of the present invention, infrared light may be emitted from a light source, so for example a laser diode may be used as the light source.
[0029] Polygons may be used for the microlenses, i.e. square, rectangular, hexagonal, octagonal, etc. shapes may be provided, so that the microlenses may be arranged with substantially no space between them. In relation to the optical properties of the microlenses, the light rays emerging from the microlenses may be substantially parallel, so that a matrix containing M x N light rays or light spots may be obtained as a result.

[0030] The camera 25 can be used as a sensor instead of a small detector for one beam. The multiple beams 51, 76 from the reference arm 50 and measurement arm 75 from the M×N matrix can be evaluated accordingly in the interference signal 85, which can further correspond to multiple M×N beams from the M×N matrix.

[0031] Such configurations according to various embodiments of the present invention may result in not just one point that can be viewed and/or evaluated, but an area that includes multiple pixels M×N corresponding to a matrix.

[0032] In laser material processing processes, the melt pool may change continuously during the ongoing operating process. Using the above-mentioned configuration, it may be possible to continuously monitor the continuously changing surface of the melt pool or its transitional front, respectively. According to various embodiments of the invention, for this purpose, so-called LiDAR (Light Detection and Ranging) sensors may be used as cameras. Black and white images may be sufficient for the camera, but cameras for color images may also be used. The frame rate may preferably be greater than 10 fps (frames per second).

[0033] Methods and uses for monitoring and controlling processes in laser material processing processes can be realized according to various embodiments of the present invention. In addition to a pictorial representation of the results of the evaluation of the interference signal, such results may be used to control or optimize the laser material processing process. Individual pixels in the matrix can be individually controlled. This means that they can be moved individually in the X and Y dimensions, if desired. For this purpose, for example, microlenses can be moved accordingly, which can change the position of the light beam and therefore further the position of the associated pixel in the interference signal.

[0034] Thus, the methods according to various embodiments of the present invention can be used to control the process of a laser material processing process, and thus ultimately control it. In this case, it can be a matter of control as well as a matter of quality assurance.

[0035] Other aspects, features, and advantages of the present invention will be readily apparent from the following detailed description, which briefly describes preferred embodiments and implementations. The present invention may be further realized in other and different embodiments, and its various details may be modified in various obvious ways without departing from the teachings and scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative and not restrictive. Additional objects and advantages of the present invention will be set forth in part in the following description, and in part will be apparent from the description, or may be inferred from the embodiments of the present invention.

[0036] Although the present disclosure includes references to specific examples, it will be understood by those skilled in the art that various modifications may be made and equivalents may be substituted without departing from the scope of the present disclosure. Additionally, modifications may be made to the disclosed examples without departing from the scope of the present disclosure. Accordingly, it is intended that the present disclosure is not limited to the disclosed examples, and that the present disclosure includes all examples that fall within the scope of the appended claims.

REFERENCE NUMERALS 1 Light source 2 Light beam 4 Lens matrix 5 Beam splitter 10 Mirror 15 Detector 20 Unknown surface 25 Camera 50 Reference arm 51 Reference beam 51 Beam 75 Measurement arm 76 Sample beam 76 Beam 85 Interference signal

Claims (15)

a laser generating a light beam, the light beam impinging on a lens matrix located between the light source and a beam splitter;
the lens matrix including M×N microlenses operable to generate a matrix of M×N light beams from the impinging light beams;
a beam splitter that directs a first portion of the M×N light beam onto a mirror in a reference arm and a second portion of the M×N light beam onto an unknown surface in a measurement arm, the first portion of the M×N light beam being reflected back to the beam splitter from the mirror and the second portion of the M×N light beam being reflected from the unknown surface back to the beam splitter;
the beam splitter operable to generate an interference signal by interfering the reflected first portion of the M×N optical beam with the reflected second portion of the M×N optical beam;
and a detector for receiving the interference signal. The device of claim 1, wherein the detector is a camera. The device of claim 1, wherein the detector is a black and white camera or a color camera. The device of claim 1, wherein the microlenses are polygonal such that the microlenses are disposed with substantially no spaces between them. The device of claim 1, wherein the mirror is coupled to a drive for moving the mirror in the direction of the beam path of the light beam. The device of claim 1, further comprising a unit for evaluating the detected interference signal, the detector being connected to the unit for evaluating data. 1. A method for monitoring an unknown surface in a laser material processing process, comprising:
generating a light beam using a laser, the light beam impinging on a lens matrix located between the light source and a beam splitter;
generating a matrix of M×N light beams from the impinging light beams using the lens matrix including M×N microlenses;
using the beam splitter to direct a first portion of the M×N light beam onto a mirror in a reference arm and a second portion of the M×N light beam onto an unknown surface in a measurement arm, where the first portion of the M×N light beam is reflected back from the mirror to the beam splitter and the second portion of the M×N light beam is reflected from the unknown surface back to the beam splitter;
generating an interference signal by interfering the reflected first portion of the M×N optical beam with the reflected second portion of the M×N optical beam at the beam splitter;
and receiving the interference signal at a detector. The method of claim 7, wherein the step of receiving the interference signal is performed by a camera. The method of claim 7, wherein the received interference signal is evaluated by an evaluation unit connected to the detector. The method of claim 9, wherein the results of the evaluation are shown as an image on a display. The method of claim 7, wherein the matrix of MxN light beams, and thus the matrix of MxN pixels of the interference signal, can be individually controlled. The method of claim 11, wherein the individually controlled light beams and pixels may include movement in the X or Y direction. The method of claim 9, wherein the evaluation is used to control a process in a laser material processing process. The method of claim 7, wherein the laser material processing process is a welding process or a material cutting process. 12. A method according to claim 11 for monitoring a joining process when joining work pieces by means of a laser beam.