Method and system for materials inspection

Abstract

Methods and systems for materials inspection are configured to perform optical coherence tomography (OCT) on a material. A power regulating device (21) in a reference arm (20) is controlled by a control logic (40). Generated OCT image data is evaluated in a computer-aided manner in order to identify and / or classify defects in the material.

Description

[0001] METHOD AND SYSTEM FOR MATERIAL TESTING

[0002] TECHNICAL AREA

[0003] The invention relates to methods and systems for material testing. In particular, the invention relates to methods and systems with which near-surface defects of a material can be detected and optionally classified.

[0004] BACKGROUND

[0005] Subsurface defects, also known as SSDs ("subsurface damage"), are structural impairments located just below the surface of a material. These defects can significantly affect material properties. Therefore, their investigation is of great importance in many fields, such as the semiconductor industry, optical materials, and precision mechanics.

[0006] In industrial settings for materials, i.e., non-biological components, conventional solid surface detection (SSD) methods include, for example, wedge polishing and etching, X-ray diffraction, or crack testing with penetrant varnishes and UV illumination. All these methods have the disadvantage of contaminating surfaces, altering material properties, and / or even destroying components.

[0007] Therefore, there remains a need for improved methods and systems for materials testing.

[0008] German patent DE 10 2008 020194 A1 discloses a method for detecting near-surface defects in a test specimen consisting at least partially of ferromagnetic material, in which a test volume of the specimen is magnetized and scanned to detect magnetic stray fields caused by defects. This method is non-destructive, but its applicability is limited. In particular, it is not suitable for non-ferromagnetic materials such as glass, optical plastics, or workpieces made from them.

[0009] WO 2005 / 085832 A2 discloses a device and a method for detecting near-surface defects in electrically conductive materials, wherein low-frequency eddy currents are generated in the material and the magnetic field altered by the defects is detected by a receiving device. This method is non-destructive, but its applicability is limited. In particular, it is not suitable for insulating materials such as glass, optical plastics, or workpieces made from them. There is therefore still a need in the field for methods and systems designed for the non-destructive testing of materials. In particular, there is a need for such methods and systems with which at least optical materials, for example, components for optical systems made of glass and / or an optical plastic, can be tested.

[0010] SUMMARY

[0011] It is an object of the present invention to provide methods and systems designed for the non-destructive testing of materials. In particular, it is an object to provide methods and systems designed for testing at least optical materials, for example, components for optical systems made of glass and / or an optical polymer. It is also an object to provide methods and systems with which measurements on a material can be performed so non-destructively that near-surface defects can be reliably detected and optionally classified compared to conventional techniques.

[0012] According to the invention, a method and a system are specified as defined in the independent claims. The dependent claims define preferred and advantageous embodiments.

[0013] According to one aspect, the invention relates to a method for material testing, which comprises: performing optical coherence tomography (OCT) on a material using an OCT array to generate OCT image data; and evaluating the OCT image data. The OCT array comprises: a measuring arm configured for scanning the material; a reference arm; a radiation source for generating coherent radiation for the measuring arm and the reference arm; and a detector for detecting a coherent superposition of the coherent radiation from the reference arm and the measuring arm. The reference arm includes at least one power control device, which is controlled by a control logic during the acquisition of the OCT image data.

[0014] Alternatively or in addition to the power regulation device in the reference arm, the measuring arm can have at least one further power regulation device and / or one further shutdown device that is controllable by the control logic.

[0015] This method achieves various technical effects. By using an OCT array, the method can be applied to the material analysis of optical materials. The OCT array can generate 2D or 3D OCT image data, enabling the identification and, optionally, the classification of near-surface defects within the material. By controlling the power regulation unit in the reference arm of the OCT array, which can be executed automatically by the control logic, the OCT imaging can be performed in such a way that the reliable identification and, optionally, classification of near-surface defects within the material is possible.

[0016] The OCT arrangement can include a first shutdown device (e.g., a first shutter) in the reference arm and / or a second shutdown device (e.g., a second shutter) in the measuring arm.

[0017] This allows for complete blockage of radiation in the reference arm and / or the measurement arm. This is particularly useful for performing one or more measurements where at least one arm is switched off, enabling the acquisition and / or evaluation of the OCT image data based on measurements taken with at least one arm switched off. This results in higher measurement quality.

[0018] The method may include: evaluating signals detected by the detector during a shutdown of the reference arm by the first shutdown device and / or during a shutdown of the measuring arm by the second shutdown device in order to detect system errors and automatically correcting the system errors.

[0019] This allows system errors to be identified and corrected. This cannot be achieved through performance adjustments (as described in the research report).

[0020] The at least one power control device and / or a shutdown device (for example, a shutter) in the reference arm can be configured to selectively and controllably switch off the reference arm. The at least one power control device can be configured as a shutdown device or can include a shutdown device that, under the control of the control logic, enables a complete shutdown (e.g., blocking of the light path) of the reference arm and / or that can assume one of two binary states ("on" and "off") under the control of the control logic. The shutdown device can be a first shutter or can include a first shutter.

[0021] This will enable various measures to improve the examination of the material using the OCT setup, for example, one, several, or all of the following: measuring an autocorrelation signal of the material and subsequently using the autocorrelation signal to improve measurement quality; adjusting, aligning, and / or maximizing a measurement signal during OCT image acquisition; performing a dark current measurement for the detector.

[0022] The additional shutdown device (for example, another shutter) can be configured to selectively and controllably switch off the measuring arm. The additional shutdown device can be configured, under the control of the control logic, to allow a complete shutdown (e.g., blocking of the light path) of the measuring arm and / or to assume one of two binary states ("on" and "off") under the control of the control logic. The additional shutdown device can be a second shutter or can include a second shutter.

[0023] This will enable various measures to improve the examination of the material using the OCT setup, for example one, several or all of the following: adjustment, alignment and / or maximization of a reference signal during OCT image acquisition; measurement and / or at least partial correction of a uniform light component.

[0024] The method can include autocorrelation signal acquisition for detecting an autocorrelation signal of the material, wherein the autocorrelation signal acquisition can include: controlling the power regulation device and / or the shutdown device for autocorrelation signal acquisition (for example, to switch off the reference arm). To switch off the reference arm, the power regulation device and / or the shutdown device can be controlled by the control logic such that radiation in the reference arm is blocked in order to perform the autocorrelation signal acquisition.

[0025] This allows the autocorrelation signal of the material to be acquired by the OCT array. The autocorrelation signal can then be used by the control logic to control the power regulation device during OCT image data acquisition, thereby improving the quality of the OCT image data.

[0026] The procedure can include: controlling the power regulation device during the acquisition of OCT image data through the control logic based on the autocorrelation signal.

[0027] This allows the autocorrelation signal to be used by the control logic when controlling the power regulation device during the acquisition of OCT image data, in order to improve the quality of the OCT image data.

[0028] The control logic can control at least one power regulation device based on an intensity variance of an interference pattern detected by the detector.

[0029] The OCT setup is designed so that the intensity variance is automatically optimized by controlling the power regulation device to achieve good OCT results. This enables the identification and / or classification of near-surface defects within the material with higher accuracy.

[0030] The control logic can control at least one power regulation device based on a uniform light component and a mixed light component of an interference pattern detected by the detector.

[0031] The OCT setup is designed to automatically optimize OCT to achieve good results. This enables the identification and / or classification of near-surface defects within the material with higher accuracy.

[0032] The control logic can control at least one power regulation device based on the intensity variance and based on detector properties, in particular based on a dynamic range of the detector.

[0033] The OCT setup is designed so that the intensity variance is automatically optimized by controlling the power regulation device, taking the detector characteristics into account, to achieve good OCT results. This enables the identification and / or classification of near-surface defects within the material with higher accuracy.

[0034] The control logic can control at least one power regulation device and one output power of the radiation source in such a way that the intensity variance largely or completely utilizes the dynamic range of the detector.

[0035] The OCT setup is designed so that the control logic automatically adjusts the power regulation device to utilize the detector's dynamic range to a large extent or completely. This enables the identification and / or classification of near-surface defects within the material with higher accuracy. Since the OCT setup is used for measurements on a material that is not a biological object, physiological factors do not need to be considered when controlling the radiation source's output power. In particular, the control logic can be configured to increase the radiation source's output power to a level that is unacceptable for biological and especially medical applications, but is suitable for materials testing.

[0036] At least one power control device can be configured to attenuate optical radiation power in the reference arm stepwise in several stages or continuously.

[0037] This allows the control logic to continuously or stepwise adjust the power regulation device, and optionally the output power of the radiation source, in several stages to achieve a desired intensity variance at the detector. The control logic can be configured to control the power regulation device, and optionally the output power of the radiation source, depending on an output signal obtained from the material under test or output data from the detector. Once the intensity variance meets a desired quality criterion, for example, by at least largely or completely covering the dynamic range of the detector, OCT imaging can be performed.

[0038] The method can include adjustment, alignment, and / or maximization of a measurement signal in the measuring arm, comprising: controlling the at least one power control device and / or a shutdown device in the control arm by the control logic in order to selectively shut down the reference arm for the adjustment, alignment, and / or maximization of the measurement signal. During the acquisition of the OCT image data, the control logic can control the at least one power control device depending on signals acquired with the reference arm switched off.

[0039] This can improve the measurement quality.

[0040] The method can alternatively or additionally include adjustment, alignment, and / or maximization of a reference signal in the reference arm, comprising: controlling the further shutdown device in the measuring arm by the control logic in order to selectively shut down the measuring arm for the adjustment, alignment, and / or maximization of the reference signal. During the acquisition of the OCT image data, the control logic can control at least one power regulation device depending on signals acquired when the measuring arm is switched off.

[0041] This can improve the measurement quality.

[0042] The method can alternatively or additionally include a correction of the static light component, comprising: controlling the further switching-off device in the measuring arm by the control logic in order to selectively switch off the measuring arm. During the acquisition of the OCT image data, the control logic can control at least one power control device depending on signals acquired when the measuring arm is switched off, in order to perform at least a partial correction of the static light component.

[0043] This can improve the measurement quality.

[0044] The method can alternatively or additionally include dark current measurement for the detector, comprising: controlling the switch-off device in the reference arm by the control logic to selectively switch off the reference arm, and controlling the further switch-off device in the measuring arm by the control logic to selectively switch off the measuring arm. The OCT arrangement can utilize the dark current measurement when acquiring the OCT image data.

[0045] This can improve the measurement quality.

[0046] The process can feature automated, complete optical dispersion correction, allowing the use of different lenses without manual reconfiguration.

[0047] This allows for further automation.

[0048] The OCT setup can include multiple lenses that can be selectively positioned (e.g., automatically by a positioning system) within a beam path of the measuring arm. The method incorporates automatic dispersion correction, which depends on which lens is positioned within the beam path of the measuring arm. The dispersion correction can be determined automatically, for example, by measurements taken with the reference arm switched off.

[0049] This allows for further automation by enabling the automatic positioning of different lenses within the beam path of the measuring arm. This is particularly useful for examining optical materials, for example, for detecting and / or classifying near-surface defects.

[0050] At least one power control device can include an iris diaphragm and an diaphragm drive for adjusting the iris diaphragm. The control logic can control the diaphragm drive.

[0051] This enables automated adjustment of the optical attenuation in the reference arm under the control of the control logic. Compared to conventional techniques, this allows OCT results that enable the identification and / or classification of near-surface defects within the material non-destructively and with higher accuracy.

[0052] The reference arm may include beam expansion optics that expand a beam of coherent radiation generated by the radiation source in the reference arm before it strikes the iris aperture.

[0053] This allows for finer adjustment of the optical attenuation in the reference arm under the control of the control logic. Compared to conventional techniques, this enables OCT results that allow for the non-destructive identification and / or classification of near-surface defects within the material with higher accuracy.

[0054] The OCT may be polarization-sensitive. The OCT setup may include a polarizer positioned between the radiation source and the reference arm, as well as the measurement arm.

[0055] This establishes the procedure for detecting polarization-dependent effects. This offers investigation possibilities with increased accuracy, for example, with regard to the detection of polarization-dependent effects that may be caused by a defect.

[0056] At least one power regulation device can be set up for light polarization-based power regulation in the reference arm.

[0057] This allows the polarization of the coherent radiation used for polarization-sensitive OCT to be efficiently used for power regulation in the reference arm as well. This is particularly advantageous when the OCT array is configured for polarization-sensitive OCT to detect and / or classify defects based on polarization-dependent scattering properties acquired by the OCT array. The OCT array may include a beam splitter through which the coherent radiation generated by the radiation source enters the reference arm and the measurement arm. The OCT array may also include a polarizer positioned between the radiation source and the beam splitter.

[0058] This allows the polarization of the coherent radiation, which is used for polarization-dependent (e.g., polarization-sensitive) OCT, to also be efficiently used for power regulation in the reference arm. Based on the polarization-dependent OCT image data acquired with the OCT array, near-surface defects can be detected and / or classified more reliably compared to conventional techniques.

[0059] The control logic can be set up to control the polarizer.

[0060] This allows for the implementation of a polarization-dependent (e.g., polarization-sensitive) OCT under the control of the control logic, whereby the power regulation in the reference arm can be coordinated by the control logic with the setting of the polarizer, which is provided between the radiation source and the beam splitter.

[0061] At least one power control device can include a first polarization filter in the reference arm. The control logic can be configured to influence the first polarization filter, for example by controlling a first polarization filter drive that mechanically adjusts the first polarization filter.

[0062] This implements a polarization-dependent (e.g., polarization-sensitive) OCT under control of the control logic, whereby power in the reference arm can be regulated by influencing the first polarization filter, for example by its automatic mechanical rotation under control of the control logic.

[0063] The OCT setup can include a second polarization filter in the measuring arm. The control logic can be configured to influence the second polarization filter, for example, by controlling a second polarization filter drive that mechanically adjusts the second polarization filter.

[0064] This implements a polarization-dependent (e.g., polarization-sensitive) OCT under the control of the control logic, whereby a light output in the measuring arm can be selectively switched off by influencing the second polarization filter, for example by its mechanical rotation under the control of the control logic.

[0065] The first polarizing filter can be positioned between the beam splitter and the iris diaphragm.

[0066] This implements a polarization-dependent (e.g., polarization-sensitive) OCT controlled by the control logic, whereby the power in the reference arm can be regulated by influencing the first polarization filter, for example, by its automatic mechanical rotation under the control logic. The beam splitter can be a polarizing beam splitter. The OCT setup can also include a controllable optical element between the radiation source and the polarizing beam splitter, for example, an X / 2 plate positioned between the polarizer and the polarizing beam splitter. The control logic can be configured to control the controllable optical element to increase the intensity variance of the interference signal detected at the detector.

[0067] This allows for power regulation in the reference arm and / or measuring arm by controlling the controllable optical element, which is done automatically under the control of the control logic, such that the intensity variance at the detector meets a desired quality criterion, for example, fully or at least largely utilizing the dynamic range of the detector.

[0068] The control logic can be configured to control both the iris aperture and the controllable optical element in such a way that the intensity variance of the interference signal detected at the detector meets a quality criterion, for example, fully or largely utilizing the dynamic range of the detector.

[0069] The material may consist of an optical material, in particular glass and / or an optical plastic.

[0070] This provides a non-destructive testing method for optical materials. OCT-based material testing techniques are particularly suitable for optical materials. Conventional non-destructive techniques that use magnetic and / or electrical measurement methods, on the other hand, are either unsuitable or insufficiently sensitive for such materials.

[0071] The material may have an optical component.

[0072] This provides a non-destructive testing method for optical workpieces. OCT-based material testing techniques are particularly suitable for optical materials. Conventional non-destructive techniques that use magnetic and / or electrical measurement methods, on the other hand, are either unsuitable or insufficiently sensitive for such materials.

[0073] The evaluation of OCT image data can include automatic detection and / or classification of near-surface defects based on the OCT image data.

[0074] This enables non-destructive detection and / or classification of near-surface defects (i.e., defects located within the material, for example, less than 50 pm or less than 30 pm from the surface).

[0075] The control logic can be configured to regulate the power control unit in the reference arm based on the properties of the material under investigation. Alternatively, the control logic can be configured to operate based on the intensity variance of the interference signals detected. Once the intensity variance of the interference signals meets a desired quality criterion, for example, largely or fully utilizing the detector's dynamic range, OCT imaging can be performed. The resulting OCT image data are then evaluated to detect and / or classify near-surface defects.

[0076] This enables non-destructive detection and / or classification of near-surface defects (i.e., defects located within the material, for example less than 50 pm or less than 30 pm from the surface) with increased reliability compared to conventional techniques.

[0077] The OCT setup can be configured to provide inverse darkfield illumination.

[0078] This reduces strong surface effects, which can occur particularly with optical materials. This enables more reliable detection and / or classification of near-surface defects compared to conventional techniques. In particular, Fresnel reflections under perpendicular illumination can be reduced.

[0079] The OCT configuration can be set up for a TD ("Time Domain") OCT.

[0080] This allows for simple material analysis. A longer measurement time, caused by the mechanical adjustment of a reflector in the reference arm during TD-OCT, is more acceptable in material analysis than, for example, in medical OCT applications.

[0081] The OCT configuration can be set up for an FD ("Frequency Domain") OCT.

[0082] This allows for material testing with short measurement times. This makes it possible to test larger numbers of materials, such as optical workpieces, per unit of time.

[0083] The radiation source can be a supercontinuum light source, for example a supercontinuum laser or a white light laser.

[0084] This allows FD-OCT to be performed in a particularly efficient manner. This enables the testing of even larger numbers of materials, such as optical workpieces, per unit of time.

[0085] The radiation source can be controlled in such a way that a spectrum of the radiation emitted by the radiation source can be controlled and influenced.

[0086] This allows the process to perform OCT data acquisition based on and depending on the properties of the material being tested.

[0087] The control logic can be configured to control the radiation source such that the bandwidth and / or center frequency of the coherent radiation depends on the material being tested. The control logic can also be configured to receive information about the material being tested via a user interface and / or to determine it automatically based on output data or in the detector's output signal.

[0088] This method performs OCT data acquisition and ultimately generates OCT image data based on the properties of the material being tested. Compared to conventional methods, this increases the accuracy with which defects, especially near-surface defects, can be identified and / or classified.

[0089] The OCT array can include multiple optical conductors, such as photonic fibers, to guide the radiation at least in the measurement arm, and optionally also in the reference arm. In this way, the OCT array can be designed as a hybrid OCT array, in which the radiation propagates both in an optical conductor and as a free beam.

[0090] This allows the OCT setup to be implemented with a more compact design compared to conventional techniques. This facilitates its use in industrial environments, particularly for testing optical materials such as optical workpieces.

[0091] The measuring arm can have a lens with a high numerical aperture (NA).

[0092] This enables reliable detection and optional classification of near-surface defects even when conventional techniques might miss or at least fail to classify near-surface defects due to low signal intensities.

[0093] The measuring arm may include a telescope and / or Alvarez plates.

[0094] This enables the radiation in the measuring arm to scan across the material being tested, even when using a high NA lens. The OCT setup is designed to allow for adjustable illumination widths.

[0095] The reference arm can have at least one axicon to generate the reference beam.

[0096] This improves the quality of the OCT image data and facilitates the detection and / or classification of near-surface defects of the material being tested.

[0097] The OCT array can have at least one, and optionally several, shutters automatically controlled by the control logic to allow switching between different operating modes. These modes can be used, for example, to measure layer thicknesses and / or tomographic effects and / or to process signal conditioning. In particular, the OCT array can be configured so that the control logic can automatically actuate the shutters to reduce or eliminate static signals.

[0098] This improves the quality of the OCT image data and facilitates the detection and / or classification of near-surface defects of the material being tested.

[0099] The method can include an evaluation of the interference signals acquired by the detector, in which a computer-aided, simultaneous multi-peak evaluation is performed. This facilitates the detection and / or classification of near-surface defects of the material under test compared to conventional techniques, particularly when measuring thin films with a thickness of less than 10 nm and / or when measuring closely spaced films that are less than 10 nm apart.

[0100] The evaluation of the interference signals detected by the detector can include computer-aided generation of the OCT image data as well as computer-aided classification of near-surface defects in the material using a data-driven evaluation method.

[0101] This allows for an automatic classification of near-surface defects in an objective manner (namely based on a data-driven evaluation method) compared to conventional techniques.

[0102] The OCT arrangement can include an interferometer, which can be designed as a Michelson interferometer, a Mach-Zehnder interferometer, or a Mirau interferometer.

[0103] This allows the basic interferometric designs used in OCT imaging of biological objects to also be used in the technique according to the invention.

[0104] The OCT setup can be configured for polarization-sensitive OCT. Accordingly, polarization-sensitive OCT can be performed during the procedure.

[0105] This results in increased contrast by processing data from the polarization-sensitive setup. This improves the reliability of detecting and / or classifying near-surface defects.

[0106] The method can be used to examine near-surface defects in materials made of non-biological material.

[0107] This method allows defects in a material's surface zone to be measured. The defects can be selected from a group consisting of cracks, near-surface defects, refractive index differences, polarization differences, and / or scattering and reflection on non-biological materials. These non-biological materials can be glasses, salts, crystals, plastics, ceramics, and / or semiconductor materials.

[0108] This method allows for the examination of materials with a penetration depth of up to 1 mm at a depth of 30 pm or less below the surface, with a resolution of 10 pm or less, for defect detection. The method enables the detection of subsurface defects in the surface boundary zone with high lateral and / or axial resolution.

[0109] The method can be a method for detecting and optionally classifying cracks (open and / or closed), cavities, pores, and / or material inhomogeneities. According to a further aspect of the invention, a system for material testing is provided. The system comprises an OCT arrangement for performing OCT on a material to generate OCT image data. The OCT arrangement includes: a measuring arm configured for scanning the material; a reference arm having at least one power control device; a radiation source for generating coherent radiation for the measuring arm and the reference arm; a detector for detecting a coherent superposition of the coherent radiation from the reference arm and the measuring arm; and control logic configured for controlling the at least one power control device. The system includes a computing system for evaluating the OCT image data.

[0110] The system can be set up to carry out the procedure according to one of the aspects or examples of implementation.

[0111] Optional features of the system according to different embodiments and the respective technical effects achieved correspond to the features and effects described with reference to the method.

[0112] The system can be a system for investigating near-surface defects in a marginal zone below the surface of the material, particularly in a marginal zone with a thickness of less than 1 mm or 30 pm or less.

[0113] Further aspects of the invention describe a use of the method and / or the system according to an exemplary embodiment in which the measuring arm and / or the reference arm is selectively switched off (i.e., a radiation path is selectively blocked) in order to perform one, several, or all of the following processes in order to improve the acquisition of the OCT image data (for example, for the investigation of near-surface defects in a marginal zone below the surface of the material):

[0114] Controlling a shutdown device (for example, at least one power control device and / or a shutter) in the reference arm to measure an autocorrelation signal in the material. This autocorrelation signal can be used to improve measurement quality.

[0115] Controlling a shutdown device (for example, at least one power control device and / or a shutter) in the reference arm to adjust, align, and maximize the measurement signal in the measuring arm. This offers advantages compared to conventional techniques where the quality of the measurement and reference signals cannot be evaluated separately.

[0116] Controlling an additional shut-off device (e.g., another power control device and / or another shutter) in the measuring arm to measure the reference signal and correct for a DC component. Controlling another shut-off device (e.g., another power control device and / or another shutter) in the measuring arm to adjust, align, and maximize the reference signal. This offers advantages compared to conventional techniques where the quality of the measurement and reference signals is not evaluated separately.

[0117] Controlling a shutdown device (for example, the at least one power control device or an additional shutter provided thereto) in the reference arm and controlling another shutdown device (for example, the further power control device and / or an additional shutter provided thereto) in the measuring arm in order to perform a dark current measurement in the detector.

[0118] The methods and systems according to exemplary embodiments of the invention achieve various effects. In particular, the methods and systems are designed for the non-destructive testing of optical materials (such as glasses, crystals, salts, and optical plastics). The methods and systems can be used for the non-destructive detection and, optionally, classification of near-surface defects with improved accuracy compared to conventional techniques.

[0119] BRIEF DESCRIPTION OF THE FIGURES

[0120] An embodiment of the invention is described with reference to the figures. In the figures, similar or identical reference numerals denote elements with similar or identical design and / or function.

[0121] Fig. 1 is a schematic representation of an OCT setup of a material testing system.

[0122] Fig. 2 is a schematic representation of another system for material testing.

[0123] Fig. 3 is a schematic representation of another system according to an exemplary embodiment.

[0124] Fig. 4 is a schematic representation of another system for material testing.

[0125] Fig. 5 is a flowchart of a process for materials testing.

[0126] Fig. 6 is a flowchart of a procedure that can be used in a material testing process.

[0127] Fig. 7 is a schematic representation to explain the functioning of the systems for material testing.

[0128] Fig. 8 is a schematic representation of intensity signals acquired by a detector of the OCT array to illustrate the functionality of the materials testing systems. Fig. 9 is a flowchart of a materials testing procedure.

[0129] Fig. 10 is a schematic block representation of a control logic of systems for materials testing.

[0130] Fig. 11 is a schematic block representation of a computing system of systems for materials testing.

[0131] Fig. 12 is a schematic representation to explain how the computer system works.

[0132] Fig. 13 is a schematic representation of components of the system for material testing.

[0133] Fig. 14 is a flowchart of a process for material testing.

[0134] Fig. 15 is a flowchart of a process for material testing.

[0135] Fig. 16 is a schematic representation of optional features of the material testing system.

[0136] Fig. 17 is a flowchart of a process for material testing.

[0137] DETAILED DESCRIPTION OF EXAMPLES OF EXECUTION

[0138] Exemplary embodiments of the invention are described with reference to the figures. In the figures, similar or identical reference numerals denote elements with similar or identical design and / or function.

[0139] The features of the exemplary embodiments can be combined with each other, unless this is expressly excluded in the following description.

[0140] Methods and systems according to the exemplary embodiments are designed for the detection, and optionally also for classification, of near-surface defects in non-biological materials, particularly in optical materials such as optical components, glass, salt, crystals, optical plastics, or other optical materials. The methods and systems utilize an OCT array for OCT data acquisition, whereby OCT image data is calculated computer-aided from the interference signals acquired by a detector of the OCT array. The OCT data acquisition is controlled by a control logic such that the power in the reference arm, and optionally also in the measurement arm, of the OCT array is selectively influenced to achieve a desired intensity variance at the detector and / or a desired proportion of mixed light relative to uniform light.In contrast to biological, especially physiological, samples, there is a lower risk of damage to the test specimen during materials testing, which allows for optimization of performance in both the reference and measurement arms with a view to achieving the most accurate OCT measurement results possible. Methods and systems according to the exemplary embodiments are specifically designed for the detection and optional classification of near-surface defects.

[0141] “Near-surface defects” are defined as defects (e.g., cavities, pores, cracks, etc.) within a test specimen that lie within or extend into a boundary zone, which may be, for example, less than 1 mm, less than 100 pm, 80 pm or less, 50 pm or less, or 30 pm or less, measured from the surface of the test specimen.

[0142] The term "defects" encompasses defects that can occur in optical materials, particularly in optical components. These defects can include one, several, or all of the following: point defects; cracks (optionally distinguishing between open and closed cracks); pores; material inhomogeneities; cavities; and inhomogeneities in the refractive index and / or polarization-dependent properties.

[0143] The term "material," as used here, includes in particular glasses, salts, crystals, plastics, ceramics, and semiconductor materials. The term "material" also specifically includes optical components made from glass, salt, crystals, optical plastics, ceramics, or semiconductor materials.

[0144] A "power regulation" can involve continuous or discrete adjustment of the power. The OCT arrangement and / or the methods according to exemplary embodiments can be configured to selectively and completely block radiation in the reference arm and / or the measurement arm using a shut-off device (for example, a shutter), for instance, to automatically perform one or more adjustments that improve the quality of the OCT image data or the signals used to reconstruct the OCT image data.

[0145] Methods and systems according to the exemplary embodiments can be configured to acquire OCT image data under inverse darkfield illumination. The term "inverse darkfield illumination," which is synonymous with the term "inverted darkfield illumination," also used in the technical field, refers to an illumination technique that can highlight certain contrasts and details in a sample that are difficult to discern in conventional brightfield. The term "inverse" does not refer to a reversal of the darkfield method itself, but rather to the fact that the illumination system and the observation system (objective) are geometrically interchanged compared to a conventional darkfield setup.

[0146] Methods and systems according to the exemplary embodiments are configured to measure microscopic damage below the surface of the test specimen with high axial resolution, for example, an axial resolution of 10 pm or less, 5 pm or less, or 3 pm or less. Alternatively or additionally, the methods and systems are configured to achieve a high lateral resolution of 10 pm or less, 5 pm or less, or 3 pm or less.

[0147] Fig. 1 shows a schematic representation of a system 10 for materials testing. The system 10 includes an OCT setup. The OCT setup can have a conventional interferometer configuration, for example, in the form of a Michaelson interferometer. The OCT setup includes a radiation source 11 for generating coherent radiation 12. The radiation source 11 can be a supercontinuum laser radiation source, for example, a supercontinuum laser. The OCT setup includes a reference arm 20 and a measurement arm 30. The coherent radiation 12 generated by the radiation source is directed into the reference arm 20 and the measurement arm 30 via a beam splitter 19. The beam splitter 19 can act as a beam splitter / beam combiner, through which a coherent superposition 17 of radiation from the reference arm 20 and the measuring arm 30 is guided to a detector 18 and detected by the detector 18.

[0148] The reference arm 20 has a reflector 28. Depending on the implementation of the OCT arrangement, the reflector 28 can be mechanically adjustable, for example for a TD-OCT.

[0149] The measuring arm 30 includes a scanner 37, which can be configured to scan the measuring beam in a one-dimensional or, preferably, a two-dimensional pattern across the material to be tested. The scanner 37 can have at least one, and advantageously at least two, controllable reflectors (for example, mirrors) for scanning the measuring beam. Adjustment of the mirrors can be performed automatically under the control of a control logic that will be described in more detail later. The measuring arm 30 includes a lens 38. The lens 38 can include a telescope and / or one or more Alvarez plates. The lens 38 can be a lens with a high NA (numerical aperture).

[0150] The reference arm 20 can have a first shutter 29. The measuring arm 30 can have a second shutter 39. The OCT arrangement can be configured to selectively actuate one or both of the shutters 29, 39 so that the radiation in the corresponding arm is blocked. The OCT arrangement can be configured so that the first shutter 29 and the second shutter 39 allow motorized actuation to block radiation in the corresponding arm.

[0151] The OCT arrangement can have a hybrid design in which – as schematically indicated in Fig. 1 – the coherent radiation is guided through an optical conductor, for example an optical fiber, in at least a part of the OCT arrangement, in particular in at least a part of the reference array, a part of the measuring arm, and an arm leading from the beam splitter 19 to the detector 18. Accordingly, a hybrid design can be implemented in the OCT arrangement in which both optical fibers and free-jet propagation are combined.

[0152] The OCT setup can be configured specifically for FD-OCT. For this purpose, the radiation source 11 can be configured as a broadband radiation source, for example, as a supercontinuum laser radiation source. Optionally, the OCT setup can be configured to perform polarization-sensitive OCT.

[0153] The radiation source 11 and the measuring arm 30 can be configured to provide inverse dark-field illumination. This makes it possible to suppress the potentially high surface reflections (e.g., Fresnel reflections) that may occur with optical materials.

[0154] The reference arm 20 has a power control device 21. A control logic 40 is set up to control the power control device 21, and optionally also the radiation source 11, in such a way that a desired intensity variance (for example, an intensity variance that fully utilizes the dynamic range of the detector 18) of the interference signal at the detector 18 is achieved and / or that a proportion of direct light is reduced compared to the mixed light component (ideally as much as possible).

[0155] System 10 can be configured such that, during initial data acquisition from the material under test, the control logic evaluates the intensity variance resulting at detector 18 to verify whether it meets a quality criterion (for example, utilization of the dynamic range of detector 18 that corresponds to at least a threshold value relative to the total dynamic range). If the quality criterion is not met, the control logic can adjust the power control device 21, and optionally also the power of the radiation source 11, to increase the intensity variance resulting at detector 18. For optical materials, no damage to the test specimen is expected, and even any damage due to excessive radiation power would be acceptable—unlike with biological (especially physiological) samples.

[0156] Advantageously, the reference arm includes a beam-expanding optic 27. The lens 27 can be arranged between the beam splitter 19 and the power control device 21. The power control device 21 can be positioned between the beam-expanding optic 27 and the reflector 28 of the reference arm 20. The reference arm 20 can have several axicons to achieve a desired beam shaping. In particular, the reference arm 20 can have one or more axicons to expand a beam in the reference arm to a beam diameter that is adapted to a (maximum) light-entry area of ​​the light control device 21. For example, the light control device 21 can have a drive-operated aperture. The one or more axicons can be configured such that the beam in the reference arm is expanded to a beam diameter that is at least equal to the maximum aperture diameter of the drive-operated aperture.

[0157] After adjusting the power in the reference arm 20, and optionally also in the measuring arm 30, the OCT arrangement can perform the actual OCT data acquisition on the material. The system 10 includes a computing system (not shown in Fig. 1) that is configured to calculate OCT image data from the OCT data acquired by the detector 18 and to evaluate this data with regard to the presence of defects in the material. The computing system can optionally be configured to perform a classification of defects. This can include, for example, the differentiation between open and closed cracks, pores, or other types of defects.

[0158] Fig. 2 shows a schematic representation of system 10 according to an exemplary embodiment. In the system 10 of Fig. 2, the power control device 21 has an iris aperture 22 and an iris aperture drive 23 (for example, a motor) for adjusting the iris aperture 22. The expanding optics 27, which may have one or more axioms, are configured to expand a beam diameter of the beam in the reference arm 20 such that the beam diameter can be at least equal to a maximum opening diameter of the iris aperture 22.

[0159] The control logic 40, which is coupled to the detector 18, is configured to control the iris diaphragm drive 23 in order to adjust the driven iris diaphragm 22. The control logic 40 can be configured to control the iris diaphragm drive 23, and optionally also the radiation source 11, such that a desired intensity variance (for example, fully utilizing the dynamic range of the detector from 0 to 100% of the intensity variance) is achieved at the detector 18 for the respective material being tested, and / or that the proportion of uniform light at the detector 18 is kept as low as possible in relation to the proportion of mixed light resulting from interference for the respective material being tested.

[0160] System 10 comprises a first shutter 24 in the reference arm 20 and a second shutter 34 in the measuring arm 30. The first shutter 24 can be mechanically movable. System 10 can include a drive device 42 for mechanically moving the first shutter 24. The second shutter 34 can also be mechanically movable. The drive device 42 can be configured to mechanically move the second shutter 34. The drive device 42 can have several independently controllable drives to selectively block radiation only in the reference arm 20, only in the measuring arm 30, or in both the reference arm 20 and the measuring arm 30. A further control logic 41, which can be integrally formed with the control logic 40 in the same device, can be configured to control the drive device 42 to perform desired blocking operations.This makes it possible to implement different operating modes, for example for depth measurement, for calibration (e.g. to determine a uniform light component) and for OCT imaging.

[0161] System 10 includes a computing system 50. Computing system 50 can comprise one or more computers, one or more servers, one or more portable computers, one or more communication terminals, or other configurations. Computing system 50 can be integrally configured with control logic 40 and optionally with further control logic 41. Computing system 50 is configured to calculate OCT image data from the OCT data acquired by detector 18 and to evaluate this data with regard to the presence of defects in the material. Computing system 50 can, in particular, perform data-driven processing of the OCT image data. The data-driven processing can include processing by at least one artificial intelligence (AI) model, in particular a trained machine learning model. Optionally, the computing system can be configured to perform a classification of defects.This can include, for example, the differentiation between open and closed cracks, pores, or other types of defects.

[0162] Fig. 3 shows a schematic representation of system 10 according to an exemplary embodiment. System 10 has an OCT array configured for polarization-sensitive OCT. This allows system 10 to offer examination possibilities with increased accuracy, for example, with regard to the detection of polarization-dependent effects that may be caused by a defect.

[0163] In system 10 of Fig. 3, the power control device 21, as already described with reference to Fig. 2, has an iris aperture 22 and an iris aperture drive 23 (for example, a motor) for adjusting the iris aperture 22. The control logic 40 is configured to adjust the iris aperture 22 by actuating the iris aperture drive 23.

[0164] The OCT arrangement of system 10 of Fig. 3 includes a polarizer 13 located between the radiation source 11 and the beam splitter 19. The reference arm 20 has a first polarization filter 25. The first polarization filter 25 can be pivotably mounted. System 10 includes a drive device 42 for mechanically pivoting the first polarization filter 25.

[0165] The measuring arm 30 has a second polarizing filter 35. The second polarizing filter 35 can be mounted so that it can pivot. The drive device 42 can be configured for mechanically pivoting the second polarizing filter 35.

[0166] The drive device 42 can have several independently controllable drives to selectively pivot only the first polarization filter 25 in the reference arm 20, only the second polarization filter 35 in the measuring arm 30, or both polarization filters 25, 35, in order to selectively block or release radiation in the corresponding arm. This allows power regulation in the reference arm to be implemented in an OCT arrangement configured for the detection of light polarization-dependent effects. Depending on the respective position of the polarization filters 25, 35, the drive device 23 can be controlled by the control logic 40 such that the intensity contrast at the detector 18 is enhanced by the power regulation in the reference arm. Optionally, the control can be configured so that the intensity contrast at the detector 18 fully or at least largely utilizes the dynamic range of the detector 18. In the embodiment of Fig.3. The power regulation in the reference arm can be achieved by adjusting the iris diaphragm under the control of the control logic 40, by adjusting the polarization filter 25, or a combination of these measures.

[0167] A further control logic 41, which can be integrally configured with the control logic 40 in the same device, can be configured to control the drive device 42 in order to perform desired aperture operations. This makes it possible to implement different operating modes, for example, for depth measurement, for calibration (e.g., to determine a uniform light component), and for OCT imaging.

[0168] Fig. 4 shows a schematic representation of system 10 according to an exemplary embodiment. System 10 has an OCT array configured for polarization-sensitive OCT. This allows system 10 to offer examination possibilities with increased accuracy, for example, with regard to the detection of polarization-dependent effects that may be caused by a defect.

[0169] In system 10 of Fig. 4, the power control device 21, as already described with reference to Fig. 2, has an iris aperture 22 and an iris aperture drive 23 (for example, a motor) for adjusting the iris aperture 22. The control logic 40 is configured to adjust the iris aperture 22 by actuating the iris aperture drive 23.

[0170] The OCT arrangement of system 10 has a beam splitter designed as a polarizing beam splitter 19p.

[0171] The OCT arrangement of system 10 of Fig. 4 includes a polarizer 13 located between the radiation source 11 and the polarizing beam splitter 19p. The OCT arrangement also includes a controllable optical element 14, for example, a controllable X / 2 plate 14, located between the polarizer 13 and the polarizing beam splitter 19p. System 10 includes further control logic 43 for controlling the controllable optical element 14. This further control logic 43 can be integrated with the control logic 40 in a single device.

[0172] During operation of the system 10, the additional control logic 43 can control the controllable optical element 14 to influence the ratio of radiation intensities in the reference arm 20 and the measuring arm 30. Together with the motorized iris diaphragm 22, the control logic 40 can cooperate with the additional control logic 43 in such a way that, depending on an output signal or output data from the detector 18, the power in the reference arm 20 and the measuring arm 30 is selectively influenced to enable high-resolution OCT imaging, which allows for the detection and, optionally, the classification of defects.

[0173] This allows power control in the reference arm of an OCT setup designed to detect light polarization-dependent effects. Depending on the specific control of the optical element, the drive device 23 can be controlled by the control logic 40 such that the intensity contrast at the detector 18 is enhanced by the power control in the reference arm. Optionally, the control can be configured so that the intensity contrast at the detector 18 fully or at least largely utilizes the dynamic range of the detector 18.

[0174] The system 10 according to Fig. 1, Fig. 2, Fig. 3 and Fig. 4 can be configured to utilize the results of the detection and / or classification of near-surface defects of the non-biological material in various ways. For example, the system 10 can have an optical output interface or another user interface 53, which may be a graphical user interface. The system 10 can be configured to provide, under the control of the computer system 50, information on the detection and / or classification of the near-surface defects identified within the material.

[0175] Alternatively or additionally, the computer system 50 can be configured to execute automatic control operations that depend on the result of the detection and / or classification of near-surface defects within the material. For example, if unacceptable near-surface defects are identified, the computer system 50 can execute a control operation that leads to the automatic rejection of the corresponding material. Alternatively or additionally, if unacceptable near-surface defects are identified in several identical materials, the computer system 50 can execute a control operation that leads to the automatic halting of a manufacturing process to allow for troubleshooting. Alternatively or additionally, if unacceptable near-surface defects are identified in several identical materials, the computer system 50 can execute a control operation that influences the manufacturing process to eliminate the unacceptable defects.

[0176] The system 10 according to Fig. 1, Fig. 2, Fig. 3 and Fig. 4 can be configured to selectively switch off the reference arm and / or the measuring arm (i.e., selectively block radiation paths in the reference arm and / or measuring arm) in order to perform one, several or all of the following processes to improve the acquisition of the OCT image data (for example, to investigate near-surface defects in a marginal zone below the surface of the material):

[0177] Controlling a shutdown device (for example, the at least one power control device 21, 22 or an additional shutter 24, 29) in the reference arm 20 to measure an autocorrelation signal in the material. The autocorrelation signal can be used by the system 10 to improve the measurement quality, for example, through automatic control and / or evaluation processes. Controlling a shutdown device (for example, the at least one power control device 21, 22 or an additional shutter 24, 29) in the reference arm 20 to adjust, align, and maximize the measurement signal in the measuring arm 30. This offers advantages compared to conventional techniques where the quality of the measurement and reference signals is not evaluated separately.

[0178] Controlling a further shut-off device (for example, the further power control device and / or a further shutter 34, 39) in the measuring arm 30 to measure the reference signal in order to correct a constant light component.

[0179] Controlling a further shut-off device (for example, the additional power control device and / or a further shutter 34, 39) in the measuring arm 30 for adjusting, aligning, and maximizing the reference signal. This offers advantages compared to conventional techniques where the quality of the measurement and reference signals is not evaluated separately.

[0180] Controlling a shutdown device (for example, the at least one power control device 21, 22 or a shutter 34, 39) in the reference arm 20 and controlling a further shutdown device (for example, the further power control device and / or a further shutter 34, 39) in the measuring arm in order to perform a dark current measurement in the detector.

[0181] Fig. 5 is a flowchart of a method 60 for material testing. The method 60 can be executed automatically by or with the system 10. The method 60 can be executed to detect and optionally classify defects, in particular near-surface defects, in an optical material.

[0182] Step 61 involves evaluating interference signals acquired by a detector in an OCT array. This evaluation can include determining the intensity variance and comparing it to the range of different intensities detectable by the detector, also referred to here as the dynamic range. The evaluation can also determine the proportion of uniform light and mixed light based on the interference signals acquired by the detector. For the evaluation in step 61, the OCT array can shine measuring light onto the material under test to determine an initial intensity distribution at the detector. This allows for the determination of how to adjust the OCT array settings to detect near-surface defects as reliably and / or accurately as possible, and optionally to classify them.The interference signals detected at step 61 are not used to determine the OCT image data unless the intensity variance meets a specific quality criterion. At step 62, the control logic (for example, control logic 40) controls a power regulation device (which may, for example, include a motorized iris diaphragm) in the reference arm of the OCT array. The control logic can optionally also control other components of the OCT array, such as the radiation source and / or other components. At step 62, the control logic controls the power regulation device and optionally other components of the OCT array such that the intensity variance detected at detector 18 for the material under test meets a specific quality criterion. Steps 61 and 62 can be repeated iteratively for this purpose.

[0183] At 63, the OCT setup performs an OCT scan on the material under test. The measuring beam is scanned across the material to acquire two-dimensional or, advantageously, three-dimensional OCT image data. The OCT can be performed as FT OCT using a supercontinuum light source, such as a white light laser.

[0184] At 64, the system (for example, computer system 50 of system 10) generates OCT image data from the data acquired by detector 18 during OCT. This can involve reconstructing the OCT image data from the multiple interference patterns acquired for different scan directions of the measurement beam. Techniques for reconstructing OCT image data from the acquired interference patterns are familiar to the specialist.

[0185] At station 64, the system (for example, computer system 50 of system 10) evaluates the OCT image data to detect and optionally classify defects. The detection and / or classification of defects based on the OCT image data may involve the application of a data-driven evaluation method, such as an AI model for object classification. Optionally, the detection and / or classification of defects based on the OCT image data may include preprocessing of the OCT image data, such as segmentation around potential defect locations.

[0186] Depending on the detected and optionally classified defects, the system can execute one or more control operations, as previously explained. For example, the computer system 50 can control a user interface 53 to output information dependent on the detected and / or classified defects. The computer system 50 can be configured to control the user interface 53 to display these markers, which indicate defects and optionally defect types, as a superimposition on the generated OCT image data. Alternatively or additionally, the computer system 50 can be configured to execute further control operations, as previously explained.

[0187] Fig. 6 is a flowchart of procedure 65 for material testing. Procedure 65 can be executed automatically by or with system 10. Procedure 65 can be executed to detect and optionally classify defects, particularly near-surface defects, in an optical material. Procedure 65 can be executed to implement step 64 of method 40 of Fig. 5.

[0188] At 66, the computing system 50 of system 10 generates OCT image data from the data acquired by the detector of the OCT array during the OCT procedure. This can involve reconstructing the OCT image data from the multiple interference patterns acquired for different scan directions of the measurement beam. Techniques for reconstructing OCT image data from the acquired interference patterns are familiar to the specialist.

[0189] At station 67, the computer system 50 analyzes the OCT image data to detect and optionally classify defects. The detection and / or classification of defects based on the OCT image data may involve the application of a data-driven evaluation method, such as an AI model for object classification. Optionally, the detection and / or classification of defects based on the OCT image data may include preprocessing of the OCT image data, such as segmentation around potential defect locations.

[0190] System 10 and / or the method according to the embodiments disclosed herein can be configured to acquire OCT image data using inverse darkfield illumination. System 10 and / or the method can thus be configured such that the illumination system and the observation system (objective 38) can be geometrically interchanged compared to a conventional darkfield setup. The following features can be implemented for this purpose:

[0191] Illumination: In (inverse) dark-field illumination, the light is directed obliquely onto the sample. Light cannot fall directly into the objective lens 17 unless it is scattered or reflected by the material. Because only the light reflected or scattered by the material reaches the objective lens 17, objects appear against a dark background. Particles, edges, and irregularities that scatter light more strongly illuminate brightly, making them easily visible. This is particularly advantageous for detecting near-surface defects.

[0192] Inverse arrangement: In inverse darkfield illumination, the objective lens 17 is positioned below the sample. The OCT arrangement can be designed such that obliquely incident light falls onto the material from above or, if necessary, from the side, and the scattered light from below is collected by the objective lens 17.

[0193] The use of inverse dark-field illumination can achieve improved defect detection in the field of materials science, especially in the detection of near-surface defects.

[0194] Fig. 7 is a schematic representation to further explain the operation of system 10. System 10 comprises an OCT array that scans a material 70 to be inspected with a measuring beam 31 generated in the measuring arm of the OCT array. Before performing the OCT imaging, at least one interference pattern 71 is initially detected on the material 70 to be inspected by the detector 18. Depending on the intensity contrast of the interference pattern 71, the control logic 40 controls the power control device 21 to increase the intensity contrast. The control logic 40 can also take into account the properties of the detector 18, in particular the range of intensities detectable by the detector 18. The control logic 40 can optionally also control the radiation source 11 or other controllable components of the OCT array to increase the intensity contrast.The control logic 40 can intervene to ensure that the intensity contrast for the respective material 70 to be tested coincides at least approximately, ideally substantially, with the dynamic range of the detector 18.

[0195] Following such automatic adjustment of the OCT configuration under the control of the control logic 40, the actual OCT image acquisition takes place, in which several further interference patterns 72 are acquired by the detector 18 and processed by the computing system 50 to generate the OCT image data 73. The further interference patterns 72 exhibit an increased intensity contrast compared to the interference pattern 71. In other words, the proportion of uniform light compared to the proportion of mixed light in the further interference patterns 72 is reduced compared to at least one initial interference pattern 71. This improves the quality of the OCT imaging and enables the detection of even small defects in the optical material 70 with higher reliability and / or higher resolution compared to conventional techniques.

[0196] Fig. 8 schematically shows interference signals detected by the detector 18. The intensity at a pixel of the detector is shown along an axis 75, while another axis 76 indicates the position of the corresponding pixel along a direction on the detector. An interference signal 78, initially detected before the OCT setup is adjusted to the specific material being tested, varies over a range that covers only a portion of the intensity range 77 detectable by the detector 18. The intensity range 77 detectable by the detector 18 is also referred to as the dynamic range. Within this intensity range 77, the detector 18 can detect differences in intensity and represent them by corresponding output values. Higher or lower intensities no longer result in a further increase or decrease of the corresponding pixel value.

[0197] A further interference signal 79, detected after the OCT arrangement has been adjusted to the respective material being tested, varies over a range that essentially coincides with the intensity range 77 detectable by the detector 18. An intensity maximum 79' of the further interference signal 79 can essentially correspond to an upper limit of the detectable intensity range 77. An intensity minimum 79" of the further interference signal 79 can essentially correspond to a lower limit of the detectable intensity range 77. This TI

[0198] In this way, the dynamic range 77 of the detector 18 is utilized by the automatic adjustment made by the control logic 40, in which the detected pixel values ​​are variable as a function of the detected intensity.

[0199] Fig. 9 is a flowchart of a method 80 for material testing. The method 80 can be executed automatically by or with the system 10. The method 80 can be executed to detect and optionally classify defects, in particular near-surface defects, in an optical material.

[0200] Step 81 involves evaluating interference signals acquired by a detector in an OCT array. This evaluation can include determining the intensity variance and comparing it to the range of different intensities detectable by the detector, also referred to here as the dynamic range. The evaluation can also determine the proportion of uniform light and mixed light based on the interference signals acquired by the detector. For the evaluation in step 81, the OCT array can shine measuring light onto the material under test to determine an initial intensity distribution at the detector. This allows for the determination of how to adjust the OCT array settings to detect near-surface defects as reliably and / or accurately as possible, and optionally to classify them.

[0201] Step 82 checks whether the intensity variance, i.e., the interference contrast, detected by detector 18 meets a quality criterion. This quality criterion may involve a comparison of the intensity variance with the dynamic range of detector 18. Alternatively or additionally, the quality criterion may include a comparison of a mixed-light component in the interference signal with a uniform-light component in the interference signal.

[0202] At 83, in response to a determination that the quality criterion is not met, the power control device 21, the radiation source 11 and / or another component of the OCT arrangement is controlled to increase the intensity contrast, i.e. to reduce the proportion of uniform light compared to the proportion of mixed light.

[0203] Steps 81, 82, and 83 can be repeated iteratively.

[0204] At 63 and 64, which we can be realized with reference to the method 60 of Fig. 5, the OCT data acquisition, the generation of OCT image data and the evaluation of the OCT image data for the detection and / or classification of near-surface defects of the optical material then take place.

[0205] Fig. 10 is a schematic representation of the control logic 40. The control logic 40 can be integrated with the computing system 50 and / or the further control logic 42, 43 in a single device. The control logic 40 has at least one interface 45, a storage system 46, and at least one processing circuit 90. The at least one interface 45 can be configured as a data interface, in particular as a communication interface for wired or wireless data exchange with the detector 18 and / or the drive 23. The control logic 40 is configured to receive input data 94 that depends on the interference signal detected by the detector 18, which is generated by the coherent superposition of the measuring beam 31 and the reference beam. The input data 94 can correspond to the output data of the detector 18 or be otherwise based on it.For example, the input data 94 can represent an intensity variance of the interference signal detected by the detector 18. The control logic 40 is configured to output control commands 95 to configure the OCT arrangement for improved (especially higher-contrast) OCT data acquisition on the material under test. The control commands 95 can include at least one control command for a motorized iris diaphragm located in the reference arm. The control command for the motorized iris diaphragm can specify a setpoint to which the iris diaphragm is to be adjusted.

[0206] The storage system 46 stores data 47, which can be used by the processing circuit 90 to process the input data 94. The data 47 can contain machine-readable instruction code, such as firmware, which can be executed by the processing circuit 90. The data 47 can contain further data, such as at least one setpoint for the intensity variance or for the ratio of direct to mixed light. The data 47 can contain instructions or other data from which the processing circuit 90 can determine how to control the motorized iris diaphragm and / or the radiation source for a given actual value of the intensity variance represented by the input data 94, in order to improve the intensity contrast during OCT.

[0207] The processing circuit 90 can be configured to perform an evaluation 91 of the input data 94 to determine whether an adjustment of the power control device 21 and / or the output power of the radiation source 11 is required. The evaluation 91 can include a comparison of the intensity contrast with the dynamic range of the detector 18.

[0208] The processing circuit 90 can be configured to perform a control action determination 92 depending on the result of the evaluation 91. The control action determination 92 can include a determination of whether and to what setpoint the motorized iris diaphragm 22 should be adjusted. The control action determination 92 can include a determination of the output power to which the radiation source 11 should be driven. The processing circuit 90 can be configured to execute an interface control 93 to generate control commands 95 and to control the at least one interface 45 for outputting the control commands 95.

[0209] To perform the various control and processing functions, the processing circuit 90 can include one or more integrated circuits. These one or more integrated circuits can, for example, include any combination of the following circuits or circuit components: an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), one or more processors, one or more controllers, one or more quantum gates, a quantum information processing circuit, or other integrated circuits.

[0210] Fig. 11 is a schematic representation of the computing system 50. The computing system 50 can be integrated with the control logic 40 and / or the further control logic 42, 43 in a single device.

[0211] The computing system 50 comprises at least one data interface 51, a storage system 52, and at least one processing circuit 55. The computing system 50 may optionally have a human-machine interface 53 or be configured for coupling with a human-machine interface 53. The at least one data interface 51 may be configured as a communication interface for wired or wireless data exchange with the detector 18. The computing system 50 is configured to receive input data 51, which includes the OCT data acquired by the detector 18. The input data may include the interference signals acquired by the detector for different scan directions of the measuring beam 31. The input data 54 may correspond to the output data of the detector 18 or be otherwise based on it.

[0212] The storage system 52 stores data 54, which can be used by the processing circuit 55 to process the input data 54. The data 54 can contain machine-readable instruction code, such as software or firmware, which can be executed by the processing circuit 55. The data 54 can also contain further data, such as parameters, optionally via parameters, of a data-driven processing technique, which is applied by the processing circuit 55 for the detection and / or classification of near-surface defects.

[0213] The processing circuit 55 can be configured to perform OCT image generation 56 to generate OCT image data from the data acquired by the detector 18 during OCT. The OCT image generation 56 can be configured to reconstruct the OCT image data from the multiple acquired interference patterns obtained for different scan directions of the measurement beam. Techniques for reconstructing OCT image data from the acquired interference patterns are familiar to the user.

[0214] The processing circuit 55 can be configured to perform an evaluation 57 of the OCT image data to detect defects based on the image and optionally classify them. The evaluation 57 can be configured such that a data-driven evaluation method is applied to the OCT image data for the detection and / or classification of defects based on the OCT image data. The data-driven evaluation method can, for example, include a computer model for object classification. The evaluation 57 can be configured such that the detection and / or classification of defects based on the OCT image data can optionally include preprocessing of the OCT image data, for example, segmentation around possible defect locations.

[0215] The processing circuit 55 can be configured to execute an interface control 58 depending on a result of the evaluation 57. The interface control 58 can be configured to control the human-machine interface 53 to provide information about the detection and / or classification of near-surface defects identified within the material. Alternatively or additionally, the interface control 58 can be configured to execute automatic control operations that depend on the result of the detection and / or classification of near-surface defects within the material. For example, if unacceptable near-surface defects are identified, the computer system 50 can execute a control operation that leads to the automatic rejection of the corresponding material.Alternatively or additionally, the interface control 58 can be configured so that, upon identification of unacceptable near-surface defects on several identical materials, the computer system 50 executes a control process that leads to the automatic halting of a manufacturing process to allow for troubleshooting. Alternatively or additionally, the interface control 58 can be configured so that, upon identification of unacceptable near-surface defects on several identical materials, the computer system 50 executes a control process that influences the manufacturing process to eliminate the unacceptable defects.

[0216] To perform the various control and processing functions, the processing circuit 55 can include one or more integrated circuits. These one or more integrated circuits can, for example, include any combination of the following circuits or circuit components: an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), one or more processors, one or more controllers, one or more quantum gates, a quantum information processing circuit, or other integrated circuits.The processing circuit 55 can advantageously include one or more circuits specifically designed for image processing, such as one or more embedded devices and / or one or more graphics processing units (GPUs) and / or tensor processing units (TPUs). Such configurations enable particularly efficient image evaluation.

[0217] The computing system 50 can be configured to apply a data-driven processing technique to the generated OCT image data in order to detect and / or classify defects. Parameters of the data-driven processing technique can be stored in the data 54. The data-driven processing technique can include a classification. The classification can be binary (presence or absence of a defect) or non-binary (determination of the defect type or determination of probabilities of different defect types).

[0218] Fig. 12 is a schematic representation of a data-driven processing technique, which can be implemented in particular as an AI model 100 (for example, a trained machine learning (ML) model). Parameters of the AI ​​model 100 can be stored in the data 54.

[0219] The Kl-Model 100 has an input 101 that can receive pixels or voxels of the OCT image data or input values ​​derived from it through preprocessing (for example, features of the OCT image data). The Kl-Model 100 has an output 102 that can output the result of defect detection or defect classification. The Kl-Model 100 has several hidden layers 103 to determine the result of defect detection or defect classification based on the input data received at input 101.

[0220] The Kl-Model 100 can include one or more deep learning (DL) models, such as CNNs (“convolutional Neural Networks”), VisionTransformers (ViTs), or other ML models.

[0221] System 10 can be designed in such a way that the functions of the control logic 40, the computing system 50 and optionally the further control logic 40 are combined in one integral device.

[0222] Fig. 13 is a schematic representation of the system 10, which includes a device 110 implementing both the control logic 40 and the computing system 50. The device 110 is configured to receive output data 111 from the detector 18 of the OCT array and, based on this, to control the drive 23 of the iris diaphragm 22 to control the power in the reference arm 20 and the radiation source 11 to control the output power of the radiation source 11. The device 10 can be configured to generate the control signals or control data 112, 113 such that interference contrast at the detector 18 is increased to enable more accurate and / or reliable detection and / or classification of near-surface defects in optical materials compared to conventional techniques. Fig. 14 is a flowchart of a method 120 for the detection and / or classification of near-surface defects in an optical workpiece.The optical workpiece can be made of glass, salt, ceramic, an optical plastic, a semiconductor material, or another optical material. Method 120 can be performed using System 10 or automatically by System 10. Method 120 can be performed using the methods already described herein.

[0223] Step 121 involves performing OCT on the optical workpiece. Step 121 may include an adjustment of the OCT setup. This adjustment can be performed automatically by the control logic 40 based on at least one interference image generated by a measurement on the optical workpiece to determine suitable settings for the motorized iris aperture and / or the radiation source. Step 121 may then perform OCT imaging using the automatically adjusted settings of the iris aperture and / or the radiation source.

[0224] At 122, near-surface defects are detected and / or classified based on an evaluation of OCT image data, which are computationally reconstructed from the interference patterns acquired by detector 18. The detection and / or classification can be image-based using data-driven evaluation techniques, in particular by using at least one trained machine learning model.

[0225] Figure 15 is a flowchart of a method 130 for material testing (for example, for the detection and / or classification of near-surface defects in an optical workpiece). The material can be an optical workpiece made of glass, salt, ceramic, an optical polymer, a semiconductor material, or another optical material. The method 130 can be performed using the system 10 or automatically by the system 10. The method 130 can be performed using the methods already described herein.

[0226] At 131, at least one measurement is performed with the measuring arm switched off and / or at least one measurement with the reference arm switched off. For this purpose, the shutter 24, 29 in the reference arm 20 and / or the shutter 34, 39 in the measuring arm 30 can be automatically controlled by the control logic 40 to enable the at least one measurement with the measuring arm switched off and / or the at least one measurement with the reference arm switched off.

[0227] At 132, an OCT is performed on the material, whereby the OCT arrangement (for example, the power control device in the reference arm) uses the measurement results recorded at 131 for the acquisition and / or evaluation of the OCT image data.

[0228] Results from at least one measurement at 131 can be used in various ways during OCT. The following are non-limiting embodiments of the system 10 and / or the method according to exemplary embodiments, one, several, or all of which can be implemented cumulatively: The shutdown device 24, 29 in the reference arm 20 enables the measurement of the autocorrelation signal in the sample. This signal can then be used by the control logic 40 and / or the computing system 50 to improve the measurement quality.

[0229] The shut-off device 24, 29 in the reference arm 20 can be used for adjusting, aligning and maximizing the measurement signal.

[0230] The further switching device 34, 39 in the measuring arm 30 can be used to measure the reference signal in order to at least partially or completely correct a constant light component in OCT.

[0231] The additional shut-off device 34, 39 in the measuring arm 30 can be used for adjusting, aligning and maximizing the reference signal.

[0232] The shut-off device 24, 29 in the reference arm 20 in combination with the further shut-off device 34, 39 in the measuring arm 30 enables a dark current measurement in the detector, which can be used to optimize the OCT (step 132).

[0233] Fig. 16 shows further features of the system 10, which can be implemented in each of the disclosed embodiments, in particular in each of the systems 10 of Figs. 1, 2, 3, and 4. In addition to the lens 38, the system 10 has a further lens 38' or several further lenses 38', 38". The control logic 40 is configured to control a positioning system 140 to change the lens 38, 38', 38" positioned in the beam path of the measuring arm 30. This can be done automatically, without requiring any mechanical operator intervention for the lens change. The lens change can be based on measurements taken with the reference arm 20 and / or the measuring arm 30 switched off. Accordingly, the control logic 40 can be set up to control the positioning system 140 depending on measurements that were carried out with the reference arm 20 switched off and / or with the measuring arm 30 switched off.

[0234] System 10 can be configured to automatically perform optical dispersion correction. The optical dispersion correction can be performed depending on the lens 38, 38', 38" positioned in the beam path of the measuring arm 30, and System 10 can be configured to control the dispersion correction based on measurements taken with the reference arm 20 and / or the measuring arm 30 switched off.

[0235] Fig. 17 is a flowchart of a method 135 for material testing (for example, for the detection and / or classification of near-surface defects in an optical workpiece). The material can be an optical workpiece made of glass, salt, ceramic, an optical polymer, a semiconductor material, or another optical material. The method 135 can be performed using the system 10 or automatically by the system 10. The method 135 can be performed using the methods already described herein. At 131, at least one measurement is performed with the measuring arm switched off and / or at least one measurement is performed with the reference arm switched off. This can be implemented as described with reference to Fig. 15.

[0236] At 136, lens positioning takes place, in which the positioning system 140 (optionally based on measurements taken with the reference arm 20 and / or the measuring arm 30 switched off) is controlled by the control logic 40 to position a desired lens from several lenses 38, 38', 38" in the beam path.

[0237] At 132, OCT is performed on the material, whereby the OCT arrangement (for example, the power control device in the reference arm) uses the measurement results acquired at 131 for the acquisition and / or evaluation of the OCT image data. This can be implemented as described with reference to Fig. 15.

[0238] At 137, an automatic dispersion correction is performed depending on the lens positioned in the beam path of the measuring arm. The automatic dispersion correction can optionally be based on measurements taken with the reference arm switched off. In particular, the available lenses 38, 38', 38" of the system 10 can be measured (for example, using a calibration object) in order to determine an associated dispersion correction for each of several lenses 38, 38', 38" of the system 10.

[0239] While exemplary embodiments have been described with reference to the figures, modifications can be implemented in further embodiments. Exemplary specific modifications and further developments have already been explained. Further modifications are possible. The following are only examples of further modifications:

[0240] For example, while an OCT setup has been described that features a Michelson interferometer, other types of interferometers can also be used.

[0241] While one OCT arrangement has been described in which power regulation in the reference arm is achieved by a motorized aperture, optionally in combination with a swiveling polarizing filter, power regulation can also be achieved in other ways by using controllable optical elements.

[0242] The methods and systems are suitable for quality control of components of optical devices, but are not limited to this.

[0243] The present disclosure also includes embodiments with any combination of features mentioned or shown in relation to various embodiments. It also includes individual features in the figures, even if they are shown there in connection with other features and / or are not mentioned above or below. Furthermore, the alternative embodiments described in the figures and the description, and individual alternatives of their features, may be excluded from the subject matter of the invention or from the disclosed subject matter.

[0244] The terms "comprise" and "have" and derivatives thereof indicate a non-exhaustive relationship and do not exclude the presence of other elements or steps. The indefinite article "a" and derivatives thereof does not preclude the presence of multiple corresponding elements. The functions of several features listed in the claims can be fulfilled by a single unit or step.

[0245] Exemplary embodiments of the invention provide improved techniques for the detection and / or classification of near-surface defects. The methods and systems are particularly suitable for detecting near-surface defects located within an optical material in a boundary zone from the surface. The methods and systems enable the non-destructive detection of such defects in optical materials.

Claims

REQUIREMENTS 1. Method for material testing, comprising Performing optical coherence tomography (OCT) on a material (70) using an OCT array (11, 18, 19, 20, 30, 40) to generate OCT image data (73); and Evaluating the OCT image data (73); wherein the OCT arrangement (11, 18, 19, 20, 30, 40) comprises: a measuring arm (30) configured for scanning the material (70); a reference arm (20); a radiation source (11) for generating coherent radiation for the measuring arm (30) and the reference arm (20); and a detector (18) for detecting a coherent superposition (17) of the coherent radiation from the reference arm (20) and the measuring arm (30), wherein the reference arm (20) comprises at least one power control device (21; 22, 23; 22, 23, 25, 41) which is controlled by a control logic (40; 40, 42, 43) when acquiring the OCT image data (73).

2. Method according to claim 1, wherein the control logic (40; 40, 42, 43) controls the at least one power control device (21; 22, 23; 22, 23, 25, 41) based on an intensity variance of an interference pattern (71; 78) detected by the detector (18).

3. Method according to claim 2, wherein the control logic (40; 40, 42, 43) controls the at least one power control device (21; 22, 23; 22, 23, 25, 41) based on the intensity variance (71; 78) and based on a dynamic range (77) of the detector (18).

4. Method according to claim 3, wherein the control logic (40; 40, 42, 43) controls the at least one power control device (21; 22, 23; 22, 23, 25, 41) and an output power of the radiation source (11) such that the intensity variance (71; 78) fully utilizes the dynamic range (77) of the detector (18).

5. Method according to one of the preceding claims, wherein the at least one power control device (21; 22, 23; 22, 23, 25, 41) is configured to attenuate an optical radiation power in the reference arm (20) stepwise in several stages or continuously.

6. Method according to one of the preceding claims, wherein the at least one power control device (21; 22, 23; 22, 23, 25, 41) has an iris aperture (22) and an aperture drive (23) for adjusting the iris aperture, wherein the control logic (40; 40, 42, 43) controls the aperture drive (23).

7. Method according to claim 6, wherein the reference arm (20) has a beam widening optic (27) which widens a beam of coherent radiation generated by the radiation source (11) in the reference arm (20) before it hits the iris aperture (22).

8. Method according to one of the preceding claims, wherein the at least one power regulation device (21; 22, 23; 22, 23, 25, 41) is provided for light polarization-based power regulation in the reference arm (20).

9. Method according to any of the preceding claims, wherein the OCT arrangement (11, 18, 19, 20, 30, 40) has a beam splitter (19; 19p) through which the coherent radiation generated by the radiation source (11) enters the reference arm (20) and the measuring arm (30), and wherein the OCT arrangement (11, 18, 19, 20, 30, 40) has a polarizer (13) provided between the radiation source (11) and the beam splitter (19; 19p).

10. Method according to claim 9, wherein the at least one power control device (21; 22, 23, 25, 41) has a first polarization filter (25) in the reference arm (20), and wherein the OCT arrangement has a second polarization filter (35) in the measuring arm (30), wherein the control logic (40; 40, 42, 43) is configured to cause an adjustment of the first polarization filter (25) and the second polarization filter (35).

11. Method according to claim 10 depending on claim 6 or 7, wherein the first polarization filter (25) is arranged between the beam splitter (19) and the iris aperture (22).

12. Method according to any one of claims 9 to 11, wherein the beam splitter is a polarizing beam splitter (19p).

13. Method according to any of the preceding claims, wherein the OCT arrangement (11, 18, 19, 20, 30, 40) comprises a first shutter (24, 29) in the reference arm (20) and a second shutter (34, 39) in the measuring arm (30), and wherein the method comprises: controlling the first shutter (24, 29) and / or the second shutter (34, 39) by the control logic to perform at least one measurement in which at least one of the reference arm (20) and / or the measuring arm (30) is switched off, wherein the acquisition of the OCT image data (73) and / or the evaluation of the OCT image data is to be carried out depending on the at least one measurement.

14. Method according to one of the preceding claims, wherein the material (70) comprises an optical workpiece, and wherein the evaluation of the OCT image data (73) comprises automatic detection and / or classification of near-surface defects in the optical workpiece (70).

15. System (10) for material testing, comprising an optical coherence tomography (OCT) arrangement (11, 18, 19, 20, 30, 40) for performing an OCT on a material (70) to generate OCT image data (73), wherein the OCT arrangement (11, 18, 19, 20, 30, 40) comprises: a measuring arm (30) configured for scanning the material (70); a reference arm (20) comprising at least one power control device (21; 22, 23; 22, 23, 25, 41); a radiation source (11) for generating coherent radiation for the measuring arm (30) and the reference arm (20); a detector (18) for detecting a coherent superposition (17) of the coherent radiation from the reference arm (20) and the measurement arm (30); and a control logic (40; 40, 42, 43) set up for controlling the at least one power control device (21; 22, 23; 22, 23, 25, 41); and a computing system (50) for evaluating the OCT image data (73).

16. System (10) according to claim 15, which is set up to carry out the method according to any one of claims 1 to 14.

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