Method and apparatus for measuring a height map of a three-dimensional object's surface using axial scanning and modulated light.

Abstract

A method for measuring a height map of the surface of a three-dimensional object using light includes varying the distance between the optical focal position of an imaging system and the object to be measured; applying modulation to the light used to illuminate and image the object to obtain optical modulation; acquiring at least one image exposed while the distance and optical modulation are being varied; determining a numerical metric at at least one image pixel sensitive to the distance and optical modulation; and determining a height map of the object from the numerical metric, optical modulation, and the change in distance. Apparatus for performing the steps of the method is also provided.

Description

[Background technology]

[0001] Microscale topographic optical imaging plays a crucial role in industrial and scientific processes, as disclosed in Zuo, C., et al., “Deep learning in optical metrology: Book review”, Light: Science and Applications 11, (Springer US, 2022), and also in Chen, BC, et al., “Lattice light-sheet microscopy: Imaging molecules to embryos at high spatiotemporal resolution”, Science 346, (2014).

[0002] An example of a topographic optical imaging application is optical inspection on a production line. This specification refers, for example, to Ebayyeh, AARMA, Mousavi, A., “A Review and Analysis of Automatic Optical Inspection and Quality Monitoring Methods in Electronics Industry”, IEEE Access 8, 183192-183271 (2020).

[0003] Further examples of microscale topographic optical imaging include the measurement of additively manufactured parts disclosed in Vilar, N., et al., “Optical system for the measurement of the surface topography of additively manufactured parts”, Meas. Sci. Technol. 33, 104001 (2022), and the three-dimensional (3D) surface measurement of biomaterials disclosed in Marrugo, AG, Gao, F., Zhang, S., “State-of-the-art active optical techniques for three-dimensional surface metrology: Book Review”, J. Opt. Soc. Am. A 37, B60 (2020).

[0004] Topographic maps are typically reconstructed from a z-stack, i.e., a collection of images acquired sequentially from different focal planes, similar to confocal microscopy. See, for example, Ji, N., Freeman, J., Smith, SL, “Technologies for imaging neural activity in large volumes”, Nat. Neurosci. 19, 1154-1164 (2016).

[0005] The process of reconstructing a topographic map through the collection of sequentially acquired images from different focal planes, as described above, can be time-consuming, especially for bulky objects requiring large mechanical displacements between the focal point and the object. This problem can be further exacerbated when pursuing submicron optical resolution. In this case, a high numerical aperture (NA) optical system with a shallow depth of field is required, resulting in the need for numerous z-planes for proper reconstruction. Consequently, commercially available surface microscopes are unsuitable for characterizing fast-moving industrial processes or rapidly evolving biological systems.

[0006] Several strategies have been developed to reduce acquisition time in topographic imaging. These can be broadly categorized into two main groups.

[0007] The first strategic group consists of techniques aimed at accelerating the assembly of the z-stack. One example is the spatiotemporal multiplexing disclosed in Cheng, A., Goncalves, JT, Golshani, P., Arisaka, K., Portera-Cailliau, C., “Simultaneous two-photon calcium imaging at different depths with spatiotemporal multiplexing”, Nat. Methods 8, 139-142 (2011).

[0008] Further examples of the first strategic group aimed at reducing acquisition time in topographic imaging are multifocal microscopy, as reported by Abrahamsson, S., et al., “Fast multicolor 3D imaging using aberration-corrected multifocus microscopy”, Nat. Methods 10, 60-3 (2013), and also by Beaulieu, DR, Davison, IG, Kilic, K., Bifano, TG, Mertz, J., “Simultaneous multiplane imaging with reverberation two-photon microscopy”, Nat. Methods 17, 283-286 (2020).

[0009] Another example of the first strategic group for shortening the acquisition time in tomographic imaging is the encoded illumination method. For example, He, H., et al., “Tomographic-Encoded Multiphoton Microscopy”, ACS Photonics (2022). doi:10.1021 / acsphotonics.2c00629, and Zunino, A., et al., “Multiplane Encoded Light-Sheet Microscopy for Enhanced 3D Imaging”, ACS Photonics (2021). doi:10.1021 / acsphotonics.1c01401, and Ren, Y. X., et al., “Parallelized volumetric fluorescence microscopy with a reconfigurable coded incoherent light-sheet array”, Light Sci. Appl. 9, (2020) disclose the encoded illumination method.

[0010] Also provided is the use of variable optical elements for fast focus control, as disclosed in Kang, S. K., Duocastella, M., Arnold, C. B., “Variable Optical Elements for Fast Focus Control”, Nat Phot. 14, 533-542 (2020).

[0011] In the above methods in the strategy for shortening the acquisition time in tomographic imaging, it has been shown that 3D information can be acquired from the sample in real time, but it has been found that the axial range is limited, it is not very user-friendly, the implementation cost is high, or the range of samples that can be characterized is limited.

[0012] [[ID=?1]] Instead, a second strategic group for reducing acquisition time in topographic imaging is based on reducing the information required for reconstructing a 3D image. This is achieved by exploiting the inherent sparsity of the most common samples. An example of such an approach is to reduce the scan volume by selecting pre-defined regions within the sample, similar to random access scanning microscopy, as disclosed, for example, by Nadella, K.M.N.S., et al., “Random-access scanning microscopy for 3D imaging in awake behaving animals”, Nat. Methods 13, 1001 - 1004 (2016). However, the information required beforehand is generally not accessible.

[0013] Instead, computational techniques such as compressive sensing are provided, as disclosed in Edgar, M.P., Gibson, G.M., Padgett, M.J., “Principles and prospects for single-pixel imaging”, Nat. Photonics 13, 13 - 20 (2019), which enable complete topographic reconstruction from images that are much fewer (by up to one order of magnitude) than conventional z-stacks.

[0014] Furthermore, the improvement in 3D imaging speed may be obtained at the expense of reconstruction fidelity. The said techniques are also computationally costly and usually require off-line processing, as reported by Gao, L., Liang, J., Li, C., Wang, L.V., “Single-shot compressed ultrafast photography at one hundred billion frames per second”, Nature 516, 74 - 77 (2014). SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] Therefore, the need for real-time topographic optical imaging of large volumes at the microscale remains. [Means for solving the problem]

[0016] This specification provides a method for measuring the height map of the surface of a three-dimensional object using light, which satisfies the above-mentioned needs and offers several notable advantages.

[0017] The strategy behind this method is a novel scanning model that does not follow the conventional sequential, plane-by-plane scanning method. The steps of this method are not limited to the order listed herein.

[0018] This method includes the step of changing the distance between the optical focal position of the imaging system and the object to be measured. This step can be performed by moving one of the object or the imaging system relative to the other, changing the optical focal position of the imaging system, and modulating the wavelength of the illumination light.

[0019] This method further includes the step of applying modulation to the light used to illuminate and image an object to obtain optical modulation.

[0020] The process also involves taking steps to acquire at least one exposed image while varying the distance and light modulation.

[0021] Further steps are taken to determine a numerical metric at at least one image pixel that is sensitive to distance and light modulation.

[0022] This method further includes the step of determining an object's height map from a numerical metric, optical modulation, and a change in distance. Thus, the height value can be determined from a numerical metric from one or more images, optical modulation applied during the acquisition of the images, and a change in distance applied during the acquisition of the images. The object's height map is obtained by repeating the determination of the height value for multiple image pixels.

[0023] The metrics described above can be based on at least one of the following: detection of structured light in the acquired image, detection of the surface texture of the object, application of spatial mathematical operators to the image sensitive to structured light or the surface texture of the object, signals from a confocal system, and signals from an interferometer.

[0024] The determined height map can be reconstructed using at least one of the following methods: applying optical modulation to decode the discrete height map, or applying optical modulation to obtain a continuous height map.

[0025] On the other hand, optical modulation can be performed by changing the intensity of light, changing the wavelength of light, changing the polarization state of light, turning the illumination on and off, and changing the relative intensity by combining multiple light sources having different characteristics.

[0026] Furthermore, optical modulation is performed through optical intensity modulation, which is implemented at a finite number of intensity levels with a given sequence unique to each image that can form a code identifying a set of distance values. In some cases, optical modulation can be implemented at two intensity levels, in which case the sequence forms a binary code that encodes a set of distance values. In other cases, optical modulation can be performed through optical intensity modulation, which is implemented with at least one of a series of optical pulses, a sine function, a sawtooth function, a square wave function, and any combination of these with various time delays.

[0027] In some cases, this method may be carried out using an interferometer as the imaging system and the optical signal of the interferometer as the numerical metric, where the optical modulation is periodic, and the period corresponds to the time required to change the distance by an amount equivalent to a multiple of half the wavelength of the irradiated light.

[0028] In some cases, this method can be carried out using multiple irradiation systems employing structured light with different patterns, so that they can be modulated independently in time.

[0029] In some cases, this method can be carried out using an imaging system with longitudinal optical chromatic aberration and an illumination system capable of modulating the wavelength of the illumination light or multiple illumination systems of different wavelengths. In this case, the change in wavelength corresponds to a change in the distance between the optical focal point and the object.

[0030] According to the method disclosed above in this specification, a reduced set of images is required to reconstruct the height map of an object. Due to the implemented distance change, each image is acquired during a focus sweep across the axial range. The axial distance range covered by each image defines the measurement range, and together with the lateral field of view of the imaging system, defines the measurement volume. Synchronized time-modulated illumination is employed during the acquisition of each image so that information about the axial position of the sample can be encoded in each image. As a result, the strong data sparsity inherent in three-dimensional topographic imaging can be utilized, enabling axial localization of objects while dramatically improving acquisition time.

[0031] This method enables high-speed 3D topographic imaging. An example of topography reconstructed using an implementation of the method described below is a surface measurement over an axial range of 100 μm from just eight images at submicron resolution. Such 3D topographic imaging can be performed at speeds impossible with conventional techniques known to date.

[0032] In contrast, conventional methods for determining the axial position of an object to be measured involve scanning the axial range across N planes and interrogating all of them. In the sense of this disclosure, interrogating means inferring whether an object exists on a given sampling plane within an axial margin corresponding to the depth of field of the imaging system, where the depth of field is the axial range at which the plane is considered to be in focus. Since each sampling plane corresponds to an image, at least N images are usually required. The number of images N depends on prior information about the sample to be measured, the characteristics of the optical system, and the scan range. However, the number of images N is usually large.

[0033] This method makes it possible to determine the axial position of an object to be measured using a reduced set of images. An exemplary basic form of this method is based on a binary search of samples, in which merged planar groups are interrogated and checked for the presence of a sample in each planar group. Such an implementation has the advantage of significantly reducing the number of queries and therefore the number of images. When implementing the binary search, the axial position of a sample can be determined using only log2(N) images. As a result, information is extracted through this method with far fewer samples / images than known methods based on sequential plane-by-plane scans.

[0034] The implementation of this binary search method involves acquiring a set of images while scanning the optical focus across the entire measurement range. Thus, information from the focal plane and all other planes is merged onto each image. The axial position of the focal plane is unknown because it depends on the sample height and constitutes the measurement quantity. During the focus sweep, illumination is turned on and off in a unique and precisely controlled sequence that differs for each image. Interrogation of each image to infer whether an object exists in the group of axial positions defined by the illumination during the focus sweep is performed by calculating a numerical metric that is sensitive to the presence of an object near the optical focal position. Determining the object height at each pixel for which the metric is calculated means determining the object's height map.

[0035] In a binary implementation of this method, the illumination has two states, and the binary code is determined by the sequence implemented during the acquisition of each image. Therefore, acquiring and binaryizing the metric value of each image means acquiring a code that identifies the height of the object. In such a binary method, the measurement range is divided into a set of discrete distance values, each identified by a code. Thus, decoding provides the distance value in the set of discrete values ​​corresponding to the height of the object. It is also possible to implement a code with more than two states. Alternatively, the modulation of the light may vary in a continuous manner, or it may be continuous and periodic. In this case, the acquisition of the object height is not limited by the discretization of the illumination sequence.

[0036] An apparatus for measuring the height map of the surface of a three-dimensional object using light through the method described above is also disclosed herein.

[0037] The apparatus includes an imaging system that defines the optical focal position. The imaging system may include at least one of a microscope system, at least one camera, at least one polarizing camera, at least one hyperspectral camera, a point scanning system, at least one polarization-sensitive detector, and at least one hyperspectral detector.

[0038] The apparatus further includes a system for changing the distance between the optical focal position of the imaging system and the object to be measured. The system may be based on the mechanical movement of the object or the imaging system that provides the relative movement. The system may also be based on changing the optical focal position of the imaging system. Changing the optical focal position of the imaging system can be achieved, for example, by moving one or more individual optical elements of the imaging system, or by incorporating a variable optical element such as a variable focus lens.

[0039] One or more illumination systems for illuminating an object to be measured are also provided. These illumination systems may be configured to project structured light onto the object. Systems for applying modulation to the light used to illuminate and image the object are also included. Each system may function independently of the others. One or more detectors may be provided for acquiring one or more images. The structured light projected onto the object may be independently modulated.

[0040] The imaging system described above may be an interferometer, for example, in which the optical modulation is periodic, and the period corresponds to the time required to change the optical focal position by a distance that is a multiple of half the wavelength of the irradiated light.

[0041] The imaging system described above may be, for example, a confocal imaging system.

[0042] The irradiation system may include at least one of the following: a system for changing the polarization state of light, and a system for changing the wavelength of light used for irradiation.

[0043] This device may include at least one of a system for determining numerical metrics and a system for reconstructing the height map of objects.

[0044] Examples not limited to this disclosure will be described below with reference to the attached drawings. [Brief explanation of the drawing]

[0045] [Figure 1] This figure schematically shows an example of the apparatus 1000 for carrying out this method. [Figure 2] This is a graph of the focus-sensitive signal S obtained through a metric based on the magnitude of the Laplacian of the image field according to equation (2), plotted for two pixels selected across the measurement range. [Figure 3] This graph shows the set of images Ii in coding sequence Mi, acquired through a conventional scan. [Figure 4] This graph, similar to Figure 3, shows the signal S sampled through a conventional scan. [Figure 5] This includes a graph showing the coding sequence Mi corresponding to a set Ii of images obtained according to this method, which implements a binary code based on Gray code. [Figure 6] This graph shows the integrated signal S3 of a single pixel at height zs, illustrating how it responds to the presence of a sample. [Figure 7] This graph shows the integrated signal S4 of a single pixel at height zs, illustrating how it responds to the presence of a sample. [Figure 8] This graph shows intensity-modulated irradiation, with three images acquired using sinusoidal modulation and a 2π / 3 relative phase shift. [Figure 9]This figure shows an example of an apparatus for carrying out this method. [Figure 10] This figure shows height map measurements using the apparatus shown in Figure 9 for (a) a tilt mirror, (b) a coin area including a star shape, and (c) an area of ​​material measure NPL B40 type AIR as defined in ISO 25178-70:2014 Geometrical product specification (GPS) - Surface texture:Areal - Part 70:Material measures (Vernier, Geneva, Switzerland: International Organization for Standardization). [Modes for carrying out the invention]

[0046] One non-limiting example of an apparatus 1000 for measuring a height map of the surface of a three-dimensional object or sample 100 using light is disclosed herein, shown in Figures 1 and 9 of the drawings. The apparatus 1000 is configured to perform the present method for measuring a height map 100 of an object using light.

[0047] In the illustrated example, the apparatus 1000 is confocal and comprises an imaging system 200 having a defined optical focal position whose field of view and axial measurement range define a volume of interest containing the sample 100 to be measured, at least one illumination system 400, an optical modulation system 700, a system 600 for changing distance, a detector 500, and a system 800 for reconstructing the height of an object.

[0048] The apparatus 1000 is configured to perform the steps of the method for determining the axial position of the object 100 to be measured.

[0049] In conventional plane-by-plane scanning methods, the measurement range is divided into N equally spaced planes, and while the object to be measured is axially scanned, signals are measured or calculated in each plane, and the axial response of each image pixel is constructed. Identifying the location of the largest axial response means measuring the height at a given pixel. This process is similar to performing a linear search, requiring a large number of images N involved in the search, i.e., axial sampling of the axial response, in which case each image represents a query that interrogates the presence of the object in each plane. In contrast, the present method allows the axial position of object 100 for a given image pixel to be determined with far fewer measurements, enabling the reconstruction of the topographic map at high speed. Reducing the number of queries results in a corresponding reduction in the number of images. In this method, instead of sampling the axial response plane by plane, information is collected from a merged group of planes in each measurement, and therefore, the interrogation of each image can check whether object 100 is in the corresponding group of planes. One way to specify a group of planes is to implement a binary code across the entire axial measurement range. If the code implements a binary search, only log2(N) images are needed to determine which axial plane the axial position of object 100 falls within. Since N is usually a large number, this method results in a significant reduction in the number of images needed to measure the height map of an object.

[0050] Extracting information using far fewer samples / images compared to conventional methods is highly advantageous for real-time topographic optical imaging of large volumes at the microscale. For example, as shown in Figure 5, the Gray code encoding sequence M iWhen used as a reference, if the measurement range Δz of interest of 400 μm is sampled conventionally in 1.6 μm steps, as in the conventional method, 250 images would be required. However, this method provides equivalent axial localization using only 8 images.

[0051] By using a combination of the relative intensity of the focus-sensitive signal and continuous light modulation, the axial position of object 100 can be calculated with high accuracy, as shown in Figure 8, as described below.

[0052] As shown in Figure 1, illumination light 300 is projected onto the object 100 through the illumination system 400 described above. In the illustrated example, the illumination light 300 is time-coded illumination 300 for illuminating the object 100 to be measured. Furthermore, the illumination system 400 may be configured to project structured light 300. Structured illumination can be performed using a transmissive chrome-on-glass mask with a checkerboard pattern projected onto the object 100.

[0053] A system for applying modulation to illumination light 300 used to illuminate and image object 100 is also provided, as well as one or more detectors 500 for acquiring one or more images. The acquired images are exposed while the distance and optical modulation are varied. Images are acquired while scanning the optical focus over the entire measurement range Δz. Thus, information from the focal plane and all other planes is merged onto each image. The axial position of the focal plane is at the height z of object 100. s It is unknown because it depends on and constitutes the quantifiable quantity. In an implementation that performs optical modulation by varying the intensity of the irradiated light at two intensity levels and setting one intensity level to zero, the irradiator 300 is turned on and off during exposure in a unique sequence that is different for each image.

[0054] Examples described herein provide a system for determining a numerical metric at at least one image pixel sensitive to distance and light modulation. The metric may be based on at least one of the following: detection of structured light in the acquired image, detection of the surface texture of an object, application of a spatial mathematical operator to an image sensitive to structured light or the surface texture of an object, a signal from a confocal system, and a signal from an interferometer.

[0055] The object's height map 100 is also determined from the aforementioned numerical metrics, optical modulation, and distance changes. An example of measuring the height map using the apparatus shown in Figure 9 is illustrated in the graphs shown in Figures 10a, 10b, and 10c of the drawing.

[0056] The apparatus 1000 further includes a system for reconstructing the height map of object 100. The aforementioned height map reconstruction system can reconstruct the aforementioned determined height map. The reconstruction system may be based on at least one of the following: applying optical modulation to decode the discrete height map, or applying optical modulation to obtain a continuous height map.

[0057] An exemplary implementation of the method described herein involves a focus-sensitive signal S i It is based on Gray code for axial encoding. Such code is based on the height z of the object, as illustrated in Figure 5 of the drawing. s To calculate the step number d that includes the binary sequence M i It is used to encode sequence M. In this example, i The irradiation is turned on and off according to the binary value.

[0058] Given irradiation sequence M i For (z), the acquired image I(x,y,M) is obtained when the distance between the object and the optical focus is changed over the measurement range. i )teeth,

number

[0059] The focus sweep is assumed to be performed at a constant speed v over the measurement range Δz, and thus z can be time-based, such as z = v·t. However, any other arbitrary relationship can be applied as long as z(t) is known and monotonic. Note that in this binary implementation, it is not possible to infer the position of the focal plane from a single focus sweep image. However, a focus-sensitive signal can be calculated from the image, and thereby a numerical metric can be calculated. Thus, based on the value of this metric, it is possible to detect whether the illumination was on or off when the object 100 was in focus during the focus sweep.

[0060] One option for the numerical metric implementing the focus-sensitive signal is the detection of high spatial frequency components in the image. Such components are generated from the sample reflectance spatial map r(x,y) or the illumination pattern L(x,y). Since PSF(x,y,z - z s ) acts as a strong low-pass filter for z ≠ z s (within the depth of field), high spatial frequency features are only recorded when M i (z = z s ) ≠ 0, and this is the focus-sensitive signal. As an example, as shown in FIG. 2, a metric based on the magnitude of the Laplacian of the image field provides such a signal:

number

number

[0061] The above information will be used in this method. i Through a simple threshold of (x,y), binary modulation M i The presence or absence of object 100 at any of the positions axially masked by (z) is detected. For example, z < (z max -z min ) / 2 when M i (z)=1 is implemented, otherwise M i If (z)=0 is implemented, S is above or below the set threshold. i The value of (x,y) indicates that the height of object 100 at (x,y) is somewhere in the first or second half of the measurement range Δz. Therefore, in conjunction with the assumption that object 100 is topographic, a well-designed sequence set {M i Using a combination of several images at (z), we can perform an axial search for the height at each pixel. That is, the measurement range Δz is set to size T=(z max -z min Dividing it into N steps of ) / N gives us the step number d corresponding to the height of the object at each pixel.

[0062] Encoding sequence M iIf the system implements basic binary code, the step number d, which includes the axial position of an object located laterally within the captured field of view, can be inferred through equation (3) as follows:

number

[0063] In the case of other arbitrary coding sequences, such as the aforementioned Gray code, the decoding step is performed before the step number d is determined. Figure 5 shows the coding sequence M according to this method, implementing the Gray code in an image with n=4. i Image set I i This shows an example of how the focus-sensitive signal S is obtained by calculating a numerical metric. i A focal-sensitive signal S is obtained. i By converting it to binary, the height z of object 100 s A Gray code is obtained for calculating step number d, which includes the following:

[0064] As described above, the conventional method based on the conventional scan shown in Figure 3 (I1…I n This indicates image acquisition, S1...S n In optical sectioning (where ∫ indicates optical sectioning), the signal is sampled at a uniform sampling rate, as illustrated in Figure 4, requiring a much larger number of samples / images compared to the methods described herein.

[0065] The imaging system's depth of field determines its ability to axially resolve the presence or absence of object 100, therefore the binary encoding sequence M iThe minimum axial step height that can be significantly implemented using this method is determined by the depth of field. Due to the convolution in equation (1), implementing smaller steps does not increase the axial resolution. However, the localization accuracy can be maximized by further utilizing prior knowledge of sparsity. This can be done by extracting information from the continuous change of a numerical metric as a function of the object's height. For example, this can be done by temporally modulating the intensity of the illumination. Alternatively, this can be done by using pulsed illumination and utilizing the axial response in equation (1). A specific example implemented using sinusoidal modulation illumination is to acquire three images with a relative phase shift of 2π / 3. The axial position of object 100 can be calculated with high accuracy using the relative intensity of the focus-sensitive signal.

[0066] If the time-modulated intensity is chosen to follow a periodic function, the calculation of the object's height is limited to the height associated with the irradiation period, and the height map wrapped in steps corresponding to the irradiation period is effectively reconstructed as follows:

number

number

[0067] An interesting implementation of this method combines the described example for calculating the wrapped height map with an implementation of a binary sequence designed to provide a means for unwrapping the height map. One option for this is to temporally sinusoidally modulate the irradiation intensity and perform a focus sweep of each image over N cycles across the measurement range Δz, as illustrated in the example shown in Figure 8. That is, the modulation in the second stage is set as follows:

number

[0068] The filtering in equation (2) is z s In order to extract high spatial frequency information that exists only in a plane close to S, j (x,y) The size is M j (z = z s ) is proportional to, and therefore,

number

[0069] Different phase shifts δ j By repeating the measurement, the axial position of object 100 can be determined. For example, the phase shift set δ j By implementing ={-2π / 3,0,2π / 3}, the axial position of object 100 can be easily determined as follows:

number

number

number

[0070] Step number d and wrapped measurement

number

[0071] Figure 9 schematically shows an example of an experimental apparatus for carrying out the present method. Apparatus 1000 includes an imaging system based on a microscope objective lens and a tube lens, an illumination system including means for LED illumination and projection of structured light, a light modulation system, and means for changing the distance between the optical focal position 200 of the imaging system and the object 100 to be measured. In this non-limiting example, this is performed by an electric linear stage configured to move the microscope objective lens relative to the object 100. The measurement range Δz is set to 100 μm. The electric stage provides an appropriate moving speed, and the camera exposure time is set accordingly, so that the object 100 moves at a constant speed across the measurement range Δz during the exposure time. In this example, a 20x / 0.45NA objective lens with a depth of field of approximately 2.6 μm is employed. Thus, the measurement range Δz can be divided into approximately N=40 steps, and the maximum number of binary modulation images is 7, 2 n-1 The smallest integer satisfying >40 is also 7. However, it is not necessary to implement many images. In this case, the measurement range Δz is divided using N=8 steps, and the step size is T=12.5 μm. Furthermore, continuous and periodic irradiation based on sinusoidal modulation intensity is implemented so that the period corresponds to the step size T. The irradiation system 400 includes a light-emitting diode (LED) with a center wavelength of 532 nm that can be easily controlled and synchronized with acquisition. The irradiation system employs structured light in the form of a checkerboard pattern implemented using a transmissive mask included in the irradiation light path. An example of a reconstructed height map implemented in the manner described herein is shown in Figure 10.

[0072] Although only one implementation example is disclosed herein, other alternatives, modifications, uses, and / or equivalents are possible. The signal to be measured may be any focus-sensitive signal, such as a focus change operator or a confocal signal. Various hardware can be used to physically scan object 100, including motorized or piezoelectric stages. Remote focusing techniques can be used to remotely control the focal position. Adjustable optical systems can also be used to implement this method. Remote focusing, adjustable optical systems, or equivalent methods may be advantageous in terms of speed because they can avoid the physical inertia associated with the relative motion of object 100 and the hardware, thus providing faster operation.

[0073] Therefore, all possible combinations of the examples described are also covered. The scope of this disclosure should not be limited by any particular example, but should be determined solely by a fair reading of the claims below. The reference numerals in parentheses in the claims relating to drawings are for the sole purpose of enhancing the understanding of the claims and should not be construed as limiting the scope of the claims.

Claims

1. A method for measuring the height map of the surface of a three-dimensional object using light, Changing the distance between the optical focal position of the imaging system and the object to be measured, To obtain optical modulation by applying modulation to the light used to illuminate and image the object, Acquire at least one exposed image while the distance and the optical modulation are being changed, Determining the distance and a numerical metric at at least one image pixel sensitive to the optical modulation, Determining the height map of the object from the numerical metric, the optical modulation, and the change in distance, A method that includes this.

2. The aforementioned change in distance is Moving one of the object and the imaging system relative to the other, Changing the optical focal position of the imaging system, and Modulating the wavelength of the irradiated light, The method according to claim 1, which is carried out by one or more of the following.

3. The aforementioned optical modulation is Changing the intensity of light, Changing the wavelength of light, Changing the polarization state of light Turning the irradiation on and off, By combining multiple light sources with different characteristics, the relative intensity can be changed. The method according to any of the claims, which is carried out by one or more of the above.

4. The method according to any one of the claims, wherein the optical modulation is performed through optical intensity modulation implemented at a finite number of intensity levels in a given sequence unique to each image that forms a code identifying the set of distance values.

5. The method according to claim 4, wherein the optical modulation is implemented at two intensity levels that form a binary code.

6. The aforementioned optical modulation is A series of light pulses, Sine function, Sawtooth function, Square wave function, and These combinations involve various time delays, The method according to any one of claims 1 to 4, which is performed through optical intensity modulation implemented in at least one of the following:

7. The aforementioned metric is, Detection of structured light in the acquired image, Detection of object surface textures, Application of spatial mathematical operators to the image that is sensitive to structured light or the surface texture of the object, Signals from the confocal system, and Signal from the interferometer, The method according to any of the claims, which is based on at least one of the above.

8. The height map determined above is Decoding discrete height maps by applying optical modulation, Applying optical modulation to obtain a continuous height map, The method according to any one of the above claims, which is reconfigured using at least one of the above.

9. An apparatus for measuring a height map of the surface of a three-dimensional object using light, according to the method of any one of claims 1 to 8, An imaging system that defines the optical focal position, A system for changing the distance between the optical focal position of the imaging system and the object to be measured, One or more irradiation systems for irradiating the aforementioned object, A system for applying modulation to the light used to illuminate and image the object, One or more detectors for acquiring one or more images, A device equipped with the following features.

10. The apparatus according to claim 9, wherein the irradiation system is configured to project structured light onto the object.

11. The apparatus according to claim 9, wherein the imaging system is an interferometer, the optical modulation is periodic, and the period corresponds to the time required to change the optical focal position by a distance that is a multiple of half the wavelength of the irradiated light.

12. The aforementioned imaging system is Microscope system, camera, Polarizing camera, Hyperspectral camera, Point Scan System, Polarization-sensitive detector, and hyperspectral detector, The apparatus according to any one of claims 9 to 11, comprising at least one of the following.

13. The irradiation system is A system for changing the polarization state of the aforementioned light, A system for changing the wavelength of the light used for irradiation, The apparatus according to any one of claims 9 to 12, comprising at least one of the following.

14. The apparatus according to any one of claims 9 to 13, comprising a system for determining the numerical metric.

15. The apparatus according to any one of claims 9 to 14, comprising a system for reconstructing the height map of the object.

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