Method and apparatus for characterizing an object

Abstract

A method for characterizing an object is provided, comprising: providing, via a support plane, coherent incident radiation at the object in each of a plurality of radiation configurations; detecting, for each of the plurality of radiation configurations, radiation intensity scattered by the object at a detector; and determining, via an iterative process, an object transport function associated with the object from the detected radiation intensity at the detector for each of the plurality of radiation configurations. The iterative process includes, for each of the plurality of radiation configurations, estimating, from the detected intensity at the detector, a support constraint at the support plane, and a current estimate of the object transport function, an incident wave function representing the incident radiation at the object and an exit wave function representing the radiation emanating from the object; determining a ratio of a sum of intensities of the exit wave functions of the plurality of radiation configurations to a sum of intensities of the incident wave functions of the plurality of radiation configurations; and updating the estimate of the object transport function from the determined ratio and an amplitude constraint.

Description

Technical Field

[0001] This invention relates to a method and apparatus for characterizing objects. Specifically, this invention relates to characterizing objects using coherent imaging. Background Technology

[0002] Coherent diffraction imaging (CDI) is a lensless coherent imaging technique widely used in fields such as biology and materials science. CDI can be used to image objects by directly determining the complex outgoing wave from recorded diffraction intensity measurements. However, recovering the phase of the outgoing wave in CDI is not straightforward, and traditional techniques have limited robustness, requiring isolated samples and simple phase transitions. An example of conventional CDI techniques is shown in S. Marchesini, “A unified evaluation of iterative projection algorithms for phase retrieval”, Rev. Sci. Instrum. 78(1)(2007)011301.

[0003] The performance of CDI has been improved by ptychography, as described by F. Pfeiffer, “X-ray ptychography,” Nat. Photon 12(1)(2018) 9–17. Ptychography provides better algorithmic convergence by recording multiple diffraction patterns with overlapping illumination regions between measurements (each diffraction pattern is generated by the change in position of the incident radiation relative to the object) and using the overlapping regions as constraints. However, multiple overlapping measurements place demands on the stability of the setup, which is not always feasible. For example, the stability required by ptychography is not available in experimental settings using X-rays or electrons or with fast sample dynamics. Furthermore, in ptychography, the function of the incident radiation must remain constant with positional changes. This can affect the lateral resolution and slicing capability of the imaging.

[0004] Coherent modulation imaging (CMI) offers an improved alternative to CDI, as described in published application EP2478407A1. CMI is a “single-shot” technique where only one illumination of the object is used, and a modulator is placed between the object and the detector to amplify the interference between wavelets of the object’s outgoing waves and facilitate phase recovery. However, in CMI, the key is the modulator function associated with the modulator, known as the prior parameter. Acquiring the modulator function, or refining it to the desired degree, requires auxiliary measurement techniques, such as stacking, to characterize the modulator.

[0005] As an alternative to the stacking technique for characterizing modulators, averaging multiple independent CMI measurements during CMI has proven effective (“Modulator refinement algorithm for coherent modulation imaging”, Wang et al., Ultramicroscopy 216(2020)113034, 29 May 2020). This averaging can refine the modulator function without requiring separate experimental characterization of the modulator. However, this technique is only suitable for refinement, i.e., when the modulator function already needs to be known with reasonable precision.

[0006] The purpose of this invention is to alleviate one or more problems in the prior art. Summary of the Invention

[0007] According to the present invention, a method, apparatus and computer-readable medium for characterizing objects are provided.

[0008] According to a first aspect, a method for characterizing at least a portion of an object is provided, comprising the steps of: providing coherent incident radiation at the object via a support plane in each of a plurality of radiation configurations; detecting, for each of the plurality of radiation configurations, the intensity of radiation scattered by the object at a detector; and determining, via an iterative process, an object transfer function associated with the object based on the intensity of radiation detected at the detector for each of the plurality of radiation configurations.

[0009] The iterative process includes: for each of the plurality of radiation configurations, estimating the incident wave function representing the incident radiation at the object and the emitted wave function representing the radiation emitted from the object, based on the intensity detected at the detector, the support constraint at the support plane, and the current estimate of the object transfer function; determining the ratio of the sum of the intensities of the emitted wave functions of the plurality of radiation configurations to the sum of the intensities of the incident wave functions of the plurality of radiation configurations; and updating the estimate of the object transfer function according to the determined ratio and amplitude constraints. That is, the determined ratio is constrained by amplitude constraints to obtain the object transfer function.

[0010] Determining this ratio defines the averaging of independent measurements taken for different radiation configurations. Advantageously, constraining this ratio with amplitude constraints enables the iterative process to converge for completely unknown objects.

[0011] The estimate of each wavefunction can be updated iteratively. In each iteration of this process, each of the incident wavefunction, the emitted wavefunction, and the object transport function can be updated. Specifically, each estimate can be updated based on the estimates made in previous iterations. For each radiation configuration, the estimate of the illumination wavefunction at the support plane is also updated iteratively.

[0012] The estimates of the incident and emitted wave functions for a given radiation configuration are based on the intensity of the corresponding radiation configuration detected at the detector.

[0013] Optionally, the amplitude constraint includes a minimum amplitude limit and a maximum amplitude limit for the object transfer function. The minimum amplitude limit and the maximum amplitude limit can be predetermined to exclude physically impossible values. In some embodiments, the amplitude constraint includes the condition |O|∈[0,1], where |O| represents the estimated amplitude of the object transfer function.

[0014] In each iteration, determining the ratio may include determining the sum of the intensities of the incident wavefunction estimated in the current iteration; and determining the sum of the intensities of the emitted wavefunction estimated in previous iterations. That is, the ratio can be determined to reflect the updated incident wavefunction. For example, in each iteration n, it can be determined based on the parameters: To determine this ratio, where E j,n-1 Let P represent the emitted wave function of the radiating configuration j in iteration n-1. j,n Let represent the incident wave function of the radiation configuration j in iteration n. The determined ratio can then be constrained by amplitude constraints to obtain an updated object transfer function.

[0015] In each iteration, determining the ratio may include determining the sum of the intensities of the incident wavefunction estimated in the previous iteration; and determining the sum of the intensities of the emitted wavefunction estimated in the current iteration. That is, the ratio can be determined to reflect the updated emitted wavefunction. In each iteration n, this can be determined based on the parameters: To determine this ratio, where E j,n Let P represent the emitted wave function of the radiative configuration j in iteration n. j,n-1 Let represent the incident wave function of the radiation configuration j in iteration n-1. The determined ratio can then be constrained by amplitude constraints to obtain an updated object transfer function.

[0016] In each iteration, the object transfer function can be updated once or multiple times. Specifically, in some embodiments, the object transfer function can be updated a first time to reflect the updated incident wave function, and can be updated a second time to reflect the updated outgoing wave function.

[0017] The iterative process may include: providing an initial estimate of the object transfer function; providing an initial estimate of the wave function associated with each radiation configuration at the support plane; and propagating the wave function back and forth between the support plane and the detector to obtain estimates of the incident wave function and the output wave function.

[0018] Optionally, the plurality of radiation configurations include: a plurality of tilt angles of the incident radiation; or, a plurality of rotation angles of the phase screen at the support plane.

[0019] This method may include terminating the iterative process based on the convergence of the object transfer function between subsequent iterations.

[0020] This method may include determining image data representing an object based on an object transfer function.

[0021] According to a second aspect, a method for characterizing at least a portion of an object is provided, comprising the steps of: providing coherent incident radiation at the object via a support plane in each of a plurality of radiation configurations, wherein each radiation configuration includes a predetermined tilt angle of the incident radiation; detecting the intensity of radiation scattered by the object at a detector for each of the plurality of radiation configurations; and determining an object transfer function associated with the object via an iterative process based on the detected radiation intensity at the detector for each of the plurality of radiation configurations.

[0022] The iterative process includes, for each of the plurality of radiation configurations, estimating the incident wave function representing the incident radiation at the object and the emitted wave function representing the radiation emitted from the object, based on a predetermined tilt angle of the radiation configuration, the intensity detected at the detector, the support constraint at the support plane, and the current estimate of the object transfer function; determining the ratio of the sum of the intensities of the emitted wave functions of the plurality of radiation configurations to the sum of the intensities of the incident wave functions of the plurality of radiation configurations; and updating the estimate of the object transfer function based on the determined ratio.

[0023] According to another aspect, a device for characterizing an object is provided. The device includes one or more electronic processors configured to operably execute computer-readable instructions to perform the method according to any of the preceding aspects.

[0024] Optionally, the device further includes: a radiation source configured to provide coherent incident radiation; and a detector configured to detect the intensity of radiation scattered by the object for each of a plurality of radiation configurations and to output detection data based on the radiation intensity.

[0025] According to another aspect, a computer-readable medium including computer software is provided, which, when executed, is configured to perform the method according to the above aspects. Attached Figure Description

[0026] The embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

[0027] Figure 1 An apparatus for performing coherent diffraction imaging (CDI) according to one embodiment is shown;

[0028] Figure 2 This is a schematic diagram of a computing device configured to perform a method according to an embodiment;

[0029] Figure 3 This is a flowchart of a method 300 for characterizing an object according to an embodiment;

[0030] Figure 4 An iterative process performed during one embodiment of method 300 is shown;

[0031] Figure 5 Example image data constructed after executing method 300 is shown; and

[0032] Figure 6 The convergence data illustrating the convergence of method 300 are shown. Detailed Implementation

[0033] Existing coherent imaging techniques have several drawbacks. The difficulty of phase retrieval means that conventional CDI may lack robustness and may only be suitable for objects with simple phase changes. Stacking offers a more robust imaging technique, but it is not suitable for unstable experimental settings or those with rapid sample dynamics. Coherent modulation imaging (CDI) provides a single-shot imaging technique, but it requires at least fairly accurate prior knowledge of the modulator function of the modulator used.

[0034] An improved coherent imaging technique, referred to herein as multiple complex illumination imaging, is provided for robustly characterizing complex outgoing waves from completely unknown objects. The disclosed technique can be used as a standalone imaging technique to image objects, or it can be used to characterize completely unknown modulators for CMI measurements. Embodiments of the invention will be described with reference to multiple complex illumination imaging as a standalone imaging technique; however, it should be understood that this characterization method can be used for other purposes, such as characterizing modulators in CMI measurements as described above.

[0035] This imaging technique utilizes incident radiation with various different radiation configurations, such as multi-angle plane light, to obtain multiple independently recorded diffraction patterns of the same object. Each radiation configuration can be characterized by different illumination wavefields, which may be unknown. For each radiation configuration, an estimate of the wavefield emitted from the unknown object can be obtained by utilizing support constraints at the support plane through which the incident radiation passes and constraints on each recorded diffraction pattern. The estimate of the object transfer function can then be iteratively updated by averaging multiple independent measurements. Advantageously, in some embodiments, iteratively updating the object transfer function in this way can serve as convergence for the unknown object by introducing amplitude constraints on the amplitude of the transfer function. The convergence of the object transfer function then makes it possible to reconstruct the wavefield leaving the object for each radiation configuration, i.e., the outgoing wave characterizing the object. The previously unknown illumination wavefield characterizing each radiation configuration can also be recovered.

[0036] In other embodiments, as an alternative to amplitude constraints, known radiation or illumination configurations, such as known tilt angles for each configuration of incident radiation, can be used as alternative constraints to facilitate convergence and reconstruct the wave field leaving the object.

[0037] Figure 1 An apparatus 100 for characterizing an unknown or partially unknown object 130 according to an embodiment of the present invention is shown. The apparatus 100 is illustrated as having a transmissive arrangement in which radiation is transmitted through the object 130. It should also be appreciated that the apparatus 100 may be arranged in a reflective configuration in which radiation is reflected from the object 130.

[0038] Device 100 includes one or more radiation sources 110 configured to provide coherent incident radiation 115 directed to object 130. In the illustrated embodiment, radiation source 110 may be a laser source 110 for providing coherent illumination wave 115, but it should be understood that laser source 110 can be readily replaced by a source of alternative types of coherent radiation, such as X-rays, electrons, or other types of coherent radiation. One or more radiation sources 110 are configured to provide incident radiation 115 for each of a plurality of different radiation configurations to record independent diffraction measurements. That is, a diffraction pattern is recorded for each radiation configuration. The plurality of different radiation configurations may be, for example, different illumination angles, also referred to herein as illumination tilt angles. The illumination angle of a radiation configuration may be defined as the angle between the axis of the coherent incident radiation 115 and the optical axis of device 100. The optical axis of device 100 may be defined as perpendicular to the sensing surface 140 of the detector. In other embodiments, radiation source 110 may provide illumination at a single angle. Multiple radiation configurations can then be provided by adjusting the illumination wave, for example, by rotating the phase screen, wherein incident illumination is provided to the object via the phase screen.

[0039] Incident radiation 115 propagates from radiation source 110 in device 100 to a support plane 120 located between radiation source 110 and object 130. Support plane 120 defines a spatial plane through which incident radiation 115 propagates. A physical support, such as a sheet of material, is located at support plane 120. The physical support may include holes that define a support region through which incident radiation propagates. Therefore, the physical support may include a sheet of material that radiation cannot substantially penetrate, except through the holes. When performing the iterative process described herein to estimate the wave field at different locations of device 100, the support constraint S(r) can be... s ) Applied to the incident radiation at the supporting plane 120, by r s This indicates that, makes

[0040]

[0041] Device 100 includes detector 140 for detecting the intensity of radiation scattered by object 130 for each of a plurality of radiation configurations. Detector 140 is configured to record a diffraction pattern corresponding to each radiation configuration. Detector 140 is configured to output detection data 145 representing the recorded diffraction pattern to computing device 200 in the form of one or more electrical signals. Detector 140 may include a plurality of detector portions, each arranged to output a value representing the intensity of radiation falling thereon. Detector 140 may be, for example, a CCD, for providing detection data 145 representing the diffraction pattern. Detection data may be transmitted to device 200 via an electrical connection. Alternatively, detection data 145 may be stored on a data storage device such as a memory and transmitted to device 200 via the memory for subsequent use in a method according to an embodiment of the invention.

[0042] Figure 2 The diagram further illustrates a computing device 200. The computing device 200 can be any suitable device with processing capabilities, such as a personal computer, server computer, or mobile device such as a tablet, laptop, or mobile phone. The computing device 200 includes one or more processors 210 for executing computer-readable instructions and one or more memory devices 220 for storing data. The memory devices 220 can be configured to store computer-readable instructions that, when executed by one or more processors 210, cause the computing device 200 to perform one or more portions of a method for characterizing an object 130 according to embodiments of the invention to be described. The computing device is communicatively coupled to a detector 140 such that the detector 140 can transmit detection data 145 to the computing device 200. This communication can be wired, for example, the computing device 200 can be electrically coupled to the detector 140, or it can be wireless, for example, via any suitable wireless communication technology such as Wi-Fi, Bluetooth, NFC, etc. In some embodiments, each of the computing device 200 and the detector 140 can be connected to one or more wired or wireless networks (such as the Internet) and can communicate via such networks.

[0043] The detection data 145 is used to determine an object transfer function (or object function) characterizing at least a portion of the object 130, as described below. The detection data 145 can also be used to recover the illumination wave field associated with each radiation configuration, where the illumination wave field is unknown or partially unknown. Optionally, the computing device can determine image data 230 associated with the object 130 based on the determined object transfer function and each illumination wave field.

[0044] Figure 3 A method 300 for characterizing an object 130 according to an embodiment of the present invention is shown. The method 300 can be executed by a processor 210 according to computer-readable instructions.

[0045] Method 300 includes step 310: providing coherent incident radiation to object 130. As described above, the incident radiation is provided by radiation source 110 via support plane 120. As described above, coherent incident radiation is provided for each of a plurality of radiation configurations. Each radiation configuration may be defined by a corresponding illumination wavefield or support wavefield at the support plane. In some embodiments, the radiation configuration and thus the illumination wavefield are at least partially unknown.

[0046] Method 300 includes step 320: detecting the intensity of radiation scattered by the object at detector 140 for each of a plurality of radiation configurations. Detector 140 is configured to record detection data 145 representing a diffraction pattern for each radiation configuration and transmit the detection data 145 representing a set of diffraction patterns to computing device 200.

[0047] Method 300 includes an iterative process 400 for determining an object transfer function associated with object 130, which can be executed by computing device 200. The estimate of the object transfer function associated with object 130 can be iteratively updated 330 using detection data 145 and several additional constraints. Computing device 200 can be configured to execute the iterative process 400 until one or more exit criteria are met. In some embodiments, the iterative process 400 terminates when it is determined in step 340 that the estimate of the object transfer function has converged, or when the process has been performed an appropriate number of iterations, such as 1000 or 2000 (other numbers are conceivable). It should be understood that alternative exit criteria can be used. For example, an error metric such as root mean square (RMS) can be defined between the diffraction intensity measured at the detector and the diffraction intensity estimated during the iteration process. When the error metric is below a threshold, it can be determined that the exit criteria have been met.

[0048] Reference Figure 4 An embodiment of the iterative process 400 is described in more detail.

[0049] Figure 4 The single iteration k of iterative process 400 is shown.

[0050] In the first iteration, an initial estimate of the incident illumination wave 115 at the support plane 120 for each radiation configuration n is used. The process 400 is initialized with an initial estimate T0 of the object transfer function. Here, 0 represents the 0th iteration of process 400, n represents the nth radiation configuration, n = 1, 2, ..., N, where there are a total of N radiation configurations. In the illustrated embodiment, the N radiation configurations include N different illumination tilt angles. In some embodiments, it is not necessary to know the tilt angle for each configuration. In other embodiments, the utilization of the tilt angle for each configuration is as described below. In initialization 405, one or more additional prior known facts can be used to improve or determine the initial estimate. For example, it may be known that the N illumination angles increase with increasing n, and this can be used to determine the wavefield at the support plane. The initial estimate. In some embodiments, N different radiation configurations can be formed by applying different modulations to the incident radiation provided by radiation source 110.

[0051] In step 410, the estimate of each illumination wave at the support plane is updated according to the support constraints. In some embodiments, step 410 includes driving all values ​​of the wave field outside the support region to zero, as follows:

[0052]

[0053]

[0054] In the equation above, This is the current estimate of the wave field at the support plane 120, i.e., the support wave field. This represents the estimate of the support wave field from the previous iteration k-1. This represents the corrected support wavefield from the previous iteration k-1 after propagation to the plane of detector 140 and back, as described below. The parameter β is defined as the feedback strength and is a predetermined constant throughout the method, defining the rate of convergence of the method. In this example, β defines the strength at which the wavefield outside the support region is driven to zero. In the illustrative example, a value of β = 0.5 is used; however, it should be understood that other values ​​may also be used, such as 0.4 or 0.6, not exclusively.

[0055] In step 420, each supporting wave field The wave is propagated to the front or incident surface of object 140 to determine the corresponding incident or probe wave field for a given radiation configuration n. The incident wave field provides an estimate of the wave field incident on object 140. The propagation of step 420, which determines the incident wave field, can be expressed as:

[0056]

[0057] P z1This represents the propagation across a distance z1 from the supporting plane 120 to the object 130, such as... Figure 1 As shown. As will be understood, this can be determined based on the distance z1 and the supporting wave field. The appropriate propagation operator can be selected based on the properties of the data. As an illustrative example, for near-field propagation, the angular spectrum method can be used. For mid-range propagation, a Fresnel propagator can be used. For far-field geometry, other propagation operators, such as the Fourier transform, can be used.

[0058] In step 425, the object transfer function T can be updated. k The estimate is to reflect the updated estimate of the incident wave field determined in step 420. The nature of the update utilizes N independent measurements and therefore independent corrections to the incident wave field determined in the previous N propagation steps. As determined in the previous iterations, the accumulation of N measurements of the estimated wave field of the emitted wave from object 140 is determined. The accumulation of N measurements of the updated incident wave field in step 420 is determined. An averaging operation is performed by calculating the ratio of these accumulations. This averaging operation is beneficial for refining the object transfer function. In some embodiments, when this refinement is further constrained by amplitude, an updated object transfer function can be determined, which advantageously converges in k = 1, ..., K iterations.

[0059] The averaging operation performed in step 425 can be defined as follows:

[0060]

[0061] In the notation above, the superscript * denotes complex conjugation. The summation is performed based on the estimated incident wave field and the estimated emitted wave field for N radiation configurations. In this embodiment, the estimated emitted wave field from the previous (k-1) iterations is combined with the updated estimate of the incident wave field as updated in step 420.

[0062] The amplitude constraint is applied to the result of the averaging operation to determine the updated object transfer function T. k A general amplitude constraint can be used, i.e., |T. k ′|∈[c min ,c max ],c min =0,c max =1. Determine the updated object transfer function |T k The amplitude constraint of ′| is as follows:

[0063]

[0064]

[0065] In step 430, the current estimate of the object's transfer function is applied to propagate each incident wave field through the object, and an estimate of each outgoing wave field emitted from the object is determined. If the object transfer function has been updated in step 420, the updated object transfer function can be used. The object transfer function can be applied by multiplying by the corresponding incident wave field.

[0066]

[0067] In the first iteration of process 400, the initial estimate T0 is used as the object transfer function.

[0068] In step 440, for each radiation configuration n, each outgoing wave field propagates across a distance z2 to detector 140 to determine an estimate of the detector wave field incident on detector 140. Two different propagation methods can be used.

[0069] In some iterations, the propagation of step 440, which determines the detector wavefield, can be expressed using the first propagation formula:

[0070]

[0071] Where P z2 This represents the propagation from the object to the detector over a distance z2, such as Figure 1 As shown. As will be understood, a suitable propagation operator can be chosen based on the distance z2. As an illustrative example, for near-field propagation, the angular spectrum method can be used. For mid-range propagation, a Fresnel propagator can be used. For far-field geometry, a Fourier propagator can also be used.

[0072] Advantageously, utilizing both the current and previous estimates of the outgoing wavefield in the aforementioned propagation helps avoid stagnation in the iterative process. In particular, it can help the iterative computation escape local minima.

[0073] In some iterations, a second propagation formula can be used alternatively to help prevent the iteration process from diverging. The second propagation formula can be, for example:

[0074]

[0075] It should be understood that in some embodiments, the same propagation formula can be used in each iteration of step 440. In other embodiments, the formula used in step 440 can be alternated depending on the iteration k. For example, a first formula can be used initially, and then a second formula can be used periodically (i.e., every predetermined number of iterations). In one embodiment, the second formula can be used every 5 iterations, but it should be understood that the predetermined number of iterations can vary.

[0076] In step 450, the known recorded diffraction pattern I is used. n (r D The updated estimate of the detector wavefield is determined by using the intensity constraint of the detector wavefield. In this embodiment, the update can be performed as follows:

[0077]

[0078] I n (r D ) represents the detector plane r D The wave field intensity detected at the location.

[0079] Then, in step 460, the inverse of the propagation operator from step 440 is used to backpropagate the updated detector wavefield to the object to obtain the updated outgoing wavefield:

[0080]

[0081] In step 470, the object transfer function T can be updated. k Estimates to reflect the updated outgoing wave field Similar to step 425, the updated properties utilize N independent measurements and N independent corrections to the incident and emitted wave fields as determined in the preceding propagation steps. This averaging operation, which determines the ratio by dividing the sum of the estimated emitted wave fields emitted from object 140 by the sum of the estimated incident wave fields incident on object 140, facilitates the refinement of the object transfer function. In some embodiments, when this refinement is further constrained by amplitude, an updated object transfer function can be determined, which advantageously converges in k = 1, ..., K iterations.

[0082] The averaging operation in step 470 can be defined as follows:

[0083]

[0084] In step 470, the updated estimate of each outgoing wave field is used by combining the estimates of the incident wave field before propagation to and from the detector plane.

[0085] Similar to step 425, amplitude constraints are applied to the result of the averaging operation to determine the updated object transfer function T. k A general amplitude constraint can be used, i.e., |T. k ′|∈[c min ,c max ],c min =0,c max =1. The updated object transfer function |T| is determined using amplitude constraints. k The following can be executed: ′|

[0086]

[0087]

[0088] In some embodiments of the invention, only one of steps 425 and 470 is performed in each iteration, so that the object transfer function is updated only once in each iteration k. In other embodiments, both steps 425 and 470 may be performed, allowing the object transfer function to be updated twice in each iteration. In this way, the object transfer function can be updated before each use to propagate the wave field through the object.

[0089] In alternative embodiments of steps 425 and / or 470, amplitude constraints may not be necessary when updating the object transfer function. In this case, alternative constraints are used during the iteration process to achieve convergence of the method. In one embodiment, this alternative constraint can be provided by utilizing a known or nearly known illumination tilt angle at the wavefield in the source plane. In this way, the initial estimate of the source wavefield is close to accurate.

[0090] In step 480, by making each emitted wave field Backpropagation through the object determines the updated incident wavefield for each radiation configuration n. This can be achieved using the updated object transfer function T′ k To calculate. The updated incident wave field can be determined as:

[0091]

[0092] In the formula above, α is a predefined constant. It has been found that α can be predefined in the range [0.1, 1.5] to provide improved algorithmic convergence. For example, in one embodiment, α can be predefined as 0.6. It should be understood that other values, such as 0.7 or 0.5, can be used.

[0093] Finally, in step 490, by making The corrected wave field at the support plane is determined by propagating backward from the object over a distance z1. This backpropagation can be defined as the inverse of the propagation operation used in step 420, as follows:

[0094]

[0095] At this point in process 400, the estimated wavefield at each location of each radiation configuration has been updated according to the constraints provided at the support plane 120 and detector 140, and the object transfer function has been updated at least once by averaging the different independent estimates and applying amplitude constraints. At this point, k is incremented and the process returns to step 410 to update the support wavefield at the support plane 120 according to the support constraints. Furthermore, the object transfer function T′ updated in the completed iterations is set... k-1 To define T k .

[0096] Process 400 continues iterating and incrementing k until one or more predetermined exit conditions are met in step 340. Specifically, the object transfer function T can be determined. k Has it converged, i.e., T? k-1 and T k The difference between the two is less than a threshold. When the condition is met, the iteration process 400 will terminate and return the latest object transfer function T. k As a result, in other embodiments, the current iteration number can be compared with a predetermined iteration number to determine whether enough iterations have been performed. In yet another embodiment, each estimated intensity of the detector wavefield can be determined against the diffraction pattern I of each known record. n (r D The error measure between the two values ​​is whether it is less than a threshold. For example, the root mean square (rms) can be used as a suitable error measure.

[0097] The computing device 200 can determine the image data 230 representing the object based on the returned object transfer function.

[0098] Figure 5 Example image data 500 determined after performing the claimed method is shown. Image data 500 includes an image 510 representing the amplitude reconstruction of the illumination wave at the support plane, an image 520 representing the phase reconstruction of the illumination wave at the support plane, an image 530 representing the amplitude reconstruction of the imaged object, and an image 540 representing the phase reconstruction of the imaged object.

[0099] Figure 6 Graph 600 shows the convergence data, illustrating the convergence of the object transfer function during characterization of the object shown in image data 500. Graph 600 displays the estimated intensity of the detector wavefield on the y-axis compared to the known recorded diffraction pattern I. n (r DThe root mean square (rms) between the estimated object transfer function and the illumination wavefield is used. It should be understood that this value represents the accuracy of the estimated object transfer function and the illumination wavefield. Figure 600 shows the number of iterations k on the x-axis. It can be seen that the estimated intensity at the detector wavefield converges rapidly relative to the known diffraction pattern, giving a root mean square of <0.05 in just 150 iterations.

[0100] Therefore, this invention provides a stand-alone coherent diffraction imaging technique for unknown objects. Importantly, it eliminates the need for overlap measurements (e.g., those required for stacking techniques) to characterize any part of the process, thus enabling the use of this technique for unstable and rapidly moving sample dynamics.

[0101] It should be understood that embodiments of the present invention can be implemented in hardware, software, or a combination of hardware and software. Any such software can be stored in the form of volatile or non-volatile memory, such as a storage device like ROM, whether erasable or rewritable, or in the form of memory, such as RAM, memory chips, devices, or integrated circuits, or on optical or magnetically readable media, such as CDs, DVDs, disks, or magnetic tapes. It should be understood that the storage device and storage medium are embodiments of machine-readable memory suitable for storing one or more programs that implement embodiments of the present invention when executed. Therefore, embodiments provide a program comprising code for implementing a system or method according to any of the preceding claims, and a machine-readable storage device for storing such a program. Furthermore, embodiments of the present invention can be transmitted electronically via any medium (e.g., communication signals carried by a wired or wireless connection), and embodiments suitably cover the same media.

[0102] Throughout the specification and claims of this application, the words “comprising” and “containing” and their variations mean “including but not limited to”, and they are not intended to (and do not) exclude other parts, additives, components, integers, or steps. Throughout the specification and claims of this application, the singular encompasses the plural unless the context requires otherwise. In particular, where indefinite articles are used, the specification should be understood to consider both the plural and singular unless the context requires otherwise.

[0103] Features, integers, properties, compounds, chemical parts, or groups described in connection with specific aspects, embodiments, or examples of the invention should be understood to be applicable to any other aspect, embodiment, or example described herein, unless incompatible therewith. All features disclosed in this specification (including any appended claims, abstract, and drawings) and / or all steps of any method or process so disclosed may be combined in any combination, unless at least some such combinations of features and / or steps are mutually exclusive. The invention is not limited to the details of any of the foregoing embodiments. The invention extends to any novel one or any novel combination of features disclosed in this specification (including any appended claims, abstract, and drawings), or any novel one or any novel combination of steps of any method or process so disclosed.

[0104] The reader’s attention is focused on all papers and documents related to this application that were submitted at the same time as or before this specification and that were made publicly available together with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A method for characterizing at least a portion of an object, comprising the following steps: Coherent incident radiation is provided at the object via a supporting plane in each of a plurality of radiation configurations; wherein, The plurality of radiation configurations include: a plurality of tilt angles of the incident radiation; Alternatively, multiple rotation angles of the phase screen at the supporting plane; For each of the plurality of radiation configurations, the intensity of radiation scattered by the object is detected at the detector; An object transfer function associated with the object is determined via an iterative process based on the radiation intensity detected at the detector for each of the plurality of radiation configurations, wherein the iterative process includes: For each of the plurality of radiation configurations, the incident wave function representing the incident radiation at the object and the exit wave function representing the radiation emitted from the object are estimated based on the intensity detected at the detector, the support constraint at the support plane, and the current estimate of the object transfer function. Determine the ratio of the sum of the intensities of the emitted wave functions of the plurality of radiation configurations to the sum of the intensities of the incident wave functions of the plurality of radiation configurations; as well as The estimate of the object transfer function is updated based on the determined ratio and amplitude constraints; Wherein, the number of the plurality of radiation configurations is N, in each iteration n The ratio is determined based on the following parameters: in E j,n-1 Iteration n-1 Radiation configuration in j The emitted wave function, P j,n Iteration n The radiation configuration described in j The incident wave function; or, in E j,n Iteration n Radiation configuration in j The emitted wave function, P j,n-1 Iteration n-1 The radiation configuration described in j The incident wave function.

2. The method as claimed in claim 1, characterized in that, The amplitude constraints include minimum and maximum amplitude limits on the object's transfer function.

3. The method as described in claim 2, characterized in that, The amplitude constraint includes conditions. [0,1], where | O | represents the magnitude of the estimated transfer function of the object.

4. The method according to any one of claims 1-3, characterized in that, The iterative process includes: Provide an initial estimate of the object's transfer function; Provides an initial estimate of the wave function associated with each radiation configuration at the support plane; as well as The wavefunction is propagated back and forth between the support plane and the detector to obtain the estimate of the incident wavefunction and the estimate of the output wavefunction.

5. The method according to any one of claims 1-3, characterized in that, It also includes terminating the iterative process based on the convergence of the object transfer function between subsequent iterations.

6. The method according to any one of claims 1-3, characterized in that, It also includes determining image data representing the object based on the object transfer function.

7. A device for characterizing an object, the device comprising one or more electronic processors configured to operable to execute computer-readable instructions to perform: The radiation source is controlled to provide coherent incident radiation at the object via a supporting plane in each of a plurality of radiation configurations; wherein... The plurality of radiation configurations include: a plurality of tilt angles of the incident radiation; Alternatively, multiple rotation angles of the phase screen at the supporting plane; Receive detection data from the detector, the detection data representing the intensity of radiation scattered by the object for each of the plurality of radiation configurations; An object transfer function associated with the object is determined via an iterative process based on the radiation intensity detected at the detector for each of a plurality of radiation configurations, the iterative process comprising: For each of the plurality of radiation configurations, the incident wave function representing the incident radiation at the object and the exit wave function representing the radiation emitted from the object are estimated based on the intensity detected at the detector, the support constraint at the support plane, and the current estimate of the object transfer function. Determine the ratio of the sum of the intensities of the emitted wave functions of the plurality of radiation configurations to the sum of the intensities of the incident wave functions of the plurality of radiation configurations; and The estimate of the object transfer function is updated based on the determined ratio and amplitude constraints; Wherein, the number of the plurality of radiation configurations is N, in each iteration n The ratio is determined based on the following parameters: in E j,n-1 Iteration n-1 Radiation configuration in j The emitted wave function, P j,n Iteration n The radiation configuration described in j The incident wave function; or, in E j,n Iteration n Radiation configuration in j The emitted wave function, P j,n-1 Iteration n-1 The radiation configuration described in j The incident wave function.

8. The device as described in claim 7, characterized in that, Also includes: A radiation source is configured to provide the coherent incident radiation; and The detector is configured to detect the intensity of radiation scattered by the object for each of the plurality of radiation configurations and to output detection data based on the radiation intensity.

9. A computer-readable medium comprising computer software, which, when executed, is configured to perform the method according to any one of claims 1 to 6.

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