Broadband coherent modulation imaging with no knowledge of the illumination spectrum distribution: publisher's note.

This publisher's note contains a correction to Opt. Lett.48, 3977 (2023)10.1364/OL.495706.

Rotational position error correction in ptychography.

Accurate determination of scan positions is essential for achieving high-quality reconstructions in ptychographic imaging. This study presents and demonstrates a method for determining the rotation angle of the scan pattern relative to the detector pixel array using diffraction data. The method is based on the Fourier-Mellin transform and cross-correlation calculation. It can correct rotation errors up to 60 deg. High-quality reconstructions were obtained for visible light and electron microscopy datasets, and intricate structures of samples can be revealed. We believe that this refinement method for rotary position errors can be valuable for improving the performance of ptychographic four-dimensional scanning transmission electron microscopy.

Broadband coherent modulation imaging with no knowledge of the illumination spectrum distribution.

Coherent diffraction imaging (CDI) is an alternative way to achieve high-performance imaging without high-quality imaging lenses. Coherent modulation imaging (CMI) improves CDI's algorithmic convergence and applicability to general samples. A high degree of coherence of the source is essential for CDI, which limits its application to ultrafast pulsed sources with an intrinsically broad spectrum. Here, we propose an algorithm to increase the tolerance of CMI to low temporal coherence that tandemly employs the Wiener and Lucy deconvolution approaches. Simulations and visible light experiments demonstrate the effectiveness of our method. This work could pave the way for implementing CMI with attosecond pulsed lasers, laboratory x-ray sources, or electron microscopes.

Performance enhancement of coherent modulation imaging in the presence of missing data.

Coherent diffraction imaging (CDI) has become a powerful imaging modality in synchrotron x-ray imaging and electron microscopy communities. In the far-field geometry, image quality of CDI depends strongly on the performance of detector; specifically, the dynamic range, pixel size, and the absence of missing data. Coherent modulation imaging (CMI), an innovative variant of CDI, improves the algorithmic convergence by inserting a modulator upstream of the detector. Here, we explore the potential of CMI in eliminating nonideal effects of detector by modifying the modulus constraint to extrapolate the missing part of diffraction pattern. Nine folds of extrapolation in area of diffraction pattern have been shown feasible in experiment; while sixteen folds in simulation. For image quality measured by Structural Similarity (SSIM), our method shows a maximum of 32% improvement over the traditional method. Our method provides a way to alleviate the effects of beamstop, gaps between modules, limited dynamic range, and limited detector size for CMI.

Surface metrology by multiple-wavelength coherent modulation imaging.

With the rapid progress of advanced manufacturing, three-dimensional metrology techniques that are able to achieve nanometer spatial resolution and to capture fast dynamics are highly desired, for which a snapshot ability and a common-light-path setup are required. Commonly used off-axis holography and phase-shifting interferometry are short in fulfilling those requirements. We studied the suitability and performance of the coherent modulation imaging (CMI) method for metrology applications. Both transparent and reflective samples are measured in visible light experiments. Thanks to its ability to retrieve separate wavefronts at different wavelengths from a single measurement, CMI allows for attaining an enlarged range of measurement free from phase wrapping by utilizing the concept of synthetic wavelength. The CMI method fulfills well the requirements for advanced metrology and can be implemented at any wavelength. We expect it would be a powerful addition to the pool of advanced metrology tools.

Accurate and Robust Calibration of the Uniform Affine Transformation Between Scan-Camera Coordinates for Atom-Resolved In-Focus 4D-STEM Datasets.

Accurate geometrical calibration between the scan coordinates and the camera coordinates is critical in four-dimensional scanning transmission electron microscopy (4D-STEM) for both quantitative imaging and ptychographic reconstructions. For atomic-resolved, in-focus 4D-STEM datasets, we propose a hybrid method incorporating two sub-routines, namely a J-matrix method and a Fourier method, which can calibrate the uniform affine transformation between the scan-camera coordinates using raw data, without a priori knowledge of the crystal structure of the specimen. The hybrid method is found robust against scan distortions and residual probe aberrations. It is also effective even when defects are present in the specimen, or the specimen becomes relatively thick. We will demonstrate that a successful geometrical calibration with the hybrid method will lead to a more reliable recovery of both the specimen and the electron probe in a ptychographic reconstruction. We will also show that, although the elimination of local scan position errors still requires an iterative approach, the rate of convergence can be improved, and the residual errors can be further reduced if the hybrid method can be firstly applied for initial calibration. The code is made available as a simple-to-use tool to correct affine transformations of the scan-camera coordinates in 4D-STEM experiments.

Quantitative phase measurements of human cell nuclei using X-ray ptychography.

The human cell nucleus serves as an important organelle holding the genetic blueprint for life. In this work, X-ray ptychography was applied to assess the masses of human cell nuclei using its unique phase shift information. Measurements were carried out at the I13-1 beamline at the Diamond Light Source that has extremely large transverse coherence properties. The ptychographic diffractive imaging approach allowed imaging of large structures that gave quantitative measurements of the phase shift in 2D projections. In this paper a modified ptychography algorithm that improves the quality of the reconstruction for weak scattering samples is presented. The application of this approach to calculate the mass of several human nuclei is also demonstrated.

Coherent modulation imaging using unknown modulators.

Coherent modulation imaging (CMI) is an effective lensless diffraction imaging method with fast algorithmic convergence and high robustness to data defects. In the reported algorithms for CMI, one important requirement is that the modulator function need to be known a priori; and an additional step for the modulator characterization is required to be carried out in advance by other methods, such as ptychography, which could be cumbersome in practice. Here, we propose an improved algorithm that allows for the transmission function of a completely unknown modulator to be recovered during the same iterative process of image reconstruction. We have verified the method in both simulations and optical experiments. This improvement would turn CMI into a more practical and standalone technique for broader applications in biology and materials science.

Numerical and experimental study of partial coherence for near-field and far-field ptychography.

High degree of coherence is essential in coherent diffraction imaging (CDI). The coherence requirement on the light source varies with the experimental configuration. As a scanning variant of CDI, ptychography has shown great potential for extensive applications. To determine the influence of partially temporal and spatial coherence on near- and far-field ptychography, we have performed a series of numerical simulations and visible light optical experiments. We demonstrated that the near-field is more robust to spatial and temporal decoherence than the far-field. In addition, the far-field is found to be more sensitive to spatial decoherence than to temporal decoherence. Our experiments also show that a known probe estimate with good spatial coherence enables the retrieval qualities to be enhanced dramatically and helps prevent falling into the local minimums in the reconstruction process. Our work would provide a valuable reference for implementing ptychography with sources of limited coherence.

Phase extraction neural network (PhENN) with coherent modulation imaging (CMI) for phase retrieval at low photon counts.

Imaging with low-dose light is of importance in various fields, especially when minimizing radiation-induced damage onto samples is desirable. The raw image captured at the detector plane is then predominantly a Poisson random process with Gaussian noise added due to the quantum nature of photo-electric conversion. Under such noisy conditions, highly ill-posed problems such as phase retrieval from raw intensity measurements become prone to strong artifacts in the reconstructions; a situation that deep neural networks (DNNs) have already been shown to be useful at improving. Here, we demonstrate that random phase modulation on the optical field, also known as coherent modulation imaging (CMI), in conjunction with the phase extraction neural network (PhENN) and a Gerchberg-Saxton-Fienup (GSF) approximant, further improves resilience to noise of the phase-from-intensity imaging problem. We offer design guidelines for implementing the CMI hardware with the proposed computational reconstruction scheme and quantify reconstruction improvement as function of photon count.

Super-resolution near-field ptychography.

Compared to far-field ptychography, near-field ptychography can reduce the requirement on the detector dynamic range, while it is able to cover a larger field of view with a fewer number of sample scans. However, its spatial resolution is limited by the detector pixel size. Here, we utilize a pixel-super-resolved approach to overcome this limitation. The method has been applied to four types of experiment configurations using planar and divergent illuminations together with two different cameras with highly contrast specifications. The proposed method works effectively for up-sampling up to 6 times. Meanwhile, it can achieve ∼5.9-fold and ∼3.1-fold resolution improvement over the 6.5-µm and 2.4-µm detector pixel size. We also demonstrate the precisely quantitative phase imaging capability of the method by using a phase resolution target. The presented method is believed to have great potential in X-ray tomography and on-chip flow cytometry.

General method for complex-wave fields registration with high fidelity.

In the field of optical imaging, the image registration method could be applied to realize a large field of view along with high resolution. The traditional image registration methods are mostly conceived for intensity images and might fail for complex-valued images. Especially, those methods do not account for the random phase offset associated with phase. In this paper, we proposed a general method for complex-wave field registration. A similar procedure has been proposed for the reconstruction of the ptychographic dataset, but here is modified for the registration of general wave fields. The method can efficiently separate the illumination and object function, refine the positions of each wavefront, and thus provide a stitched wide-field object wave with high fidelity. Simulation and experimental results applied to register the wave fields obtained from digital holographic microscopy are given to verify the feasibility of the method. This method would have potential applications in large-field high-resolution microscopy, adaptive imaging, remote sensing and the measurement of structured optical fields.

Reconstruction method of a ptychographic dataset with unknown positions.

Wavefield drift or wobbling occurs quite often in coherent scanning systems such as satellite laser communication, laser pointing of high-power lasers, or microscopy. The uncertainty of wavefront positions might result in blurred images or large measurement errors. Here we propose an iterative approach that can retrieve both the drift positions and complex-valued distribution of the wavefield from a ptychographic diffraction intensity dataset. We demonstrate the feasibility and effectiveness of the method in numerical simulation and an optical experiment. The method requires little a priori knowledge and thus would open up new opportunities in many fields.

Hollow Electron Ptychographic Diffractive Imaging.

We report a method for quantitative phase recovery and simultaneous electron energy loss spectroscopy analysis using ptychographic reconstruction of a data set of "hollow" diffraction patterns. This has the potential for recovering both structural and chemical information at atomic resolution with a new generation of detectors.

Nuclear incorporation of iron during the eukaryotic cell cycle.

Scanning X-ray fluorescence microscopy has been used to probe the distribution of S, P and Fe within cell nuclei. Nuclei, which may have originated at different phases of the cell cycle, are found to show very different levels of Fe present with a strongly inhomogeneous distribution. P and S signals, presumably from DNA and associated nucleosomes, are high and relatively uniform across all the nuclei; these agree with X-ray phase contrast projection microscopy images of the same samples. Possible reasons for the Fe incorporation are discussed.

Study on the Multi-Spectral True Temperature Pyrometer for Explosion Transient of Thermo-Baric Explosives.

The high temperature and destructive power, made it difficult to test the explosion temperature of thermo-baric explosive. To effectively assess heat damage effect of thermo-baric explosive, multi-spectral high temperature measurement system is applied to transient high temperature test of thermo-baric explosive. The emissivity and the true temperature of explosion flame are calculated by using the secondary measurement method. In the data acquisition system, the test instrument achieves data collection and transmission 500 meters away in combination with optical fiber sensing technology and under the precondition to guarantee the participants safety. The measurement results show that the designed measurement system has the advantages of simple operation, high safety and better application prospect.

Karyotyping human chromosomes by optical and X-ray ptychography methods.

Sorting and identifying chromosomes, a process known as karyotyping, is widely used to detect changes in chromosome shapes and gene positions. In a karyotype the chromosomes are identified by their size and therefore this process can be performed by measuring macroscopic structural variables. Chromosomes contain a specific number of basepairs that linearly correlate with their size; therefore, it is possible to perform a karyotype on chromosomes using their mass as an identifying factor. Here, we obtain the first images, to our knowledge, of chromosomes using the novel imaging method of ptychography. We can use the images to measure the mass of chromosomes and perform a partial karyotype from the results. We also obtain high spatial resolution using this technique with synchrotron source x-rays.

Coherent x-ray imaging of collagen fibril distributions within intact tendons.

The characterization of the structure of highly hierarchical biosamples such as collagen-based tissues at the scale of tens of nanometers is essential to correlate the tissue structure with its growth processes. Coherent x-ray Bragg ptychography is an innovative imaging technique that gives high resolution images of the ordered parts of such samples. Herein, we report how we used this method to image the collagen fibrillar ultrastructure of intact rat tail tendons. The images show ordered fibrils extending over 10-20 µm in length, with a quantifiable D-banding spacing variation of 0.2%. Occasional defects in the fibrils distribution have also been observed, likely indicating fibrillar fusion events.

Observations of artefacts in the x-ray ptychography method.

X-ray ptychography, a scanning coherent diffraction imaging method, was used to reconstruct images of a "Siemens star" test pattern with amplitude and phase contrast. While studying how the use of illumination with an increased bandwidth results in clear improvements in the quality of image reconstructions, we found that an artificial change in the overall distance scale factor of the algorithm leads to a systematic response in the image, which is reproduced with an incorrect number of spokes. This pathology is explained by the conflict between the length scales set by the scan and by the diffraction patterns on the detector.

Mitigating Strain Accumulation in Li2RuO3 via Fluorine Doping.

Lithium ruthenium oxide (Li2RuO3) is an archetypal lithium rich cathode material (LRCM) with both cation and anion redox reactions (ARRs). Commonly, the instability of oxygen redox activities has been regarded as the root cause of its performance degradation in long-term operation. However, we find that not triggering ARRs does not improve and even worsens its cyclability due to the detrimental strain accumulation induced by Ru redox activities. To solve this problem, we demonstrate that F-doping in Li2RuO3 can alter its preferential orientation and buffer interlayer repulsion upon Ru redox, both of which can mitigate the strain accumulation along the c-axis and improve its structural stability. This work highlights the importance of optimizing cation redox reactions in LRCMs and provides a new perspective for their rational design.