Single-shot Coherent Diffractive Imaging Research Articles

Single-shot multi-wavelength coherent diffractive imaging based on sparse representation and modulation optimization

As a powerful lensless imaging method, coherent diffractive imaging reconstructs an object from its diffraction pattern by computational phase retrieval algorithm. The reconstruction quality relies heavily on the coherence of the illumination and suffers from artifacts or fails under partially coherent imaging conditions, such as the illumination by broadband or multi-wavelength source. Here, we demonstrate a single-shot coherent diffractive imaging of multi-wavelength illumination by using sparse representation and modulation optimization. Sparse representation is utilized in the phase retrieval algorithm to reduce the ambiguity of solutions caused by multi-wavelength aliasing. Furthermore, phase modulation is optimized by maximum likelihood estimation based on Cramér–Rao lower bound and is applied to encode sufficient information in diffraction patterns. Simulations and experiments have been complemented to verify the effectiveness of the proposed method.

Three-dimensional femtosecond snapshots of isolated faceted nanostructures.

The structure and dynamics of isolated nanosamples in free flight can be directly visualized via single-shot coherent diffractive imaging using the intense and short pulses of x-ray free-electron lasers. Wide-angle scattering images encode three-dimensional (3D) morphological information of the samples, but its retrieval remains a challenge. Up to now, effective 3D morphology reconstructions from single shots were only achieved via fitting with highly constrained models, requiring a priori knowledge about possible geometries. Here, we present a much more generic imaging approach. Relying on a model that allows for any sample morphology described by a convex polyhedron, we reconstruct wide-angle diffraction patterns from individual silver nanoparticles. In addition to known structural motives with high symmetries, we retrieve imperfect shapes and agglomerates that were not previously accessible. Our results open unexplored routes toward true 3D structure determination of single nanoparticles and, ultimately, 3D movies of ultrafast nanoscale dynamics.

Khảo sát khả năng phục hồi ảnh của thuật toán tích chập trong phương pháp chụp ảnh nhiễu xạ sử dụng chùm tia X kết hợp không hoàn toàn

This research is aimed to investigate the ability of the convolutional algorithm to reconstruct the image of sample in coherent diffractive imaging using partially coherent X-ray beams. This work is performed using different degrees of coherence for the illuminating wavefield and different types of sample. The obtained results in this research allow to explore the ability to apply the convolutional algorithm in single-shot coherent diffractive imaging using partially coherent X-ray beams.

Shapes of rotating superfluid helium nanodroplets

Author(s): Bernando, C; Tanyag, RMP; Jones, C; Bacellar, C; Bucher, M; Ferguson, KR; Rupp, D; Ziemkiewicz, MP; Gomez, LF; Chatterley, AS; Gorkhover, T; Muller, M; Bozek, J; Carron, S; Kwok, J; Butler, SL; Moller, T; Bostedt, C; Gessner, O; Vilesov, AF | Abstract: Rotating superfluid He droplets of approximately 1 μm in diameter were obtained in a free nozzle beam expansion of liquid He in vacuum and were studied by single-shot coherent diffractive imaging using an x-ray free electron laser. The formation of strongly deformed droplets is evidenced by large anisotropies and intensity anomalies (streaks) in the obtained diffraction images. The analysis of the images shows that in addition to previously described axially symmetric oblate shapes, some droplets exhibit prolate shapes. Forward modeling of the diffraction images indicates that the shapes of rotating superfluid droplets are very similar to their classical counterparts, giving direct access to the droplet angular momenta and angular velocities. The analyses of the radial intensity distribution and appearance statistics of the anisotropic images confirm the existence of oblate metastable superfluid droplets with large angular momenta beyond the classical bifurcation threshold.

Direct single-shot phase retrieval from the diffraction pattern of separated objects.

The non-crystallographic phase problem arises in numerous scientific and technological fields. An important application is coherent diffractive imaging. Recent advances in X-ray free-electron lasers allow capturing of the diffraction pattern from a single nanoparticle before it disintegrates, in so-called ‘diffraction before destruction' experiments. Presently, the phase is reconstructed by iterative algorithms, imposing a non-convex computational challenge, or by Fourier holography, requiring a well-characterized reference field. Here we present a convex scheme for single-shot phase retrieval for two (or more) sufficiently separated objects, demonstrated in two dimensions. In our approach, the objects serve as unknown references to one another, reducing the phase problem to a solvable set of linear equations. We establish our method numerically and experimentally in the optical domain and demonstrate a proof-of-principle single-shot coherent diffractive imaging using X-ray free-electron lasers pulses. Our scheme alleviates several limitations of current methods, offering a new pathway towards direct reconstruction of complex objects.

Increasing the Brightness of Cold Ion Beams by Suppressing Disorder-Induced Heating with Rydberg Blockade.

A model for the equilibrium coupling of an ion system with varying initial hard-sphere Rydberg blockade correlations is used to quantify the suppression of disorder-induced heating in Coulomb-expanding cold ion bunches. We show that bunches with experimentally achievable blockade parameters have an emittance reduced by a factor of 2.6 and increased focusability and brightness compared to a disordered bunch. Demonstrating suppression of disorder-induced heating is an important step in the development of techniques for the creation of beam sources with sufficient phase-space density for ultrafast, single-shot coherent diffractive imaging.

Extending the potential of x-ray free-electron lasers to industrial applications—an initiatory attempt at coherent diffractive imaging on car-related nanomaterials

Recent advances in x-ray free-electron lasers (XFELs) open up new pathways for contributing to industrial research-and-development activities. In this article, we describe our initiatory attempt at using the SPring-8 Ångström compact free-electron laser (SACLA) for industrial applications. The attempt was conducted by the authors through the industry-academia partnership program initiated by RIKEN, aimed at examining the potential of XFELs for the analysis of car-related nanomaterials. Using the infrastructures developed at SACLA, we performed single-shot coherent diffractive imaging experiments on automotive exhaust catalysts and succeeded in obtaining the reconstructed images. This effort has paved the way for the future use of XFELs in the research-and-development activity of automotive exhaust catalysts.

The linac coherent light source single particle imaging road map.

Intense femtosecond x-ray pulses from free-electron laser sources allow the imaging of individual particles in a single shot. Early experiments at the Linac Coherent Light Source (LCLS) have led to rapid progress in the field and, so far, coherent diffractive images have been recorded from biological specimens, aerosols, and quantum systems with a few-tens-of-nanometers resolution. In March 2014, LCLS held a workshop to discuss the scientific and technical challenges for reaching the ultimate goal of atomic resolution with single-shot coherent diffractive imaging. This paper summarizes the workshop findings and presents the roadmap toward reaching atomic resolution, 3D imaging at free-electron laser sources.

Single-Shot X-Ray Coherent Diffractive Imaging of Superfluid He Nanodroplets

Single-shot coherent diffractive imaging (CDI) experiments were performed on pure and doped helium nanodroplets using femtosecond X-ray pulses from the Linac Coherent Light Source (LCLS). The superfluid nature of helium droplets presents a rare opportunity to study the onset of macroscopic quantum phenomena in finite, sub-micron scale systems. Despite the small X-ray scattering cross sections of atomic helium, high-quality single-shot CDI data were obtained that give direct access to sizes and shapes of individual nanodroplets. The diffraction patterns from helium droplets doped with xenon atoms differ starkly from the patterns from pure droplets. Strong indications for the formation of complex xenon structures inside the superfluid helium environment are observed, giving access to information about the structure and aggregation dynamics of the dopant species. The results are discussed with respect to the hydrodynamic properties of the superfluid droplets and compared to those of classical drops. An outlook on femtosecond time-resolved CDI experiments to study dynamics in pure and Xe-doped He nanodroplets will be given based on a new undulator-based X-ray pump/X-ray probe technique that is currently under development at LCLS.

Noise-robust coherent diffractive imaging with a single diffraction pattern

The resolution of single-shot coherent diffractive imaging at X-ray free-electron laser facilities is limited by the low signal-to-noise level of diffraction data at high scattering angles. The iterative reconstruction methods, which phase a continuous diffraction pattern to produce an image, must be able to extract information from these weak signals to obtain the best quality images. Here we show how to modify iterative reconstruction methods to improve tolerance to noise. The method is demonstrated with the hybrid input-output method on both simulated data and single-shot diffraction patterns taken at the Linac Coherent Light Source.

Method for Single-Shot Coherent Diffractive Imaging of Magnetic Domains

In preparation for real space studies of magnetic domains in a pump-probe setup at free-electron laser sources, it is necessary to develop an imaging method compatible with the linearly polarized radiation available at these sources. We present results from a prototype experiment performed at the synchrotron source BESSY II, using a modification of existing phase retrieval techniques. Our results show that it is possible to image magnetic domains in real space using linear polarized light, and we introduce the concept of a reliability map of our reconstructions using Gabor transforms.