Ab initio nonrigid X-ray nanotomography

Abstract: Reaching the full potential of X-ray nanotomography, in particular for biological samples, is limited by many factors, of which one of the most serious is radiation damage. Although sample deformation caused by radiation damage can be partly mitigated by cryogenic protection, it is still present in these conditions and, as we exemplify here using a specimen extracted from scales of the Cyphochilus beetle, it will pose a limit to the achievable imaging resolution. We demonstrate a generalized tomographic model, which optimally follows the sample morphological changes and attempts to recover the original sample structure close to the ideal, damage-free reconstruction. Whereas our demonstration was performed using ptychographic X-ray tomography, the method can be adopted for any tomographic imaging modality. Our application demonstrates improved reconstruction quality of radiation-sensitive samples, which will be of increasing relevance with the higher brightness of 4th generation synchrotron sources

A modern look at a medieval bilayer metal leaf: nanotomography of Zwischgold

Many European sculptures and altarpieces from the Middle Ages were decorated with Zwischgold, a bilayer metal leaf with an ultra-thin gold face backed by silver. Zwischgold corrodes quickly when exposed to air, causing the surface of the artefact to darken and lose gloss. The conservation of such Zwischgold applied artefacts has been an obstinate problem. We have acquired quantitative, 3D nanoscale images of Zwischgold samples from 15th century artefacts and modern materials using ptychographic X-ray computed tomography (PXCT), a recently developed coherent diffractive imaging technique, to investigate the leaf structure and chemical state of Zwischgold. The measurements clearly demonstrate decreasing density (increasing porosity) of the leaf materials and their corrosion products, as well as delamination of the leaves from their substrate. Each of these effects speak to typically observed issues in the conservation of such Zwischgold applied artefacts. Further, a rare variant of Zwischgold that contains extremely thin multiple gold layers and an overlapping phenomenon of Zwischgold with other metal leaves are observed through PXCT. As supportive data, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray analysis (EDX) were performed on the medieval samples

Forecasting the properties of the solar wind using simple pattern recognition

An accurate forecast of the solar wind plasma and magnetic field properties is a crucial capability for space weather prediction. However, thus far, it has been limited to the large-scale properties of the solar wind plasma or the arrival time of a coronal mass ejection from the Sun. As yet there are no reliable forecasts for the north-south interplanetary magnetic field component, Bn (or, equivalently, Bz). In this study, we develop a technique for predicting the magnetic and plasma state of the solar wind Δt hours into the future (where Δt can range from 6 h to several weeks) based on a simple pattern recognition algorithm. At some time, t, the algorithm takes the previous Δt hours and compares it with a sliding window of Δt hours running back all the way through the data. For each window, a Euclidean distance is computed. These are ranked, and the top 50 are used as starting point realizations from which to make ensemble forecasts of the next Δt hours. We find that this approach works remarkably well for most solar wind parameters such as v, np, Tp, and even Br and Bt, but only modestly better than our baseline model for Bn. We discuss why this is so and suggest how more sophisticated techniques might be applied to improve the prediction scheme

gauss_matrix.m

An example of code to create a guassian blurring sparse matri

poly_wave_matrix.m

An example of code to create a PolyCDI (multiwavelength) sparse matri

Ptychographic coherent diffractive imaging with orthogonal probe relaxation

Ptychography is a scanning coherent diffractive imaging (CDI) technique that relies upon a high level of stability of the illumination during the course of an experiment. This is particularly an issue for coherent sources where the beam intensity is usually tightly focused on the sample in order to maximize the photon flux density on the illuminated region of the sample. We present a method that includes limited stability of the illumination probe into the ptychography reconstruction. We have tested our reconstruction method in a proof of concept experiment, where the beam instability of a visible light source was emulated using a piezo driven mirror, and also in a short wavelength microscopy setup using a high harmonic generation source in the extreme ultraviolet range. Our work is showing a natural extension of the ptychography method that paves the way to use ptychographic imaging with any limited pointing stability coherent source such as free electron or soft X-ray lasers.</span

Ab initio nonrigid X-ray nanotomography

Abstract: Reaching the full potential of X-ray nanotomography, in particular for biological samples, is limited by many factors, of which one of the most serious is radiation damage. Although sample deformation caused by radiation damage can be partly mitigated by cryogenic protection, it is still present in these conditions and, as we exemplify here using a specimen extracted from scales of the Cyphochilus beetle, it will pose a limit to the achievable imaging resolution. We demonstrate a generalized tomographic model, which optimally follows the sample morphological changes and attempts to recover the original sample structure close to the ideal, damage-free reconstruction. Whereas our demonstration was performed using ptychographic X-ray tomography, the method can be adopted for any tomographic imaging modality. Our application demonstrates improved reconstruction quality of radiation-sensitive samples, which will be of increasing relevance with the higher brightness of 4th generation synchrotron sources

Nonlinear Ptychographic coherent diffractive imaging

Ptychographic Coherent Diffractive Imaging (PCDI) is a significant advance in imaging allowing the measurement of the full electric field at a sample without use of any imaging optics. So far it has been confined solely to imaging of linear optical responses. In this paper we show that because of the coherence-preserving nature of nonlinear optical interactions, PCDI can be generalised to nonlinear optical imaging. We demonstrate second harmonic generation PCDI, directly revealing phase information about the nonlinear coefficients, and showing the general applicability of PCDI to nonlinear interactions. Data supports the paper &quot;Odstrcil, Michal, Baksh, Peter, Gawith, Corin, Vrcelj, Ranko, Frey, Jeremy and Brocklesby, William (2016) Nonlinear ptychographic coherent diffractive imaging. Optics Express&quot;</span

Ptychographic imaging with a compact gas-discharge plasma extreme ultraviolet light source

We report the demonstration of scanning-probe coherent diffractive imaging method (also known as ptychographic CDI) using a compact and partially-coherent gas-discharge plasma source of extreme ultraviolet (EUV) radiation at 17.3\,nm wavelength. Until now, CDI has been mainly carried out with coherent, high-brightness light sources, such as 3rd generation synchrotrons, X-ray free-electron lasers and high harmonic generation. Here we performed ptychographic lensless imaging of an extended sample using a compact, lab-scale source. The CDI reconstructions were achieved by applying constraint relaxation to the CDI algorithm. Experimental results indicate that our method can handle the low spatial coherence, broadband nature of the EUV illumination as well as the residual background due to visible light emitted by the gas-discharge source. The ability to conduct ptychographic imaging with lab-scale and partially coherent EUV sources is expected to significantly expand the applications of this powerful CDI method. This dataset supports the article entitled &quot;Ptychographic imaging with a compact gas-discharge plasma extreme ultraviolet light source&quot; in Optics Letters</span