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The Talbot effect has been revived in many fields of modern optics. As a key number of self-imaging, the fundamental Talbot length plays a crucial role in many applications. However, the inspection of the Talbot carpet for determining the Talbot length is applicable only if the 2D field distribution behind the grating is represented by a 1D cross section. In this Letter, we show an effective way to overcome this limitation to explore the self-imaging of gratings with complex 2D periodicities. For that purpose, the near-field diffraction is analyzed using the Pearson correlation coefficient of the intensity distribution in Fourier space. We report results on linear, ring, and spiral gratings.

Elastic diffuse neutron scattering of an Fe-21.9 at.% Al single crystal was measured at 878, 966 and 1073 K. The separated short-range order scattering revealed the building elements of the B2 structure as the characteristic local atomic arrangement for all states investigated. Effective pair interaction parameters, obtained by the inverse Monte-Carlo method, were found to depend on temperature, thus prohibiting a determination of possible ground state structures from the high-temperature measurements. An additional X-ray study of single-crystalline Fe-18.2 at.% Al aged at 598 K, gave no indication for B32 as ground state structure.

Imaging with THz radiation has proved an important tool for both fundamental science and industrial use. Here we review a class of THz imaging implementations, named coherent lensless imaging, that reconstruct the coherent response of arbitrary samples with a minimized experimental setup based only on a coherent source and a camera. After discussing the appropriate sources and detectors to perform them, we detail the fundamental principles and implementations of THz digital holography and phase retrieval. These techniques owe a lot to imaging with different wavelengths, yet innovative concepts are also being developed in the THz range and are ready to be applied in other spectral ranges. This makes our review useful for both the THz and imaging communities, and we hope it will foster their interaction.

Imaging through scattering materials is of utmost importance, especially for security and biomedical imaging. Unlike the rest of the electromagnetic spectrum, terahertz radiation is a non-ionizing probe and allows imaging deep through non-conducting materials with sub-millimeter resolution. Here, we propose a coherent imaging technique reconstructing two objects, hidden one behind the other, from relative shifts between them. Experimental reconstructions at λ=96.5  μm of amplitude and phase objects hidden behind a glass fabric sample are presented. The hidden objects are retrieved with a lateral resolution of ≈1.5λ and a depth resolution of ≈λ/10. Besides envisioning its use in non-invasive imaging, we anticipate that, in selected applications, the suggested approach can replace a similar phase retrieval technique, namely ptychography.

We realized a phase retrieval technique using terahertz (THz) radiation as an alternative to THz digital holography, named THz ptychography. Ptychography has been used in x-ray imaging as a groundbreaking improvement of conventional coherent diffraction imaging. Here we show that ptychography can be performed at THz frequencies too. We reconstructed an amplitude and a phase object with both simulated and real data. Lateral resolution accounts to <2λ, while depth variations as low as λ/30 can be assessed.

Transmission terahertz (THz) spectroscopy on heterogeneous materials often shows structured spectra due to interference of waves passing through the object along different optical paths. Of special interest is wood with its strong birefringence and pronounced orientation-dependent structure. In this paper, we show that at specific polarization angles, the THz transmission spectra show gaps at distinct frequencies. The frequency changes of these gaps can be used for a fast and accurate determination of the dependence of birefringence on humidity. We present results for spruce and beech with different sample thicknesses and orientations, and study and model their optical properties as a function of water content.

Diffuse wide-angle neutron scattering has been measured for 58Ni–5.8 at% Ti at room temperature after quenching from 777 K, and for 58Ni–9.6 at% Ti at 1103 K. The fitted sets of short-range order and static displacement parameters are similar to those found in a previous investigation of short-range ordered Ni–8.9 at% Al. Applying a Bragg-Williams model, the coherent solvus of the γ phase is well reproduced. Neither the displacement parameters nor the phonon dispersion branches measured along 〈ξξξ〉 for the sample containing 9.6 at% Ti show any signs of instability of the short-range ordered face centered cubic structure.

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By means of a quantitative analysis of extensive elastic neutron scattering experiments performed on theTc=78 K superconductor DyBa2Cu4O8 it is shown that two-dimensional (2D) antiferromagnetic Dy ordering in the (a,b)-plane remains stable in the whole temperature range fromTN=(1.10±0.02) K down to 7 mK. The magnetic difference pattern with good angular resolution fits well to the Warren equation for scattering on 2D systems with powder averaging. Consequently, the fitted sublattice magnetisation is found to have a 2D Ising character. Moreover, the Dy3+ crystal-field levels were determined by inelastic neutron scattering. From the resulting crystal-field parameters we calculate the sublattice magnetisation of Dy3+ at saturation to beµDy,CEF=6.0µB in good agreement withµDy,obs=(5.9±0.5)µB as measured by neutron diffraction.

Highly unusual magnetic ordering stabilised by nuclear 165Ho polarisation is found to exist below TN = 190 mK in HoBa2Cu3O7 by means of low-temperature neutron scattering experiments. The three-dimensional antiferromagnetic ordering corresponding to K = [0,1/2,1/2] is imperfect, due to finite correlation length xc = 29 Å along the c=axis. The observed temperature dependence of the magnetic order parameter is in excellent agreement with mean-field calculations taking into account crystal field, exchange and hyperfine interactions.