Matter-wave optics: Observing an ultracold atomic cloud expanding in free fall

This Highlight showcases the Research Paper entitled Collective-Mode Enhanced Matter-Wave Optics (Phys. Rev. Lett. 127, 100401 (2021), DOI: 10.1103/Phys- RevLett.127.100401).

Simple device for spectroscopy laboratory exercises

Undergraduate physics laboratory exercises are very important in shaping students’ attitude to science, especially for future teachers. Recently, it is necessary to look for ways to easily create large quantities of experimental sets, not only for institutional use, but also for sets that can be produced in large quantities and distributed for use in distance learning. In this paper, we briefly describe the various ways to support the teaching of wave optics, and then describe one of the possible methods for performing undergraduate spectroscopic measurements using a 3D printed spectroscope and light source.

2 × 2 Matrices: Manifolds, Realizations, Applications

Both geometric and wave optical models, as well as classical and quantum mechanics, realize linear transformations with matrices; for plane optics, these are 2×2 and of unit determinant. Students and some researchers could assume that the structure of this matrix group is fairly evident and hardly interesting. However, the properties and applications even of this lowest 2×2 case are already unexpectedly rich. While in mechanics they cover classical angular momentum, quantum spin, and represent ‘2+1’ relativity, in optical models they lead from the geometrical description of light propagation in the paraxial regime to wave optics via linear canonical transforms requiring a more penetrating view of their manifold structure and multiple covers. The purpose of this review article is to highlight the topological space of 2×2 matrices as it applies to classical versus quantum and wave models, to underline how the latter requires the double cover of the former, thus using 2×2 matrices as an alternative viewpoint of the quantization process, beside the traditional characterization by commutation and non-commutations of position and momentum.

Quantitative analysis of speckle-based X-ray dark-field imaging using numerical wave-optics simulations

The dark-field signal measures the small-angle scattering strength and provides complementary diagnostic information. This is of particular interest for lung imaging due to the pronounced small-angle scatter from the alveolar microstructure. However, most dark-field imaging techniques are relatively complex, dose-inefficient, and require sophisticated optics and highly coherent X-ray sources. Speckle-based imaging promises to overcome these limitations due to its simple and versatile setup, only requiring the addition of a random phase modulator to conventional X-ray equipment. We investigated quantitatively the influence of sample structure, setup geometry, and source energy on the dark-field signal in speckle-based X-ray imaging with wave-optics simulations for ensembles of micro-spheres. We show that the dark-field signal is accurately predicted via a model originally derived for grating interferometry when using the mean frequency of the speckle pattern power spectral density as the characteristic speckle size. The size directly reflects the correlation length of the diffuser surface and did not change with energy or propagation distance within the near-field. The dark-field signal had a distinct dependence on sample structure and setup geometry but was also affected by beam hardening-induced modifications of the visibility spectrum. This study quantitatively demonstrates the behavior of the dark-field signal in speckle-based X-ray imaging.