Topological photonics with scattering media

Scattering media, being ubiquitous in nature and critically important for assessments (e.g., biological tissues), are often considered as nuisance in optics. Here we show that it is not always the case and scattering media could be essential in providing elements of topological photonics. We demonstrate that topological darkness can be realised in the presence of scattering media due to the transverse nature of electromagnetic waves and the hairy ball theorem. We describe realizations of topological darkness in a scattering medium comprising composite gold nanostructures produced by a low-cost technique of laser structuring of thin metal films. Our results can be useful for a variety of tasks, including topological nanophotonics, optical label-free biosensing, and biomedical photonics

How the War in Ukraine Affects Food Security

The war in Ukraine has caused severe disruption to national and worldwide food supplies. Ukraine is a major exporter of wheat, maize, and oilseeds, staples that are now suffering a war-triggered supply risk. This paper describes the background of the problem and illustrates current trends by outlining some of the measures that may be deployed to mitigate the conflict’s impacts on achieving SDG 2 (Zero hunger), especially focusing on ending hunger, achieving food security, improving nutrition, and promoting sustainable agriculture. In order to understand the main research strands in the literature that are related to food security in the context of wars, the authors adopted a bibliometric literature review based on the co-occurrence of terms technique, conducted with 631 peer-reviewed documents extracted from the Scopus database. To complement the bibliometric assessment, ten case studies were selected to narrow down the food insecurity aspects caused by the war in Ukraine. The co-occurrence analysis indicated four different thematic clusters. In the next stage, an assessment of the current situation on how war affects food security was carried out for each one of the clusters, and the reasons and possible solutions to food security were identified. Policy recommendations and theoretical implications for food security in the conflict context in Ukraine were also addressed

Nonlinear spin control by terahertz-driven anisotropy fields

Future information technologies, such as ultrafast data recording, quantum computation or spintronics, call for ever faster spin control by light. Intense terahertz pulses can couple to spins on the intrinsic energy scale of magnetic excitations. Here, we explore a novel electric dipole-mediated mechanism of nonlinear terahertz-spin coupling that is much stronger than linear Zeeman coupling to the terahertz magnetic field. Using the prototypical antiferromagnet thulium orthoferrite (TmFeO3), we demonstrate that resonant terahertz pumping of electronic orbital transitions modifies the magnetic anisotropy for ordered Fe3+ spins and triggers large-amplitude coherent spin oscillations. This mechanism is inherently nonlinear, it can be tailored by spectral shaping of the terahertz waveforms and its efficiency outperforms the Zeeman torque by an order of magnitude. Because orbital states govern the magnetic anisotropy in all transition-metal oxides, the demonstrated control scheme is expected to be applicable to many magnetic materials