Three-Dimensional Grain Boundary Spectroscopy in Transparent High Power Ceramic Laser Materials

Using confocal Raman and fluorescence spectroscopic imaging in 3-dimensions, we show direct evidence for Nd3+-Nd3+ interactions across grain boundaries (GBs) in Nd3+:YAG laser ceramics. It is clearly shown that Nd3+ segregation takes place at GBs leading to self-fluorescence quenching which affects a volume fraction as high as 20%. In addition, we show a clear trend of increasing spatial inhomogeneities in Nd3+ concentration when the doping levels exceeds 3 at%, which is not detected by standard spectrometry techniques. These results could point the way to further improvements in what is already an impressive class of ceramic laser materials.Comment: 8 pages including Figures. submitted to Optics Express (Nov 07

Two-phonon coupling to the antiferromagnetic phase transition in multiferroic BiFeO3

A prominent band centered at around 1000-1300 cm-1 and associated with resonant enhancement of two-phonon Raman scattering is reported in multiferroic BiFeO3 thin films and single crystals. A strong anomaly in this band occurs at the antiferromagnetic Neel temperature. This band is composed of three peaks, assigned to 2A4, 2E8, and 2E9 Raman modes. While all three peaks were found to be sensitive to the antiferromagnetic phase transition, the 2E8 mode, in particular, nearly disappears at TN on heating, indicating a strong spin-two phonon coupling in BiFeO3.Comment: 12 pages with figure

Familial hypercholesterolaemia in children and adolescents from 48 countries: a cross-sectional study

Background: Approximately 450 000 children are born with familial hypercholesterolaemia worldwide every year, yet only 2·1% of adults with familial hypercholesterolaemia were diagnosed before age 18 years via current diagnostic approaches, which are derived from observations in adults. We aimed to characterise children and adolescents with heterozygous familial hypercholesterolaemia (HeFH) and understand current approaches to the identification and management of familial hypercholesterolaemia to inform future public health strategies. Methods: For this cross-sectional study, we assessed children and adolescents younger than 18 years with a clinical or genetic diagnosis of HeFH at the time of entry into the Familial Hypercholesterolaemia Studies Collaboration (FHSC) registry between Oct 1, 2015, and Jan 31, 2021. Data in the registry were collected from 55 regional or national registries in 48 countries. Diagnoses relying on self-reported history of familial hypercholesterolaemia and suspected secondary hypercholesterolaemia were excluded from the registry; people with untreated LDL cholesterol (LDL-C) of at least 13·0 mmol/L were excluded from this study. Data were assessed overall and by WHO region, World Bank country income status, age, diagnostic criteria, and index-case status. The main outcome of this study was to assess current identification and management of children and adolescents with familial hypercholesterolaemia. Findings: Of 63 093 individuals in the FHSC registry, 11 848 (18·8%) were children or adolescents younger than 18 years with HeFH and were included in this study; 5756 (50·2%) of 11 476 included individuals were female and 5720 (49·8%) were male. Sex data were missing for 372 (3·1%) of 11 848 individuals. Median age at registry entry was 9·6 years (IQR 5·8-13·2). 10 099 (89·9%) of 11 235 included individuals had a final genetically confirmed diagnosis of familial hypercholesterolaemia and 1136 (10·1%) had a clinical diagnosis. Genetically confirmed diagnosis data or clinical diagnosis data were missing for 613 (5·2%) of 11 848 individuals. Genetic diagnosis was more common in children and adolescents from high-income countries (9427 [92·4%] of 10 202) than in children and adolescents from non-high-income countries (199 [48·0%] of 415). 3414 (31·6%) of 10 804 children or adolescents were index cases. Familial-hypercholesterolaemia-related physical signs, cardiovascular risk factors, and cardiovascular disease were uncommon, but were more common in non-high-income countries. 7557 (72·4%) of 10 428 included children or adolescents were not taking lipid-lowering medication (LLM) and had a median LDL-C of 5·00 mmol/L (IQR 4·05-6·08). Compared with genetic diagnosis, the use of unadapted clinical criteria intended for use in adults and reliant on more extreme phenotypes could result in 50-75% of children and adolescents with familial hypercholesterolaemia not being identified. Interpretation: Clinical characteristics observed in adults with familial hypercholesterolaemia are uncommon in children and adolescents with familial hypercholesterolaemia, hence detection in this age group relies on measurement of LDL-C and genetic confirmation. Where genetic testing is unavailable, increased availability and use of LDL-C measurements in the first few years of life could help reduce the current gap between prevalence and detection, enabling increased use of combination LLM to reach recommended LDL-C targets early in life

All-optical modulation of laser light in amorphous silicon-filled microstructured optical fibers

Amorphous silicon is deposited within optical fibers by a high pressure microfluidic deposition process and characterized via Raman spectroscopy. All-optical modulation of 1.55 µm light guided through the silicon core is demonstrated using the free carrier absorption generated by a 532 nm pump pulse. Modulation depths of up to 8.26 dB and modulation frequencies of up to 1.4 MHz are demonstrated

Spatial coherence from Nd3+ quantum emitters mediated by a plasmonic chain

Controlling the coherence properties of Rare Earth emitters in solid-state platforms in the absence of an optical cavity is highly desirable for quantum light-matter interfaces and photonic networks. Here, we demonstrate the possibility of generating directional and spatially coherent light from Nd3+ ions coupled to the longitudinal plasmonic mode of a chain of interacting Ag nanoparticles. The effect of the plasmonic chain on the Nd3+ emission is analyzed by Fourier microscopy, revealing the presence of an interference pattern in which the Nd3+ emission is enhanced at specific directions, as a distinctive signature of spatial coherence. Numerical simulations corroborate the need of near-field coherent coupling of the emitting ions with the plasmonic chain mode. The work provides fundamental insights for controlling the coherence properties of quantum emitters at room temperature and opens new avenues towards Rare Earth based nanoscale hybrid devices for quantum information or optical communication in nanocircuits

Emergent room temperature polar phase in CaTiO3 nanoparticles and single crystals

Polar instabilities are well known to be suppressed on scaling materials down to the nanoscale, when the electrostatic energy increase at surfaces exceeds lowering of the bulk polarization energy. Surprisingly, here we report an emergent low symmetry polar phase arising in nanoscale powders of CaTiO3, the original mineral named perovskite discovered in 1839 and considered nominally nonpolar at any finite temperature in the bulk. Using nonlinear optics and spectroscopy, X-ray diffraction, and microscopy studies, we discover a well-defined polar to non-polar transition at a TC = 350 K in these powders. The same polar phase is also seen as a surface layer in bulk CaTiO3 single crystals, forming striking domains with in-plane polarization orientations. Density functional theory reveals that oxygen octahedral distortions in the surface layer lead to the stabilization of the observed monoclinic polar phase. These results reveal new ways of overcoming the scaling limits to polarization in perovskites