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Magnetic fields can have profound effects on the motion of electrons in quantum materials. Two-dimensional (2D) electron systems subject to strong magnetic fields are expected to exhibit quantized Hall conductivity, chiral edge currents, and distinctive collective modes referred to as magnetoplasmons and magnetoexcitons. Generating these propagating collective modes in charge-neutral samples and imaging them at their native nanometer length scales have thus far been experimentally elusive tasks. In this study, we visualize propagating magenetoexction polaritons at their native length scales and report their magnetic-field-tunable dispersions in near-charge-neutral graphene. Imaging of these collective modes and their associated opto-electrical responses at the sample edges is enabled by innovations to our cryogenic near-field optical microscope that allows us to nano-image the optical responses of 2D materials in magnetic fields up to 7 Tesla. This novel nano-magneto-optics approach represents a new paradigm for exploring and manipulating magnetopolaritons in specimens with low carrier doping via harnessing high magnetic fields.

Supplemental Digital Content is available in the text., Objectives: Early detection of neonatal hearing impairment moderates the negative effects on speech and language development. Universal neonatal hearing screening protocols vary in tests used, timing of testing and the number of stages of screening. This study estimated the cost-effectiveness of various protocols in the preparation of implementation of neonatal hearing screening in Albania. Design: A micro-simulation model was developed using input on demography, natural history of neonatal hearing impairment, screening characteristics and treatment. Parameter values were derived from a review of the literature and expert opinion. We simulated multiple protocols using otoacoustic emissions (OAE) and automated auditory brainstem response (aABR), varying the test type, timing and number of stages. Cost-effectiveness was analyzed over a life-time horizon. Results: The two best protocols for well infants were OAE followed by aABR (i.e., two-stage OAE-aABR) testing in the maternity ward and single-aABR testing. Incremental cost-effectiveness ratios were €4181 and €78,077 per quality-adjusted life-year gained, respectively. Single-aABR screening led to more cases being detected compared to a two-stage screening program. However, it also resulted in higher referral rates, which increased the total costs of diagnostics. Multi-staged screening decreased referral rates but may increase the number of missed cases due to false-negative test results and nonattendance. Conclusions: Only the 2-stage OAE-aABR (maternity ward) protocol was below the willingness-to-pay threshold of €10,413 for Albania, as suggested by the World Health Organization, and was found to be cost-effective. This study is among the few to assess neonatal hearing screening programs over a life-time horizon and the first to predict the cost-effectiveness of multiple screening scenarios.

Objective: To inventory provision and features of childhood hearing screening after the newborn period (CHS), primarily in Europe. Design: From each participating country or region, experts provided information through an extensive questionnaire: implementation year, age at screening, test method, pass criteria, screening location, screener profession, and quality indicators: coverage, referral, follow-up and detection rates, supplemented by literature sources. Study sample: Forty-two European countries or regions, plus Russia, Malawi, Rwanda, India, and China. Results: CHS was performed universally with pure-tone audiometry screening (PTS) in 17 countries or regions, whereas non-universal CHS was performed in eight with PTS or whisper tests. All participating countries with universal PTS had newborn hearing screening. Coverage rate was provided from three countries, detection rate from one, and referral and follow-up rate from two. In four countries, universal PTS was performed at two ages. Earliest universal PTS was performed in a (pre)school setting by nurses (n = 9, median age: 5 years, range: 3–7), in a healthcare setting by doctors and nurses (n = 7, median age: 4.5 years, range: 4–7), or in both (n = 1). Conclusions: Within universal CHS, PTS was mostly performed at 4–6 years by nurses. Insufficient collection of data and monitoring with quality indicators impedes evaluation of screening.

Author(s): Chen, X; Yao, Z; Xu, S; McLeod, AS; Gilbert Corder, SN; Zhao, Y; Tsuneto, M; Bechtel, HA; Martin, MC; Carr, GL; Fogler, MM; Stanciu, SG; Basov, DN; Liu, M | Abstract: The underlying physics behind an experimental observation often lacks a simple analytical description. This is especially the case for scanning probe microscopy techniques, where the interaction between the probe and the sample is nontrivial. Realistic modeling to include the exact details of the probe is widely acknowledged as a challenge. Due to various complexity constraints, the probe is often only approximated in a simplified geometry, leading to a source for modeling inconsistencies. On the other hand, a well-trained artificial neural network based on real data can grasp the hidden correlation between the signal and the sample properties, circumventing the explicit probe modeling process. In this work we show that, via a combination of model calculation and experimental data acquisition, a physics-infused hybrid neural network can predict the probe-sample interaction in the widely used scattering-type scanning near-field optical microscope. This hybrid network provides a long-sought solution for accurate extraction of material properties from tip-specific raw data. The methodology can be extended to other scanning probe microscopy techniques as well as other data-oriented physical problems in general.

Objectives: To assess the performance of newborn hearing screening (NHS) programmes, through selected quality measures and their relationship to protocol design. Design: NHS coverage, referral, follow-up and detection rates were aggregated. Referral rates were compared to age at screening step 1, number of steps, and test method: OAE or aABR. Study sample: A questionnaire on existing hearing screening was completed by experts from countries in Europe, plus Russia, Malawi, Rwanda, India and China. Results: Out of 47 countries or regions, NHS coverage rates were reported from 26, referral rates from 23, follow up from 12 and detection rates from 13. Median coverage rate for step 1 was 96%. Referral rate from step 1 was 6–22% where screening may be performed 24 h, and 4% for >72 h. Referral rates to diagnostic assessment averaged 2.1% after one to two steps using OAE only, 1.7% after two steps including aABR, and 0.8% after three to four steps including aABR. Median detection rate for bilateral permanent hearing impairment ≥40dB was 1 per 1000 infants. Conclusion: Referral rates were related to age, test method and number of screening steps. Quality measures were not available for many NHS programmes.

Newborn hearing screening (NHS) varies regarding number and type of tests, location, age, professionals and funding. We compared the provision of existing screening programmes.A questionnaire containing nine domains: demography, administration, existing screening, coverage, tests, diagnosis, treatment, cost and adverse effects, was presented to hearing screening experts. Responses were verified. Clusters were identified based on number of screening steps and use of OAE or aABR, either for all infants or for well and high-risk infants (dual-protocol).Fifty-two experts completed the questionnaire sufficiently: 40 European countries, Russia, Malawi, Rwanda, India and China.It took considerable effort to find experts for all countries with sufficient time and knowledge. Data essential for evaluation are often not collected. Infants are first screened in maternity wards in most countries. Human development index and health expenditure were high among countries with dual protocols, three screening steps, including aABR, and low among countries without NHS and countries using OAE for all infants. Nationwide implementation of NHS took 6 years, on average.The extent and complexity of NHS programmes are primarily related to health expenditure and HDI. Data collection should be improved to facilitate comparison of NHS programmes across borders.

Author(s): Neal, SN; Kim, HS; O'Neal, KR; Haglund, AV; Smith, KA; Mandrus, DG; Bechtel, HA; Carr, GL; Haule, K; Vanderbilt, D; Musfeldt, JL | Abstract: We employ synchrotron-based near-field infrared spectroscopy to reveal the vibrational properties of bulk, few-sheet, and single-sheet members of the MPS3 (M=Mn, Fe, Ni) family of materials and compare our findings with complementary lattice dynamics calculations. MnPS3 and the Fe analog are similar in terms of their symmetry crossovers, from C2/m to P3¯1m, as the monolayer is approached. These states differ as to the presence of a C3 rotation around the metal center. On the other hand, NiPS3 does not show a symmetry crossover, and the lack of a Bu symmetry mode near 450 cm-1 suggests that C3 rotational symmetry is already present, even in the bulk material. We discuss these findings in terms of local symmetry and temperature effects as well as the curious relationship between these symmetry transformations and those that take place under pressure.

BACKGROUND: Estimates of children and adolescents with disabilities worldwide are needed to inform global intervention under the disability-inclusive provisions of the Sustainable Development Goals. We sought to update the most widely reported estimate of 93 million children METHODS: We analyzed Global Burden of Disease Study 2017 data on the prevalence of childhood epilepsy, intellectual disability, and vision or hearing loss and on years lived with disability (YLD) derived from systematic reviews, health surveys, hospital and claims databases, cohort studies, and disease-specific registries. Point estimates of the prevalence and YLD and the 95% uncertainty intervals (UIs) around the estimates were assessed. RESULTS: Globally, 291.2 million (11.2%) of the 2.6 billion children and adolescents (95% UI: 249.9–335.4 million) were estimated to have 1 of the 4 specified disabilities in 2017. The prevalence of these disabilities increased with age from 6.1% among children aged CONCLUSIONS: The number of children and adolescents with these 4 disabilities is far higher than the 2004 estimate, increases from infancy to adolescence, and accounts for a substantial proportion of all-cause YLD.

Objectives The EUSCREEN study compares the cost-effectiveness of paediatric hearing screening programmes and aims to develop a cost-effectiveness model for this purpose. Alongside and informed by the development of the model, neonatal hearing screening (NHS) is implemented in Albania. We report on the first year. Methods An implementation plan was made addressing objectives, target population, screening protocol, screener training, screening devices, care pathways and follow up. NHS started January 1st, 2018 in four maternity hospitals: two in Tirana, one in Pogradec and one in Kukes, representing both urban and rural areas. OAE-OAE-aABR was used to screen well infants in maternity hospitals, whereas aABR-aABR was used in neonatal intensive care units and in mountainous Kukes for all infants. Screeners’ uptake and attitudes towards screening and quality of screening were assessed by distributing questionnaires and visiting the maternity hospitals. The result of screening, diagnostics, follow up and entry into early intervention were registered in a database and monitored. Results Screeners were keen to improve their skills in screening and considered NHS valuable for Albanian health care. The number of “fail” outcomes after the first screen was high initially but decreased to less than 10% after eight months. In 2018, 11,507 infants were born in the four participating maternity hospitals, 10,925 (94.9%) of whom were screened in the first step. For 486 infants the result of screening was not registered. For the first screen, ten parents declined, eight infants died and one infant was discharged before screening could be performed. In 1115 (10.2%) infants the test either could not be performed or the threshold was not reached; 361 (32,4%) of these did not attend the second screen. For the third screen 31 (34.4%) out of 90 did not attend. Reasons given were: parents declined (124), lived too far from screening location (95), their infant died (11), had other health issues (7), or was screened in private clinic (17), no reason given (138). Conclusions Implementation of NHS in Albania is feasible despite continuing challenges. Acceptance was high for the first screen. However, 32.4% of 1115 infants did not attend the second screen, after a “fail” outcome for the first test.

We report picosecond bunch length measurements using an interferometric method for a 3 MeV electron beam having bunch charge ranging from 1 to 14 pC. The method senses the single-cycle sub-terahertz (THz) pulse emitted by each electron bunch as coherent transition radiation which, in turn, is analyzed using a Michelson-type interferometer, forming an interferogram that is then processed to yield the nominal electron bunch length. This sub-THz coherent radiation intensity was measured using a quasi-optical detector (QOD) operated at room temperature. This experiment was quite challenging since the divergence angle of the sub-THz pulse emitted by the low-energy electron bunch exceeds ±10°, and its pulse energy at the entrance to the detector was as low as 100 pJ. When compared to a conventional helium-cooled silicon composite bolometer designed for frequencies above 0.5 THz, the QOD provided much better signal-to-noise ratio in the ∼80 GHz frequency range, which was critical for the successful measurement of the bunch length.

Universal newborn hearing screening (UNHS) has turned out to be the most effective way to identify congenital paediatric sensorineural hearing loss. Screening principles and methods, possible screening failures, management of control intervals, screenings for late-onset hearing loss and how to communicate the results of UNHS are core areas of the first section.

The prognosis of childhood hearing impairment depends upon the type of hearing disorder diagnosed, its severity and time of onset, the time points at which the hearing impairment was detected and treatment begun, the nature and quality of the treatment and of professional and family support and the presence of associated disorders.

Ferroic materials are well known to exhibit heterogeneity in the form of domain walls. Understanding the properties of these boundaries is crucial for controlling functionality with external stimuli and for realizing their potential for ultra-low power memory and logic devices as well as novel computing architectures. In this work, we employ synchrotron-based near-field infrared nano-spectroscopy to reveal the vibrational properties of ferroelastic (90\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}^{\circ }$$\end{document}∘ ferroelectric) domain walls in the hybrid improper ferroelectric Ca\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}_{3}$$\end{document}3Ti\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}_{2}$$\end{document}2O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}_{7}$$\end{document}7. By locally mapping the Ti-O stretching and Ti-O-Ti bending modes, we reveal how structural order parameters rotate across a wall. Thus, we link observed near-field amplitude changes to underlying structural modulations and test ferroelectric switching models against real space measurements of local structure. This initiative opens the door to broadband infrared nano-imaging of heterogeneity in ferroics., Ferroic domain walls are nano-objects that are considered functional elements in future devices. Here, the authors study phonons across ferroelastic domain walls by synchrotron-based near-field infrared nano-spectroscopy and relate these changes to the order parameter which helps to understand domain wall dynamics.

The first NSLS-II beamline for infrared and THz spectroscopy recently began operations. The design incorporates features for reaching from the near-UV (~40,000 cm-1) to millimeter waves (~2 cm-1). The high brilliance synchrotron source will be used for a variety of spectroscopic techniques including microspectroscopy, magnetospectroscopy, ellipsometry and materials under extreme pressures and temperatures. Interestingly, the intrinsically short electron bunches (~15 ps rms) results in stable coherent radiation to be observed down to 5 GHz during normal operations.

Author(s): Zhang, J; McLeod, AS; Han, Q; Chen, X; Bechtel, HA; Yao, Z; Gilbert Corder, SN; Ciavatti, T; Tao, TH; Aronson, M; Carr, GL; Martin, MC; Sow, C; Yonezawa, S; Nakamura, F; Terasaki, I; Basov, DN; Millis, AJ; Maeno, Y; Liu, M | Abstract: The Mott insulator Ca2RuO4 is the subject of much recent attention following reports of emergent nonequilibrium steady states driven by applied electric fields or currents. In this paper, we carry out infrared nano-imaging and optical-microscopy measurements on bulk single crystal Ca2RuO4 under conditions of steady current flow to obtain insight into the current-driven insulator-to-metal transition. We observe macroscopic growth of the current-induced metallic phase, with nucleation regions for metal and insulator phases determined by the polarity of the current flow. A remarkable metal-insulator-metal microstripe pattern is observed at the phase front separating metal and insulator phases. The microstripes have orientations tied uniquely to the crystallographic axes, implying a strong coupling of the electronic transition to lattice degrees of freedom. Theoretical modeling further illustrates the importance of the current density and confirms a submicron-thick surface metallic layer at the phase front of the bulk metallic phase. Our work confirms that the electrically induced metallic phase is nonfilamentary and is not driven by Joule heating, revealing remarkable new characteristics of electrically induced insulator-metal transitions occurring in functional correlated oxides.

Percolation processes are ubiquitous in nature and are responsible for many critical phenomena such as first-order phase transitions and infectious epidemic networks. The optical properties of a percolative medium can generally be captured by the effective medium approximation (EMA) when the degree of percolation and the properties of the constituent materials are properly addressed. However, the important local collective responses of nanoclusters in the deep subwavelength regime are often only phenomenologically addressed in the standard EMA formalism. A comprehensive method that measures local light–matter interactions and registers how the local responses influence global optical properties has yet to be established on a firm basis. In this paper, we use infrared nano-imaging/spectroscopy to investigate percolative gold films in the vicinity of the critical percolation threshold. We demonstrate experimentally and theoretically that the near-field spectra yield quantitative information of the characteristic length scale of the local gold clusters and their relative oscillator strengths. As a result, EMA analysis can be augmented with near-field nano-spectroscopy to yield better predictability of the far-field reflection spectrum at the corresponding spectral range.

Scattering-type scanning near-field optical microscopy (s-SNOM) has been widely used to characterize strongly correlated electronic, two dimensional, and plasmonic materials, and it has enormous potential for biological applications. Many of these materials exhibit anisotropic responses that complicate the extraction of dielectric constants from s-SNOM measurements. Here, we generalize our recently developed approach for retrieving the near-field scattering signal from isotropic systems and apply it to anisotropic dielectrics. Specifically, we compare our theoretical results with experimental measurements on modestly anisotropic sapphire that exhibit strong resonances at the infrared frequency range. Good agreement with the experimental result is found. Our result is important for understanding the near-field response of low damping, anisotropic polaritonic states in dielectric media.

The honeycomb iridate ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ has received much attention as a candidate to realize a quantum spin liquid state, but the nature of its insulating state remains controversial. We found that the material exhibits structural transitions at 3 and 10 GPa. The former is accompanied by 166-meV suppression of the activation gap, but the energies for the low-lying interband transitions change by less than 10 meV. This can be reconciled in a picture in which the application of high pressure barely shifts the electronic bands, but rather merely broadens them. First-principles calculations uncover a strong correlation between the band gap and the $\ensuremath{\beta}$ angle of the monoclinic structure, indicating non-negligible interlayer coupling. These results offer clear evidence for a spin-orbit Mott insulating state in ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ and are inconsistent with the quasimolecular orbital model.

Este artículo trata los temas de elección informada (informed choice) y la oferta de servicios para niños sordos y sus familias. En primer lugar, describe en líneas generales el trasfondo de por qué la elección informada ha llegado a ser una cuestión de tanta importancia en el contexto inglés. A continuación describe las primeras fases de un proyecto de investigación y desarrollo, diseñado para orientar tanto a profesionales como a los padres en un planteamiento de elección informada. Estas fases constan de una revisión detallada de la literatura y una serie de consultas con distintos proveedores de servicios profesionales y padres de niños sordos. Se presentan quince principios clave que se han derivado de estas fases de recogida de datos. Con ellos se fundamenta nuestra comprensión de las complejidades en lo que constituye la elección informada. Se aportan también ejemplos verídicos del documento de orientación profesional y del manual para padres. Éstos sirven para subrayar las dificultades que se encuentran a la hora de transformar estas cuestiones fundamentales en documentos prácticos y útiles, tanto para padres como para profesionales.

A low-cost optical feedback system using dynamic mirrors has been developed at the NSLS for stabilizing the position and direction of an infrared synchrotron beam against thermal drift and mechanical noise. The system design has some unique features that potentially simplify installation into an existing infrared beamline. We describe the system and its features along with some performance results.

A diverse panel of experts convened in Bad Ischl, Austria, in June of 2012 for the purpose of coming to consensus on essential principles that guide family-centered early intervention with children who are deaf or hard of hearing (D/HH). The consensus panel included parents, deaf professionals, early intervention program leaders, early intervention specialists, and researchers from 10 nations. All participants had expertise in working with families of children who are D/HH, and focus was placed on identifying family-centered practice principles that are specific to partnering with these families. Panel members reported that the implementation of family-centered principles was uneven or inconsistent in their respective nations. During the consensus meeting, they identified 10 agreed-upon foundational principles. Following the conference, they worked to refine the principles and to develop a document that described the principles themselves, related program and provider behaviors, and evidence supporting their use (drawing upon studies from multiple disciplines and nations). The goal of this effort was to promote widespread implementation of validated, evidence-based principles for family-centered early intervention with children who are deaf and hard of hearing and their families.

We analyze the response of a BCS-type superconductor exposed to a strong THz pulse using the FDTD method in combination with a model time-dependent susceptibility having an explicit dependence on the superconductor's energy gap Δ. In the analysis, the energy gap is allowed to be time varying through its dependence on the current density, along with a relaxation time related to the inelastic electronic scattering rate. The model accounts for 3rd harmonic generation effects and can be applied to the case of an incident, strong-field, single or few cycle pulse for which significant nonlinear effects can occur.

We present the first comprehensive broadband optical spectroscopy data on two insulating phases of vanadium dioxide (VO2): monoclinic M2 and triclinic. The main result of our work is that the energy gap and the electronic structure are essentially unaltered by the first-order structural phase transition between the M2 and triclinic phases. Moreover, the optical interband features in the M2 and triclinic phases are remarkably similar to those observed in the well-studied monoclinic M1 insulating phase of VO2. As the energy gap is insensitive to the different lattice structures of the three insulating phases, we rule out Peierls effects as the dominant contributor to the opening of the gap. Rather, the energy gap arises from intra-atomic Coulomb correlations., 5 pages, 4 figures

Rotatable retarders have been developed for applications in spectroscopic, full Mueller Matrix ellipsometry in the far-IR spectral range. Several materials, such as silicon, KRS-5, and a commercial polymer plastic (TOPAS) have been utilized to achieve a fully adjustable retardation between 0° and 90°. Experimental characteristics of the rotatable retarders that utilize three- and four-bounce designs are compared with calculations. We discuss the effect of light focusing on the performance of these rotatable retarders.

A Fourier Transform Infrared Spectrometer (FTS) was used to obtain the transmission spectra of candidate materials for use as infrared (IR) filters in cryogenic receivers. The data cover the range from 50 cm−1 (∼1.5 THz), well below the peak of the 300 K black body spectrum, to 5000 cm−1 (∼150 THz), Z-cut quartz, Goretex, Zitex G and Zitex A, High Density Polyethylene (HDPE), Teflon (PTFE), Fluorogold and Black Polyethylene were measured. The relative effectiveness of each material as a filter is determined by integrating the transmission spectrum multiplied by the Planck distribution to obtain a normalized attenuation for the mid-IR band. Measurements at both room temperature and 8 K are compared.

When viewed at frequencies below about 8 THz (250 cm-1; 30 meV) the ab-plane optical conductivity of the cuprate superconductors (in their normal state) is well described by a Drude model. Examples include optimally-doped YBa2Cu3O7-δ and Bi2Sr2CaCu2O8; even the underdoped phases have a Drude character to their optical conductivity. A residual Drude-like normal fluid is seen in the superconducting state in most cases; the scattering rate of this quasiparticle contribution collapses at Tc.

This article concerns the first stage of a research and development project that aimed to produce both parent and professional guidelines on the promotion and provision of informed choice for families with deaf children. It begins with a theoretical discussion of the problems associated with the concept of informed choice and deaf child services and then focuses specifically on why a metastudy approach was employed to address both the overcontextualized debate about informed choice when applied to deaf children and the problems associated with its investigation in practice with families and professionals. It presents a detailed analysis of the conceptual relevance of a range of identified studies "outside" the field of deafness. These are ordered according to 2 main conceptual categories and 7 subcategories - (a) the nature of information: "information that is evaluative, not just descriptive" "the difficulties of information for a purpose" "the origins and status of information" and "informed choice and knowledge, not informed choice and information" and (b) parameters and definitions of choice: "informed choice as absolute and relative concept", "preferences and presumptions of rationality", and "informed choice for whom?" Relevant deaf child literature is integrated into the discussion of each conceptual debate in order both to expand and challenge current usage of informed choice as applied to deaf children and families and to delineate possible directions in the planning of the next stage of the main project aimed at producing parent/ professional guidelines. © 2006 Oxford University Press.

We report the production of high power (20watts average, ∼ 1 Megawatt peak) broadbandTHz light based on coherent emission fromrelativistic electrons. Such sources areideal for imaging, for high power damagestudies and for studies of non-linearphenomena in this spectral range. Wedescribe the source, presenting theoreticalcalculations and their experimentalverification. For clarity we compare thissource with one based on ultrafast lasertechniques.

Infrared radiation from synchrotron storagerings serves as a high-brightness source fordiffraction-limited microspectroscopy inboth the mid- and far-infrared spectralranges. Mid-infrared absorption, due to localvibrational modes within complex molecules,is shown to be sensitive to small chemicalchanges associated with certain diseases.Farinfrared modes are believed to result from thefolding or twisting of larger, morecomplex molecules. The ability for thesynchrotron source to perform microscopy ata frequency of 1 THz is demonstrated.

Terahertz (THz) radiation, which lies in the far-infrared region, is at the interface of electronics and photonics. Narrow-band THz radiation can be produced by free-electron lasers and fast diodes. Broadband THz radiation can be produced by thermal sources and, more recently, by table-top laser-driven sources and by short electron bunches in accelerators, but so far only with low power. Here we report calculations and measurements that confirm the production of high-power broadband THz radiation from subpicosecond electron bunches in an accelerator. The average power is nearly 20 watts, several orders of magnitude higher than any existing source, which could enable various new applications. In particular, many materials have distinct absorptive and dispersive properties in this spectral range, so that THz imaging could reveal interesting features. For example, it would be possible to image the distribution of specific proteins or water in tissue, or buried metal layers in semiconductors; the present source would allow full-field, real-time capture of such images. High peak and average power THz sources are also critical in driving new nonlinear phenomena and for pump-probe studies of dynamical properties of materials.

We measured the spectroscopic response of stripe- and vortex-containing ${\mathrm{ErMnO}}_{3}$ in order to uncover the electronic properties of the domain walls. We quantify Born effective charge and polarization differences using the lattice behavior, analyze the local rare earth environment from the $f$-manifold excitations, and reveal how shifts in the charge transfer excitations impact the band gap. The increased Born charge, polarization, and band gap in the vortex-containing material are brought together with a discussion of hybridization and wall density effects. The domain wall optical constants are strongly frequency dependent.

The characteristics of topological insulators are manifested in both their surface and bulk properties, but the latter remain to be explored. Here we report bulk signatures of pressure-induced band inversion and topological phase transitions in ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}\mathrm{Se}$ ($x=0.00$, 0.15, and 0.23). The results of infrared measurements as a function of pressure indicate the closing and the reopening of the band gap as well as a maximum in the free carrier spectral weight. The enhanced density of states near the band gap in the topological phase gives rise to a steep interband absorption edge. The change of density of states also yields a maximum in the pressure dependence of the Fermi level. Thus, our conclusive results provide a consistent picture of pressure-induced topological phase transitions and highlight the bulk origin of the novel properties in topological insulators.

Optical properties of hexagonal multiferroic oxides RMnO3 ,w hereR = Ho, Er, Tm, Yb, and Lu, have been studied in the far-infrared spectral range between 100 and 2000 cm −1 and temperatures between 1.5 and 300 K by means of several experimental techniques: Mueller matrix spectroscopic ellipsometry, rotating analyzer ellipsometry, and optical transmission spectroscopy. Spectra of the optical phonons are described in terms of the temperature dependencies of their frequency, damping, and oscillator strength. For all studies, oxide materials’ clear signatures of the spin-phonon interaction have been found below the temperature of the antiferromagnetic phase transition TN due to magnetic ordering of Mn 3+ spins. A decrease of the ionic radius for R 3+ ions between Ho 3+ and Lu 3+ in the corresponding RMnO3 compounds resulted in systematic variation of the frequency for several optical phonons. A magnetic excitation at 190 cm −1 was observed at low temperatures below TN and interpreted as resulting from two-magnon absorption.

The high brightness, broad spectral coverage and pulsed characteristics of infrared synchrotron radiation enable time-resolved spectroscopy under throughput-limited optical systems, as can occur with the high-field magnet cryostat systems used to study electron dynamics and cyclotron resonance by far-infrared techniques. A natural extension for magnetospectroscopy is to sense circular dichroism, i.e. the difference in a material’s optical response for left and right circularly polarized light. A key component for spectroscopic circular dichroism is an achromatic 1 4 wave retarder functioning over the spectral range of interest. We report here the development of an in-line retarder using total internal reflection in high-resistivity silicon. We demonstrate its performance by distinguishing electronic excitations of differing handedness for GaAs in a magnetic field. This 1 4 wave retarder is expected to be useful for far-infrared spectroscopy of circular dichroism in many materials.

Synopsis Synchrotron-based infrared microscopic measurements have been performed on various hair transverse sections, sampled either from the heads of Caucasian or Afro-American subjects. Lipid content of various virgin hair transverse sections was established, with an unprecedented resolution. The variations in shape and intensity of the CH2, CH3, amide I and amide II bands, before and after lipid removal by solvent extraction, were profiled, showing clearly that Caucasian hair often contains lipids localized inside the medulla and to a lesser extent inside the cuticle. This statement does not hold for the Afro-American hair analysed. For this, the FT-IR spectra do not change within the hair section and are insensitive to solvent extraction. The importance of the origin of hair on its physical and chemical properties has to be taken into account in future investigations. Resume Par utilisation de la microscopie infra-rouge utilisant le rayonnement synchrotron, la repartition des lipides sur la section de cheveux vierges (caucasiens et afro-americains), a pu etre comparee avec une resolution spatiale jamais egalee. La forme et l'intensite des bandes CH2, CH3, amide I et amide II, avant et apres delipidation par solvants ont ete obtenues. Il apparait que pour le cheveu caucasien, les lipides sont majoritairement localises dans la medule et dans la cuticule en quantite moindre. Ceci n'est pas le cas pour les cheveux afro-americains: leur spectre infra-rouge est le meme sur toute la section et est insensible a la delipidation. L'origine des cheveux est donc particulierement importante pour l'etude de leurs proprietes physico-chimiques.

We report the temperature-dependent infrared spectra of pure, deuterated, Zn-doped, and 2,6-dimethyl-substituted samples of the S = 1/2, one-dimensional Quantum Heisenberg Antiferromagnet (QHAF) copper pyrazine dinitrate (Cu(C4H4N2)(NO3)2). Of the more than 100 vibrational modes observed in the spectra, nearly one-third of them unexpectedly soften throughout the temperature range of investigation (300−5 K). We discuss the temperature dependence of the vibrational spectra in terms of several different models for mode softening. On the basis of detailed structural information and a comparison of the infrared spectra between pure copper pyrazine dinitrate and its chemically modified relatives, we conclude that the unusual softening observed in this low-dimensional molecular magnet is due to enhanced interchain hydrogen bonding with decreasing temperature.

We report the observation of multiparticle coherent emission in the very far infrared from bunched electrons in an electron storage ring. The emission occurs in quasi-periodic bursts, and only when the electron beam current exceeds a threshold value, suggesting an instability-driven modulation of the electron bunch density. For the operating conditions reported, the spectral content of the coherent emission is peaked near a wavelength of 7 mm. This wavelength is much shorter than the nominal electron bunch length, indicating the presence of a density modulation within the bunch.

(2000). The impact of infrared synchrotron radiation in biology: Past, present and future. Synchrotron Radiation News: Vol. 13, No. 5, pp. 31-38.

The instrumentation and performance of the new infrared beamline U12IR at the National Synchrotron Light Source of Brookhaven National Laboratory is described. This beamline utilizes infrared synchrotron radiation from a bending magnet. A combination of beamline design features and spectroscopic instrumentation allows the facility to reach the extremely low frequency limit of ∼2 cm−1 (i.e., 60 GHz or a photon energy of 250 μeV). The infrared light from the synchrotron emission at U12IR is compared to standard thermal sources and reveals substantial benefits for the study of small samples. In particular, the intensity of the synchrotron radiation in the far infrared can be as much as 200 times greater than that from a blackbody when millimeter-sized samples are measured. The effects of diffraction and noise on beamline performance are also discussed.

A Bruker model IFS 125HR Fourier transform interferometer has been installed and its performance tested using high-brightness, far-infrared synchrotron radiation. Results of absorption measurements for the rotational modes of water vapor demonstrate a nearly 10-fold improvement in signal-to-noise when compared with the instrument’s internal high-pressure Hg arc lamp source.

The potentiality of synchrotron infrared microspectrometry was investigated for in situ analysis of fluid inclusions and volatiles of particular geological interest. Thanks to the intrinsic high brightness of the synchrotron infrared source, areas as small as a few μm2 can be probed, providing a high-contrast analysis of small inclusions in geological materials. We have identified organic components in such small volumes in their liquid and gaseous phase, thus allowing a deeper analysis of oil-water inclusions entrapped in diagenetic cements. Such detailed analysis opens up new perspectives in petroleum reservoir evolution studies. The high signal-to-noise ratio of spectra obtained in small volume allows a fast and accurate chemical mapping of the inclusion components. Drastic refraction effects preclude, at the present state, a quantitative analysis of either the volume or the thickness of the individual inclusions. Traces of volatiles such as CO2 and H2O are easily detected in the vitreous and gaseous part of the glass melt fluid inclusions. We have also profiled the hydroxyl concentration near a wall, and calculated the hydrogen diffusion coefficient in anhydrous minerals such as diopside.

We review the properties of infrared synchrotron radiation and particularly those of the beamlines at the NSLS, Brookhaven National Laboratory. We show how this unique, pulsed broadband source with its 1000-fold brightness advantage over thermal sources has been utilized for research programs in surface science, solid-state physics and microscopy and discuss plans for 5 new beamlines at the NSLS.

We report the observation of two signatures of a pressure-induced topological quantum phase transition in the polar semiconductor BiTeI using x-ray powder diffraction and infrared spectroscopy. The x-ray data confirm that BiTeI remains in its ambient-pressure structure up to 8 GPa. The lattice parameter ratio c/a shows a minimum between 2.0-2.9 GPa, indicating an enhanced c-axis bonding through pz band crossing as expected during the transition. Over the same pressure range, the infrared spectra reveal a maximum in the optical spectral weight of the charge carriers, reflecting the closing and reopening of the semiconducting band gap. Both of these features are characteristics of a topological quantum phase transition, and are consistent with a recent theoretical proposal., revised final version

Vanadium dioxide (VO2) undergoes a phase transition at a temperature of 340 K between an insulating monoclinic M1 phase and a conducting rutile phase. Accurate measurements of possible anisotropy of the electronic properties and phonon features of VO2 in the insulating monoclinic M1 and metallic rutile phases are a prerequisite for understanding the phase transition in this correlated system. Recently, it has become possible to grow single domain untwinned VO2 microcrystals which makes it possible to investigate the true anisotropy of VO2. We performed polarized transmission infrared micro-spectroscopy on these untwinned microcrystals in the spectral range between 200 cm-1 and 6000 cm-1 and have obtained the anisotropic phonon parameters and low frequency electronic properties in the insulating monoclinic M1 and metallic rutile phases. We have also performed ab initio GGA+U total energy calculations of phonon frequencies for both phases. We find our measurements and calculations to be in good agreement., 19 pages, 7 figures, 4 tables

Reflection and transmission as a function of temperature (7-300 K and 5-300 K respectively) have been measured on single crystals of the multiferroic compound FeTe2O5Br utilizing light spanning from the far infrared to the visible. The complex dielectric function and other optical properties were obtained via Kramers-Kronig analysis and by fits to a Drude-Lortentz model. Analysis of the anisotropic excitation spectra via Drude-Lorentz fitting and lattice dynamical calculations have led to the observation of 43 of the 53 modes predicted along the b axis of the monoclinic cell. The phonon response parallel to the a and c axes are also presented. Assignments to groups (clusters) of phonons have been made and trends within them are discussed in light of our calculated displacement patterns.

The vortex-state electrodynamics of s-wave superconductors has been studied by infrared spectroscopy. Far-infrared transmission and reflection spectra of superc onducting Nb0.5Ti0.5N and NbN thin films were measured in a magnetic field perpendicular to the film surface , and the optical conductivity was extracted. The data show clear reduction of superconducting signature. We consider the vortex state as a twocomponent effective medium of normal cores embedded in a BCS superconductor. The spectral features are well explained by the Maxwell-Garnett theory. Our analysis supports the presence of magnetic-fieldinduced pair-breaking effects in the superconducting component outside of the vortex cores. The vortex or Abrikosov state exists in type-II superconductors subjected to magnetic fields between Bc1 and Bc2. In this state the field penetrates the superconductor in the form of quantized tubes of flux, or vortices. The superconducting gap is zero inside the vortex cores and finite outside so that each vortex may be considered to have a core of normal metal, surrounded by superconductor [1, 2]. Because vortex quantization renders the material an inhomogeneous system, it necessarily affects the electrodynamics of the s uperconductor. The microwave response of the vortex state has been extensively studied theoretically [3‐5] and experimentally [6‐11]. However the picture is still incomplete in the infrared region spanning the superconducting gap [12, 13]. In this Letter we address the infrared electrodynamics of the vortex state. We obtain the complex optical conductivity of type-II superconductors and compare our results to calculations of a superconductor-normal metal mixture using the two key models for the effective conductivity of an inhomogeneous system: that of Garnett [14] (the so-called “Maxwell-Garnett theory” or MGT) and that of Bruggeman [15] (sometimes called the “effective-medium approximation” or EMA). We also compare our results to a theory of viscous motion of vortices driven by currents in the superconductor [3]. We find that only the MGT gives a good description of experiment, and then only when pairbreaking by the magnetic field [16‐18] is considered. That it does so is reasonable considering the topology of the vortex state: normal regions surrounded entirely by a connected superfluid. As pointed out some years ago [19], this is the topology of the MGT: the inclusions are embedded in a host medium and are correlated to stay apart. In contrast, the EMA allows percolation of the minority constituent at some critical concentration, something that does not happen in the vortex state until the upper critical field, when the entire material is in the normal state. We studied type-II superconducting thin films of BCS superconductors Nb0.5Ti0.5N and NbN, which are widely used in superconducting magnets [20], RF cavities [21], and photodetectors [22]. The 10 nm Nb0.5Ti0.5N film was grown on a quartz substrate in Ar and N2 gas with a NbTi target, and the 70 nm NbN film grown on a MgO substrate in N2 atmosphere using Nb, both by reactive magnetron sputtering [23, 24]. The substrates have negligible absorption in the spectral range of interest (10‐ 100 cm −1 ) for T < 20 K. We performed the experiment at Beamline U4IR of the National Synchrotron Light Source, Brookhaven National Laboratory. The beamline is equipped with a Bruker IFS 66v FT-IR spectrometer, modified to use synchrotron radiation and a superconducting magnet for low-temperature magneto-spectroscopy. A composite silicon bolometer operating at T ∼1.5 K detects far-infrared radiation with high sensitivity. Both sample s were cooled to 2 K (≪ Tc) in zero field, and their transmission and reflection measured in magnetic fields from 0‐10 T, with the field direction normal to the sample sur