A global trend towards miniaturization and multiwavelength performance of nanophotonic devices drives research on novel phenomena, such as bound states in the continuum and Mietronics, as well as surveys for high-refractive index and strongly anisotropic materials and metasurfaces. Hexagonal boron nitride (hBN) is one of the promising materials for future nanophotonics owing to its inherent anisotropy and prospects of high-quality monocrystal growth with an atomically flat surface. Here, we present highly accurate optical constants of hBN in the broad wavelength range of 250-1700 nm combining imaging ellipsometry measurements, scanning near-field optical microscopy and first-principles quantum mechanical computations. hBN's high refractive index, up to 2.75 in the ultraviolet (UV) and visible range, broadband birefringence of â¼0.7, and negligible optical losses make it an outstanding material for UV and visible range photonics. Based on our measurement results, we propose and design novel optical elements: handedness-preserving mirrors and subwavelength waveguides with dimensions of 40 nm operating in the visible and UV ranges, respectively. Remarkably, our results offer a unique opportunity to bridge the size gap between photonics and electronics.
Optical nanoresonators are key building blocks in various nanotechnological applications (e.g., spectroscopy) due to their ability to effectively confine light at the nanoscale. Recently, nanoresonators based on phonon polaritons (PhPs)-light coupled to lattice vibrations-in polar crystals (e.g., SiC, or h-BN) have attracted much attention due to their strong field confinement, high quality factors, and their potential to enhance the photonic density of states at mid-infrared (mid-IR) frequencies, where numerous molecular vibrations reside. Here, we introduce a new class of mid-IR nanoresonators that not only exhibit the extraordinary properties previously reported, but also incorporate a new degree of freedom: twist tuning, i.e., the possibility of controlling their spectral response by simply rotating the constituent material. To achieve this result, we place a pristine slab of the van der Waals (vdW) α-MoO3 crystal, which supports in-plane hyperbolic PhPs, on an array of metallic ribbons. This sample design based on electromagnetic engineering, not only allows the definition of α-MoO3 nanoresonators with low losses (quality factors, Q, up to 200), but also enables a broad spectral tuning of the polaritonic resonances (up to 32 cm-1, i.e., up to ~6 times their full width at half maximum, FWHM ~5 cm-1) by a simple in-plane rotation of the same slab (from 0 to 45°). These results open the door to the development of tunable and low-loss IR nanotechnologies, fundamental requirements for their implementation in molecular sensing, emission or photodetection applications.
Refraction between isotropic media is characterized by light bending towards the normal to the boundary when passing from a low- to a high-refractive-index medium. However, refraction between anisotropic media is a more exotic phenomenon which remains barely investigated, particularly at the nanoscale. Here, we visualize and comprehensively study the general case of refraction of electromagnetic waves between two strongly anisotropic (hyperbolic) media, and we do it with the use of nanoscale-confined polaritons in a natural medium: α-MoO3. The refracted polaritons exhibit non-intuitive directions of propagation as they traverse planar nanoprisms, enabling to unveil an exotic optical effect: bending-free refraction. Furthermore, we develop an in-plane refractive hyperlens, yielding foci as small as λp/6, being λp the polariton wavelength (λ0/50 compared to the wavelength of free-space light). Our results set the grounds for planar nano-optics in strongly anisotropic media, with potential for effective control of the flow of energy at the nanoscale.
Polaritons with directional in-plane propagation and ultralow losses in van der Waals (vdW) crystals promise unprecedented manipulation of light at the nanoscale. However, these polaritons present a crucial limitation: their directional propagation is intrinsically determined by the crystal structure of the host material, imposing forbidden directions of propagation. Here, we demonstrate that directional polaritons (in-plane hyperbolic phonon polaritons) in a vdW crystal (α-phase molybdenum trioxide) can be directed along forbidden directions by inducing an optical topological transition, which emerges when the slab is placed on a substrate with a given negative permittivity (4H-silicon carbide). By visualizing the transition in real space, we observe exotic polaritonic states between mutually orthogonal hyperbolic regimes, which unveil the topological origin of the transition: a gap opening in the dispersion. This work provides insights into optical topological transitions in vdW crystals, which introduce a route to direct light at the nanoscale.
Large optical anisotropy observed in a broad spectral range is of paramount importance for efficient light manipulation in countless devices. Although a giant anisotropy has been recently observed in the mid-infrared wavelength range, for visible and near-infrared spectral intervals, the problem remains acute with the highest reported birefringence values of 0.8 in BaTiS3 and h-BN crystals. This issue inspired an intensive search for giant optical anisotropy among natural and artificial materials. Here, we demonstrate that layered transition metal dichalcogenides (TMDCs) provide an answer to this quest owing to their fundamental differences between intralayer strong covalent bonding and weak interlayer van der Waals interaction. To do this, we made correlative far- and near-field characterizations validated by first-principle calculations that reveal a huge birefringence of 1.5 in the infrared and 3 in the visible light for MoS2. Our findings demonstrate that this remarkable anisotropy allows for tackling the diffraction limit enabling an avenue for on-chip next-generation photonics.
An experience of using, at the State Sanitary and Epidemiologic Supervision (SSES), the Control X-ray Dosimeter (DRK-1) to calculate the dose-square product in the radiation-and-hygienic evaluation of medical X-ray units of different types is described in the paper. The qualitative evaluation monitoring applicable to X-ray equipment is based on the finding and subsequent analysis of graphic dose-square relationships, i.e. anode voltage(measured manually or by X-ray exposure meter), exposition time, anode current, and current-time product. Real graphs for both normally functioning and for malfunctioning units are depicted. The unit radiation output is described.
Radiography/instrumentation , Radiometry/instrumentation , Technology, Radiologic/instrumentation , Diagnostic Equipment , Equipment Design , Quality Control , Radiation Dosage
The effective dose obtained by a patient on X-ray diagnostic studies may be determined by the Russian and foreign devices that measure the product of the absorbed dose by the radiation area while using the transition factors presented. They are calculated by the published data on the surface and effective doses per exposure unit, which are obtained on the phantoms by thermoluminescence dosimetry by taking into account the area of radiation, anode voltage, and projection, which characterize the standard conditions for performing basic X-ray diagnostic studies of adults and children (5 age groups). In the anode voltage range 40-120 kV, the factors are 10(-4) to 2.10.cm2) with errors of about +/- 32%.
Radiography/statistics & numerical data , Adult , Child , Humans , Radiation Dosage , Radiometry/instrumentation , Radiometry/statistics & numerical data
Basic Russian documents providing radiation safety for a patient during X-ray studies are dealt with. They identify 3 groups of individuals exposed to radiation with relevant annual control levels of an effective dose, necessitates to keep a radiation dose log, and enlists of individual protective means, etc. During different X-ray diagnostic studies, the patient's effective dose may be estimated by the table from the guidelines or from the readings. The characteristics of Russian apparatuses (ID-01 is under production, DRIM-1 has undergone technical and clinical tests) and foreign (PTW-Diamentor E, M1, M2, M3 and VacuDAP 2001) apparatuses which measure the exposure dose are product.
Radiation Protection/instrumentation , Radiography/instrumentation , Humans , Radiation Dosage , Radiometry/instrumentation , Russia
The method of extracorporeal shock-wave lithotripsy (ESWL) is widely practiced in urology as effective and less traumatic. Utilization of x-ray and video control during ESWL sessions raises the problem of radiation protection of the patient and medical personnel as well as registration of the exposure dose for estimation of further permissible doses. The examination covered 48 patients of different age suffering from urolithiasis. All of them received ESWL treatment using units URAT (Russia) and LITOSTAR (Germany) having x-ray positioning. It was found that mean effective dose load for LITOSTAR unit was higher than for URAT unit. The larger part of the dose is generated while localizing the stone and focusing. URAT is furnished with logements protecting vital organs. This is of particular importance for children. ESWL departments with TV x-rat system should meet the requirements for jobs with occupational hazards. In multisession lithotripsy dynamic monitoring should be performed by ultrasound X-ray examination should be employed only in growing dilatation of the renal pelvis, prodromal signs of acute pyelonephritis and failure of the effects to eliminate concrements.
Lithotripsy , Urinary Calculi/diagnostic imaging , Adult , Child , Dose-Response Relationship, Radiation , Humans , Lithotripsy/methods , Radiography , Urinary Calculi/therapy
Based on the requirements to x-ray equipment and its modern characteristics, the authors validate the 5-130 keV range for radiation registration in radiation control of x-ray examination rooms. Experimentally derived graphic representation of the sensitivity of S2010 dosimeter in this energy interval shows that the error of measurements of radiation less than 26 keV is exceedingly over 25%, recorded in the certificate. Experimentally determined angular anisotropy for the 109Cd radiation shows that a corporal angle of 0.04 pi sr corresponds to a relative sensitivity of 0.8. The narrow aperture of the pickup necessitates its careful orientation during measurements. The proper background of the dosimeter is 0.05 mR/h in the 4 to 14 keV range and 0.01 mR/h in the 14 to 140 keV range with the external background equal to 1.5 microR/h.
Radiography , Radiometry/instrumentation , Technology, Radiologic , Americium , Cadmium Radioisotopes , Humans , Iron Radioisotopes , Radiation Dosage , Radiography/instrumentation , Sensitivity and Specificity , Technology, Radiologic/instrumentation
A solid-phase enzyme immunoassay of human lactoferrin was developed, which was used in diagnosis of some septic diseases. The test system developed enabled lactoferrin to be measured in the blood serum and plasma of healthy volunteers: 955.8 +/- 74.4 and 405.5 +/- 27.7 mg/e, respectively. This assay may be used also in measurement of blood serum lactoferrin levels in various pathological states and particularly applied for detection of postnatal pyoseptic failures before their clinical manifestations.
Lactoferrin/blood , Sepsis/diagnosis , Humans , Immunoenzyme Techniques , Neutrophils/metabolism , Reference Values , Sepsis/metabolism
Psychophysiological predictors of gestosis have been determined in pregnant women followed up at an antenatal clinic. They typically exhibited anxiety states with increased neuroticism, an introverted personality, impairment of brainstem-subcortical relations due to dysfunctions of nonspecific units of the visceral brain and their activating effects on the normal cortex, exaggerated cutaneous galvanic reflexes. A clinical follow-up of women at an increased risk showed the onset of edematous nephrotic gestosis in 62.8% and hypertensive gestosis in 37.2% of pregnancies, indicating a predictive value of the identified risk factors.
Individuality , Pre-Eclampsia/psychology , Adolescent , Adult , Female , Humans , Pre-Eclampsia/epidemiology , Pregnancy , Pregnancy Trimester, Third , Prognosis , Psychological Tests , Psychophysiology , Risk Factors
