Bulletin of the Russian Academy of Sciences: Physics最新文献

We have presented a theoretical model of light diffraction on multilayer inhomogeneous holographic diffraction structures formed in polymer-dispersed nematic liquid crystals with a spatially varying period. Numerical simulation of the diffraction characteristics of such structures was performed to evaluate their performance as optical spectral filters for dense wavelength division multiplexing communication systems. The results obtained can serve as a basis for the further development of spectral filters.

We have studied the optical properties of a regular array of plasmonic nanoantennas in the form of subwavelength metal spherical particles partly embedded in a metal substrate with a hollow gap between the particles and the substrate. Using gold, a representative plasmonic material, for the particles and the substrate, we have demonstrated that the nanoantenna array possesses two distinct resonances, which may be tuned by varying the parameters of the individual nanoantennas and the grating period. Particular attention is given to the scenario when the two resonances overlap producing an asymmetric Fano-like resonant feature in the array’s reflection spectrum. The possibility of using the nanoantenna array under study for refractometric measurements is considered. Apart from refractometry, the results obtained in this work can find application in the development of novel nanophotonic functional elements for concentration, enhancement and redistribution of the electromagnetic field.

Nanoscale ultraviolet (UV) and visible light sources are promising for applications in wearable optoelectronic, medical treatment devices and LED applications. Mercury lamps previously employed as UV sources need to be replaced by alternative environmentally friendly sources such as III-nitride-based light emitting diodes (LEDs). In this work, the first flexible UV-A and visible light emitting diodes based on AlGaN/GaN and InGaN/GaN core-shell microwires are demonstrated. The developed devices contain a composite microwire/polydimethylsiloxane membrane with flexible transparent electrodes. It is shown that single-walled carbon nanotube electrodes are preferable and provide a stable electrical contact to the membrane with a high transparency in the and visible spectral ranges. The flexible UV-A and stretchable UV-B membranes demonstrate electroluminescence around 345 and 320 nm. Applying the SWCNT-based electrodes with specific meander-shape current paths provides the stretchability and optical stability of the LED structures. The obtained results pave the way for flexible and elastic inorganic light-emitting diodes to be employed in sensing, detection of fluorescent labels or light therapy.

The interaction between the electric charges of the electron and hole plays a key role in the formation of a quantum exciton states, their energy spectrum, and the exciton lifetime. In a spatially indirect exciton (IX), in which the electron and hole are separated by a transition layer this interaction directly depends on the geometric parameters of the interface–indirect exciton (IX–interface) system. In this study, the influence of the IX–interface system geometry on the energy spectrum binding of the IX is analytically investigated. It is rigorously demonstrated that the geometric parameters are quantized. The effective permittivity of the interface becomes dependent on the orbital and magnetic quantum numbers of the IX. The IX binding energy has nonlinear dependence of on the geometric parameters. Geometry shapes the fine structures of the IX states, as well as the exciton absorption, reflection, and luminescence spectra of the heterostructure. All these manifestations of geometry are accessible to experimental observation. This allows the use of the IX‒interface geometry for exciton spectroscopy of the interface layer. The geometry can be controlled by polarized light and an electric field. This allows the use of quantum geometric states of IX as qubits. Fine structures of the binding energy spectra of the ground state of IX were modeled for two planar heterostructures, SiO₂/Si₃N₄ and GaAs/CdSe. It should be noted that the obtained conclusions are valid not only for planar layered heterostructures.

The enhancement of photoluminescence in colloids represents a vital field of photonics, advancing real-world applications in lighting, sensing, and beyond. A colloidal ternary system CeF₃–YF₃–TbF₃ emits green photoluminescence (PL) under ultraviolet pulsed pumping. In this paper, we demonstrate that introducing gold nanoparticles (Au NPs) to the colloidal solution enhances PL via indirect optical transitions. Contrary to common expectations, larger Au NPs with a diameter of 95 nm exhibit a 2.5-fold enhancement in PL, whereas smaller Au NPs enabling a high-Q plasmon resonance, shows significantly less enhancement. Herein, we represent a novel mechanism for PL enhancement enabled by green PL acting as the pump source.

On the surface of diamond plate with (100) and (110) orientations the graphitized structures are created by excimer KrF laser irradiation (λ = 248 nm, τ = 20 ns). The electrical resistance of graphitized layers is measured in different directions. Anisotropy of electrical properties is discovered and studied. The obtained results open new possibilities for using laser methods to modify diamond materials and can be used to improve the conductivity of structures in new diamond-based photonic and electronic elements.

The development of advanced infrared-operating optical devices is facing the problem of Fresnel reflection losses at the surface of optical components, caused by mismatch between their refractive index and that of the surrounding environment, limiting in its turn the devices’ practical efficiency. This task becomes especially challenging when designing optical systems that rely on the utilization of nonlinear optical single-crystals, typically exhibiting a rather high refractive index (n > 2) in the near-IR spectral range with a corresponding strong index jump at the air-crystal interface and increased Fresnel losses. Unreliable methods, based on deposition of antireflection thin-film coatings onto the crystal surface, are being rapidly replaced by high-resolution, but low-performance, lithographic techniques for fabrication anti-reflective nanostructures (ARNs) directly on the surface of nonlinear optical crystals. However, direct lithography-free technologies are undoubtedly demanded to convert proof-of-concept demonstrations of broadband high-transmittance properties of ARNs into real practical applications. Here, anti-reflection relief representing laser-induced periodic surface structures (LIPSS) was fabricated on a novel and promising IR-transparent LiInS₂ (LIS) single crystals by direct femtosecond laser nanopatterning. The effects of applied laser pulse energy and scanning velocity on the morphological features (nanotrenches periodicity and height modulation amplitude) and the structural-phase composition of produced LIPSS were systematically investigated and characterized by means of scanning electron microscopy and Raman spectroscopy. Fourier-transform infrared spectroscopy revealed a 10%-increased transmittance within NIR spectral range of one-sided LIPSS-patterned LIS crystal, compared to the untreated one. This study confirms the prospects of direct laser printing as a high-performance and high-resolution technology for fabrication of anti-reflective nanostructures on the surface of functional nonlinear optical crystals, applicable in noninvasive medical diagnostics, broadband laser spectrometers, nonlinear bio- and chemosensing and so on.

Ferroelectric domain inversion by nano-scale tips of atomic-force microscopes shows a strong (mu )m-sized lateral domain expansion upon application of voltage pulses. We propose a simple self-consistent physical model of this phenomenon based on the concept of domain-wall conduction. The model is capable of a quantitative explanation of a large body of experimental data relevant to lithium niobate crystals. It provides not only the necessary charge compensation far from the tip, but also the absence of the known electrostatic field singularities at the domain edges.

The vibrational properties and crystal structures of rare-earth oxides, specifically yttrium (Y₂O₃) and lanthanum (La₂O₃) ones, were investigated using a combination of density functional theory (DFT) calculations and experimental Raman spectroscopy. Simulated Raman scattering spectra for the reference oxides enabled the identification of vibrational mode symmetries for each phase. By correlating the measured spectra of high-entropy (Y_0.2Eu_0.2Gd_0.2La_0.2Er_0.2)₂O₃ ceramics with DFT results, the crystal structure of the material was determined, and the symmetries of its vibrational modes were assigned. Comparative analysis revealed the presence of the principal La₂O₃ vibrational mode of E_g symmetry at 365 cm^–1 in the high-entropy ceramics. DFT-based modeling provides a useful tool for probing the optical characteristics of rare-earth oxides and can support structural and vibrational characterization. The calculated Raman spectra showed good agreement with both existing theoretical data and experimental results within the acceptable calculation error. This result confirms the applicability of DFT-based modeling for probing the optical characteristics of high-entropy materials, and rare-earth oxide ceramics.

Nanosecond laser structuring of aluminum alloy was investigated to optimize microchannel geometry for enhanced capillary rise. Microchannels with varying density of scan lines were fabricated and characterized. Medium densities yielded the highest deionized water rise velocity and stable transport, following the Lucas–Washburn law. The efficiency was attributed to hierarchical micro/nanostructures and the aluminum oxide layer formed during processing, enhancing hydrophilicity. High densities caused channel merging, reducing flow directionality. Results demonstrate the potential of nanosecond lasers for producing cost-effective, high-performance supercapillary surfaces.