PECULIAR PROPERTIES OF ELECTROMAGNETIC RADIATION PROPAGATION IN PHOTONIC CRYSTALLINE METAL-DIELECTRIC SYSTEMS BASED ON OPALS

The article studies the propagation of electromagnetic waves in metal-dielectric systems based on opals. We revealed anomalous transmission and absorption of light by hybrid plasmon- photonic layered heterostructures associated with the excitation of surface plasmon polaritons propagating along the metal-dielectric interface. The position of maxima in the reflection spectra of nanocomposites, obtained by filling the opal matrix with metal by the electrothermodiffusion method, is explained by the Bragg diffraction, and the asymmetric form of the spectral curves is attributed to the Fano resonance.

All-Dielectric Phase-Gradient Metasurface Performing High-Efficiency Anomalous Transmission in the Near-Infrared Region

We propose and numerically demonstrate a phase-gradient metasurface with high anomalous transmission efficiency and a large anomalous refraction angle that consists of discontinuous regular hexagonal nanorods supported by a silica substrate. The metasurface achieves high anomalous transmission efficiency and a full 2$$\pi$$ π phase shift for the wavelength range of 1400–1600 nm. At a central wavelength of approximately 1529 nm, the total transmission efficiency reaches 96.5%, and the desired anomalous transmission efficiency reaches 96.2%, with an anomalous refraction angle as large as 30.64. With the adjustment of the period and the number of nanorods per periodic interval, the anomalous transmission efficiency exceeds 69.6% for a large anomalous refraction angle of 68.58. The superior performance of the proposed design may pave the way for its application in optical wavefront control devices.

Structural Analysis of Low Defect Ammonothermally Grown GaN Wafers by Borrmann Effect X-ray Topography

X-ray topography defect analysis of entire 1.8-inch GaN substrates, using the Borrmann effect, is presented in this paper. The GaN wafers were grown by the ammonothermal method. Borrmann effect topography of anomalous transmission could be applied due to the low defect density of the substrates. It was possible to trace the process and growth history of the GaN crystals in detail from their defect pattern imaged. Microscopic defects such as threading dislocations, but also macroscopic defects, for example dislocation clusters due to preparation insufficiency, traces of facet formation, growth bands, dislocation walls and dislocation bundles, were detected. Influences of seed crystal preparation and process parameters of crystal growth on the formation of the defects are discussed.

Size Effects in Optical and Magneto-Optical Response of Opal-Cobalt Heterostructures

Search for new types of efficient magnetoplasmonic structures that combine high transparency with strong magneto-optical (MO) activity is an actual problem. Here, we demonstrate that composite heterostructures based on thin perfectly-arranged opal films and a perforated cobalt nanolayer meet these requirements. Anomalous transmission appears due to periodic perforation of Co consistent with the regular set of voids between opal spheres, while resonantly enhanced MO response involves the effects of surface plasmon-polariton (SPP) excitation at opal/Co interface or those associated with photonic band gap (PBG) in opal photonic crrystals. We observed the enhancement of the MO effect of up to 0.6% in the spectral vicinity of the SPP excitation, and several times less strong effect close to the PBG, while the combined appearance of PBG and SPP decreases the resultant MO response. Observed resonant magneto-optical properties of opal/Co heterostructures show that they can be treated as functional self-assembled magnetoplasmonic crystals with resonantly enhanced and controllable MO effect.

All-dielectric Phase-gradient Metasurface Performing High-efficiency Anomalous Transmission in the Near-infrared Region

We propose and numerically demonstrate a phase-gradient metasurface with high anomalous transmission efficiency and great anomalous refraction angle, which consists of discontinuous regular hexagonal nanorods supported by a quartz substrate. The metasurface achieves high anomalous transmission efficiency and full 2 phase shift for the wavelength range of 1400-1600 nm. At the central wavelength around 1504 nm, the total transmission efficiency reaches 97.9%, and the desired anomalous transmission efficiency is up to 96.1% with an anomalous refraction angle as large as 30.09°. By adjusting the period and the number of nanorods in one unit cell, the anomalous refraction angle can reach 68.03°, and the anomalous transmission efficiency exceeds 60% within a bandwidth of 50 nm. Theresults are more excellent than those of most present phase-gradient metasurface structures. The superior performance of the proposed structure may pave the way for its application in wavefront control optical devices.

Формирование изображения краевой дислокации при аномальном прохождении рентгеновского излучения

The image formation features of section and projection topograms of an edge dislocation normal to a crystal surface are considered for the case of X-ray anomalous transmission. Experimental images are analyzed using the numerical simulation of diffraction experiment. The new mechanism of an image formation of defects arranged near an output crystal surface is proposed. The distinctions of dislocation topographic images from local disorientation rosettes of reflecting planes are noted.