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Self-assembled opal crystals (bulk silica opals and PMMA thin opal films)have been studied by atomic force microscopy (AFM) and optical spec-troscopy. Reflectance and transmittance spectra (R(λ) and T (λ), respectively)as well as spectra of ellipsometric parameters Ψ(λ) and Δ(λ)demonstratepronounced changes with changing the angle of light incidence. Diameters ofspheres obtained from AFM-images correspond to those obtained from Braggfit to the diffraction resonance dispersions. The band of light losses detected byellipsometry at the spectral range of avoided band crossing of opal eigenmodeswas assigned to the energy exchange between these modes

The generation of T waves in a deep ocean by an earthquake in its epicentral region is often observed, but the mechanism of the excitation of the acoustic waves travelling horizontally with the speed of sound remains controversial. Here, the hypothesis is investigated that the abyssal T waves are generated by the scattering of ballistic sound waves by surface and internal gravity waves in the ocean. Volume and surface scattering are studied theoretically in the small perturbation approximation. In the 3-50 Hz typical frequency range of the observed T waves, the linear internal waves are found to lack the necessary horizontal spatial scales to meet the Bragg scattering condition and contribute appreciably to the T-wave excitation. In contrast, the ocean surface roughness has the necessary spatial scales at typical sea states and wind speeds. The efficiency of the acoustic normal modes' excitation at surface scattering of the ballistic body waves by wind seas and sea swell is quantified and found to be comparable to that of the established mechanism of the T-wave generation at downslope conversion at the seamounts. The surface scattering mechanism is consistent with key observational features of the abyssal T waves, including their ubiquity, low-frequency cutoff, presence on seafloor sensors, and weak dependence on the earthquake focus depth.

Although a wide variety of techniques have been developed to date for the fabrication of high-quality colloidal photonic crystals (CPCs) using monodisperse silica and polystyrene microparticles, poly(N-isopropylacrylamide) (PNIPA) hydrogel microparticles have rarely been utilized for the preparation of active CPCs despite the intriguing feature of temperature-responsive volume changes. This report describes the promising potential abilities of PNIPA hydrogel microparticles for sensor and laser applications. Monodisperse PNIPA hydrogel microparticles were synthesized by emulsion polymerization, and the microparticle diameter was finely controlled by adjusting the surfactant concentration. Such hydrogel microparticles spontaneously formed uniform CPCs with visible Bragg reflection even in fluid suspensions. The addition of small amounts of ionic substances into the centrifuged and deionized CPC suspensions enabled the on-demand color switching between Bragg reflection and white turbidity with temperature, leading to temperature- and ion-sensing applications. Moreover, our expanding experiments successfully demonstrated the optically excited laser action with a single and narrow peak from CPC suspensions with light-emitting dyes by the photonic band gap effect. After the light-emitting dyes were simply removed from the CPC suspensions by centrifugation, the purified PNIPA hydrogel microparticles were permanently reusable as the CPC laser microcavities to generate the laser action at other wavelengths using different dyes. This study contributes the circular economy concept using reusable hydrogel microparticles for the realization of a sustainable society.

The double crystal diffraction structure based on Bragg diffraction is the core component of the monochromator that is widely used in synchrotron radiation beam lines and monochromatic X-ray radiation devices. The stability of monochromatic X-rays produced by using the T-structure double crystal monochromator at National Institute of Metrology was investigated experimentally. Due to its structural defects, the X-ray flux of the T-structured double crystal monochromator shows poor long-term stability. Inspired by the Channel-cut monochromator structure, we designed a new double crystal monochromator structure to improve the long-term stability of the X-ray flux. Experiments showed that the stability of the monochromatic X-ray flux for the new double crystal monochromator structure was better than 1.0%@1 h, and the energy region and flux rate of the monochromatic X-rays are significantly improved. This work provides a stable and reliable monochromatic X-ray source for the calibration of X/γ detectors such as satellite load detectors, which will contribute to the development of X/γ detection technology.

A tight-binding theoretical model which describes the vibration properties of a new type of mechanical metamaterial, the coupled-resonator phononic metamaterial (CRPM), is developed. This metamater...

High-power and highly stable 980 nm semiconductor lasers are widely used in fiber laser pumping and instrumentation applications. We report on a distributed Bragg reflector (DBR) semiconductor lase...

Certain nematic liquid crystals, e.g., those formed by banana-shaped molecules, can exhibit a low-temperature twist-bend nematic (Ntb) phase. Upon addition of chiral dopants, a chiral version of the twist-bend phase (N*tb) can be observed below the conventional chiral nematic (N*) phase, while under electric field the N* phase is transformed into a specific state known as "heliconical cholesteric". In this work, we have studied the well-known Ntb-forming system CB7CB:CB6OCB with addition of 5CB and chiral dopants (ChD) using optical microscopy, differential scanning calorimetry (DSC), and measurements of temperature-dependent optical transmission using optical microscopy. Effects of 5CB and different chiral dopants (of steroid or non-steroid nature) upon thermal stability of Ntb phase were analyzed, and selective reflection in the visible range could be observed in the N* phase with a sufficiently high ChD content. As a peculiar feature, sharp unwinding of the cholesteric helix was observed at lower temperatures when approaching the N*tb phase, which appears to be similar to the helix unwinding close to the smectic-A transition., Comment: 32 pages, 10 figures

In a powder diffraction experiment the resolution function defines the instrumental contribution to the peak widths as a function of the Bragg angle. The Caglioti formula is frequently applied to model the instrumental broadening and used in structural refinement. The parameters in the Caglioti formula are linked to physically meaningful parameters for most diffraction geometries. However, this link is lost for the now very popular powder diffraction geometry using large 2D area detectors. Here we suggest a new physical model for the instrumental broadening specifically developed for powder diffraction data measured with large 2D area detectors. The model is verified using data from two synchrotron diffraction beamlines with the Pilatus2M and MAR345 detectors. Finally, a functional form is proposed to replace the Caglioti formula for this geometry in the Rietveld method and profile refinements.

Noncollinear triple acousto-optic diffraction of Bessel light beams by ultrasound in uniaxial crystals is investigated. An expression for the complex vector amplitude of a wave diffracted under exact Bragg synchronism conditions is obtained in vector-matrix form. The diffracted light beams display triple Bragg diffraction with different efficiencies when a Bessel light beam propagates at a small angle to the crystal optical axis. Diffraction where the diffracted light beams have the same intensity is possible if the Bragg synchronism conditions are exactly fulfilled. This diffraction feature is not observed without Bragg synchronism. The light intensity in the third diffraction order is significantly reduced (down to zero) with large frequency detuning of the Bragg synchronism.

We demonstrate the facile tuning of uniform Bragg reflection color from red to blue by uniaxial compression of gel films containing single-crystalline loosely packed colloidal crystals. The tuned colors can be fixed by photopolymerization of a polymer precursor solution contained in the compressed gel films. We demonstrate the facile tuning of uniform Bragg reflection color from red to blue by uniaxial compression of gel films containing single-crystalline loosely packed colloidal crystals. The tuned colors can be fixed by photopolymerization of a polymer precursor solution contained in the compressed gel films.

Distinct ‘hidden’ phases of a technologically relevant thermoelectric material, which are identical in terms of composition and periodic crystal structure, but differ on a local scale, are observed and can be controlled through synthesis conditions. The local structure is explained in terms of a vacancy repulsion model, and relaxations around vacancies are characterized., Although crystalline solids are characterized by their periodic structures, some are only periodic on average and deviate on a local scale. Such disordered crystals with distinct local structures have unique properties arising from both collective and localized behaviour. Different local orderings can exist with identical average structures, making their differences hidden to Bragg diffraction methods. Using high-quality single-crystal X-ray diffuse scattering the local order in thermoelectric half-Heusler Nb1−x CoSb is investigated, for which different local orderings are observed. It is shown that the vacancy distribution follows a vacancy repulsion model and the crystal composition is found always to be close to x = 1/6 irrespective of nominal sample composition. However, the specific synthesis method controls the local order and thereby the thermoelectric properties thus providing a new frontier for tuning material properties.

The difference in the diffracted intensity of the σ- and π-polarized components of an X-ray beam in powder diffraction has generally been treated according to equations based on dipole scattering, also known as kinematic X-ray scattering. Although this treatment is correct for powders and post-sample analyzers known to be of high mosaicity, it does not apply to systems configured with nearly perfect crystal incident-beam monochromators. Equations are presented for the polarization effect, based on dynamical diffraction theory applied to the monochromator crystal. The intensity of the π component relative to the σ component then becomes approximately proportional to |cos 2θm| rather than to cos22θm, where θm is the Bragg diffraction angle of the monochromator crystal. This changes the predicted intensities of X-ray powder diffraction patterns produced on instruments with incident-beam monochromators, especially in the regions far from 2θ = 90° in the powder pattern. Experimental data, based on well known standard reference materials, are presented, confirming that the dynamical polarization correction is required when a Ge 111 incident-beam monochromator is used. The dynamical correction is absent as an option in the Rietveld analysis codes with which the authors are familiar.

Plasmonic modes in optical cavities can be amplified through stimulated emission. Using this effect, plasmonic lasers can potentially provide chip-integrated sources of coherent surface plasmon polaritons (SPPs). However, while plasmonic lasers have been experimentally demonstrated, they have not generated propagating plasmons as their primary output signal. Instead, plasmonic lasers typically involve significant emission of free-space photons that are intentionally outcoupled from the cavity by Bragg diffraction or that leak from reflector edges due to uncontrolled scattering. Here, we report a simple cavity design that allows for straightforward extraction of the lasing mode as SPPs while minimizing photon leakage. We achieve plasmonic lasing in 10-μm-long distributed-feedback cavities consisting of a Ag surface periodically patterned with ridges coated by a thin layer of colloidal semiconductor nanoplatelets as the gain material. The diffraction to free-space photons from cavities designed with second-order feedback allows a direct experimental examination of the lasing-mode profile in real- and momentum-space, in good agreement with coupled-wave theory. In contrast, we demonstrate that first-order-feedback cavities remain "dark" above the lasing threshold and the output signal leaves the cavity as propagating SPPs, highlighting the potential of such lasers as on-chip sources of plasmons.

Lens-less imaging of crystals with coherent X-ray diffraction offers some unique possibilities for strain-field characterization. It relies on numerically retrieving the phase of the scattering amplitude from a crystal illuminated with coherent X-rays. In practice, the algorithms encode this amplitude as a discrete Fourier transform of an effective or Bragg electron density. This short article suggests a detailed route from the classical expression of the (continuous) scattering amplitude to this discrete function. The case of a heterogeneous incident field is specifically detailed. Six assumptions are listed and quantitatively discussed when no such analysis was found in the literature. Details are provided for two of them: the fact that the structure factor varies in the vicinity of the probed reciprocal lattice vector, and the polarization factor, which is heterogeneous along the measured diffraction patterns. With progress in X-ray sources, data acquisition and analysis, it is believed that some approximations will prove inappropriate in the near future.

International audience; An experimental comparison is reported here between two equivalent resonant subwavelength metasurfaces made of long aluminum beams glued closely together on a thin aluminum plate. One metasurface has a random distribution of the resonator beams, and the other has a regular square lattice of pitch 1.5 cm. The random lattice shows the “resonant” behavior of a typical metasurface, with a wide full bandgap for the first A0 Lamb mode. Instead, the regular square lattice combines Fano resonance with Bragg scattering at the edges of the passband, thus creating anisotropy and a pseudo bandgap. Comparisons with numerical simulations are performed, with good agreement with the experimental data. The multimodal response of the beams is also responsible for double negativity in a narrow frequency band, and the event of a pseudo bandgap around this same flexural resonance. In addition, the scattering regimes for both the random and regular metasurfaces are characterized using coherent and incoherent signal analysis.

It has been demonstrated recently via simulations in a duct that the sound transmission loss of porous materials can be increased with embedded periodic scatterers [Jena and Qiu, J. Acoust. Soc. Am. 147, 978-983 (2020)]. In this paper, the insertion loss (IL) of two types of finite size structures constructed by installing two parallel porous sheets within rows of periodic scatterers is investigated in free field. One structure uses rigid cylindrical shells, while the other uses split ring shells, which are obtained by making uniform vertical slits in cylindrical shells. The simulation results show that the mixed structure has larger IL than the summation of the ILs of the individual periodic scatterers and two parallel porous sheets in the frequency range after the first bandgap due to Bragg diffraction, and an additional peak in IL is introduced for the split ring scatterers due to their local resonance. The amplitude, frequency, and bandwidth of the resonance peak can be tuned by changing the geometry of the slit for some specific broadband sound absorption. Finally, the experiment results obtained in an anechoic chamber are presented to support the simulation results and analyses.

With the increase in dimensions of optical elements in addition to ever rising demand for aspherical optics, the millimeter-scale periodic waviness that is naturally produced by machining (such as diamond turning) process in precision optical engineering has been one of the most crucial issues in the development of high surface quality optical elements. Even an extremely small waviness can affect the laser beam profile significantly through interference caused by Bragg scattering. This paper presents a novel method for improving a laser beam profile by utilizing the characteristics of Bragg scattering without requiring established final surface finishing processes such as optical polishing. By engraving an artificial periodic structure with a period of a few hundred microns, the Bragg scattering angle that influences the formation of interference fringes in the laser beam profile was drastically enlarged. Consequently, the quality of the beam profile was improved at a propagation distance where the 0th and 1st (− 1st) order beam modes are spatially separated, only by diamond turning machining without the surface finishing process. In addition, this approach represents an important contribution to green technology, which seeks energy saving and waste reduction in the optical surface manufacturing process.

Restraints extracted from molecule-in-cluster optimizations of separate disorder components permit improved least-squares modelling of experimental crystal structures, and considering energy barriers alongside enthalpy differences further enables the distinguishing of disorder into static and dynamic., Distinguishing disorder into static and dynamic based on multi-temperature X-ray or neutron diffraction experiments is the current state of the art, but is only descriptive, not predictive. Here, several disordered structures are revisited from the Cambridge Crystallographic Data Center ‘drug subset’, the Cambridge Structural Database and own earlier work, where experimental intensities of Bragg diffraction data were available. Using the molecule-in-cluster approach, structures with distinguishable conformations were optimized separately, as extracted from available or generated disorder models of the respective disordered crystal structures. Re-combining these ‘archetype structures’ by restraining positional and constraining displacement parameters for conventional least-squares refinement, based on the optimized geometries, then often achieves a superior fit to the experimental diffraction data compared with relying on experimental information alone. It also simplifies and standardizes disorder refinement. Ten example structures were analysed. It is observed that energy differences between separate disorder conformations are usually within a small energy window of RT (T = crystallization temperature). Further computations classify disorder into static or dynamic, using single experiments performed at one single temperature, and this was achieved for propionamide.

Periodic elastic waveguides, such as rods, beams, and shafts, exhibit frequency bands where wave reflections at impedance discontinuities cause strong wave attenuation by Bragg scattering. Such frequency bands are known as stop bands or band gaps. This work presents a shape optimization technique for one-dimensional periodic structures. The proposed approach, which aims to maximize the width of the first band gap, uses as tuning parameters the spatial Fourier coefficients that describe the shape of the cell cross-section variation along its length. Since the optimization problem is formulated in terms of Fourier coefficients, it can be directly applied to the Plane Wave Expansion (PWE) method, commonly used to obtain the dispersion diagrams, which indicate the presence of band gaps. The proposed technique is used to optimize the shape of a straight bar with both solid and hollow circular cross-sections. First, the optimization is performed using the elementary rod, the Euler-Bernoulli and Timoshenko beam, and the shaft theoretical models in an independent way. Then, the optimization is conducted to obtain a complete band gap in the dispersion diagrams, which includes the three wave types, i.e., longitudinal, bending, and torsional. All numerical results provided feasible shapes that generate wide stop bands in the dispersion diagrams. The proposed technique can be extended to two- and three-dimensional periodic frame structures, and can also be adapted for different classes of cost functions.

In this article, a structure based on one-dimensional photonic crystals that can be used for both angle sensing and refractive index sensing is proposed, which is achieved by optical Tamm state. Under Bragg scattering, its features are investigated by the transfer matrix method. This sensing structure is based on a multi-frequency absorption structure, which can achieve an absorption rate higher than 0.9 for three to four frequency points at the same time. The studied results demonstrate that the absorption peaks of such an absorption structure can be changed from three to four by adjusting the number of periods and silver layer thickness. Absorption peaks can occur red and blue shifts employing tailoring the thickness of defect and the angle of the incident light. By altering the thickness of the defect and the number of periods, the interval between the absorption peaks can be dominated. They are all with high-quality factors and can be used to bring about a high absorption sensor for the refractive index or angle. When it acts as a refractive index sensor, the operating range can cover from 2 to 2.7, whose sensitivity and average figure of merit are 32.3 THz/RIU and 100. If the presented device is used as an angle sensor, those values will become 0.5 THz/degree and 1.2, and its measuring range is from 25° to 70°. It can be said that the emergence of this special sensing structure will be possible to have a broad application prospect in the field of measurement.

Measurements and methods of mitigation for small-angle neutron scattering instrument background caused by extraneous scattering from surfaces are presented., Measurements, calculations and design ideas to mitigate background caused by extraneous scattering in small-angle neutron scattering (SANS) instruments are presented. Scattering includes processes such as incoherent scattering, inelastic scattering and Bragg diffraction. Three primary sources of this type of background are investigated: the beam stop located in front of the detector, the inside lining of the detector vessel and the environment surrounding the sample. SANS measurements were made where materials with different albedos were placed in all three locations. Additional measurements of the angle-dependent scattering over the angular range of 0.7π–0.95π rad were completed on 16 different shielding materials at five wavelengths. The data were extrapolated to cover scattering angles from π/2 to π rad in order to estimate the materials’ albedos. Modifications to existing SANS instruments and sample environments to mitigate extraneous scattering from surfaces are discussed.

Diffraction in quasicrystals is in logarithmic order and icosahedral point group symmetry. Neither of these features are allowed in Bragg diffraction, so a special theory is required. The present work displays exact agreement between the analytic metric with a numeric description of diffraction in quasicrystals that is based on quasi-structure factors. So far, we treated the hierarchic structure as ideal; now, we detail the theory by including two significant features: firstly, the steady state wave function of the incident radiation demonstrates how harmonics, in metrical space and time, enable coherent interaction between the periodic wave packet and hierarchic quasicrystal; secondly, mapping of the hierarchic structure for any influence of defects will allow estimation of possible error margins in the analysis. The hierarchic structure has the required logarithmic periodicity: superclusters, containing about 103 atoms, convincingly map phase contrast images; while higher orders leave space for subsidiary speculation. The diffraction is completely explained for the first time.

A mathematical model of the signal formation process at the output of acousto-optic delay line (AODL) with direct detection has been proposed. This model is used to derive an equation of the AODL transient response. This equation is used to derive a formula for the pulse response characteristic that is utilized to determine the AODL voltage frequency transfer factor. The exponential notation of the frequency transfer factor is discussed. Analytical expression for the amplitude-frequency response of AODL with direct detection is obtained, and its numerical analysis is carried out. The analysis results have been experimentally tested on an appropriate mock-up. The results of experimental investigations confirmed the validity of the proposed mathematical model.

Photonic crystals (PCs) have attracted intense interest for sensing applications. Photonic crystal hydrogels (PCHs) consist of both periodic PCs and stimuli-responsive hydrogels, which can act as a sensing system for the detection of specific analytes. In PCHs, the hydrogel system undergoes volume phase transitions (VPT, swelling or shrinkage) upon exposure to external stimuli. The VPT of the hydrogel causes the photonic stopband of the PCs within the hydrogel to change, which shifts the Bragg diffraction peak wavelengths. Based on this sensing mechanism, a variety of PCH sensors that can respond to external stimuli, such as humidity, temperature, pH, hazardous chemicals and biological species, have been reported. In this review, we overview the response mechanism, preparation methods, and biosensing applications of three-dimensional (3D) and two-dimensional (2D) PCHs. 3D and 2D PCH biosensors are systematically summarized according to the types of the target analytes. At the end of this review, we also propose the prospects of PCHs in the field of biosensing.

High-quality Hg1–xCdxTe (MCT) single crystals are essential for two-dimensional infrared detector arrays. Crystal quality plays an important role on the performance of these devices. Here, the dislocations present at the interface of CdZnTe (CZT) substrates and liquid-phase epitaxy grown MCT epilayers are investigated using X-ray Bragg diffraction imaging (XBDI). The diffraction contributions coming from the threading dislocations (TDs) of the CZT substrate and the MCT epilayers are separated using weak-beam conditions in projection topographs. The results clearly suggest that the lattice parameter of the growing MCT epilayer is, at the growth inception, very close to that of the CZT substrate and gradually departs from the substrate's lattice parameter as the growth advances. Moreover, the relative growth velocity of the MCT epilayer around the TDs is found to be faster by a factor of two to four compared with the matrix. In addition, a fast alternative method to the conventional characterization methods for probing crystals with low dislocation density such as atomic force microscopy and optical interferometry is introduced. A 1.5 mm × 1.5 mm area map of the epilayer defects with sub-micrometre spatial resolution is generated, using section XBDI, by blocking the diffraction contribution of the substrate and scanning the sample spatially.

Reported here are the development and application of new capabilities in the RMCProfile software for structural refinements using the reverse Monte Carlo (RMC) method. An algorithm has been implemented to enable the use of arbitrary peak-shape functions in the modeling of Bragg diffraction patterns and instrumental resolution effects on total-scattering data. This capability eliminates the dependence of RMCProfile on preset functions, which are inadequate for data produced by some total-scattering instruments, e.g. NOMAD at the Spallation Neutron Source (SNS) at Oak Ridge, Tennessee, USA. The recently developed procedure for the instrument-resolution correction has been modified to improve its accuracy, which is critical for recovering nanoscale structure. The ability to measure fine details of local and nanoscale structures with high fidelity is required because such features are increasingly exploited in the design of materials with enhanced functional properties. The new methodology has been tested via RMC refinements of large-scale atomic configurations (distances up to 8 nm) for SrTiO3 using neutron total-scattering data collected on the Polaris and NOMAD time-of-flight powder diffractometers at the ISIS facility (Didcot, Oxfordshire, UK) and SNS, respectively. While the Polaris instrument is known to provide the high-quality data needed for RMC analysis, the similar and sound atomic configurations obtained from both instruments confirmed that the NOMAD data are also suitable for RMC refinements over a broad distance range.

The multibeam acousto-optical Bragg diffraction of laser radiation is considered. This is splitting of an initial beam into several independently controlled beams (channels) without substantial light-power losses. Practically significant relationships that determine the conditions for implementing the multibeam diffraction and its main parameters have been obtained. It is shown that the necessary condition is the form of control radio signal that is close to a frequency (phase) modulated signal. Experimental studies were conducted on a polarization-insensitive acousto-optic deflector based on a paratellurite crystal. Practical applications of the multibeam diffraction are shown: laser image deposition, multichannel transmission (switching) of optical information, and the formation of the laser-beam profile.

We consider phase transitions in chiral magnets using the results of classical Monte Carlo calculations. As the model, we consider the spin-lattice Hamiltonian of a classical spin system, in which the exchange interaction between spin and the Dzyaloshinskii–Moriya interaction are taken into account. We analyze the behavior of the magnetic heat capacity, magnetic susceptibility, and the Bragg scattering intensity as functions of the model parameters. The results are compared with experimental data.

A constraint $$g_{A}^{2}\leq 4.5\times10^{-24}\big(g^{2}+1/\lambda_{A}^{2}\big)$$ on the constant gA of a new short-range (spin—orbit) interaction between nucleons, which is due to the exchange by a light spin-1 boson with the mass mA = ħ/λAc, has been obtained from experimental data on the transmission of neutrons through a noncentrosymmetric perfect crystal near the Bragg reflection characterized by the reciprocal lattice vector g. This constraint is the best in the interaction radius range λA = 10−12−10−5 m.

A 632.8-nm radiation-induced change in the conductivity of a regular domain structure (RDS) formed in a 5% MgO:LiNbO3 crystal has been detected for the first time. As a result, the relaxation rate for the Bragg diffraction efficiency on the RDS, which is observed after the application of an external electric field, increases with the intensity of a probe beam. This dependence is linear in the initial stage of relaxation caused by the screening of the external field because of the redistribution of charges over tilted conductive domain walls of the RDS. For the probe beam with an intensity of 49 mW/mm2, the induced effective conductivity of the RDS, which is estimated as σeff = 3.5×10−9Ω−1m−1, is more than four orders of magnitude higher than the dark conductivity of the single-domain MgO:LiNbO3 sample.

Application of the acousto-optic (AO) Bragg diffraction in the processing of 2D images is analyzed. It is shown that conventional Bragg diffraction can be used for 2D processing provided that the zero-order diffraction is supplemented with the diffraction to an additional (side) order. A 2D contour of an optical image is experimentally detected using the first-order diffraction of radiation with a wavelength of 0.63 × 10–4 cm. An AO cell made from ТеО2 single crystal is used as an AO filter of spatial frequencies. Diffraction orders are formed in such an AO cell due to AO interaction with an acoustic wave with a frequency of 26 MHz.

Beryllium reflectors are used at spallation neutron sources in order to enhance the low-energy flux of neutrons emanating from the surface of a cold and thermal moderator. The design of such a moderator/reflector system is typically carried out using detailed Monte-Carlo simulations, where the beryllium reflector is assumed to behave as a poly-crystalline material. In reality, however, inhomogeneities in the beryllium could lead to discrepancies between the performance of the actual system when compared to the modeled system. The dependence of the total cross-section in particular on crystallite size, in the Bragg scattering region, could influence the reflector performance, and if such an effect is significant, it should be taken into account in the design of the moderator/reflector system. In this paper, we report on the preliminary results of using cross-section libraries, which include corrections for the crystallite size effect, in spallation source neutronics calculations.

There is represented an information about phase inverters with split load. It is noted the problem of provision of identity of different polar signals at split loads. There are mentioned the specificities of Bragg’s diffraction in context of shaping of two different polar signals. It is shown that in case of modification of the frequency of electric signal at the input of acousto-optic modulator the diffraction order shifts in the plane which is perpendicular to the optical axis. It is represented the structural circuit of acousto-optic phase inverter with split load. For generation of two different polar signals the deflected beam is divided into two beams biased in the same direction. Slits in the screens are placed correspondingly at the left and at the right halves of the shaped beams. It is researched the theoretic aspects of generation of different polar signals which are used for numerical analysis of the proposed circuit functionality. The results of the theoretic researches are proved experimentally. It is represented the circuit of the experimental set. Experimental sample of the phase inverter is made using acousto-optical modulator fabricated from glassy photo elastic material of TF-7 type. Laboratory sample of photo receiving device is used for experimental researches. There are represented the results of experimental researches and it is shown their identical match the theoretic researches results.

We address the nonlinear dynamics of binary Bose-Einstein condensates with mutually symmetric spinor components trapped in an optical lattice. The interaction between the repulsive Lee–Huang–Yang nonlinearity and the intercomponent attraction as well as Bragg scattering of an optical lattice results in formation of multi-peaked quantum droplets. Even- and odd-symmetric droplets can bifurcate from Bloch modes of the corresponding periodic systems. Linear stability analysis corroborated by direct evolution simulations reveals that even-symmetric droplets with different norms and different number of peaks can evolve stably at the same chemical potential, i.e., multi-stable droplets are possible in the present scheme. Besides the droplets in the semi-infinite gap, the properties of droplets in the first finite bandgap are also discussed. Both even- and odd-symmetric droplets are stable in almost their whole existence domains. We reveal that optical lattice plays an important role for the stabilization of droplets, in sharp contrast to the nonlinear system without a lattice modulation. We, thus, furnish a paradigmatic example of multi-stable quantum droplets held in optical lattices.

Precision X-ray methods for absolute and relative determination of crystal lattice parameters (interplanar distances) are described and compared, including the X-ray divergent-beam (Kossel) technique, the Bond method, the Renninger method, the back reflection method, the interference method, and the method of standards. It is shown that for most of the considered methods, a relative accuracy of ∼ 10−5 – 10−6 for determining the lattice parameters is usually achievable, with the last two methods giving a much greater accuracy, at the level of ∼ 10−8 – 10−9 .

Using the two-dimensional recurrence relations of X-ray dynamical diffraction, a numerical simulation of reflection and transmission intensity in a cylindrical crystal has been performed. It is shown that for crystals with a small radius Bragg diffraction is realized. For crystals of large radius, Bragg–Laue diffraction occurs, which is characterized by Bragg diffraction on the upper part of the crystal, as well as the presence of Pendellösung oscillations inside the cylindrical crystal. The reciprocal space maps of dynamical and kinematical diffraction have been calculated.

Journal of synchrotron radiation 27(5), 1200 - 1208 (2020). doi:10.1107/S1600577520009789, Nanoprobe X-ray diffraction (nXRD) using focused synchrotron radiation is a powerful technique to study the structural properties of individual semiconductor nanowires. However, when performing the experiment under ambient conditions, the required high X-ray dose and prolonged exposure times can lead to radiation damage. To unveil the origin of radiation damage, a comparison is made of nXRD experiments carried out on individual semiconductor nanowires in their as-grown geometry both under ambient conditions and under He atmosphere at the microfocus station of the P08 beamline at the third-generation source PETRA III. Using an incident X-ray beam energy of 9 keV and photon flux of 10$^{10}$ s$^{−1}$, the axial lattice parameter and tilt of individual GaAs/In$_{0.2}$Ga$_{0.8}$As/GaAs core–shell nanowires were monitored by continuously recording reciprocal-space maps of the 111 Bragg reflection at a fixed spatial position over several hours. In addition, the emission properties of the (In,Ga)As quantum well, the atomic composition of the exposed nanowires and the nanowire morphology were studied by cathodoluminescence spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy, respectively, both prior to and after nXRD exposure. Nanowires exposed under ambient conditions show severe optical and morphological damage, which was reduced for nanowires exposed under He atmosphere. The observed damage can be largely attributed to an oxidation process from X-ray-induced ozone reactions in air. Due to the lower heat-transfer coefficient compared with GaAs, this oxide shell limits the heat transfer through the nanowire side facets, which is considered as the main channel of heat dissipation for nanowires in the as-grown geometry., Published by Wiley-Blackwell, [S.l.]

Diffraction gratings with large angular dispersion rates are central to obtaining high spectral resolution in grating spectrometers operating over a broad spectral range from infrared to soft X-ray domains. The greatest challenge is of course to achieve large dispersion rates in the short-wavelength X-ray domain. Here it is shown that crystals in non-coplanar asymmetric X-ray Bragg diffraction can function as high-reflectance broadband soft X-ray diffraction gratings with dispersion rates that are at least two orders of magnitude larger than those that are possible with state-of-the-art man-made gratings. This opens new opportunities to design and implement soft X-ray resonant inelastic scattering (RIXS) spectrometers with spectral resolutions that are up to two orders of magnitude higher than what is currently possible, to further advance a very dynamic field of RIXS spectroscopy, and to make it competitive with inelastic neutron scattering. Examples of large-dispersion-rate crystal diffraction gratings operating near the 930 eV L 3 absorption edge in Cu and of the 2.838 keV L 3-edge in Ru are presented.

Many important aspects of the dynamic thermo-mechanical response of materials occur at the mesoscale, i.e. a physical scale of interactions smaller than what can be adequately described by homogenous behaviors, yet larger than the scale of the atomic lattice. Concurrent advancements in computational power, continuum theory, and experimental diagnostics are enabling unprecedented understanding of such interactions. However, we cannot develop a sufficient level of confidence in such mesoscale capability until the constitutive description of the underlying constituents is reliably representative of their actual physical behavior. Therefore, there is a strong need to combine experimental, modeling, and data-science techniques to validate models of the thermomechanical response of individual single crystals. One experimental diagnostic with high potential impact to shock physics and materials science is in-situ x-ray diffraction. This paper is primarily focused on simulation of x-ray diffraction in shock physics, but with an aim toward quantifying parametric uncertainty of simulation models. We develop and demonstrate a data-science and model-driven approach to constrain the parameterization of continuum models of crystal lattice deformation associated with the shock response of crystalline materials. The framework is built around the connection between continuum hydrodynamic simulations of lattice deformation and a new Bragg diffraction simulation code, BarberShop. The dynamic deformation of a crystal lattice is modeled using the DiscoFlux model within an arbitrary Lagrangian-Eulerian hydrodynamic code, FLAG. These detailed continuum simulations of lattice deformation can be computationally slow, thus a statistical model is used to emulate the evolution of lattice deformation fields in time and across the considered model parameter space. Emulated lattice deformation fields can then be generated rapidly for any combination of physics model parameters. In turn, these fields can be fed into BarberShop to realize a rapid prediction of Bragg diffraction patterns associated with particular values of physics model parameters. The framework enables parameterization of the single crystal model to obtain Bragg diffraction patterns that most closely resemble a corresponding measurement. Furthermore, the framework naturally provides sensitivities of the lattice deformation to the physics parameters. We highlight the utility of this framework through the application to a synthetic closed-loop inverse problem leading to the parameterization of a single crystal material model. As a model problem, we consider the dynamic response of the energetic molecular crystal, cyclotrimethylenetrinitramine (or RDX), under dynamic compression induced by simulated flyer plate impact experiments.

Terahertz (THz) waveguide Bragg grating is experimentally demonstrated on the basis of a mechanical assembly that includes a metal-grating sheet and a metal parallel-plate waveguide (PPWG). Bragg frequency waves, which are also called phase-matching waves, are efficiently coupled from the free space on the basis of the designed parameters of the air gap width, the metal grating thickness, and the PPWG taper angle. These optimal parameters are critical to reflect the Bragg frequency waves with a transversely resonant field across the metal grating. For other THz waves that are not phase matching to the meal grating vector, transverse resonance simultaneously occurs. However, these waves propagate forward as waveguide modes. PPWG-assembled metal grating thus performs highly distinct Bragg frequencies in the waveguide transmittance when the noisy resonance field, not following Bragg law, is exactly constrained by the waveguide scheme. Given that all components of the waveguide Bragg grating are made of metal without dielectric perturbation, a series of strong Bragg resonant modes in a wide bandwidth and a hollow-core chamber is potentially facilitated for THz gas sensors.