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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.

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...

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.

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.

Instrumentation used in the diagnostic of signals in fusion experiment needs protection against surges in signal power, which emerges from the electron cyclotron resonance heating (ECRH). In this article, a design methodology for the development of selective single notch waveguide is presented. The design of the notch filter is a circular corrugated waveguide that has been modeled based on the second-order Bragg-resonance condition. The device operation is between 75 and 105 GHz (i.e., $W$ -band), and a single stopband frequency is achieved. The magnitude of stopband transmission is further improved by modifying the corrugation geometry, where selected corrugations are combined periodically inside the waveguide. The proposed design allows the propagation of HE11 mode. Due to the Bragg condition, the LP12 mode is observed at the frequency of stopband resonance, i.e., 94 GHz. The proposed device was fabricated, and the measured transmission coefficient ( $S_{21}$ ) was observed in coherence with the simulated $S_{21}$ profile. The notch filter finds an important application in wideband signal diagnostics of electron cyclotron emission (ECE) and reflectometry in the fusion plasma experiments.

A numerical simulation has been performed to study the effect of the mismatch of layer thicknesses of multilayer Laue lenses (MLLs) on X-ray focusing. The spatial distributions of X-ray intensities in the bulk of a lens have been calculated with different gradients of the variation of the period of a MLL. It has been shown that the focal length, as well as the focal spot size, decreases with an increase in the mismatch of layer thicknesses of the MLL. The calculated focal spot size are significantly different from the values reported in other works. A physical nature of the focusing by the MLL has been revealed. It is determined by the Bragg diffraction and is not related to the configuration of the Fresnel zone plate.

Lensless Fourier transform holography has been developed. By treating Bragg diffraction waves as object waves and a transmitted spherical wave as a reference wave, these two waves are interfered and recorded as holograms away from the reciprocal plane. In this method, reconstruction of holograms requires only one Fourier transform. Application of this method to analyze vortex beams worked well and their amplitude and phase distributions were obtained on the reciprocal plane. By combining the conventional holography with the developed lensless Fourier transform holography, we can reconstruct and analyze electron waves from the real to reciprocal space continuously.

High-power semiconductor laser systems based on 1.5 – 1.6 μm single-frequency distributed feedback (DFB) lasers with a sidewall Bragg diffraction grating are developed and their current – voltage, light – current, and spectral characteristics are experimentally studied. The characteristics of conventional lasers with a Fabry – Perot cavity and DFB lasers fabricated from one and the same heterostructure are compared. At a pump current not exceeding 700 mA, a conventional laser with a cavity length of 1.6 mm and a mesa-stripe width of 3 μm emits a power no lower than 200 mW versus 150 mW of the DFB laser; both lasers are mounted in a housing 11 mm in diameter. The DFB laser mounted in a butterfly housing emits a power no lower than 100 mW at the exit of the single-mode cable at a pump current not exceeding 500 mA, which, at a 60 % coupling efficiency, corresponds to a power no lower than 165 mW; the side-mode suppression ratio in this case is no lower than 53 dB. It is shown that the wavelength deviation with changing pump current and temperature is almost an order of magnitude lower for the DFB laser than for the conventional laser.

Specific features of spectral properties of volume reflection holograms are determined, namely, broadening of the spectral response (reflex) contour toward both the short-wave and long-wave spectral ranges in the case where the angle of incidence of the white-light probing beam differs from the direction of reference wave propagation in hologram recording. This effect is essentially different from the known angular dependence of the reflex of the elementary volume reflection grating. A theoretical explanation for experimental data is provided, and formulas are derived, which are used to calculate the transmission spectra of the studied gratings. These spectra are found to be qualitatively consistent with the experiment.

Investigation of the spectral response of graphene-dielectric (SiO2)-based periodic structure was made in the far-infrared (IR) to the mid-IR frequency range, and the effects of different parametric and operational conditions on the transmission characteristics were explored. The presence of stop-bands, followed by Bragg reflection harmonics, in the low-frequency regime was observed exploiting the bilayer graphene (BLG) sheets. The width of stop-bands could be tuned by altering the number of periods as well as the chemical potential of BLG. The formation of a stop-band (with a transmission dip positioned at ~16 THz) having a span of ~3 THz was noticed, which is possibly a very large stop-bandwidth reported so far. The structure was also analyzed upon introducing a defect layer of MgF2 having a thickness smaller than the dielectric medium. This results in shifting the position of stop-bands of the structure. The characteristics of transmission spectra were found to be greatly depending on the chemical potential (of BLG) and other operating conditions - the feature that triggers the usefulness of the proposed structure in the design of optical modulators, tunable narrow-band filters, broad-band reflectors and biosensing applications.

Significant progress has been made in the study of electromagnetic wave scattering from the sea surface. Essential results were obtained in solving applied problems, but there are still unsolved problems in the scattering theory. The radar backscatter cross section is usually used to solve remote sensing tasks, although the Doppler spectrum (DS) of the scattered microwave signal contains more information about sea waves. The concept of a two-scale model of the scattering surface is used in this article. Correct allowance for large-scale waves, in comparison with radar wavelength, in deriving theoretical formulas enabled us to develop a modified Bragg scattering model. It is based on the previously developed scattering model that is refined here to take into account the contribution of the horizontal component of the orbital velocity to the DS. It is shown that allowance for large-scale waves limits the growth of the radar cross section of the Bragg component with a decrease in the incidence angle, which allows using the resonant scattering model at small incidence angles. An additional result is that the modified model of the DS can also be used in the range of middle incidence angles because it takes into account the contribution of the horizontal component of the orbital velocity. It is shown that if the correlation between large-scale and small-scale components of sea waves is neglected, the new formulas pass into the known formulas for the DS within the framework of the Bragg scattering model.

Holography has been identified as a vital platform for three-dimensional displays, optical encryption, microscopy and artificial intelligence through different physical dimensions. However, unlike the wavelength and polarization divisions, orbital angular momentum (OAM) of light, despite its helical wavefront being an independent physical dimension, has not been implemented as an information carrier for holography due to the lack of helical mode index selectivity in the Bragg diffraction formula. Here, we demonstrate OAM holography by discovering strong OAM selectivity in the spatial-frequency domain without a theoretical helical mode index limit. As such, OAM holography allows the multiplexing of a wide range of OAM-dependent holographic images with a helical mode index spanning from −50 to 50, leading to a 10 bit OAM-encoded hologram for high-security optical encryption. Our results showing up to 210 OAM-dependent distinctive holographic images mark a new path to achieving ultrahigh-capacity holographic information systems harnessing the previously inaccessible OAM division. The orbital angular momentum degree of freedom is used to demonstrate 10 bit holographic images with a helical mode index spanning from −50 to 50.

We present a novel method of temporal modulation of X-ray radiation for time resolved experiments. To control the intensity of the X-ray beam, the Bragg reflection of a piezoelectric crystal is modified using comb-shaped electrodes deposited on the crystal surface. Voltage applied to the electrodes induces a periodic deformation of the crystal that acts as a diffraction grating, splitting the original Bragg reflection into several satellites. A pulse of X-rays can be created by rapidly switching the voltage on and off. In our prototype device the duty cycle was limited to ∼1 ns by the driving electronics. The prototype can be used to generate X-ray pulses from a continuous source. It can also be electrically correlated to a synchrotron light source and be activated to transmit only selected synchrotron pulses. Since the device operates in a non-resonant mode, different activation patterns and pulse durations can be achieved.

In this study, we reveal a novel aerial display system, to the best of our knowledge, that combines volume hologram mirrors with a dihedral corner reflector array (DCRA). The suggested aerial display has a see-through capability, which allows for a new design of aerial displays by combining with other types of displays. Furthermore, the virtual image, which frequently disrupts the observation of aerial images, can be suppressed by the Bragg condition of the volume hologram. The color dispersion in the holograms is efficiently compensated by employing features of the DCRA. The findings of preliminary experiments are demonstrated using a DCRA device and full-color hologram mirrors.

In this paper, we report on a crystal based x-ray imaging system fielded at the OMEGA EP laser facility. This new system has a pointing accuracy of +/100 μm, a temporal resolution down to 100 ps (depending on backlighter characteristics), variable magnification, and a spatial resolution of 21.9 µm at the object plane at a magnification of 15×. The system is designed to use a crystal along the crystal plane that satisfies the Bragg condition for the x ray of interest. The thin crystal is then bent into a spherical geometry and attached to a glass backing substrate to hold it in the diagnostic, and the x rays are imaged onto a charge coupled device. We report on data acquired with the new Los Alamos National Laboratory supplied spherical quartz crystal to image the Mn He-α 6.15 keV line emission.

We theoretically investigate light scattering from an array of atoms into the guided modes of a waveguide. We show that the scattering of a plane wave laser field into the waveguide modes is dramatically enhanced for angles that deviate from the geometric Bragg angle. We derive a modified Bragg condition, and show that it arises from the dispersive interactions between the guided light and the atoms. Moreover, we identify various parameter regimes in which the scattering rate features a qualitatively different dependence on the atom number, such as linear, quadratic, oscillatory or constant behavior. We show that our findings are robust against voids in the atomic array, facilitating their experimental observation and potential applications. Our work sheds new light on collective light scattering and the interplay between geometry and interaction effects, with implications reaching beyond the optical domain., Comment: 6 pages, 3 figures

We demonstrated the first, 5th order ~790-805 nm edge-emitting semiconductor distributed feedback Bragg reflection waveguide laser with a side-mode suppression ratio of 49 dB and a corresponding linewidth of 207 kHz.

It is shown that information on the spatial correlation of nano-objects embedded in a crystalline matrix can be retrieved by analysing the X-ray scattering around the Bragg reflections of the host matrix. Data are reported for vertically aligned Ni and CoNi alloy nanowires (NWs) in an SrTiO3 matrix. When the Bragg condition is fulfilled for the matrix and not for the NWs, the latter can be approximated by voids, and the scattering around the matrix reflections contains information on the self-correlation of the NWs (i.e. on their diameter d) and on the correlation between NWs (interdistance D). Nondestructive synchrotron X-ray diffraction data provide information on these values averaged over large areas, complementing local transmission electron microscopy observations. The measurements show that off-Bragg scattering around the matrix reflections can be exploited to study the spatial correlation and morphology of embedded nano-objects, independently of their crystallinity or strain or the presence of defects.

This Letter presents, to the best of our knowledge, the first report of a narrow-linewidth ∼ 790 − 800 n m edge-emitting semiconductor distributed feedback Bragg reflection waveguide diode laser ( D F B 2 R L ). The D F B 2 R L s were fabricated using a ridge waveguide structure with 5th order, surface-etched grating forming the wavelength selective element. Unbonded devices with a 500 µm cavity length exhibited continuous wave threshold currents in the region of 25 mA with an output power of 2.5 mW per (uncoated) facet at 100 mA drive current. The devices operated in a single longitudinal mode, with side-mode suppression ratio (SMSR) as high as 49 dB and linewidths as low as 207 kHz. Devices maintained single mode operation with high SMSR over a 9 nm wavelength range as the temperature was swept from 15°C to 50°C.

Willis coupling, also known as pressure-velocity cross coupling, in acoustic materials has received much attention in the past years. This effect has been found useful in acoustic metasurface designs for wave redirection. We find that Willis coupling in phononic crystals also provides rich physics to manipulate waves. Here, we report the extreme asymmetric lateral sound beaming effect in a two-dimensional phononic crystal composed of Willis scatterers. By matching the second-order Bragg scattering with two leaky guided modes (a quadrupole resonance and a cross-coupling-induced dipole resonance), a normally incident wave is redirected towards the positive and negative directions orthogonal to the incident wave with different amounts of energy. Simulation and experimental results demonstrate the extraordinary asymmetric lateral beaming effect in the Willis medium. The results presented here may find applications in the design of tunable beam splitters and waveguides.

We show that carbon nanopeapods are an ideal artificial superlattice to induce band modulation of thermal phonons. Based on spectral energy density analysis, we found that a periodic deformation in carbon nanotubes induced by fullerene encapsulation leads to zone folding of phonon dispersions up to near the maximum frequency. The zone-folding effect gives rise to phonon band gaps caused either by Bragg reflection or mode hybridization, and this reduces group velocity. This was quantified to play the leading role in reduction of thermal conductivity by the fullerene encapsulation. The strain modulation of thermal phonon bands opens a possibility to control material thermal conductivity.

International audience; In the past decades, Bragg scattering has been considered to be an important scattering mechanism of microwave backscattering from sea surfaces. However, as reported in many recent literatures, non-Bragg scattering (which is often attributed to wave breaking) also makes a significant impact on radar scattering, especially for Horizontal–Horizontal (HH) polarized radar signals. To date, we know far less about non-Bragg scattering than Bragg scattering. Herein, this paper carries out an investigation on non-Bragg scattering and its effect on radar echoes at moderate incidence angles, both for oil-free and oil-covered sea surfaces. This paper firstly presents a systematic comparison of several sea spectra commonly used for the simulation of microwave scattering from sea surfaces. It is found that none of them perform well for the description of Bragg waves. Then, the “pure” Bragg wave spectra are inverted in the framework of the two-scale model (TSM) and geophysical model functions (GMFs). The normalized radar cross sections (NRCS) related to total scattering, non-Bragg scattering, and “pure” Bragg scattering in C, X, and Ku-bands are simulated under various conditions (i.e., incidence angles, wind speeds, and wind directions). Quantitative assessments of the relative contributions of non-Bragg scattering to total scattering are conducted. We also perform a survey on the non-Bragg scattering from the oil-covered sea surface. This article provides some new insights for a better understanding of the non-Bragg microwave scattering from rough sea surfaces at moderate incidence angles.

The lattice dynamics of bismuth nanoislands induced by ultrafast laser excitation is studied by ultrafast electron diffraction. The decay times of the Bragg peak intensity depend on the diffraction order. For 5-nm flat nanoislands, the decay time of the (110) diffraction order is close to the A1g optical phonon decay time. When the thickness is increased to ∼16 nm, the excitation energy is dissipated into low energy phonons, making energy transport diffusive, thus leading to a longer decay time. The temporal evolution of the (012) Bragg diffraction peak shows a two exponential decay with a second decay time of ∼40 ps emerging when the nanoislands are 5 nm thick and the laser fluence is lower than 1.5 mJ/cm2. This second decay may be attributed to a phonon bottleneck caused by size restriction.

We report on the manufacture of low power consumption UV sensor based on n-ZnO/p-Si Junction. The ZnO thin film was prepared through RF sputtering process. The X-ray diffraction analysis and scanning electron microscopy reveal that the prepared ZnO films exhibit single diffraction peak at a Bragg angle of approximately 34.28° with a homogeneous distribution of nanosized structures. The pn junction exhibit good rectifying behaviour with rectifying ratio of approximately 800 at ± 2 V. At zero bias voltage, the prepared UV photodiode shows the highest photo-to-dark current ratio with a stable dynamic behaviour under the illumination of 360 nm UV light. The prepared UV photodiode show dual polarity behaviour with different proposed sensing mechanisms.

A new radiation-hard germano-silicate glass optical fiber with a pure silica glass buffer and a boron-doped silica glass inner cladding was fabricated for temperature sensor application based on the fiber Bragg grating (FBG) under γ-ray irradiation environment. The temperature dependences of optical attenuation at 1550.5 nm and Bragg reflection wavelength shift from 18 °C to 40 °C before the γ-ray irradiation were about 4.57×10−4 dB/ °C and 5.48 pm/ °C, respectively. The radiation-induced optical attenuation at 1550.5 nm and the radiation-induced Bragg reflection wavelength shift under the γ-ray irradiation with the total dose of 22.85kGy at 35 °C were about 0.03dB/m and 0.12nm, respectively, with the γ-ray irradiation sensitivity of 5.25×10−3 pm/Gy. The temperature and the γ-ray irradiation dependence of optical attenuation at 1550.5nm in the FBG written fiber with boron-doped silica glass inner cladding were about 6 times and 4 times lower than that in the FBG written fiber without boron-doped silica glass inner cladding under a temperature change from 18 °C to 40 °C and the γ-ray irradiation with the total dose of 22.85 kGy at 35 °C, respectively. Furthermore, the effect of temperature increase on the Bragg reflection wavelength of the FBG written fiber with boron-doped silica inner cladding was much larger about 1000 times than that of the γ-ray irradiation. However, no influence on the reflection power of the Bragg wavelengths and the full width at half maximum (FWHM) bandwidth under temperature and the γ-ray irradiation change was found. Also, after the γ-ray irradiation with the dose of 22.85kGy, no significant change in the refractive index was found but the residual stresses developed in the fiber were slightly relaxed or retained.

Phononic crystals (PnCs) are a kind of synthetic composite materials with spatial periodicity. Owing to the unique properties, such as the band gaps (BGs), defect mode, wave localization, and wave beaming, PnCs have been applied in acoustic filters, vibration isolation, noise reduction, and sonar detection, attracting increasing attention in recent years. Among these useful properties, the filter characteristics of PnCs have consistently been a popular research topic. Notably, these existing works primarily focus on the multi-channel output of the same frequency, or the single-channel output of the different frequencies. Studies that investigate a multi-channel output with different frequencies, or specified frequencies, are rare. Most of a filter’s functionality is achieved through structures composed of local resonant PnCs, which usually require a more cumbersome design and more expensive costs. However, compared to local resonant PnCs, Bragg scattering PnCs are more commonly accepted in practical applications because of their simple design and easily available materials. Accordingly, this paper studies the multi-channel output of different frequencies by adopting Bragg scattering PnCs. The finite element methods (FEM) of the band structure and transmission spectrum are performed with COMSOL. The BG in the ΓX direction of the band diagram is used as the test target. Periodic plates with criss-crossed elliptical holes can provide wider BGs because of their symmetry breaking. Based on such finding, a two-channel waveguide structure consisting of three representative volume elements (RVE) of different sizes (A, B and C) is constructed, and the two-channel filtering performance is subsequently investigated by the finite element analysis. The research frequency range is set from 0 to 18 kHz. By comparing three RVE’s energy band structures, we can see that the frequency range of BG of A is almost between those of B and C, with relatively small overlap BG. Such BG characteristic can be utilized for the broadband filtering application. When the elastic wave propagates in the two-channel PnC structure consisting of three different sizes, there is supposed to be three situations. (1) When the frequency range of the input excitation is between 5.15 and 7.55 kHz, the elastic wave can pass through the up-channel consisting of A and B, but is forbidden to propagate through C due to the BG. (2) When the frequency range of the input excitation is between 7.55 and 15.16 kHz, the wave is not allowed to propagate neither through up or down-channel because of the BG of A. (3) When the frequency falls into the range between 15.16 and 18 kHz, then the down-channel formed by A and C is the only choice for the wave to pass through. According to the theoretical model, a two-channel PnC plate of acrylic material (PMMA) is fabricated to conduct the transmission experiments. The experimental data agree well with the numerical results, which indicate that the directional transmission of elastic waves within different frequency ranges in a two-channel structure can be achieved by adjusting the size of the three RVE. This paper could provide a novel approach for the application of PnCs in multi-channel filtering.

In order to achieve monochromatic X-rays of higher energy, and so as to calibrate the hard X-ray satellite-borne detectors and to test the energy response at high energy values, a hard X-ray test facility which is based on a single crystal monochromator was designed and built. The facility consists of four parts, namely the X-ray source, the collimating structure, the single crystal monochromator and the detectors. In this work, silicon crystals Si111, Si220, Si551 were utilized in the monochromator to achieve monoenergetic X-ray photons, which is based on crystal Bragg diffraction. By means of adjusting Bragg angle, different energy values can be obtained. The 21–301 keV monochromatic X-rays were realized and studied in this work. The experiment results indicate that there is a good linear relationship between monochromatic light flux and X-ray tube current. The broadening of energy spectra gets wider with increasing energy value, thus worsening the energy resolution. Stability of the hard X-ray test facility was studied, and results suggest that the energy stability is better than 0.4% within 50 h. Besides, the stability of monochromatic light flux is better than 1.4% within 50 h. Therefore, the hard X-ray test facility has a wide energy range and shows very good performance about stability. Thus, it can be used to carry out some experiments, especially to calibrate the hard X-ray satellite-borne detectors. This work will be helpful to the development of the X-ray astronomy.

In this letter, we propose a novel approach for optical single-sideband (SSB) generation by utilizing four-wave mixing Bragg scattering (FWM-BS). The scheme comprises three stages: the initial FWM-BS stage, the spectral phase control stage, and the final FWM-BS stage. Constructive or destructive interference can occur between the sidebands generated in the two FWM-BS stages, depending on the spectral phase mask applied between the stages. By applying an appropriate phase mask, one sideband can be eliminated by destructive interference, while the other sideband is magnified by constructive interference, thus realizing SSB generation. Both upconverted and downconverted SSB generations can be achieved. To verify the scheme, we experimentally demonstrate 50-GHz optical frequency upconversion and downconversion separately for multi-channel 16-Gbaud QPSK signals.

We present here an unexpected relationship to predict the structural phase transition directly and unambiguously from the Bragg angle versus ionization energy plot. We first expose the changes to the F-band optical absorption energy peak in alkali halides so as to justify why the Bragg angle (2$$\theta$$) versus ionization energy plots for both anions and cations can be used to detect structural phase transition during substitutional doping or systematic changes to chemical composition. In principle, this plot can be extended to predict structural phase transition for all types of solid via doping, which includes cuprates, manganites, topological insulators and cathode materials used in lithium-ion batteries, but, unfortunately, not Fermi metals. The said plot can be implemented in all X-ray diffractometers as an additional feature to predict structural phase transition.

X-ray free-electron lasers (XFELs)1,2 are widely operated on the basis of self-amplified spontaneous emission (SASE)3,4, where spontaneous radiation from the electron beam is amplified along the magnetic field in undulators. Despite their high intensities, SASE-XFELs have a broad spectrum due to the stochastic starting-up process5. To narrow the bandwidth, self-seeding has been proposed6,7 and recently demonstrated8,9, where the seed pulse produced by monochromatizing the SASE-XFELs from the first section of undulators using a thin crystal in transmission geometry is amplified in the remaining undulators. Here, we present an efficient self-seeding scheme using the Bragg reflection to produce a seed pulse. We applied this scheme to SPring-8 Angstrom Compact free-electron LAser (SACLA)10, and produced nearly Fourier-transform-limited XFEL pulses that correspond to an increase in spectral brightness by a factor of six compared with SASE-XFELs. This achievement will not only enhance the throughput of present XFEL experiments but also should open new opportunities for X-ray science. A nearly Fourier-limited X-ray free-electron laser beam is generated by a self-seeding scheme. The beam in the first half of the undulators is monochromatized via Bragg reflection, and is subsequently amplified in the remaining undulators.

An accurate theory of the new method of two-beam X-ray diffractometry using synchrotron radiation has been developed. In this method, a beam from the source is reflected from two monochromator crystals without changing direction and then is collimated by a slit with a relatively small size. A diffraction reflection curve (DRC) is obtained by recording the integrated intensity during crystal sample rotation near the Bragg angle for a certain energy, specified by the monochromator. The theory accurately takes into account the influence of the source sizes, the distances, and the slit size on the formation of experimental DRC. It is shown that a practically intrinsic DRC of crystal sample can be obtained even for symmetric reflections from the monochromator crystals and crystal sample if the Bragg angle in the monochromator crystals exceeds the Bragg angle in the crystal sample by a factor of 2 or more. The slit size should to be optimized to exclude its influence on the DRC.

Initially, all that was known about diffraction in quasicrystals was its point group symmetry; nothing was known about the mechanism. The structure was more evident, and was called quasiperiodic. From mapping the Mn atoms by phase-contrast, optimum-defocus, electron microscopy, the progress towards identifying unit cell, cluster, supercluster and extensive hierarchic structure is evident. The structure is ordered and uniquely icosahedral. From the known structure, we could calculate structure factors. They were all zero. The quasi structure factor is an iterative procedure on the hierarchic structure that correctly calculates diffraction beam intensities in 3-dimensional space. By a creative device, the diffraction is demonstrated to occur off the Bragg condition; the quasi-Bragg condition implies a metric that enables definition and measurement of the lattice constant. The reciprocal lattice is the 3-dimensional diffraction pattern. Typically, it builds on Euclidean axes with coordinates in geometric series, but it also transforms to Cartesian coordinates.

A new scheme of two-beam X-ray diffractometry on the “X-Ray Crystallography and Physical Materials Science” (XCPM) beamline at the Kurchatov Synchrotron Radiation Source (KSRS) has been experimentally investigated. The scheme includes a standard double-crystal monochromator and a narrow slit installed in front of the sample. Measurements have been performed for the Si 111 and 311 reflections in the monochromator and the Si 111 and 220 reflections in the sample crystal. It is shown that this scheme allows one to obtain a near-proper diffraction reflection curve even in the case of symmetric diffraction if the Bragg angle for the monochromator exceeds the Bragg angle for the crystal sample by a factor of 2 or more. The experimental results coincide well with the theory.

A technique to synthesize a new category of radar cross-section (RCS)-reduction metasurfaces is presented. The appealing feature of the proposed technique is that by representing the generalized Snell–Descartes’ law of reflection in the form of array factor, it unifies the two most widely studied and well-established modern RCS-reduction methods: checkerboard metasurfaces and gradient index metasurfaces. More importantly, it refines the concepts of both of these metasurfaces and overcomes numerous limitations associated with them. It can synthesize the RCS-reduction metasurfaces which can be placed along with almost any existing metasurface, without replacing the original metasurface that may be designed to serve a specific purpose, to reduce its RCS. The proposed technique is fundamentally based on scattering cancellation, and it is validated using artificial magnetic conductor technology for several configurations. Moreover, a phasor representation is developed and implemented for complex configurations to make the synthesis simpler and more insightful. Finally, to display the versatility of the proposed technique, an example of RCS-reduction metasurface has been synthesized and introduced to an existing high-gain metasurface ground plane available in the literature. This paper is confined to the conventional specular direction.

Circular corrugated waveguides are often used in fusion applications at single, multiple, or broadband millimeter frequencies due to their low ohmic loss, expected large frequency bandwidth, and direct coupling to free-space Gaussian modes. For single-frequency corrugated waveguide systems, transmission line components can be optimized to the desired frequency. For broadband or multiple-frequency applications, this is not possible. The goal of this paper is to demonstrate that the frequency bandwidth of circular corrugated waveguides can be compromised by diffraction losses to miter bends and gaps. It is shown that if the corrugation depth differs significantly from $\lambda $ /4, a theory can substantially underpredict the gap and miter bend losses. The simulations are also shown to compare favorably to experimental measurements. To improve the transmission line performance in large frequency bandwidth systems, such as 33–165 GHz reflectometry, reducing the number of miter bends may, therefore, be necessary. For the improvement of performance in narrower frequency bandwidth or multiple-frequency systems, especially high-powered systems, wavelength-dependent techniques may be applicable. One such application is shown for a Bragg reflection technique to reduce the thermal load to insulating ceramic rings in a dc break component for multiple-frequency ITER electron cyclotron heating transmission lines.

Polarization orientation angle (POA) is an important parameter of polarimetric radar scattering from slopes in mountainous region. It is known that surface tilted in azimuth direction and buildings not aligned in the along-track direction induce polarization orientation shifts. Earlier research has established orientation angle as a function of radar imaging geometry and surface slopes, and that POA estimation can be derived from polarimetric radar data using circular polarization. Besides these, polarimetric scattering from steep slopes and its relation to POA remain not well understood. In this paper, we address these issues by adopting a tilted surface model based on Bragg scattering. We have found that, as the azimuthal slope increases, $\vert $ VV $\vert $ decreases at a faster rate than $\vert $ HH $\vert $ , they become equal, when POA is ±45°, and $\vert $ HH $\vert >\vert $ VV $\vert $ afterward. In other words, the Pauli component, $\vert $ HH - VV $\vert $ reduced to zero at POA = ± 45°, and the typical Bragg scattering characteristics of $\vert $ VV $\vert >\vert $ HH $\vert $ does not apply when steep slope is present inducing $\vert $ POA $\vert > 45^{\circ }$ . Furthermore, the cross-pol $\vert $ HV $\vert $ does not always increase with azimuth slope but also reaches a maximum then decreases to zero. In addition, we investigate the effect of soil moisture on polarimetric SAR (PolSAR) scattering characteristics of steep terrain and the effect of vegetation over surface on POA estimation. The latter is demonstrated with NASA/JPL TOPSAR L-band PolSAR data and C-band InSAR data. Another significance of this paper is that it provides a direct and rigorous derivation of POA equations. The earlier version was derived from a different concept.

This paper investigates the work of an acousto-optic modulator (AOM). The first part of the experiment seeks to provide practice in aligning of the AOM modulator and measure the diffraction efficiency into the first order which is found to be (85%) in total agreement with the manual operation. The relative phases of the m=0, m=+1, m= -1 diffraction order is measured to have π phase shift relative to un diffracted beam. The transfer function of the AOM from experiment data is found to have a curve which follows a sine squared curve that obtained by theoretical measurement. The basic properties of the modulator are also measured which include, Bragg diffraction angle, speed of sound, modulation depth ,frequency response and the results are compared to the theoretical results.

Next-generation, high-brilliance x-ray photon sources call for new x-ray optics. Here we demonstrate the feasibility of using monolithic diamond channel-cut crystals as high-heat-load, beam-multiplexing, narrow-band, mechanically-stable x-ray monochromators with high-power x-ray beams at cutting-edge, high-repetition-rate x-ray free-electron laser (XFEL) facilities. The diamond channel-cut crystals fabricated and characterized in these studies are designed as two-bounce Bragg reflection monochromators directing 14.4-keV or 12.4-keV x-rays within a 15-meV-bandwidth to $^{57}$Fe or $^{45}$Sc nuclear resonant scattering experiments, respectively. The crystal design allows out-of-band x-rays within a $\simeq 1$-eV XFEL bandwidth to be transmitted with minimal losses to alternative simultaneous experiments. Only $\lesssim 2$\% of the incident $\simeq 100$-W x-ray beam is absorbed in a 50-$\mu$m-thick first diamond crystal reflector, ensuring that the monochromator crystal is highly stable. Other x-ray optics applications of diamond channel-cut crystals are anticipated., Comment: 9 pages, 11 figures

The issues of forming the required radiation pattern of an adaptive antenna array for scanning the atmosphere using small-element antennas in vertical sensing radars are considered in the article. These radars operate in pulsed mode and use Fresnel and Bragg Scattering from turbulent formations and various reflections of electromagnetic waves in various atmosphere layers. Low-element adaptive antenna arrays have low cost, high mobility and low hardware costs for organizing atmospheric scanning. The subject of intensive research is adaptive antenna arrays application in radar and radio navigation systems. It allows to form the required directional pattern, to electrically scan the space by changing the amplitude-phase distribution on the adaptive antenna arrays elements, to increase the probability of receiving useful signal, including signals reception against the background of multipath. The results of modeling special radiation patterns for different configurations of antenna arrays with a small number of antenna elements are presented.

Resolve onboard the x-ray satellite X-Ray Imaging and Spectroscopy Mission (XRISM) is a cryogenic instrument with an x-ray microcalorimeter in a Dewar. A lid partially transparent to x-rays (called gate valve or GV) is installed at the top of the Dewar along the optical axis. Because observations will be made through the GV for the first few months, the x-ray transmission calibration of the GV is crucial for initial scientific outcomes. We present the results of our ground calibration campaign of the GV, which is composed of a Be window and a stainless steel mesh. For the stainless steel mesh, we measured its transmission using the x-ray beamline at ISAS. For the Be window, we used synchrotron facilities to measure the transmission and modeled the data with (i) photoelectric absorption and incoherent scattering of Be, (ii) photoelectric absorption of contaminants, and (iii) coherent scattering of Be changing at specific energies. We discuss the physical interpretation of the transmission discontinuity caused by the Bragg diffraction in polycrystal Be, which we incorporated into our transmission phenomenological model. We present the x-ray diffraction measurement on the sample to support our interpretation. The measurements and the constructed model meet the calibration requirements of the GV. We also performed a spectral fitting of the Crab nebula observed with Hitomi SXS and confirmed improvements of the model parameters.

We propose a table-top linearly polarized hard X-ray source by using a tilted shock-front injection in a laser wakefield accelerator (LWFA) to achieve comprehensive control of both polarization and energy of X-ray. By using shock-front injection, the electron bunches are injected during a sharp transition of plasma density. The length of density transition is significantly shorter than the plasma wavelength and offers a highly localized injection. In regular injection methods, such as self and ionization injection, the majority of electrons are injected radially symmetrically. Particle-in-cell (PIC) simulations show the tilted shock front breaks radial symmetry of injection and creates coherent in-plane oscillation of electrons. The coherence of electron bunches is maximized around 30 degrees which leads to a linearly polarized betatron radiation. The polarization of the resulting X-ray is analyzed by Bragg diffraction after collimation by a polycapillary lens.

We analyze the transfer function of a three-dimensional atomic Bragg beamsplitter formed by two counterpropagating pulsed Laguerre-Gaussian laser beams. Even for ultracold atomic ensembles, the transfer efficiency depends significantly on the residual velocity of the particles as well as on losses into higher diffraction orders. Additional aberrations are caused by the spatial intensity variation and wavefront curvature of the Laguerre-Gaussian laser beam envelope, studied with (3+1)-dimensional numerical simulations. The temporal pulse shape also affects the transfer efficiency significantly. Thus, we consider the practically important rectangular, Gaussian, Blackman, and hyperbolic secant pulses. For the last, we can describe the time-dependent response analytically with the Demkov-Kunike method. The experimentally observed stretching of the $\ensuremath{\pi}$-pulse time is explained from a renormalization of the simple Pendell\"osung frequency. Finally, we compare the analytical predictions for the velocity-dependent transfer function with effective (1+1)-dimensional numerical simulations for pulsed Laguerre-Gaussian laser beams, as well as experimental data, and find very good agreement considering a mixture of Bose-Einstein condensate and thermal cloud.

Volume Bragg Gratings (VBG) are inscribed in the bulk of non-conventional photosensitive glasses tailored with silver by means of femtosecond laser irradiation. Thanks to intrinsic features of the spatial distribution of silver-sustained inscribed structures, it is possible to fabricate gratings with sub-wavelength periodic refractive index modulation. As a result, the achieved VBG target first-order Bragg reflection in the VIS - NIR spectral range. This work paves the way to manufacturing more complex optical devices, such as Waveguide Bragg Gratings.

The reflection power from 12.6 mm diameter high-voltage power lines located between two islands was evaluated using a 76 GHz helicopter forward-looking low transmitting power millimeter-wave radar. Firstly, the specifications of the radar system are discussed. Then, reflection power measurements are carried out with a distance of 370 m between the radar and the high-voltage power lines. Both the specular reflection and Bragg scattering are measured with different incident angles. In addition, it is confirmed that a maximum 30 dB signal-to-noise ratio is obtained.

Periodic structures have gained attention in the research community since they show attenuation zones in their frequency response, called bandgaps. In this paper, the interactions of two mechanisms of bandgap formation in mono-coupled periodic structures are examined, i.e., Bragg scattering and local resonators. With reference to longitudinal elastic waves, an analytical study is carried out to describe in detail the formation of bandgaps. Local resonators are implemented via piezoelectric inserts shunted with a resonating electrical circuit for which a non-traditional model is needed since the study concerns higher frequencies with respect to those of the subwavelength regime. Design maps and tuning formulas are developed not only for the case of infinite structures, but also for the finite case, highlighting the role of the number of unit cells and that of resonances in the attenuation zones. Among the possible tuning strategies of local resonators, it is shown that the mutual influence between elastic and electric parameters is able to produce a wider attenuation zone, bridging Bragg scattering bandgaps thanks to the effect of local resonators. The analytical findings of this paper are validated with numerical results in an example application.

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ DATA DESCRIPTION FOR "Difference-frequency generation in an AlGaAs Bragg-reflection waveguide using an on-chip electrically-pumped quantum dot laser" Alexander Schlager ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ also available as readme.txt 2021-06-16 Table of Contents ───────────────── 1) Figure 2 - Lasing Threshold 2) Figure 3 - Difference Frequency Generation 3) Table 1 - Conversion Efficiency 4) Figure A3 - Temperature Dependency 5) Table A3 - Further Conversion Efficiencies Each filename pre-pended with the figure/table number of the main and supplementary text that it contributes to. All files relevant to each figure/table are included. All numeric data is presented in tab separated variable (in a '*.txt' file) which can be opened with standard spreadsheet or text editing programs. Aside from the JSI ('FIG3c-JSI.txt') and the temperature dependency of the internal laser spectrum ('FIGA3a-laser-temp.txt') all the plots are directly generated with a Latex package called `pgfplots'. For the two exceptions a high resolution image ('*.png') has been generated with Wolfram Mathematica and imported via 'pgfplots'. The code used to process this data and calculate e.g. the conversion efficiencies is not contained in this repository, but can be requested from the authors if required. 1) Figure 2 - Lasing Threshold ══════════════════════════════ 'FIG2-threshold-data.txt' contains the raw data of the lasing threshold measurement. Column 1 and 2 contain the current and its standard deviation in Ampere and column 3 and 4 the optical power and its standard deviation in micro Watt after a measurement time of 30 seconds. 'FIG2-inset-540mA.txt' and 'FIG2-inset-700mA.txt' contain the data representing the spectra of the internal laser below and above lasing threshold. Column 1 is the wavelength in nanometers and column 2 the signal strength in kCounts/s and MCounts/s for a current of 540mA and 700mA, respectively. 2) Figure 3 - Difference Frequency Generation ═════════════════════════════════════════════ 'FIG3b-example-data.txt' contains a background subtracted dataset utilizing the internal laser and a seed wavelength of 1614nm. Column 1 is the wavelength in nanometers and column 2 the signal strength in Counts per second (Hz). This data has been averaged for an acquisition time of 300 seconds. 'FIG3c-JSI.txt' contains processed data for the joint spectral intensity. The DFG peaks collected in the measurements (such as in 'FIG3b-example-data.txt') have been fitted with a Gaussian function and these functions have been utilized to generate the data in this file. This allows us to properly show the Full-Width-Half-Maximum of the measured spectrum and get rid of residual background light from e.g. the telecom seed laser near the degeneracy. This data has been corrected for the bandpass filters utilized in the experiment and the detection efficiency of our detector at different wavelengths. It has then be renormalized to ease the creation of the plot. The raw data for the individual wavelength settings are not included in this repository, but can be requested from the authors if required. The data for Fig. 3d) is included 3) Table 1 - Conversion Efficiency (next section). 3) Table 1 - Conversion Efficiency ══════════════════════════════════ 'TAB1-DFG-power-int-1626nm.txt', 'TAB1-DFG-power-ext-1619nm.txt' and 'TAB1-DFG-power-pas-1510nm.txt' include the data to get the slope for the conversion efficiency for the internal laser, the external laser and the passive sample, respectively. Column 1 and 2 describe the optical power and its standard deviation of the seed laser within the waveguide in milli Watt (for correction, see supplementary materials) for a measurement time of 30 seconds. Column 3 and 4 contain the signal strength of the DFG light in counts/s (Hz) and its poissonian standard error of mean for an acquisition time of 300 seconds (internal), 10 seconds (external) and 2 seconds (passive). To extract the signal strength, we simple take sum of the maximum of the corresponding peak in the raw data (such as in 'FIG3b-example-data.txt') and its nearest neighbors, as this corresponds to the peak width of about 1-2 nm. The raw data are not included in this repository, but can be requested from the authors if required. 4) Figure A3 - Temperature Dependency ═════════════════════════════════════ 'FIGA3a-laser-temp.txt' contains the spectra of the internal laser for different temperature settings as shown in the supplementary materials. Column 1 is the temperature in °C, column 2 the wavelength in nanometers and column 3 the normalized signal strength. Note, that the picture used in Fig. A3a) is only a small cutout of the spectra, but contains all the important information, as there is only background below 788nm and above 794nm. 'FIGA3b-shg-type0.txt', 'FIGA3b-shg-type1.txt' and 'FIGA3b-shg-type2.txt' contain the spectral information of the type-0, type-1 and type-2 second harmonic generation process, respectively. This data has been processed already, as it contains the peak maximum position (column 3) and half-width-half-maximum (column 4) in nanometers extracted from Gaussian fits for the individual SHG spectra at different temperatures in °C (column 1) with an accuracy of 0.05°C (column 2). The maximum peak position is used to create the thick line and the half-width-half-maximum is used to create the slightly transparent bands in Fig. A3b). The raw data are not included in this repository, but can be requested from the authors if required. 'FIGA3c-spectrum-693mA.txt' and 'FIGA3c-spectrum-700mA.txt' include the raw internal laser spectrum at a temperature of 3.5°C and 693mA and 700mA of current, respectively. Column 1 is the wavelength in nanometers and column 2 the normalized laser power. 'FIGA3d-shg-spectrum.txt' shows the second harmonic generation spectrum of the type-2 process in our waveguide at a temperature of 3.5°C. Column 1 is the wavelength in nanometers and column 2 the normalized SHG power. This data has been generated by measuring the maximum of the SHG spectrum for different pump laser wavelengths. This way, we can extract the SHG spectrum at a much higher resolution by slowly varying the laser wavelength in steps of 0.01nm. The raw data are not included in this repository, but can be requested from the authors if required. 5) Table A3 - Further Conversion Efficiencies ══════════════════════════════════════════════ All files starting with 'TABA3-DFG-power-*.txt' include the data to get the slope for the conversion efficiency for the internal laser, the external laser and the passive sample shown in the supplementary materials, respectively. Aside from additional wavelength settings for the telecom seed laser, the description is exactly the same as in 3) Table 1 - Conversion efficiency.

Miniaturization of devices has been a primary objective in microelectronics and photonics for decades, aiming at denser integration, enhanced functionalities and drastic reduction of power consumption. Headway in nanophotonics is currently linked to the progress in concepts and technologies necessary for applications in information and communication, brain inspired computing, medicine and sensing and quantum information. Amongst all nanostructures, semiconductor photonic crystals (PhCs) occupy a prominent position as they enable the fabrication of quasi ultimate optical cavities. Low threshold laser diodes or Raman lasers , low power consuming optical memories , efficient single photon sources or single photon quantum gates are impressive examples of their capabilities. We report the demonstration of about 20 micron long PhC semiconductor optical parametric oscillator (OPO) at telecom wavelength exploiting nearly diffraction limited optical modes. The pump power threshold is measured below 0.2 mW. Parametric oscillation was reached through the drastic enhancement of Kerr optical Four Wave Mixing by thermally tuning the high Q modes of a nanocavity into a triply resonant configuration. Miniaturization of this paradigmatic source of coherent light paves the way for quantum optical circuits, dense integration of highly efficient nonlinear sources of squeezed light or entangled photons pairs., submitted manuscript

International audience; We present an implementation of the Maxwell-Bloch (MB) formalism for the study of x-ray emission dynamics from periodic multilayer materials whether they are artificial or natural. The treatment is based on a direct Finite-Difference-Time-Domain (FDTD) solution of Maxwell equations combined with Bloch equations incorporating a random spontaneous emission noise. Besides periodicity of the material, the treatment distinguishes between two kinds of layers, those being active (or resonant) and those being off-resonance. The numerical model is applied to the problem of Kα emission in multilayer materials where the population inversion could be created by fast inner-shell photoionization by an x-ray free-electron-laser (XFEL). Specificities of the resulting amplified fluorescence in conditions of Bragg diffraction is illustrated by numerical simulations. The corresponding pulses could be used for specific investigations of non-linear interaction of x-rays with matter.