Bragg Angle Research Articles

An experiment demonstrating the capability of a symmetrical layout type double crystal monochromator controlled using electronic cam technology

A demonstration test of a newly developed double crystal monochromator was performed on beamline BL06 in the NewSUBARU synchrotron radiation facility of Hyogo University. Due to the symmetrical layout of the 1st crystal and 2nd crystal units of the monochromator, a maximum rotation speed of the main axis of up to 5.0 degrees/sec could be achieved. The monochromator is controlled by a newly developed control board programmed with an electronic cam algorithm. The control system allows the speed of both Z1 and Z2 axes to be successively synchronized as the Bragg angle changes. The Z 1 and Z 2 axes are moved apart by equal amounts from the center of gravity of the monochromator as the Bragg angle is increased. Also, the speed at which the Z1 and Z2 axes are moved apart increases with larger Bragg angle. This newly developed monochromator can maintain a stable exit beam height just as well as previous mechanical cam type monochromators proved on the height of the exit beam measured by an encoder system and observed by fluorescent screen. Due to the symmetrical layout and newly developed control system, the monochromator is suitable for industrial use because it can handle a wide energy range and allows high-throughput experiments to be carried out.

High-resolution x-ray monochromatic imaging for laser plasma diagnostics based on toroidal crystal

Monochromatic x-ray imaging is an essential method for plasma diagnostics related to density information. Large-field high-resolution monochromatic imaging of a He-like iron (Fe XXV) K α characteristic line (6.701 keV) for laser plasma diagnostics was achieved using a developed toroidal crystal x-ray imager. A high-index crystal orientation Ge 〈531〉 wafer with a Bragg angle of 75.37° and the toroidal substrate were selected to obtain sufficient diffraction efficiency and compensate for astigmatism under oblique incidence. A precise offline assembly method of the toroidal crystal imager based on energy substitution was proposed, and a spatial resolution of 3–7 μm was obtained by toroidal crystal imaging of a 600 line-pairs/inch Au grid within an object field of view larger than 1.0 mm. The toroidal crystal x-ray imager has been successfully tested via side-on backlight imaging experiments of the sinusoidal modulation target and a 1000 line-pairs/inch Au grid with a linewidth of 5 μm using an online alignment method based on dual positioning balls to indicate the target and backlighter. This paper describes the optical design, adjustment method, and experimental results of a toroidal crystal system in a laboratory and laser facility.

Double-spherically bent crystal scheme of stigmatic x ray monochromatic backlit imaging.

We propose an aberration-free monochromatic x ray backlit imaging scheme using a combination of convex and concave spherically bent crystals. This configuration works with a wide range of Bragg angles, satisfying the conditions for stigmatic imaging at a particular wavelength. However, the assembly accuracy of the crystals must meet the Bragg relation criteria for spatial resolution to increase the detection efficiency. Here, we develop a collimator prism with a cross reference line engraved on a plane mirror to adjust a matched pair of Bragg angles as well as the intervals between the two crystals and the object to be coupled with the detector. We explore the realization of monochromatic backlighting imaging with a concave Si-533 crystal and a convex α-Quartz-2023 crystal, obtaining a spatial resolution of approximately 7 µm and a field of view of at least 200 µm. To the best of our knowledge, this is the best spatial resolution of monochromatic images of a double-spherically bent crystal to date. Our experimental results are presented to demonstrate the feasibility of this imaging scheme with x rays.

Interaction of two-photon NOON state with ultrasonic wave

The paper presents a classical and quantum description of the diffraction of two light beams incident on an ultrasonic wave at a positive and negative Bragg angle. The quantum description of the interaction with the ultrasonic wave was carried out for the two-photon NOON state. Study of diffraction of entangled pair of photon was performed in Mach–Zehnder interferometer wherein an output beam splitter is replaced by ultrasonic wave. It has been shown theoretically and experimentally that when a pair of photons generated from a parametric down-conversion was incident on two input ports of Mach–Zehnder interferometer with an acousto-optical beam splitter, then two-photon beats are observed at the output of the interferometer. The phenomenon of two-photon beats with the double frequency of the ultrasonic wave is the result of the Doppler effect on the ultrasonic wave. Time-correlated single-photon counting method was used to register the phenomenon of two-photon beats. The method of calibrating the interferometer with the use of an additional light source was presented in detail, which guarantees the observation of interaction of two-photon NOON state with ultrasonic wave.Graphical abstract

Stability control method of double crystal monochromator based on hybrid control algorithm

The Bragg angle stability of the DCM (double crystal monochromator) in synchrotron radiation facilities is critical for beam position, flux and resolution of hard X-ray beam lines. Generally, the vibration caused by LN2 cooling system is the most critical factor affecting the stability of DCM. In this paper, aiming at the stability of DCM, we propose the stability control method of double crystal monochromator base on hybrid control algorithm. The numerical results show that the stability of the DCM in the pitch direction can be greatly improved by this active vibration control method under LN2 mode. The angular displacement RMS value in the pitch direction decreased from about 358.52 nrad to about 0.071nrad, which decreased by 99.98%. Proposed method is of great significance to the research of ultra-high stability DCM in synchrotron radiation facilities all over the world.

Influence of ZnO: Ce3+/ Eu3+ doped and co-doped nanopowders on the properties of poly (ε-caprolactone) nanocomposites

In this work the novel poly (ε-caprolactone) (PCL)/ZnO: Ce3+, Eu3+ nanocomposites have been prepared through the solution casting method using acetophenone as solvent. The properties of the final composites were investigated by XRD, SEM, TGA, DSC, UV and PL. Diffraction patterns showed crystalline peaks at Bragg angles 2θ = 21.3° and 23.6° for PCL and the nanocomposite. Nanosphosphors are clearly dispersed and seem to have occupied PCL micro-cavities with expected elemental composition. The degree of crystallinity and overall thermal stability of the PCL nanocomposites are lower than of the pristine polymer. UV–vis transmittance spectra of the PCL showed absorption edge at lower wavelengths than all nanocomposites and nanopowders. There is an apparent improvement in the luminescent properties of the solution casted nanocomposites. In fact, the luminescence intensity of the co-doped nanocomposite samples has increased roughly10 times compared to PCL.

A new μ-high energy resolution fluorescence detection microprobe imaging spectrometer at the Stanford Synchrotron Radiation Lightsource beamline 6-2.

Here, we describe a new synchrotron X-ray Fluorescence (XRF) imaging instrument with an integrated High Energy Fluorescence Detection X-ray Absorption Spectroscopy (HERFD-XAS) spectrometer at the Stanford Synchrotron Radiation Lightsource at beamline 6-2. The X-ray beam size on the sample can be defined via a range of pinhole apertures or focusing optics. XRF imaging is performed using a continuous rapid scan system with sample stages covering a travel range of 250 × 200mm2, allowing for multiple samples and/or large samples to be mounted. The HERFD spectrometer is a Johann-type with seven spherically bent 100mm diameter crystals arranged on intersecting Rowland circles of 1m diameter with a total solid angle of about 0.44% of 4π sr. A wide range of emission lines can be studied with the available Bragg angle range of ∼64.5°-82.6°. With this instrument, elements in a sample can be rapidly mapped via XRF and then selected features targeted for HERFD-XAS analysis. Furthermore, utilizing the higher spectral resolution of HERFD for XRF imaging provides better separation of interfering emission lines, and it can be used to select a much narrower emission bandwidth, resulting in increased image contrast for imaging specific element species, i.e., sparse excitation energy XAS imaging. This combination of features and characteristics provides a highly adaptable and valuable tool in the study of a wide range of materials.

Two-dimensional atom localization and formation of waveguide channels using Bragg diffraction law

Atoms of four-level atomic medium are doped in a crystal slab of silica which is immersed in a four-level atomic medium. We incorporated Bragg law in the Rabi frequencies of the driving fields and obtained absorption spectrum which exhibits atom localization inside the crystal plane and generation of waveguide channels. Varying the Bragg angle θ, leads to a number of localized peaks and craters. The number of peaks decreases as we increase the Bragg angle θ from π/8 to π/2 and the peaks disappear beyond this angle. The localization probability is independent of the Bragg angle, while the spatial resolution varies with change in Bragg angle. However, the probe detuning and amplitudes of Rabi frequencies change the localization probability. Inside the optical lattice of the silica crystal, waveguide channels and particle traps are generated which may be utilized to guide electromagnetic radiations and trap quantum particles. This work is useful for coherent control information of crystal planes, optical trapping, waveguide channels of nano crystals and data storage.

Diffracted beam interferometry – Differential phase contrast image of an amorphous thin film material

Differential phase contrast based on diffracted beam interferometry is used to explain the good phase contrast found of an amorphous thin film material deposited on the surface of a gold (Au) crystal substrate. An electron biprism is used to interfere two symmetrically diffracted beams generated by the Au crystal substrate that carried the phase of the amorphous material specimen. Bragg diffraction from the Au crystal substrate is used to explain why the phase of the amorphous thin film material is so well phase imaged. The phase of the amorphous material that was deposited on the specimen’s upper surface of the Au crystal substrate is canceled and thus not revealed in the phase image whereas the phase due to the amorphous material deposited on the bottom surface of the Au crystal substrate does not cancel due to having a lateral phase shift in the amorphous material specimen plane proportional to the substrate thickness and Bragg angle of the diffracted beams. The lateral phase shift enabled differential phase contrast of the amorphous material specimen.

On the possibility of ultrafast Kossel diffraction

We discuss the possibility of realizing time-resolved Kossel diffraction experiments for providing indications on the crystalline order or the periodic structure of a material. We make use of the interaction of short, ultra-intense laser pulses with a solid target, which generates short bursts of hot electrons. Penetrating inside a layered sample (i.e., a crystal or an artificial multilayer material), these electrons ionize inner-shell electrons so that the subsequent radiative filling of K-shell vacancies results in a strong Kα emission that is enhanced in the Bragg directions corresponding to the period of the material. We present simulations of angle-resolved Kα emission, which displays so-called Kossel patterns around the Bragg angles. We then discuss possible experiments appropriate for laser facilities delivering short and intense pulses.

Dislocation Contrast Analysis in Weak Beam Synchrotron X-Ray Topography

Synchrotron monochromatic beam X-ray topography has been widely applied to characterize structural defects in SiC crystals. Using ray tracing simulations, the dislocation contrast in X-ray topography under strong diffraction conditions (diffraction takes place at or near Bragg angle) has been intensively investigated. However, the contrast and the configurations of the dislocation images recorded under weak diffraction conditions have not been fully investigated. Recently, we demonstrated that the contrast of dislocations in synchrotron grazing incidence topography under weak diffraction conditions can also be analyzed and interpreted by applying ray tracing principles. In this study, we have extended the application of the ray tracing method to analyze the dislocation contrast in weak beam synchrotron back reflection and rocking curve topography. The ray tracing method is shown to successfully simulate and correlate the contrast of threading screw dislocations at various positions on the rocking curve and thus allow to determine the signs of Burgers vectors.

Design and analysis of holographic optical elements for their use as couplers with appreciable efficiency at different optical transmission windows

The diffraction efficiency of a recorded Holographic optical element changes with change in wavelength of reconstruction wave even for on-Bragg angle reconstruction. Diffraction efficiency also falls with change in angle of reconstruction with respect to Bragg angle for reconstruction wave of a given wavelength. Therefore, to achieve appreciable diffraction efficiency operation of Holographic Optical Elements at different operating wavelengths, processing parameters namely film-thickness (d), depth of refractive index modulation (Δn), and fringe spacing (ᴧ) must be optimized accordingly. In present work thickness (d) of the film of the recording medium, depth of refractive index modulation (Δn), and fringe spacing (ᴧ) have been optimized for holographic optical elements to be recorded in dichromated gelatin medium to achieve maximum efficiency operation for three different optical transmission windows 800–900 nm, 1250 – 1350 nm and 1500–1600 nm operating at wavelengths 850 nm, 1310 nm, and 1550 nm respectively. A pair of such designed holographic optical elements can advantageously be used for coupling laser light from one fiber end to another fiber end. It is further shown that a single coupler consisting of properly designed holographic optical elements may be used for optical transmission windows 1250–1350 nm and 1500–1600 nm operating at wavelengths 1310 nm, and 1550 nm respectively.

Purely spectrometric method to measure the bias refractive index including its dispersion and the swelling or shrinking of holographic materials

A novel method to determine the application relevant parameters of holographic film materials is presented. The procedure is capable of measuring the refractive index n 0 of the unrecorded material at the recording wavelength λ 0 , the bias refractive index n ( λ ) of the recorded medium including its dispersion, and the shrinkage parameter S . Measurements rely on spectrometer data only, i.e., there is no necessity for Bragg angle determination. Experimental data for the holographic film material HX 200 from Covestro are presented. Theoretical analysis suggests that the method is equally well suited to determine the relevant temperature dependencies, too.

Spin rate influenced structural and optical characteristics of Zn0.95Al0.03Ni0.02O thin films

The film formation, structural, optical and electrical characteristics of spin coated films are governed by the various processing parameters. Hence it is indeed necessary to examine the consequence of various deposition parameters of spin coating method. Using the spin-coating method transparent Zn0.95Al0.03Ni0.02O thin films were coated on a glass substrate. The spectroscopic and analytical methods are used to examine the importance of spin rate on the optical and structural characteristics of deposited thin films. The prepared thin films are having a favoured c-axis orientation of crystallites, which deteriorates as the spin rate increases. Furthermore, the observed peak shift to higher Bragg angle and decrease in intensity peaks with spin rate indicates the films have a higher crystallinity. In order to assess the effect of spin rate, various structural parameters (such as, crystallite size, stress, lattice micro-strain, dislocation density and lattice constants) were estimated using various analytical equations. The size of the crystallites was discovered to decrease as the spin rate of the substrate increased. The optical properties of the films show that they are having transparency about 90 % in the visible wavelength region. The ultra-violet peak observed to be redshifted with spin rate shows decrease in the value of band gap energy. The results suggest that the optical and structural characteristics can be tailored by changing the spin rate, which are the potential candidates for the optoelectronic devices.

The influence of K substitution on the structural, optical and magnetic properties of LaFeO3 perovskites

Single-phase lanthanum ferrite oxides doped potassium (K) with various composition of La1-xKxFeO3 (0.0≤ x ≤ 0.3) were successfully prepared using cost-effective precursors via a solid-state reaction route. The influence of K substitution at La site of LaFeO3 on its structural, optical, and magnetic properties have been studied. X-ray diffraction (XRD) results indicated that all synthesized samples were a polycrystalline single-phase orthorhombic perovskite structure, with peaks shifting to higher Bragg angles by increasing K amount. Direct bandgap energy (Eg) of La1-xKxFeO3 samples was dramatically decreased from 2.28 eV to 1.22 eV with increasing the amount of K substitution in the LaFeO3 Lattice. Magnetic hysteresis loops show that the obtained samples have a ferromagnetic response at room temperature with enhanced magnetization from 0.16 to 1.72 emu/g with increasing the K concentration. The changes of the optical and magnetic properties attributed to the crystal structure defects resulting from the replacement of La3+ by K1+, which cerate oxygen vacancies due to the variation in the valence state ratio of Fe4+/Fe3+. The enhanced magnetization and tunable Eg in the visible region make La1-xKxFeO3 (0.0≤ x ≤ 0.3) promising materials for environmental applications such as solid oxides fuel cells (SOFC) and photocatalysis.

Polymorphic transitions of V-type amylose upon hydration and dehydration

In the current study, V6, V7 and V8 amyloses were prepared, their crystalline polymorphic transitions upon hydration at different moisture conditions examined by wide-angle X-ray diffraction (XRD), and the relative degrees of crystallinity calculated. Upon the formation of V7 or V8 crystals, the XRD peaks shifted to lower Bragg angles as compared to V6h due to the expansion of the amylose helices. Conditioning at 75% equilibrium relative humidity (ERH) transformed V6a and V7 amyloses to the V6h pattern. Long-term vapor hydration at 100% ERH or total hydration by immersion in water transformed all V-type XRD patterns to the B-type with decreased degrees of crystallinity. Upon dehydration by ethanol wash, the relative crystallinities of all V-type amyloses were increased, while the crystalline patterns remained mostly unchanged. Such explicit study of polymorphic transitions revealed by XRD can help establish optimal conditions for the encapsulation of bioactive compounds with V-type amyloses and provide insights for novel food product developments.

Wide-angle acousto-optic devices based on isotropic light scattering in biaxial crystals

Using the example of a rhombic crystal of alpha-iodic acid, a detailed study of new variants of acousto-optic isotropic light scattering in oblique sections of biaxial crystals, whose refractive surface contains a concave portion, is carried out. For these cases, the frequency dependences of the Bragg angles and the ranges of acousto-optic interaction are calculated. The possibility of implementing a unique, simultaneously broadband and wide-angle variant of light scattering is established. It is shown that the two-dimensional transfer function of such acousto-optic geometry has a complex X-shaped structure that has no analogues among uniaxial crystals. The possibility of applying this diffraction regime in light beam spatial filtering devices is studied.

Corrosion Improvement of 304L Stainless Steel by ZrSiN and ZrSi(N,O) Mono- and Double-Layers Prepared by Reactive Cathodic Arc Evaporation

Zr-based nitrides and oxynitrides were deposited by reactive cathodic arc evaporation in monolayer and double-layer structures with the aim of increasing the corrosion protection of 304L stainless steel (SS) in a biomedical aggressive environment. All coatings had a total thickness of 1.2 µm. Compared to the bare substrate, the surface roughness of the coated samples was higher, the presence of microdroplets being revealed by scanning electron micrography (SEM). The X-ray diffraction investigation of the ZrN phases revealed that the peaks shifted towards lower Bragg angles and the lattice constants increased as a result of Si and O2 inclusion in ZrN lattice, and of the ion bombardment characteristic of the cathodic arc method, augmented by the applied bias substrate. SS/ZrSiN/ZrSi(N,O) showed the best corrosion performance in an acidic environment (0.9% NaCl and 6% H2O2; pH = 4), which was ascribed to the blocking effect of the interfaces, which acted as a corrosion barrier for the electrolyte ingress. Moreover, the aforementioned bilayer had the highest amount of Si and O in the composition of the top layer, forming a stable passive layer with beneficial effects on corrosion protection.

Pure Nuclear Bragg Reflection due to Combined Magnetic and Quadrupole Interaction in Fe3O4

A pure nuclear Bragg reflection due to the combined magnetic and quadrupole interaction in the B-site Fe of Fe3O4 has been investigated. The 10 10 0 reflection (Bragg angle θB = 46.48°), which is e...

Bragg condition for scattering into a guided optical mode

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.