Multi-beam Diffraction Research Articles

Акустооптическое управление энергетическим 2D-профилем лазерного луча

The acousto-optic control of the energy profile of laser radiation is considered. A highly efficient multibeam Bragg diffraction mode with a combination of beams close in angular space, forming an averaged pattern in the form of a single beam, is used. In this case, the two-dimensional intensity profile is realized as a product of two independent one-dimensional profiles. On the basis of a polarization-independent two-coordinate acousto-optic deflector, several profiles (including a close to uniform one) were experimentally obtained with a total efficiency of no less than 85% and a profile change time of about ten microseconds. This method can be used in systems for processing materials with powerful lasers.

Multibeam Electron Diffraction.

One of the primary uses for transmission electron microscopy (TEM) is to measure diffraction pattern images in order to determine a crystal structure and orientation. In nanobeam electron diffraction (NBED), we scan a moderately converged electron probe over the sample to acquire thousands or even millions of sequential diffraction images, a technique that is especially appropriate for polycrystalline samples. However, due to the large Ewald sphere of TEM, excitation of Bragg peaks can be extremely sensitive to sample tilt, varying strongly for even a few degrees of sample tilt for crystalline samples. In this paper, we present multibeam electron diffraction (MBED), where multiple probe-forming apertures are used to create multiple scanning transmission electron microscopy (STEM) probes, all of which interact with the sample simultaneously. We detail designs for MBED experiments, and a method for using a focused ion beam to produce MBED apertures. We show the efficacy of the MBED technique for crystalline orientation mapping using both simulations and proof-of-principle experiments. We also show how the angular information in MBED can be used to perform 3D tomographic reconstruction of samples without needing to tilt or scan the sample multiple times. Finally, we also discuss future opportunities for the MBED method.

Acousto-Optic Devices Based on Multibeam Diffraction

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.

Recording 4D-STEM Datasets at a Range of Beam Tilts Simultaneously with Multi-Beam Electron Diffraction

Recording 4D-STEM Datasets at a Range of Beam Tilts Simultaneously with Multi-Beam Electron Diffraction

A review of physical principles and applications of acousto-optic deflectors on the basis paratellurite

Deflectors based on Bragg non-axial anisotropic diffraction in a paratellurite crystal are considered. Practically significant relations connecting the main parameters are obtained, the factors limiting the diffraction efficiency and the angular scanning range are determined. The mode of multibeam acousto-optic diffraction as a method of creating a multichannel optical information output system is considered. A review of several new, practically implemented methods for increasing the main functional parameters of deflectors is presented. The possibility of using the diffraction mode in the second Bragg maximum in terms of sound amplitude to extend the scanning band is shown. The two-crystal scheme of the deflector, which can significantly improve the efficiency of diffraction, expand the scanning range and create a polarization-insensitive deflector, is considered. Acousto-optic switch of fiber-optic channels was developed. The possibility of using multibeam acousto-optic diffraction to improve the energy efficiency of laser radiation by modifying its profile is established

X-ray multi-beam resonant diffraction analysis of crystal symmetry for layered perovskite YBaCuFeO5

The open question of crystal symmetry for YBaCuFeO5, still under debate, is resolved by using diffraction anomalous fine structure and resonant multi-beam X-ray diffraction at the Fe and Cu K edges. The different asymmetric intensity distributions observed at 7, 7.1305 and 8.9945 keV give direct evidence that the space group of YBaCuFeO5 should be P4/mmm with the distance between Cu and apical O atoms longer than that between Fe and O atoms. This approach provides a direct way to resolve detailed structural symmetry which is indeterminate in conventional Bragg diffraction.

Study La0.5Sr1.5MnO4with Multi-Beam X-ray Diffraction

We have used resonant multi-beam diffraction with the primary reflections G=(h/2 h/2 0) and G=(h/4 h/4 0) (h is an odd number) to investigate the charge ordering and Jahn-Teller distortion, respectively, in La0.5Sr1.5MnO4 low temperature phase. While the Renninger scans with G=(h/2 h/2 0) shows several Aulfhellung-type four-beam diffraction, most of the multi-beam diffraction with G=(h/4 h/4 0) has an Umweganregung-type nature. A detailed study of multi-beam diffraction anomalous fine structure (M-DAFS) of (0 0 0)/(3/2 3/2 0)/(1 -1 0)/(5/2 1/2 0) OUT diffraction is carried out. Its triplet invariant phase approach 1800when the x-ray energy is tuned away from manganese K-edge, and approach 900when the x-ray energy is tuned on manganese K-edge. In other words, its multi-beam diffraction profile shows strong asymmetry when (3/2 3/2 0) diffraction intensity is dominated by Jahn-Teller distortion, and becomes more symmetric when charge ordering dominated. This characteristic can be successfully simulated by tensor form dynamical x-ray diffraction theory accompanied with FDMNES software [1] calculations.

Adaptive multibeam laser cutting of thin steel sheets with fiber laser using spatial light modulator

Laser cutting with multibeam diffraction pattern using an adaptive optics is studied. Infrared (IR) continuous single-mode fiber laser with maximum power of 200 W is applied to laser cutting of thin metal sheets, together with liquid crystal on silicon spatial light modulator (SLM). SLM can be used as the adaptive diffractive optical element, which can modify intensity profile of the laser beam almost arbitrary. In studies single Gaussian laser beam was divided into multiple spots. It was found out that with this way it is possible to enhance the cutting quality and also decrease pressure of the needed assist gas. Multibeam configuration enabled to laser cut burr free with 50% less protection gas pressure compared to single beam laser cutting with conventional optics.

Numerical simulation of a reflective diffraction fiber interferometer

Numerical simulation was used to demonstrate the possibility of designing a two-mirror multibeam reflective diffraction interferometer using a single-mode fiber with a cladding. The method is based on the calculation of the multimode and multibeam interference of the cladding modes in the fiber describing the diffraction on a diffuser made in the form of an insert of a different fiber as part of one of the interferometer mirrors. It is shown based on bulk optics that using certain optimization, one can obtain a reflection-response function profile of this interferometer similar to that of the transmission-response function of a Fabry-Perot interferometer.

Thermal efficiency of pulsed laser radiation increased by methods of multibeam acousto-optic diffraction

Bragg multibeam acousto-optic diffraction of pulsed laser radiation (with 150-ns pulse duration) has been studied under conditions of significant overlap between the neighboring beams. It is established that the initial beam with a Gaussian angular distribution of intensity can be transformed into diffracted radiation with a nearly rectangular profile of intensity provided that the laser pulse duration is much shorter than the period of interference beats in the overlapping regions. Using this circumstance, it is possible to increase the efficiency of high-power lasers in material processing (laser cutting, welding, engraving, etc.) with a threshold character of the radiation effect. This possibility was experimentally verified for a fiber laser operating at a 1.07 μm wavelength.

High-efficiency multibeam acousto-optic diffraction of pulsed light with nonequidistant beams

Acousto-optic diffraction of pulsed laser radiation on a multifrequency acoustic wave has been studied. It is established that the high efficiency of diffraction (i.e., the formation of a multibeam optical field with low losses) can be also achieved for a nonequidistant set of frequencies and, hence, nonuniform distribution of beams in the angular space. Results of experimental verification of the proposed approach are presented.

Microfluidic refractometer with integrated optical fibers and end-facet transmission gratings

We demonstrated a microfluidic refractometer with an integrated high resolution transmission grating. This grating was fabricated by UV nanoimprinting on the end facet of a multimode optical fiber which was then placed in the plan of the microfluidic device and perpendicular to a microchannel. On the opposite side of the channel, three cleaved optical fibers were added for the light collection of the zeroth and the +/- first diffraction orders. A white light source was used for illumination and the diffraction beams were analyzed with a minispectrometer. The transmission grating was merged in the sample solution of the channel, providing a refractive index-dependent diffraction efficiency. As expected, the diffraction efficiency of the zeroth and the +/- first diffraction orders are different, both being reliable for the refractive index monitoring. Such a white source and multibeam diffraction analysis also allows monitoring the sample absorption or fluorescence, thereby providing a more accurate determination of the sample refraction index.

Diffraction of pulsed laser radiation from an acoustic wave with frequency- and phase-shift keying

Bragg acoustooptic diffraction of nanosecond pulsed laser radiation from a frequency- and/or phase-keyed acoustic wave is studied experimentally and theoretically for exact synchronization of laser pulses and signal keying. It is shown that the diffraction field for short pulses is practically stationary and is determined by the positions of acoustic signal keying over signal aperture. The application of this type of signals for the formation of a multibeam diffraction pulsed radiation field is considered. A method is proposed for transforming the angular spectrum of laser radiation intensity from the initial Gaussian to a nearly rectangular spectrum. This may considerably increase the efficiency of high-power technological lasers used in material processing (laser cutting, welding, engraving, etc.), in which the action of radiation is of the thresh-old type in light intensity. The possibility of correcting the angular intensity distribution for a pulsed fiber laser, which increases the thermal efficiency of radiation from such a laser, is established experimentally.

Switch multiplexer of fiber-optic channels based on multibeam acousto-optic diffraction

The peculiarities of the multibeam acousto-optic Bragg diffraction of light by a multifrequency acoustic signal are investigated. The investigation is related to design of fiber-optic space division switch multiplexer 1xN. It is proved that a specialized two-dimensional acousto-optic deflector can perform high efficiency multifunctional light switching of fiber-optic channels. The device has advanced characteristics--the number of channels is up to a few hundred, the switching time is about a few microseconds, and the cross talk is limited to -45 dB.

Coherent and intense multibeam generation by the apex of sharp nano-objects: Electron half-circular prism

Mutually coherent multiple electron beams (multibeam) were generated from diffraction at the apex of sharp nano-objects, especially carbon nanotubes, in a field emission projection microscope. Simulation using a simple scalar diffraction model showed that the apex of sharp nano-objects played the role of an electron half-circular prism, deflecting an electron beam through a constant angle toward the prism axis. The multibeam diffraction pattern gave a high visibility of ∼0.8 and high intensity.

Revealing all types of threading dislocations in GaN with improved contrast in a single plan view image

In this letter, we demonstrate a transmission electron microscope based technique which reveals all types of threading dislocations (TDs) in GaN with high contrast over a relatively large area, even if the specimen is bent. This method uses a bright-field image with the crystal oriented at the ⟨1–21–3⟩ zone axis, taken using multi-beam diffraction conditions. Such an image reveals all screw, edge, and mixed types of threading dislocations. The multi-beam imaging technique described here for GaN is more generally applicable to counting the total dislocation density in a wide range of materials and structures.

0 0 1] zone-axis bright-field diffraction contrast from coherent Ge(Si) islands on Si(0 0 1)

Coherent Ge(Si)/Si(0 0 1) quantum dot islands grown by solid source molecular beam epitaxy at a growth temperature of 700°C were investigated using transmission electron microscopy working at 300 kV. The [0 0 1] zone-axis bright-field diffraction contrast images of the islands show strong periodicity with the change of the TEM sample substrate thickness and the period is equal to the effective extinction distance of the transmitted beam. Simulated images based on finite element models of the displacement field and using multi-beam dynamical diffraction theory show a high degree of agreement. Studies for a range of electron energies show the power of the technique for investigating composition segregation in quantum dot islands.

X-ray multi-beam diffraction and imaging at a 90° Bragg reflection with partially coherent radiation

A significant enhancement of the anomalous transmission in the multiple-beam diffraction geometry 008/404/4̄04/044/04̄4 was experimentally examined using synchrotron radiation. The experiment was performed on the 1 km beamline BL29XU at the SPring-8 facility in Japan. High resolution rocking curves of the directly transmitted beam were measured in the vicinity of the exact backscattering position. A collimation effect in the transmitted beam was observed in a slit image. The experimental results were compared with theoretical simulations based on x-ray dynamical theory, and they were found to be in agreement with experimental ones.

X-ray resonance multi-beam diffraction: experiments and the perturbative Bethe approximation

X-ray resonance multi-beam diffraction: experiments and the perturbative Bethe approximation

Multiple diffraction data analysis for macromolecular crystals in stereoscopic multibeam imaging.

A detailed analysis of multiple diffraction data collected by the stereoscopic multibeam imaging technique from a tetragonal lysozyme crystal is reported. Calculations based on the dynamical theory are employed to account for diffraction profiles obtained with Bragg-angle scan in stereoscopic imaging and the conventional azimuthal scan in Renninger arrangement. The formation of a multibeam intensity profile and the relationship and mutual influence between the two scans are investigated. A simple practical method of quantitative estimation of the reflection phases of structure-factor multiplets from the experimental data obtained with two inversion-symmetry-related diffractions is proposed. The procedures for data handling and for distinguishing "partial" diffraction images from "full" diffraction images are also developed considering multibeam diffraction geometry and experimental conditions. These procedures thus provide a practical way of reconstructing diffraction profiles for experimental phase determination for macromolecular crystals.