Showing papers on "Diffraction published in 1976"
TL;DR: In this article, a time-dependent three-space-dimensional laser beam propagation is described, where the authors use a discrete Fourier transform (DFT) method for diffraction problems.
Abstract: The computation of time-dependent three-space-dimensional laser beam propagation is described. The methods are applicable to the propagation of high energy laser beams through the atmosphere in the presence of a horizontal wind and turbulence for most situations of interest. Possible cases are propagation of cw beams through stagnation zones, multi-pulse propagation, including the self-consistent treatment of pulse self-blooming, and propagation involving transonic slewing. The solution of the Maxwell wave equation in Fresnel approximation is obtained by means of a discrete Fourier transform method, which, surprisingly, gives excellent results for diffraction problems. The latter provide a stringent test for the accuracy of any solution method. Considerable use is also made of discrete Fourier transform methods in solving the hydrodynamic equations. The treatment of turbulence is based on the generation of random phase screens at each calculation step along the propagation path. In a time-dependent calculation the random phase screens can be either made to move with the wind at a given propagation position or generated anew for each successive time.
1,105 citations
TL;DR: In this paper, the symmetry properties of the convergent beam and bend extinction contour patterns were examined by means of a graphical representation of the diffraction groups, together with a table showing how these groups are related to specimen point groups and under certain assumptions to crystal point groups.
Abstract: The convergent beam and bend extinction contour techniques of electron microscopy are capable of providing much more information than can be obtained from conventional diffraction patterns and it is the objective of this work to examine the symmetry properties of each of these patterns. The diffraction of fast electrons by a thin parallel-sided slab has been studied by group theory and by a graphical construction. We find that the pattern symmetries may be described by thirty-one diffraction groups and that each of these diffraction groups is isomorphic to one of the point groups of diperiodic plane figures and to one of the thirty-one Shubnikov groups of coloured plane figures. A graphical representation of each diffraction group is given, together with tables showing how the diffraction groups are related to the specimen point groups and under certain assumptions to the crystal point groups. These tables assume the symmetric Laue condition and ignore the presence of irreducible lattice translations normal to the slab. By using the tables, crystal point groups can be obtained from convergent beam or bend contour patterns. The method is demonstrated by experiments on several materials, but particularly on germanium and gallium-arsenide specimens since the similarity of these materials exemplifies the sensitivity of the technique.
375 citations
TL;DR: In this article, X-ray diffraction data showed that there are at least two forms of amorphous solid water which differ in density and second nearest-neighbor oxygen-oxygen distribution.
Abstract: X‐ray diffraction data show that there are at least two forms of amorphous solid water which differ in density and second nearest‐neighbor oxygen–oxygen distribution. (a) The lower density form, made at 77 °K, has a diffraction pattern consistent with a structure that has oxygen–oxygen nearest‐neighbor tetrahedral symmetry on average, and a nearest neighbor O–O separation of 2.76 A with small dispersion. The density of this material is estimated to be 0.94 g cm−3. While it is not possible to uniquely define the structure, the data available support the notion that its fundamental characteristic is the existence of a randomized network of hydrogen bonds with O–O–O angular distribution derived from (i.e., centered about) that of ice Ih. Comparison of neutron diffraction and x‐ray diffraction data suggests strongly that the first shell hydrogen bonds are nearly linear and that orientational correlations between water molecules are limited to nearest neighbors. (b) The higher density form, made at 10 °K, has a diffraction pattern similar to, yet distinctively different from, that of the high temperature deposit. The O–O nearest neighbor distance is the same, 2.76 A, but the dispersion in this separation is larger in the low temperature form. The diffraction pattern shows an extra peak at 3.3 A, corresponding to about 1.4 molecules, the existence of which is responsible for the estimated higher density, namely 1.1 g cm−3. The data are consistent with several models which share the feature of introducing small O–O–O angles into the structure. We discuss the relationships between our data, and inferences from the data, and the corresponding data for liquid water.
291 citations
TL;DR: From data, phase diagrams describing the gel-sol equilibrium can be constructed; the phase diagrams correspond well with those described in the literature which were constructed using spin-label probes or from x-ray diffraction patterns.
Abstract: The fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene in phospholipid vesicles is a function of the physical state of the lipid. Below the phase transition, the polarization approaches the theoretical maximum for total immobilization while above the phase transition the fluorescence becomes nearly completely depolarized. The discontinuity in the temperature dependence of polarization occurs within a temperature range under 5 degrees C in the case of pure phospholipids, but for mixed phospholipids occurs over a temperature range greater than 20 degrees C. From these data, phase diagrams describing the gel-sol equilibrium can be constructed; the phase diagrams correspond well with those described in the literature which were constructed using spin-label probes or from x-ray diffraction patterns. The marked change in polarization at the phase transition may be related to the packing of the probe molecule into the lipid bilayer: fluorescence measurements on oriented bilayers indicate that below the phase transition the long axis of the probe is oriented perpendicular to the plane of the membrane while above the transition the probe is oriented randomly relative to the plane of the membrane.
247 citations
26 Jan 1976
TL;DR: In this paper, the Fraunhofer diffraction of a parallel beam of mono-chromatic light by the moving droplets is used to focus a stationary light pattern onto a multielement photo-detector to measure the diffracted light energy distribution.
Abstract: : In order to verify the various theoretical models of practical combustion systems, experimental measurements are urgently required. A number of laser instrumentation systems which do not disturb the flow are being devised to satisfy this need. This study describes a technique which has been developed for the measurement of droplet or solid particle size distribution. These measurements are required, for example, as the input to mathematical models of combustion which include evaporation. The technique is based on the Fraunhofer diffraction of a parallel beam of mono-chromatic light by the moving droplets. A Fourier transform lens is used to focus a stationary light pattern onto a multielement photo-detector to measure the diffracted light energy distribution. A mini-computer program translates the light energy distribution into the corresponding, unique, droplet size distribution. The droplets or particles are classified into 31 size groups spanning two decades of diameter, (e.g. 5 micrometers to 500 micrometers using a 300 mm focal length Fourier transform lens).
214 citations
TL;DR: In this paper, the diffracted field according to Keller's geometrical theory of diffraction (GTD) can be expressed in a particularly simple form by making use of rotations of the incident and reflected fields about the edge.
Abstract: Diffraction of an arbitrary electromagnetic optical field by a conducting curved wedge is considered. The diffracted field according to Keller's geometrical theory of diffraction (GTD) can be expressed in a particularly simple form by making use of rotations of the incident and reflected fields about the edge. In this manner only a single scalar diffraction coefficient is involved. Near to shadow boundaries where the GTD solution is not valid, a uniform theory based on the Ansatz of Lewis, Boersma, and Ahluwalia is described. The dominant terms, to the order of k^{-1/2} included, are used to compute the field exactly on the shadow boundaries. In contrast with the uniform theory of Kouyoumjian and Pathak, some extra terms occur: one depends on the edge curvature and wedge angle; another on the angular rate of change of the incident or reflected field at the point of observation.
206 citations
TL;DR: In this article, the authors investigated the behavior of converging weak shock waves near three different kinds of focus, and found that the behavior at the focus is nonlinear and that diffraction shocks participate in a Mach reflexion process near the focus, whose development is determined by competition between the convergence of the sides of the focusing front and acceleration of its central portion.
Abstract: This paper reports an experimental investigation, using shadowgraphs and pressure measurements, of the detailed behaviour of converging weak shock waves near three different kinds of focus. Shocks are brought to a focus by reflecting initially plane fronts from concave end walls in a large shock tube. The reflectors are shaped to generate perfect foci, aretes and caustics. It is found that, near the focus of a shock discontinuity, a complex wave field develops, which always has the same basic character, and which is always essentially nonlinear. A diffracted wave field forms behind the non-uniform converging shock; its compressive portions steepen to form diffraction shocks, while diffracted expansion waves overtake and weaken the diffraction shocks. The diffraction shocks participate in a Mach reflexion process near the focus, whose development is determined by competition between the convergence of the sides of the focusing front and acceleration of its central portion. In fact, depending on the aperture of the convergence and the strength of the initial wave, the three-shock intersections of the Mach reflexions either cross on a surface of symmetry or remain uncrossed. In the former case, which is observed if the shock wave is relatively weak, the wavefronts emerge from focus crossed and folded, in accordance with the predictions of geometrical acoustics theory. In the latter, the strong-shock case, the fronts beyond focus are uncrossed, as predicted by the theory of shock dynamics. It is emphasized that in both cases the behaviour at the focus is nonlinear. The overtaking of the diffraction shocks by the diffracted expansions limits the amplitude of the converging wave near focus, and is the mechanism by which the maximum amplification factor observed at focus is determined. In all cases, maximum pressures are limited to rather low values.
203 citations
07 Apr 1976
171 citations
01 May 1976
TL;DR: In this article, material parameters necessary for optimum design of surface-acoustic-wave (SAW) devices are reviewed, including velocity, coupling coefficient, power flow angle, temperature coefficients, propagation loss and equivalent circuit parameters.
Abstract: Material parameters necessary for optimum design of surface-acoustic-wave (SAW) devices are reviewed. Velocity, coupling coefficient, power flow angle, temperature coefficients, propagation loss (including air loading, diffraction, and beam steering), and equivalent circuit parameters are considered. A brief introduction to the nature of surface waves is followed by sufficient theoretical information to allow full understanding and derivation of the properties and parameters cited above. A convenient tabular summary of important SAW material properties is included.
167 citations
TL;DR: The variation of the intensities with swelling of the lamellar system as water content increased was used to assign phases to the diffraction spectra and electron density profiles for bilayers of dipalmitoyl and egg lecithin were derived.
164 citations
TL;DR: In this article, the scattering of nearly monoenergetic He and Ne atoms of thermal energies from the clean (001) face of LiF at low temperature was investigated using molecular beam techniques, and diffraction peaks were resolved over a wide range of incident and final angles.
TL;DR: In this paper, the transition state in binary f.c. based systems is characterized by the repetition of interpenetrating polyhedral clusters of atoms occupying lattice sites and having the macroscopic composition.
Abstract: The 'transition' state in binary f.c.c. based systems is assumed to be characterized by the repetition of interpenetrating polyhedral clusters of atoms occupying lattice sites and having the macroscopic composition. Its mathematical formulation leads to relations between the short-range order (SRO) coefficients, which in turn impose conditions on the distribution in reciprocal space of the diffuse intensity as observed in electron diffraction patterns. It follows that for a given cluster type the diffuse intensity can only differ from zero along certain surfaces or curves. The effect of deviations from the ideal composition of the clusters is briefly discussed. The theory allows an explanation of available diffraction data on certain binary alloys in the initial stages of ordering i.e. in the 'transition' state between the SRO state and the long-range order (LRO) state.
TL;DR: Tsai et al. as mentioned in this paper proposed a wideband guided-light beam-deflector using tilting surface acousto-optic Bragg devices, which achieved state-of-the-art performance.
Abstract: [45] C. S. Tsai, Le T. Nguyen. M. A. Alhaider, “Wideband Acoustotwo Tilting Surface Acoustic Waves,” Appl. Phys. Lett. 26, optic Guided-Light Beam Deflector Using Tilting Surface 140-143, February 15,1975. Acoustic Waves,” 1974 Ultrasonics Symposium Proceedings, [47] C. S. Tsai, M. A. Alhaider, Le T. Nguyen and B. Kim, “WideIEEE Cat.. # 74. C H 0 896-1SU. 768-772. band Guided-Wave Acoustooptic Bragg Devices Using Multiple [46] C. S. Tsai, Le T: Nguyen, 8. K.’Yao and M. A. Alhaider, “HighTilting Surface Acoustic Waves,” Talk-36, Conference on Laier performance Acousto-optic Guided-light Beam Device Using Engineering and Applications, Washington, D. C., May 1975
TL;DR: In this article, the structure of CaCl2 aqueous solutions was studied by means of x-ray diffraction and it was demonstrated that the solutions can be treated as being composed of independent hydrated ions, and for this reason the structural problem was limited to the study of close hydration.
Abstract: The structure of several CaCl2 aqueous solutions was studied by means of x‐ray diffraction. It is demonstrated that the solutions can be treated as being composed of independent hydrated ions, and for this reason the structural problem is limited to the study of close hydration. This description allows the calculation of structure functions in very good agreement with experimental data when using coordination number six and octahedral geometry for both the ionic species present.
TL;DR: Flexoelectric effects are observed in both the nematic and smectic phases of BBMBA and CBOOA as mentioned in this paper, and the use of a symmetric interdigital electrode in the homeotropic geometry facilitated the unambiguous separation of linear and quadratic electro-optic effects.
Abstract: Flexoelectric effects are observed in both the nematic and smectic‐A phases of p‐butoxybenzal‐p‐ (β‐methylbutyl) aniline (BBMBA) and p‐cyano‐benzylidine‐p‐octyloxyaniline (CBOOA). This is the first reported observation of flexoelectricity in smectic phases. The use of a symmetric interdigital electrode in the homeotropic geometry facilitated the unambiguous separation of linear and quadratic electro‐optic effects. Both the interdigital electrodes and those liquid‐crystal deformations that are quadratic in the voltage act as optical diffraction gratings with a spacing that corresponds to the repeat distance d for adjacent electrodes. In contrast linear electro‐optic effects give rise to diffraction gratings with twice this spacing since adjacent electrodes have opposite voltages. Diffraction maxima due to the linear effects are halfway between the maxima due to the other effects. Using optical heterodyne detection, the intensity of the diffraction maxima believed to arise from the linear effect are indeed ...
TL;DR: In this article, a procedure for the digital processing of fiber diffraction patterns to yield a quasi-continuous map representing a central section through the cylindrically averaged intensity transform of the specimen is described.
Abstract: A procedure is described for the digital processing of fibre diffraction patterns to yield a quasi-continuous map representing a central section through the cylindrically averaged intensity transform of the specimen. No assumptions are required about the nature of the specimen other than that it has fibre-type symmetry. The specimen intensity transform can be used to obtain integrated intensities for discrete reflections from microcrystalline fibres that are potentially as accurate as those obtained from crystals. Improved procedures for extracting structure amplitudes from specimens with continuous layer lines are also described.
TL;DR: In this paper, the statistical properties of speckle intensity variations produced by coherent light in the far-field diffraction plane of an iluminated area of an object are studied experimentally as a function of the radius of an illuminating beam over the object and are found to have a relation to its surface roughness and correlation lenght.
TL;DR: Questions of optimizing the signal intensity and contrast are examined by considering the detector configuration in relationship to the form of the convergent beam diffraction pattern formed in the detector plane and the implications for the use of diffraction patterns information to enhance the imaging process are considered.
TL;DR: In this article, the negative electron-spin polarization has not been observed in earlier experiments on polycrystalline films, and the authors exclude an interpretation based on a simple band theory of magnetism.
Abstract: Photoelectrons emitted from nickel single-crystal surfaces defined by low-energy-electron diffraction and Auger-electron-spectroscopy analysis exhibit negative electron-spin polarization at threshold. The abrupt change from negative to positive polarization occurs at $h\ensuremath{\omega}\ensuremath{\simeq}\ensuremath{\Phi}+0.05$ eV, where $\ensuremath{\Phi}$ is the work function. This excludes an interpretation based on a simple band theory of magnetism and also explains why the negative electron-spin polarization has not been observed in earlier experiments on polycrystalline films.
TL;DR: In this paper, the magnetic properties of the hydrides were determined and compared with the original compounds and it was shown that the magnetic moment per Fe atom is much larger in hydride phases.
TL;DR: The structure of a specific acyl-enzyme intermediate in the elastase-catalysed hydrolysis of N-carbobenzoxy-L-alanyl-p-nitrophenol ester has been determined by X-ray diffraction at 3.5 A resolution as discussed by the authors.
Abstract: The structure of a specific acyl-enzyme intermediate in the elastase-catalysed hydrolysis of N-carbobenzoxy-L-alanyl-p-nitrophenol ester has been determined by X-ray diffraction at 3.5 A resolution. The acyl-enzyme was stabilised by cooling the crystal to −55°C during substrate addition and data collection.
TL;DR: In this paper, the ordering and domain grolth kinetics of Ni 3 Fe have been studied over the temperature range 434-497°C using electron microscopl and X-ral diffraction.
TL;DR: Guananosine-5′-phosphate crystallizes from neutral solutions of NaCl in bundles of hair-like crystals which give a fiber-like X-ray diffraction pattern which indicates that the monomers are arranged in a structure similar to the arrangement of residues in poly(rG).
TL;DR: A technique and apparatus for obtaining the elastic constant E/(1 + ν) in selected crystallographic directions for the purpose of calibrating x-ray diffraction residual stress measurement methods is described in this article.
Abstract: A technique and apparatus are described for obtaining the elastic constant E/(1 + ν) in selected crystallographic directions for the purpose of calibrating x-ray diffraction residual stress measurement methods. The preparation of a simple rectangular beam specimen with two active electrical resistance strain gages applied to the test surface is described. Samples are clamped in a diffractometer fixture designed to minimize displacement errors, and loaded in four-point bending to several stress levels below the proportional limit. A method is described for calculating E/(1 + ν) and an estimate of the experimental error. Values of E/(1 + ν) obtained for several alloy-(hkl) combinations are presented. The results indicate that several alloys of current commercial interest exhibit significant elastic anisotropy.
TL;DR: In this paper, the inplane scattering of H2 molecules at thermal energies from the (001) face of LiF was studied at low temperatures, by means of nozzle beam techniques, and both elastic and rotationally inelastic diffraction peaks were resolved over a wide range of incident and final angles.
Abstract: The in‐plane scattering of H2 molecules at thermal energies from the (001) face of LiF was studied at low temperatures, by means of nozzle beam techniques. Both elastic and rotationally inelastic diffraction peaks were resolved over a wide range of incident and final angles. Taking into account the properties of the supersonic beam, diffraction probabilities were derived for the observed peaks. A discussion of the results in light of the present theories is given. The large probability of occurrence of rotational transitions in the presence of the surface is pointed out.
PARC1
TL;DR: In this paper, an equation for TM-mode coupling coefficients in DFB-based double-heterostructure GaAs with rectangular, triangular, and sawtooth-shaped teeth was derived.
Abstract: An equation is derived for TM-mode coupling coefficients in guided-wave distributed feedback (DFB) lasers. Results for GaAs:GaAlAs double-heterostructure lasers with rectangular, triangular, and sawtooth-shaped teeth, various Bragg diffraction orders, and transverse mode numbers are presented for TM modes and compared with those for TE modes. Generally, but not always, coupling coefficients for TE modes exceed those for TM modes.
TL;DR: In this paper, a review of the diffraction of hadronic waves is presented, where material is chosen that could be fitted into a logical structure Diffraction in optics and its extension to hadronic wave, diffraction in hadron--nucleus collisions, diffusion scattering and dissociation in hadRON--hadron collisions, present approaches to the pomeron, and diffraction excitation seen as pomerone exchange are covered.
Abstract: The review of the diffraction of hadronic waves is not a complete presentation, but rather material is chosen that could be fitted into a logical structure Diffraction in optics and its extension to hadronic waves, diffraction in hadron--nucleus collisions, diffraction scattering and dissociation in hadron--hadron collisions, present approaches to the pomeron, and diffraction excitation seen as pomeron exchange are covered (JFP)
TL;DR: X-ray diffraction photographs of protein single crystals have been obtained using synchrotron radiation produced by an electron-positron storage ring and the tunable nature of the source and the low angular divergence of the beam make the source very useful for single crystal protein diffraction studies.
Abstract: X-ray diffraction photographs of protein single crystals have been obtained using synchrotron radiation produced by an electron-positron storage ring. The diffracted intensities observed with this unconventional source are a factor of at least 60 greater than those obtained with a sealed x-ray tube using the same crystal and instrumental parameters. Diffraction data have been collected by the precession method to higher resolution and using smaller protein crystals than would have been possible with a conventional source. The crystal decay rate in the synchrotron beam for several proteins appears to be substantially less than that observed with Ni-filtered Cu radiation. The tunable nature of the source (which allows selective optimization of anomalous contributions to the scattering factors) and the low angular divergence of the beam make the source very useful for single crystal protein diffraction studies.
TL;DR: The results therefore support the original hypothesis by Clark and Branton (1968) that disk membranes fracture along some interior hydrophobic plane, presumably the region of terminal methyl groups at the center of the lipid bilayer.
TL;DR: In this article, integro-differential equations are formulated for the general problem of electromagnetic diffraction by an aperture in a planar conducting screen of infinite extent separating two half spaces of different electromagnetic properties.
Abstract: Integro-differential equations are formulated for the general problem of electromagnetic diffraction by an aperture in a planar conducting screen of infinite extent separating two half spaces of different electromagnetic properties. With the aperture specialized to the case of an infinite slot, equations appropriate for TE and for TM illumination are deduced from those for the general aperture. These slot equations are solved numerically, and results are presented for several cases of interest.