Axial Diffraction Pattern Research Articles

Enhanced multiple-plane phase retrieval using a transmission grating

Multiple-plane phase retrieval method can recover the complete complex amplitude of the optical field by recording a series of axial diffraction patterns at different distances. However, accurate measurement of the initial distance from the object to the sensor, which is important for high-precision reconstruction, is still difficult. In this paper, we propose to use the diffraction of grating to determine the initial distance. The object is firstly replaced by a transmission grating, and the corresponding diffraction pattern on the first measurement plane is captured. Then combining the grating equation, the initial distance can be obtained. On this basis, the object plane is included in the iterative process. Compared with the original method which only iterates between the measurement planes, the recovered optical field with the proposed method has higher accuracy, better robust to noise, and can avoid the time-consuming digital refocusing process. Numerical simulations and optical experiments are carried out to prove the effectiveness of the proposed method.

Phase retrieval using axial diffraction patterns and a ptychographic iterative engine.

We propose a phase retrieval method using axial diffraction patterns under planar and spherical wave illuminations. The proposed method uses a ptychographic iterative engine (PIE) for the phase retrieval algorithm. The proposed approach uses multiple diffraction patterns. Thus, adjusting the alignment of each diffraction pattern is mandatory, and we propose a method to adjust the alignment. In addition, a random selection of the measured diffraction patterns is used to further accelerate the convergence of the PIE-based optimization. To confirm the effectiveness of the proposed method, we compare the conventional and proposed methods using a simulation and optical experiments.

Sarcomere-Length Dependence of the Low Angle X-Ray Pattern from Skeletal Muscle Fibers at Rest and during Isometric Contraction

X-ray patterns were recorded from bundles of 2-3 fibers of R. Esculenta at 4°C at rest and at the plateau of an isometric tetanus (T0) at sarcomere length (SL) 2.0 to 3.6 μm at the ID02 beamline at the European Synchrotron Radiation Facility, Grenoble. The patterns were normalized by the intensity of the 1,0 equatorial reflection at rest at each experimental SL to compensate for variation of diffracting mass with SL and between fibers. The axial diffraction pattern from resting fibers was independent of SL in the range 2.0-2.6 μm; in the range 2.6-3.0 μm the intensity and interference fine structure of the meridional M3 reflection from the axial repeat of the myosin heads along the filaments was constant, but its spacing (SM3) increased. The intensity of the first myosin layer line decreased in this SL range, indicating decreased helical ordering of the myosin heads. The intensity of the 44nm merdional reflection associated with myosin binding protein C was constant up to SL 2.7 μm, but much reduced for SL>2.7 μm. At T0, the M3 reflection intensity was smaller at longer SL, in proportion to the overlap between thick and thin filaments. The interference fine structure of the M3 was independent of SL up to 2.8 μm; at longer SL it varied between preparations and SM3 reduced with increasing SL. The SL-dependence of the M3 reflection at T0 indicates that the detached myosin heads in the non-overlap region of the thick filament are axially disordered compared with actin-attached heads in the overlap region, although the axial center of mass of the detached and attached heads is similar. Supported by Ente Cassa di Risparmio di Firenze, FIRB-Futuro in Ricerca, MRC and ESRF.

Lattice-preferred orientations in post-perovskite-type MgGeO 3 formed by transformations from different pre-phases

Lattice-preferred orientations (LPOs) of post-perovskite (PPv)-type MgGeO 3 formed by transformations from two different pre-phases, orthopyroxene (OPx) and perovskite (Pv), were studied using radial and axial X-ray diffraction techniques combined with a laser-heated diamond-anvil cell. When the PPv was made from Pv, strong LPO was formed in the PPv immediately after the transformation with an alignment of the (0 0 1) or (0 1 1) plane almost perpendicular to the compression axis. This present result contrasts markedly from that observed when the PPv was formed from OPx and those reported on MgGeO 3-PPv and (Mg,Fe)SiO 3-PPv transformed from OPx, in which the (1 0 0) or (1 1 0) plane was aligned to the compression axis. It was clarified that when the PPv-type MgGeO 3 is formed in diamond-anvil cells, it has strong transformation-induced LPO from the beginning even before plastic deformation occurs, and that its characteristics depend on the pre-phase before the transformation. The formed transformation-induced LPO of PPv did not change in spite of further compression using a conventional gasket because the sample became too thin to deform. However, by using a diamond gasket technique, we were able to deform the PPv at room temperature, resulting in significant variations of the relative intensities of several diffraction peaks. The change in the axial diffraction patterns can be explained only by assuming that the (0 0 1) plane aligns almost perpendicularly to the compression axis. The present results suggest that the (0 0 1) is a dominant slip plane in MgGeO 3-PPv at room temperature. If one makes the assumption that the dominant slip system(s) of silicate PPv deformed in the D″ layer is or are identical to that of germanate PPv at room temperature, then a large S-wave polarization anisotropy in the Earth's D″ layer would be explained by the small degree of deformation-induced LPO of the PPv phase that is expected to exist in this layer.

ＤＡＣを用いたＭｇＧｅＯ３ポストペロブスカイト相の塑性変形実験と選択配向の観察

X-ray diffraction (XRD) measurement in radial geometry using a diamond anvil cell (DAC) and synchrotron radiation is a powerful tool to investigate lattice preferred orientations (LPO) of high-pressure materials such as post-perovskite (PPv) -type phases. Recent experimental and theoretical reports about LPO of PPv-type phases and problems of deformation experiments were reviewed in this article. Our results of radial and axial XRD measurements and deformation experiments on MgGeO3-PPv were shown also. When the MgGeO3-PPv was formed in DAC, it had strong LPO from the beginning even before making the plastic deformation and the LPO changed depending on the pre-phase before the transformation. Pressure variation of axial diffraction patterns of MgGeO3-PPv during plastic deformation were obtained for the first time by using a diamond gasket technique.

Topology and crystal growth of natural chrysotile and polygonal serpentine

Through detailed HRTEM examination of a number of serpentinite specimens, the microstructures of textures and individual chrysotile and polygonal fibers are reviewed and their probable growth processes anticipated. It is recalled that five-fold symmetry is ubiquitous among these fibers and that their axial diffraction pattern is insensitive to their deformation or unequal development. 15- and 30-sectored fibers of polygonal serpentine are described by a fan-like arrangement of flat lizardite sectors, with radiating sector boundaries occupied by arrays of partial dislocations. In each case, the layer stacking sequence varies from one sector to the next. Crystal growth of chrysotile probably occurs by thick, curved sectors closing up as tubules, which subsequently develop to a critical size controlled by local storage of elastic energy. For a strict elastic control we may envision the use of chrysotile geometry as an indicator of departure from equilibrium. A solid-state transformation, chrysotile-to-polygonal serpentine, is likely to be driven by the release of elastic energy stored in chrysotile. Diameter growth of polygonal serpentine is no longer limited by elasticity constraints, so allowing “giant” size and tight intergrowth of those fibers.

Variations of the axial intensity pattern formed by a focused truncated gaussian beam

This paper investigates the merger of the extreme points in the axial diffraction pattern formed by a gaussian beam passing through a lens and aperture system. Equations giving the locations of the merger points are derived, and the numerical results obtained are displayed by using the merger loop diagrams, which show how the axial intensities are varying from a very fluctuating distribution into a smoother one as predicted by the theory of focusing of a non-truncated gaussian beam.

The structure of F-actin and of actin filaments isolated from muscle

The filaments of the contractile apparatus have been isolated from a wide variety of smooth and striated muscles and examined in negatively-stained preparations in the electron microscope. In all cases there are thin filaments which are indistinguishable from the filaments in F-actin preparations. The filament consists of two helically-wound strands composed of subunits which appear to be alike and approximately spherical. The arrangement of the subunits corresponds to that of the scattering centres in one of the possible structures for actin deduced by Selby & Bear (1956) from the moderate-angle X-ray diffraction pattern of intact dried muscle. The number of globular subunits per turn of the helix (if integral) is 13 (cf. either 13 or 15 in the models proposed from diffraction data). The spacing of the subunits along each strand is 56·5 A (cf. 55 A in the models proposed from diffraction data). The cross-over points of the two twisted strands are spaced at intervals of 349 A along the filament (cf. either 351 A or 406 A in the models proposed from diffraction data). The overall diameter of the filament is about 80 A. It is shown in the case of rabbit skeletal muscle that this result is consistent with the quantity of actin in that muscle. There is good evidence that each of the globular subunits seen in the electron microscope represents one actin monomer. The structure of actin alone does not account for (i) the approximately 400 A axial periodicity observed in the I-substance of fibrils in the electron microscope, or (ii) the reflection at about 400 A observed in the axial diffraction pattern of intact muscle. It is suggested that both (i) and (ii) could be due to the combination of actin with other material, possibly tropomyosin B.