<title>Effects of light polarization and crystal orientation on the holographic recording efficiency in doped LiNbO<formula><inf><roman>3</roman></inf></formula> crystals</title>

AbstractLight polarization effects on a holographic grating recording in a glassy chalcogenide a-As40S15Se45 film has been experimentally studied and compared with previously studied glassy molecular azobenzene film 8a at 633, using s − s,p − p, CE-1 and CE-2 circular-elliptic recording-beam polarizations (differing by light electric field rotation directions). The azocompound exhibited much higher self-diffraction efficiency (SDE) and diffraction efficiency whereas chalcogenide was more sensitive. Their recording efficiency polarization dependences also were different. SDE up to 45% was achieved in 8a with p − p and up to 2.6% in a-As40S15Se45 with CE-2 polarized recording beams. The polarization changes in the diffraction process were studied as well in these and other materials (11, 16, 19 and a-As2S3 film, LiTaO3:Fe crystal). It was found that light polarization changes in the process of diffraction from gratings recorded vectorially by s−p polarizations depended on chemical composition, wavelength, and exposure time. Vector gratings with SDE up to 25% were recorded in 8a, rotating a linear polarization by 90°. No light polarization changes were found in azobenzene 19 and chalcogenide films and in LiTaO3:Fe crystal, thus showing a vector recording of scalar holograms. The recording mechanisms in azocompounds and chalcogenides are discussed and compared.

Download Full-text

Photo-Induced Holographic Recording in an Optically Active Cholesteric Liquid Crystal Layer

Optical Data Processing and Storage ◽

10.1515/odps-2018-0001 ◽

2018 ◽

Vol 4 (1) ◽

pp. 1-7

Author(s):

A. Chanishvili ◽

N. Ponjavidze ◽

G. Petriashvili ◽

G. Chilaya ◽

A. Jullien ◽

...

Keyword(s):

Liquid Crystal ◽

Cholesteric Liquid Crystal ◽

Polarization Plane ◽

Thick Layer ◽

Light Polarization ◽

Optically Active ◽

Holographic Recording ◽

Isotropic Liquid ◽

Nonlinear Beam ◽

Beam Coupling

Abstract A few microns thick layer of an optically active cholesteric liquid crystal is realized by using a photoisomerizable nematic component and a chiral dopant. It is shown that such a photosensitive optically active medium can be used as a holographic material for optical information and dynamic grating recording. The photo-induced gratings are written by exploiting the light-induced photoisomerization phase transition from an optically active chiral liquid crystal to an isotropic liquid, which results in the rotation of the light polarization plane from 90 to 0 degrees and corresponding to maximum, respectively, zero transmittance. The results highlight applications in the field of optical storage by the recording of static gratings, as well as in the feld of nonlinear beam-coupling via the holographic writing of dynamic gratings

Download Full-text

Spherulitic crystal growth in the prodissoconch larval of Crassostrea virginica

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100076263 ◽

1983 ◽

Vol 41 ◽

pp. 518-519

Author(s):

George G. Cocks ◽

Louis Leibovitz ◽

DoSuk D. Lee

Keyword(s):

Crystal Structure ◽

Crassostrea Virginica ◽

Crystal Orientation ◽

Developmental Changes ◽

Gastrula Stage ◽

Orthorhombic Crystal ◽

Orthorhombic Crystal Structure ◽

Stages Of Growth ◽

Early Stages ◽

Initial Deposition

Our understanding of the structure and the formation of inorganic minerals in the bivalve shells has been considerably advanced by the use of electron microscope. However, very little is known about the ultrastructure of valves in the larval stage of the oysters. The present study examines the developmental changes which occur between the time of conception to the early stages of Dissoconch in the Crassostrea virginica(Gmelin), focusing on the initial deposition of inorganic crystals by the oysters.The spawning was induced by elevating the temperature of the seawater where the adult oysters were conditioned. The eggs and sperm were collected separately, then immediately mixed for the fertilizations to occur. Fertilized animals were kept in the incubator where various stages of development were stopped and observed. The detailed analysis of the early stages of growth showed that CaCO3 crystals(aragonite), with orthorhombic crystal structure, are deposited as early as gastrula stage(Figuresla-b). The next stage in development, the prodissoconch, revealed that the crystal orientation is in the form of spherulites.

Download Full-text

The Interpretation of Crystal Lattice Images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010009600x ◽

1972 ◽

Vol 30 ◽

pp. 550-551

Author(s):

J. M. Cowley ◽

Sumio Iijima

Keyword(s):

Crystal Orientation ◽

Diffraction Theory ◽

Phase Changes ◽

Electron Wave ◽

Crystal Lattices ◽

Heavy Atoms ◽

Lattice Images ◽

The Right ◽

Intuitive Interpretation ◽

Suitable Approximation

The imaging of detailed structures of crystal lattices with 3 to 4Å resolution, given the correct conditions of microscope defocus and crystal orientation and thickness, has been used by Iijima (this conference) for the study of new types of crystal structures and the defects in known structures associated with fluctuations of stoichiometry. The image intensities may be computed using n-beam dynamical diffraction theory involving several hundred beams (Fejes, this conference). However it is still important to have a suitable approximation to provide an immediate rough estimate of contrast and an evaluation of the intuitive interpretation in terms of an amplitude object.For crystals 100 to 150Å thick containing moderately heavy atoms the phase changes of the electron wave vary by about 10 radians suggesting that the “optimum defocus” theory of amplitude contrast for thin phase objects due to Scherzer and others can not apply, although it does predict the right defocus for optimum imaging.

Download Full-text