Effect of recording conditions on the anisotropic diffraction of volume holographic gratings

The anisotropic Bragg diffraction of the volume holographic gratings in photorefractive crystals are investigated based on the model of anisotropic coupled-wave theory. The effect of the initial intensity ratio and the recording angles of the two recording waves on the anisotropic Bragg diffraction properties is discussed. It is shown that both the ratio of the initial intensity and the incident angles of the recording waves are selective action for the anisotropic Bragg diffraction efficiency of the volume holographic gratings, while these two recording conditions are not selective action for the isotropic Bragg diffraction. Furthermore, the Bragg phase matching condition of anisotropic diffraction is analyzed when the recording angles change. (C) 2006 Elsevier GmbH. All rights reserved.

Photochromic diarylethene for polarization holographic optical recording

Photochromic diarylethene, 1,2-bis[2-methyl-5-(3-fluorophenyl)-3-thienyl] perfluorocyleopentene (1a), was synthesized. The compound showed good photochromic reactions both in solution and in PMMA matrix by photo-irradiation. Using the diarylethene lb/PMMA film as recording medium and a He-Ne laser for recording and readout, four types of polarization holographic optical recording were accomplished for the first time. The results show that the orthogonal circular polarization recording is the best method for holographic optical recording when the target photochromic diarylethene is used as recording material. (c) 2006 Published by Elsevier B.V.

Characteristics of recording and thermal fixing in lithium niobate

We present a theoretical model in which the band-transport equations and the coupled-wave equations are considered to study the two thermal-fixing methods (simultaneous fixing and postfixing) in Fe:LiNbO3. We found that, in simultaneous fixing, the existing ionic-grating affects the writing of the electronic grating by reduction of the coupling gain, and the grating envelope of the fixed-index grating is quite uniform inside the photorefractive crystal in comparison with the method of postfixing. The resulting diffraction efficiency of the fixed-volume grating is dependent mainly on the initial intensity modulation of the two writing beams. A set of experiments is also presented. (C) 1998 Optical Society of America.

Theoretical investigation of nonvolatile holographic storage in doubly doped lithium niobate crystals

We have studied theoretically the inherent mechanisms of nonvolatile holographic storage in doubly doped LiNbO3 crystals. The photochromic effect of doubly doped LiNbO3 crystals is discussed, and the criterion for this effect is obtained through the photochromism-bleach factor a = S(21)gamma(1)/S(11)gamma(2) that we define. The two-center recording and fixing processes are analytically discussed with extended Kukhtarev equations, and analytical expressions for recorded and fixed steady-state space-charge fields as well as temporal behavior during the fixing process are obtained. The effects of microphysical quantities, the macrophotochromic effect on fixing efficiency, and recorded and fixed steady-state space-charge fields, are discussed analytically and numerically. (C) 2002 Optical Society of America.

Diffraction of an ultrashort pulsed beam with arbitrary polarization state from a volume holographic grating in LiNbO3 crystals

Based on a modified coupled wave theory of Kogelnik, we have studied the diffraction of an ultrashort pulsed beam with an arbitrary polarization state from a volume holographic grating in photorefractive LiNbO3 crystals. The results indicate that the diffracted intensity distributions in the spectral and temporal domains and the diffraction efficiency of the grating are both changed by the polarization state and spectral bandwidth of the input pulsed beam. A method is given of choosing the grating parameters and input conditions to obtain a large variation range of the spectral bandwidth of the diffracted pulsed beam with an appropriate diffraction efficiency. Our study presents a possibility of using a volume holographic grating recorded in anisotropic materials to shape a broadband ultrashort pulsed beam by modulating its polarization state.

Three-dimensional coupled wave study for finite-sized anisotropic volume holographic gratings under ultrashort pulsed beam readout

The three-dimensional coupled wave theory is extended to systematically investigate the diffraction properties of finite-sized anisotropic volume holographic gratings (VHGs) under ultrashort pulsed beam (UPB) readout. The effects of the grating geometrical size and the polarizations of the recording and readout beams on the diffraction properties are presented, in particular under the influence of grating material dispersion. The wavelength selectivity of the finite-sized VHG is analyzed. The wavelength selectivity determines the intensity distributions of the transmitted and diffracted pulsed beams along the output face of the VHG. The distortion and widening of the diffracted pulsed beams are different for different points on the output face, as is numerically shown for a VHG recorded in a LiNbO3 crystal. The beam quality is analyzed, and the variations of the total diffraction efficiency are shown in relation to the geometrical size of the grating and the temporal width of the readout UPB. In addition, the diffraction properties of the finite-sized and one-dimensional VHG for pulsed and continuous-wave readout are compared. The study shows the potential application of VHGs in controlling spatial and temporal features of UPBs simultaneously. (C) 2007 Optical Society of America

Phase mapping of domain kinetics in lithium niobate by digital holographic interferometry

The phase mapping of domain kinetics under the uniform steady-state electric field is achieved and investigated in the LiNbO3 crystals by digital holographic interferometry. We obtained the sequences of reconstructed three-dimensional and two-dimensional wave-field phase distributions during the electric poling in the congruent and near stoichiometric LiNbO3 crystals. The phase mapping of individual domain nucleation and growth in the two crystals are obtained. It is found that both longitudinal and lateral domain growths are not linear during the electric poling. The phase mapping of domain wall motions in the two crystals is also obtained. Both the phase relaxation and the pinning-depinning mechanism are observed during the domain wall motion. The residual phase distribution is observed after the high-speed domain wall motion. The corresponding analyses and discussions are proposed to explain the phenomena.

Optical setup and analysis of disk-type photopolymer high-density holographic storage

A relatively simple scheme for disk-type photopolymer high-density holographic storage based on angular and spatial multiplexing is described. The effects of the optical setup on the recording capacity and density are studied. Calculations and analysis show that this scheme is more effective than a scheme based on the spatioangular multiplexing for disk-type photopolymer high-density holographic storage, which has a limited medium thickness. Also an optimal beam recording angle exists to achieve maximum recording capacity and density. (C) 2002 Society of Photo-Optical Instrumentation Engineers.

Dual-wavelength photochromic fulgides for parallel recording memory

Two photochromic fulgides, 2-{2-[4-(N,N-dimethylnilino)-5-methyl-4-oxazoly]}ethylidene-4-(1-methylethylidene) tetrahydrofuran-2,5-dione (A) and 3-(1,2-dimethyl-5-phenyl-3-pyrolloethylidene)-4-(1-methylethylidene)tetrahydrofuran-2,5-dione (B), doped in PMMA as candidates of dual-wavelength optical memory for parallel recording has been investigated. With 488 nm-laser and 650 nm-laser, both "cross" and "star" images are recorded on the fulgides-PMMA film and read out clearly, respectively. Crosstalk between two fulgides in PMMA matrix and nondestructive readout has also been explored. The results show that no significant cross-talk is detected between them, and nondestructive readout is up to 201 times. (C) 2005 Elsevier B.V. All rights reserved.

Experimental study on polarization holographic storage in genetic mutant BR-D96N film

Recording with both parallel and orthogonal linearly polarized lights, polarization holographic storage in genetic mutant BR-D96N film is reported with both transmission type geometry and reflection type geometry. Polarization properties of diffraction light and scattering light are discussed for two different cases, parallel polarization recording and orthogonal polarization recording. It shows that, compared with recording with parallel polarization lights, orthogonal polarization holography can separate the diffraction light from the scattering noise, therefore improving the signal-to-noise ratio. It also shows that, compared with reconstruction with reference light, reconstruction with phase conjugated wave of the reference light can improve the signal-to-noise ratio of the reconstructed diffraction image, and also the wave-front aberration of the object light introduced by irregular phase object in the optical pass-way can also be corrected effectively, which ensures that the reconstructed diffraction image has a better fidelity. The preliminary angle-multiplexed volume holographic storage multiplexed by transmission type geometry and reflection type geometry is demonstrated in the BR-D96N film. Experiment shows that there is no cross-talk between the two pages of images except for some scattering noises.

Electron trapping materials for use in a picosecond infrared streak camera

We describe our research on the employment of an infrared upconversion screen made of electron trapping material (ETM) in combination with the high sensitivity of the S-20 photocathode responsive to visible radiation to produce a streak camera arrangement capable of viewing and recording infrared incident pulses. The ETM-based upconversion screen converts 800-1600 nm infrared radiation to visible light which is viewed or recorded by the S-20 photocathode. The peak values of the upconversion efficiency are located at 1165 nm for CaS:Eu, Sm and 1060 nm for CaS:Ce, Sm. The present experiment showed time resolution was 12.3 ps for a CaS:Eu, Sm screen and 8.4 ps for a CaS:Ce, Sm screen. The minimum detectability is 4.8 x 10(-9) J/mm(2) (minimum detectability of the coupled visible streak camera is 8.3x10(-10) J/mm(2)). Other parameters, such as spatial resolution and dynamic range, have also been measured and analyzed. The results show ETM can be used in the measurement of infrared ultrafast phenomena up to picosecond time domain. In consideration of the limited number of trapped electrons in ETM, the infrared-sensitive streak camera consisting of an ETM-based upconversion screen is suitable to operate in the single shot mode. (C) 1999 American Institute of Physics. [S0034-6748(99)00112-4].

Effects of Microstructural Heterogeneity on the Spallation Behavior of Materials

It is of utmost importance to understand the spallation behaviour of heterogeneous materials. In this paper, a driven nonlinear threshold model with stress fluctuation is presented to study the effects of microstructural heterogeneity on continuum damage evolution. The spallation behavior of heterogeneity material is analyzed with this model. The heterogeniety of mesoscopic units is characterized in terms of Weibull modulus m of strength distibution and stress fluctuation parameter k. At high stress, the maximum damage increases with m; while at low stress, the maximum damage decreases. In addition, for low stress, severe stress fluctuation causes higher damage; while for high stress, causes lower damage.

Fracture mechanics of piezoelectric materials

This paper presents an analysis of crack problems in homogeneous piezoelectrics or on the interfaces between two dissimilar piezoelectric materials based on the continuity of normal electric displacement and electric potential across the crack faces. The explicit analytic solutions are obtained for a single crack in an infinite piezoelectric or on the interface of piezoelectric bimaterials. For homogeneous materials it is found that the normal electric displacement D-2, induced by the crack, is constant along the crack faces which depends only on the remote applied stress fields. Within the crack slit, the perturbed electric fields induced by the crack are also constant and not affected by the applied electric displacement fields. For bimaterials, generally speaking, an interface crack exhibits oscillatory behavior and the normal electric displacement D-2 is a complex function along the crack faces. However, for bimaterials, having certain symmetry, in which an interface crack displays no oscillatory behavior, it is observed that the normal electric displacement D-2 is also constant along the crack faces and the electric field E-2 has the singularity ahead of the crack tip and has a jump across the interface. Energy release rates are established for homogeneous materials and bimaterials having certain symmetry. Both the crack front parallel to the poling axis and perpendicular to the poling axis are discussed. It is revealed that the energy release rates are always positive for stable materials and the applied electric displacements have no contribution to the energy release rates.

FEM Simulations and Optimization about Residual Stresses in Coating Structures with Functionally Graded Materials Layer

An elasto-plastic finite element method is developed to predict the residual stresses of thermal spraying coatings with functionally graded material layer. In numerical simulations, temperature sensitivity of various material constants is included and mix