Search results for "FFR"
showing 10 items of 1798 documents
Photorefraction demonstrations using electrooptic PLZT ceramics modulators
2003
PLZT ceramics electrooptic (EO) modulator was designed for demonstrations and student's laboratory works to study photorefraction using Ar+ laser (λ = 514 nm). PLZT element had an aperture of 1.5 x 8 mm2 and thickness of 1.5 mm. Reading of recorded patterns was realized by applying to the element the biasing electric field. The most efficient writing took place for ceramics composition PLZT 8.75/65/35. The total intensity of two writing beams was up to 300 mW, the applied electric field during writing -- up to 20 kV/cm. The diffraction efficiency depended on the applied biasing reading electric field EBR . For the reading He-Ne laser the diffraction efficiency η ≈ 0.48 was obtained at the b…
NUMERICAL-EXPERIMENTAL METHOD FOR THE ANALYSIS OF RESIDUAL STRESSES IN COLD-EXPANDED HOLES
2012
Hole cold expansion is a technique widely used to improve the fatigue life of components with holes, e.g. bolted or riveted joints. As it has been demonstrated in literature by analytical, numerical and experimental analyses carried out by several authors, the compressive residual stresses introduced by the hole cold expansion have a beneficial influence on both the static and the fatigue strength of the treated component, because they reduce significantly the typical stress peaks around the hole due to stress concentration. In the literature, various analyses of the residual stresses introduced by the hole cold expansion have been performed by using several methods such as X-ray diffractio…
Holographic recording of surface relief gratings in tolyle-based azobenzene oligomers
2008
Abstract Holographic recording of surface relief gratings (SRG) in tolyle-based azobenzene oligomer films have been carried out at 514.5 nm. It was experimentally studied by spectroscopic and AFM methods. The maximum surface modulation amplitude was 35 nm. SRG formation is explained by the mean-field model and by the photodegradation of chromophores enabling the directional mass transport as the result of trans–cis transformations. The conclusion is made that SRG are stable but the diffraction efficiency (DE) changes are due to the complementary decaying amplitude-phase gratings. Strong polarization dependences of transmitted and reflected DE are found. They are explained by the diffraction…
Analysis of acousto-optic tunable filter performance for imaging applications
2010
Acousto-optic tunable filters (AOTFs) can be used as spec- tral filters in multispectral imaging applications. Acousto-optic crystals diffract a single wavelength from a broadband light beam, depending on the applied radio frequency signal. However, experimental measurements show that the actual performance is far from the expected behavior. We present an experimental characterization of several commercial off-the- shelf AOTFs for the implementation of multispectral imaging instruments. The diffraction performance of three bare crystals is compared, while a fourth AOTF crystal is mounted on the optical path of a multispectral im- ager to evaluate its performance. The experiments show that t…
Enhanced diffraction of light in GaAs microcavities
1995
We theoretically analyze the diffraction of light by gratings that are photogenerated in Fabry–Perot microcavities. The coupled-wave theory of volume gratings is combined with appropriate boundary conditions to yield expressions for the diffraction efficiency. Multiple round trips within the cavity are seen to increase the effective grating thickness and therefore the efficiency. Numerical calculations specific to GaAs microcavities show that the diffraction efficiency can be enhanced by more than 2 orders of magnitude at the resonant wavelengths.
Artificially inscribed defects in opal photonic crystals
2005
Opals are three-dimensional photonic crystals, self-assembled from dielectric spherical beads into a face-centered cubic lattice. By introducing intentional defects in the crystal lattice, one modifies features such as spontaneous emission and the directionality of diffracted light. We here present a method for the artificial introduction of a lattice of such intentional defects in self-assembled poly(methyl methacrylate) (PMMA) photonic crystals by means of electron beam lithography. The inscribed defects are of the size of an individual bead, providing a broad spectral range between adjacent resonance peaks. This opens for devices with single line transmission in the photonic band gap, as…
Dispersion-compensated Lau-like processor
2004
We present a diffractive lens-based optical assembly with which to achieve high-contrast Lau-like interferential fringes with totally incoherent illumination.
Spatial soliton formation in photonic crystal fibers
2003
We demonstrate the existence of spatial soliton solutions in photonic crystal fibers (PCF's). These guided localized nonlinear waves appear as a result of the balance between the linear and nonlinear diffraction properties of the inhomogeneous photonic crystal cladding. The spatial soliton is realized self-consistently as the fundamental mode of the effective fiber defined simultaneously by the PCF linear and the self-induced nonlinear refractive indices. It is also shown that the photonic crystal cladding is able to stabilize these solutions, which would be unstable otherwise if the medium was entirely homogeneous.
<title>Forward diffracted parametric X radiation from a thick Tungsten single crystal at 855 MeV electron energy</title>
2007
Features of forward diffracted Parametric X-Radiation (PXR) were investigated at experiments with the 855 MeV electron beam of the Mainz Microtron MAMI employing a 410 micrometer thick tungsten single crystal. Virtual photons from the electron field are diffracted by the (10-1) plane at a Bragg angle of 3.977 degree. Forward emitted radiation was analyzed at an energy of 40 keV with the (111) lattice planes of a flat silicon single crystal in Bragg geometry. Clear peak structures were observed in an angular scan of the tungsten single crystal. The results were analyzed with a model which describes forward diffracted PXR under real experimental conditions. The experiments show that forward d…
Assessment of the out-plane and in-plane ordering of high quality ZnO nanorods by X-ray multiple diffraction
2013
Abstract ZnO nanorods grown on buffered and non buffered sapphire substrates have been investigated by X-ray multiple diffraction using Renninger scans of the ZnO(0001) and ZnO(0003) forbidden reflections. In this technique the diffracted X-ray beam is simultaneously diffracted by several sets of planes, providing information on the broadening in different directions, as well as from nanorods, and from the layer on which they grow. The intensities and angular widths of peaks obtained by azimuthal and omega scans have been analyzed, making a direct comparison with conventional measurements of the full width at half-maximum of symmetric and asymmetric reflections. The analysis leads to establ…