Search results for "Physics::Optics"
showing 10 items of 1958 documents
Dielectric Properties of PMN-PNN+2%Li2O Ferroelectric Ceramics at Low and Infra-Low Frequencies
2014
AbstractA study of dielectric response to weak and strong measuring fields at temperatures of the diffuse phase transition in lead-magnesium niobate—lead-nickel niobate (PMN-PNN) containing an admixture of lithium is reported. A relaxor behaviour of the ceramic compound manifesting itself by a substantial shift of the temperature of dielectric permittivity maximum with field intensity and frequency is detected. Specific features of the dielectric nonlinearity observed at temperatures considerably higher than the temperature of the low-frequency dielectric permittivity maximum are related to extension of the range of phase transition to higher temperatures. This extension is related to forma…
PHASE TRANSITIONS IN THE PLZT x/85/15 SOLID SOLUTIONS
2008
ABSTRACT Role of a La on the nature of phase transition in the PLZT x/85/15 is compared with the PLZT compositions of lower Zr/Ti ratio. Thermal dependence of the dielectric permittivity, thermal expansion and elastic modulus reveal sequential transfer from macroscopic ferroelectric to antiferroelectric and nonpolar state, if La concentration is increased. Diffused, from frequency independent thermal dependence of dielectric permittivity for compositions in certain La concentration range above 4 at% coexist with the well expressed phase transition between paraelectric and antiferroelectric phases.
Supplementary optical phase transition in photorefractive coherent oscillator
2001
The semilinear photorefractive coherent oscillator with two counterpropagating pump waves may exhibit two optical phase transitions: one from a disordered state of wide-angle photorefractive scattering into a high-ordered state with the immobile photorefractive grating and the other one from the state with immobile grating into the state with two moving photorefractive gratings. We show, both experimentally and from calculations, that two these phase transitions are the second-order phase transitions.
Experimental and theoretical study on the optical properties of LaVO4 crystals under pressure
2018
We report optical absorption and luminescence measurements in pure and trivalent neodymium (Nd3+) doped LaVO4 crystals up to 25 GPa. Nd3+ luminescence has been employed as a tool to follow the structural changes in the crystal. We also present band-structure and crystal-field calculations that provide the theoretical framework to accurately explain the observed experimental results. In particular, both optical absorption and luminescence measurements evidence that a phase transition takes place close to 12 GPa. They also provide information on the pressure dependence of the band-gap as well as the emission lines under compression. We found drastic changes in the optical properties of LaVO4 …
Crystal chemistry and phase transitions in mixed niobates crystallizing with tetragonal tungsten bronze structure
1990
Abstract New compounds crystallizing with tungsten bronze structure are reported. A dielectric study and X-ray analysis at various temperatures have allowed to describe some phase transitions.
EoP250. Recent advances in transparent ferroelectric ceramics research and applications
1992
Abstract The studies of field-induced lattice rearrangement and field-induced phase transition (PT), laser beam effects in transparent ferroelectric ceramics (TFC), dopant and radiation effects in PLZT, Kerr effect demonstration and application of an intracavity matrix-addressed spatial-time modulator are discussed.
Spectroscopic ellipsometry applied to phase transitions in solids: possibilities and limitations
2009
The possibilities of in situ spectroscopic ellipsometry applied to phase transitions investigation in oxide thin films and crystals are examined in this work, along with the use of various parameters calculated from ellipsometric data (band gap energy Eg, refractive index n and surface roughness) together with the directly measured main ellipsometric angles psi and Delta, for the detection of phase transitions. The efficiency of spectroscopic ellipsometry on "surface" phase transition and its sensitivity to surface defects are also demonstrated.
Kinetics of dielectric response in SBN-75 ceramics at infra-low frequencies under illumination
2014
A study of the photo-dielectric effect in ferroelectric SBN-75 ceramics of a broad phase transition under light of small intensity is reported. Relations determining kinetics of the infra-low frequency dielectric response under light and after illumination are obtained from experimental measurements revealing the features of the behaviour of relaxation time constants of the dielectric polarisation with temperature.
Structured-light imaging through scattering
2016
We present a structured illumination technique to image objects hidden beneath scattering. The sample is computationally retrieved from a known ensemble of light patterns codified onto a digital micromirror device and photocurrent fluctuations provided by a detector with no spatial resolution. Results of laboratory experiments will be shown. Article not available.
Full field automated evaluation of the quarter wave plate retardation by phase stepping technique
2002
Quarter wave plates are optical elements commonly used in photoelasticity to obtain circularly polarized light. They divide the incident light field into two linearly polarized orthogonal components with a phase difference of a quarter of the light wavelength. Due to the tolerance in manufacturing, however, the actual phase shifting produced by the plates is affected by an error, which noticeably influences the photoelastic measurements performed by means of various automated methods. This paper presents a technique, based on the phase stepping method, for the full field automatic evaluation of the quarter wave plate error.