Search results for "intensity"
showing 10 items of 1091 documents
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.
Amorphous semiconductor-electrolyte junction
1987
Abstract The photoelectrochemical behaviour of amorphous anodic films on niobium (a-Nb 2 O 5 ) grown in a wide range of thicknesses (20 ⩽ d ox ⩽ 25 nm) is presented. The influence of the wavelength, light intensity and film thickness on the photocharacteristics of the a-Nb 2 O 5 /electrolyte junction is investigated. Expressions for the photocurrent curves under steady-state conditions are derived by assuming a variable efficiency of photocarrier generation and different distributions of the electrical potential inside the amorphous films. The influence of the light intensity on the photocharacteristics and the existence of a sub-band-gap photoresponse are explained by assuming a finite den…
Automated photoelasticity in white light: Influence of quarter-wave plates
1995
This paper deals with the influence of optical retarders on the isochromatic fringes obtained by automated white light photoelasticity using methods such as those based on spectral content analysis (SCA) and on primary colour (red, green and blue) analysis. In the following the light intensity equations of dark- and light-field polariscopes with both crossed and parallel optical retarders are reviewed. In particular, it is shown that the retardance error of the quarter-wave plates produces an attenuation of the maximum intensity in dark field and an increase of minimum intensity in light field. Experimental evidence of the influence of optical retarders is also shown.
Limitation of fourier transform photoelasticity: Influence of isoclinics
2000
The application of the Fourier transform to photoelasticity was used in the evaluation of the retardation using a carrier system of fringes. In photoelasticity, the light intensity from the analyzer in a circular polariscope depends on both the retardation (isochromatics) and the isoclinic parameter. The theoretical analysis shows that the angle between the principal stresses in the model and in the carrier system of fringes influences the evaluation of the retardation (isochromatics), as occurs when misaligned compensators (namely, Babinet) are used. As a consequence, this method may not be applied as a full-field technique, although the error is small if the angle between the principal st…
Numerical simulations and experimental measurements of the stress intensity factor in perforated plates
2008
A numerical procedure, which combines two hybrid finite element formulations, was developed to analyse the stress intensity factors in cracked perforated plates with a periodic distribution of holes and square representative volume elements. The accuracy of the method in predicting the stress intensity factor was verified by a comparison with experimental measurements, carried out by a photoelasticity method, and by commercial finite element software. Several simulations were executed by varying both the crack length and the hole diameters, and the effects of the holes on the stress intensity factor are illustrated. The method shows high accuracy and efficiency, as small differences were ob…
Near band edge recombination mechanisms in GaTe
2003
GaTe samples of p-type have been investigated by analyzing the photoluminescence (PL) response for different excitation intensities at energies higher than the band gap. The PL intensity variation of recombination peaks as a function of the excitation intensity has been measured and fitted by a power law. The results show some particular features that do not appear in other III-V and II-VI compound semiconductors. These features can be interpreted by means of the recombination dynamics of the carriers in the band-gap edges. The expressions for the coefficients associated with different recombination rates and the relations between them are derived and used for understanding the recombinatio…
Cathodoluminescence and photoluminescence study of plastically deformed ZnTe bulk single crystals
2001
Samples of zinc telluride bulk single crystals, which were deformed in uniaxial compression, have been studied by photoluminescence (PL) and cathodoluminescence (CL). As a particular feature the deformed samples present a PL emission band peaked at 603 nm, whose intensity increases as the plastic deformation does. This band is related to the density of dislocations produced during the interaction of slip systems. This hypothesis is supported by CL images. which reveal the activation of the successive slip systems corresponding to different levels of deformation.
Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition
2015
Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies (Vo) were identified in ZnO nanorods (NRs) grown by low cost chemical bath deposition. A transient behaviour in the photoluminescence (PL) intensity of the two Vo states was found to be sensitive to the ambient environment and to NR post-growth treatment. The largest transient was found in samples dried on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV exposure exhibited a transient behaviour in full agreement with the PL transient, indicating a clear role of atmospheric O-2 on the surface defect states. A model fo…
Measurement of the atmospheric muon flux with a 4 GeV threshold in the ANTARES neutrino telescope
2010
A new method for the measurement of the muon flux in the deep-sea ANTARES neutrino telescope and its dependence on the depth is presented. The method is based on the observation of coincidence signals in adjacent storeys of the detector. This yields an energy threshold of about 4 GeV. The main sources of optical background are the decay of 40K and the bioluminescence in the sea water. The 40K background is used to calibrate the efficiency of the photo-multiplier tubes.
Directionality of light emission in three-dimensional opal-based photonic crystals (Invited Paper)
2005
Experimental and theoretical studies of the emission directionality diagrams of a perylene dye covering the inner surface of three-dimensional opal-based photonic crystals with incomplete photonic bandgap are reported. Directionality diagram of emission intensity is interpreted in terms of the spontaneous emission suppression by photonic band gap and the emission enhancement due to photon focusing phenomenon. A theoretical model is based on the classical analysis of an angular distribution of the radiated power of a point dipole.