1,721,031 research outputs found
Photovoltaic spectroscopy of exciton structures in Zn(1-x)Cd(x)Se/ZnSe multiple quantum wells
No full textDOPED RARE EARTHS ORTHOSILICATES USED AS OPTICAL DEVICES FOR RECORDING INFORMATION
No full textThe present invention refers in a first aspect therof to a new method for information storage and retrieval by means of rrare earth doped hortosilicates having a trap density comprised between 10^15 and 10^20 traps/cm3 and to devices using such a new method for storing and retrieving informatio
Effective Linewidth in Raman Spectra of Titanium Dioxide Nanocrystals
No full textRaman spectra of nanocrystals titanium dioxide are discussed and the correlation between the band shape of the
allowed A1g Raman mode and the crystals dimensions is discussed. Data on Raman spectra are reconsidered in the framework
of a modified "hard confinement" model (MHC). The proposed model is based on the idea of using an effective
linewidth parameter, which is a function of the effective dimension of the nanostructure, in spite of the intrinsic Raman
band linewidth.
The comparison with standard hard confinement model reveals better agreement with the experimental results for the
MHC model up to 6 nm. Moreover, the analysis permits to improve the knowledge of the phonon dispersion curve as well
as the intrinsic Raman bulk parameters. An analytical form of the size-dependent peak-position in nanocrystals, useful for
an approximated size estimation, has been explicated. The general structure of the model permits to extended the MHC to
other nano-sized materials
Phonon characterization of nano-crystals by Raman spectroscopy
No full textProposed herein is a method based on the Levenberg–Marquadt technique to retrieve an approximated
average phonon dispersion curve from Raman spectra of nano-sized crystals. To this end we deal with
a modified form of the well-known phonon confinement model in which the intrinsic linewidth C0 is
replaced by an effective linewidth C. An application to experimental results obtained on TiO2 nano-crystals
is presented as a test of the method
Fiber Bragg grating growth simulation using an inverse scattering matrix approach
No full textABSTRACTFiber Bragg gratings are playing an important role in the field of optical telecommunications and sensors. We have simulated the growth of gratings, longitudinally written in the core of germanosilicate optical fibers by an Ar+ laser. Following a Kramer-Kronig model, absorption in the Germanium Oxygen deficient centers band (∼240 nm) is considered to be responsible for the fiber photosensitivity and a two photon absorption process models the dynamics of the refractive index variation.The spatial propagation of light along the grating is described by the coupled wave theory and is calculated by using an inverse scattering matrix technique. The predicted physical properties of the gratings, reflectivity and temporal dispersion of propagating light as a function of wavelength and input power, show that a sustained growth is possible. A good agreement with previous simulations and experiments is found.</jats:p
On the mixed nature of the 740 cm(-1) band in wurtzite GaN films: A polarized Raman scattering investigation
No full textA detailed study of the polarized Raman scattering of wurtzite GaN films is presented, focusing on the nature of the band centered at 740 cm(-1) observed in the X(Z, Z)X configuration. The origin of this band is ascribed to the mixed contribution of the A I and E, longitudinal phonon modes coupled with the free carrier excitation. The spectral profile of the 740 cm-1 Raman band has been successfully reconstructed through a linear combination of the A(1)-E-1 longitudinal phonon plasmon-coupled modes, leading to a free carrier concentration in good agreement with Hall effect measurements
Absorption spectrum of Ge-doped silica samples and fiber preforms in the vacuum ultraviolet region
No full textWe report absorption measurements in the vacuum ultraviolet (VUV) spectral region on Ge-doped silica samples grown through chemical vapor deposition (CVD) and fiber preforms grown through modified chemical vapor deposition (MCVD) with GeO2 doping concentration from 0.3 to 4.0 mol%. We observed in all spectra an absorption band at 5.15 eV and a structure at about 7.0 eV. We observed differences in the absorption spectrum between Ge-doped silica samples and fiber preforms in the shape and relative amplitude of optical absorption bands. The intensity of defect-related bands depends on the Ge concentration and distribution. Differences in Ge concentration and distribution are due to the preparation methods and growing condition
Vacuum ultraviolet absorption in silica samples
No full textOptical absorption analysis in the ultraviolet and vacuum ultraviolet region from 4.0 to 9.0 eV has been performed
on dierent silica materials. We analysed natural and synthetic silica samples, both as grown and irradiated with
dierent irradiations, neutrons, c, and ultraviolet photons. Regardless of irradiation we always observed in the spectrum
of irradiated samples the growth of the band at 5.8 eV, a band attributed to the E0 paramagnetic center. Comparing
this absorption under dierent irradiation, we suggest the B2 and E absorption bands are not correlated and
therefore cannot be assigned to the same defect
Photoluminescent and paramagnetic centers in gamma irradiated porous silica , Journal of Non Crystalline Solids, 351/21-23, 1784-86 (2005)
No full text- …
