1,720,990 research outputs found
Role of the Zhang-Rice-like exciton in optical absorption spectra of CuGeO3 and CuGe1-xSixO3 single crystals
No full textThe optical excitations in pure and Si-substituted CuGeO3 are investigated in the 15-300 K temperature range. A structure, detected for the E field parallel to the c axis of the crystals at about 3.2 eV, is due to the formation of a Zhang-Rice-like (ZR) exciton. The weak oscillator strength is due to the low mobility of the ZR-like exciton between the edge-sharing CuO4 plaquettes of CuGeO3. The temperature dependence of the ZR-like energy is explained by a renormalization effect involving phonon-electron interactions or changes in spin ordering, while the increase of ZR-like exciton intensity with the Si content is argued to arise from a different hybridization of the Si-O bond with respect to Ge-O
Microstructural modification of LiNbO3 crystals induced by femtosecond laser irradiation
No full textMicrostructural modifications were induced by femtosecond laser irradiation on lithium mobate (LN) crystals and investigated by means of optical microscopy and micro-Raman spectroscopy. Commercial z-cut congruent LN substrates were irradiated with focused ultra-short laser pulses at 810 nm, generated by a Ti:Sapphire oscillator or an amplified Ti:Sapphire laser system.
At the focus region, either refractive index changes or material removal were observed by varying the irradiation conditions. The Raman spectrum shows in the illuminated regions the insurgence of Raman modes, which are forbidden in the used-scattering geometry. This phenomenon increases gradually by approaching the ablation region, where nobium oxides and Li-deficient surfaces are formed for the low energy and high repetition rate pulses from the Ti:Sapphire oscillator. Amorphous surfaces are obtained for high energy and low repetition rate pulses from the amplified Ti:Sapphire laser system. (c) 2005 Elsevier B.V. All rights reserved
Ablation of Lithium Niobate through femtosecond nonlinear absorption
No full textFemtosecond laser processing is a promising alternative technique for manufacturing photonic elements such as gratings, micro-holes, and microchannels in different type of transparent materials. The effect of the irradiation of commercial Lithium Niobate substrates with a Ti-Sapphire oscillator with repetition rate 82 Mhz, energy per pulse 20 nJ, pulse duration of 130 fs and an amplified Ti-Sapphire laser system with repetition rate 1 kHz, energy per pulse 1 mJ, and pulse duration of about 130 fs are compared. The investigation of microstructural modifications induced by femtosecond irradiation through optical microscopy and micro-Raman spectroscopy is reported
Optical and structural modification induced in LiNbO3 by femtosecond laser irradiation
No full textMicrometer-size structural modifications are induced in Lithium Niobate through femtoseconod laser irradiation and analysed by mean of confocal Raman spectroscop
Microstructural modification of LiNbO3 crystals induced by femtosecond laser irradiation
No full textIn this work we report on the study of microstructural modifications induced by femtosecond laser irradiation on Lithium Niobate crystals by means of optical microscopy and micro-Raman spectroscopy
MicroRaman investigation of optical quality lithium niobate wafers
No full textMicroRaman spectroscopy has been used for the surface characterization of lithium niobate (LiNbO3) crystals. 3" wafers with different Li/Nb ratio, i.e., conventional congruent (CLN) and quasi-stoichiometric LiNbO3 have been analyzed. A correlation between the width of the 150cm-1 and 870cm-1 line and the crystal composition has been found. A narrowing of the linewidths for quasi-stoichiometric crystals has been observed, showing an ordered structure, if compared with CLN. The 870cm-1 line has been used to study the surface quality of 3" Z-cut CLN crystals after the wafering process. The presence of a surface structural disorder up to 30micron has been found. Various etching methods have been employed in order to minimize both the thickness of the damaged layer and the degree of damage during the wafer slicing and polishing processes. A reliable surface stress release method has been found for optical surface finishing of LiNbO3 substrate
Photoluminescent processes in K1-xLixTaO3
No full textA study of blue-green photoluminescence of K1-xLixTaO3 single crystals, under UV irradiation, was performed in the range 15-120 K. It was shown that the emission is strongly enhanced and thermally more stable with respect to pure KTaO3, up to similar to 40 K. Above this point the yield of emission decreases abruptly with an Arrhenius-like behaviour controlled by an activation energy of 70-100 meV. After low temperature excitation, a thermoluminescence spectrally very similar to PL and giving rise to a glow peak around 30 K is also observed. Correlations with recent results on photoconductivity and thermally stimulated currents are illustrated. An argument in favour of close-pair recombinations between Ta4+ and O- centres is proposed
Micro-Raman Analysis on LiNbO3 Substrates and Surfaces: Compositional Homogeneity and Effects of Etching and Polishing Processes on Structural Properties
No full textIn this work we report on micro-Raman analysis on lithium mobate (LN) substrates in order to study the compositional homogeneity of the crystals and to clear up the effects of etching and polishing processes on the surface of wafers and crystals.
The fact that the linewidth of some Raman modes scale with the composition of LN crystals, together with the use of a confocal. microscope, allowed a three-dimensional determination of the sample stoichiometry and of the crystalline quality. This local tool can supply additional information, which can be complementary to the electro-optic coefficients, carefully measured as well in order to check functional parameters.
Raman spectra from buried regions were obtained on as-grown, etched and polished crystals and wafers. The depth profile of the peak energy and the linewidth of the Raman mode at 872 cm(-1) indicate that mechanical processing of surfaces causes, in some cases, structural modifications till a depth of 15 mu m. (c) 2006 Elsevier Ltd. All rights reserved
- …
