58 research outputs found
Impurity effects and charge transport in ABO3 single crystal oxides: Photorefractivity-oriented and basic studies
No full textNon linear optical, dielectric, magnetic properties of ABO3 single crystal oxides let the implementation of acousto-optic, electro-optic, photonic, spintronic devices. In particular, significant role is played by the ferroelectric and photorefractive materials, where the photo-induced change in refractive indexes requires charge transport and impurities which support charge transfer, space charge formation and localization with accompanying electric field. Besides, ABO3 paraelectric perovskites regularly reveal newel effects connected with charge transport, e.g., photo-induced polar state recently reported for SrTiO3 and KTaO3. In this work we review our recent investigation, pointing out our studies of photo-transport in SrTiO3, Cu-doped KTaO3 and LiNbO3:Hf
Photoconductivity and the structural phase transiting in SrTiO3
No full textDetailed photoconductivity measurements have been performed in nominally pure SrTiO3 in order to elucidate the effect of the antiferrodistorsive cubic-tetragonal phase transition.
Small features in the photoconductivity's temperature dependence in the phase transition region were found using low intensity interband UV or 514 nm light illumination.
Such features are associated with a transformation of the defect system controlling the photoconductivity.
At the same time, the temperature behavior of the photoconductivity spectral maximum reveals a rather unusual
feature which is connected with changes in the absorption band edge structure in the phase transition region. (c) 2006 Elsevier Ltd. All rights reserved
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
Thermoreflectance spectra of diamond and zinc-blende semiconductors in the vacuum-ultraviolet region
No full textMicrostructural 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
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