Emergence of Structural Anisotropy in Optical Glasses Treated to Support Second Harmonic Generation (original) (raw)

Evidence of microscopic-scale modifications in optical glasses supporting second harmonic generation

Physics Letters A, 1998

We explore, by means of inelastic neutron scattering, the extent of changes in dynamic correlations induced by thermal poling of vitreous SiO2. The measured vibrational density of states shows an excess of modes in certain frequency regions as well as a narrowing of the 100 meV peak. These findings indicate that such alterations cannot be ascribed to the appearance of new well defined vibrational modes, such as those coming from localized topological defects, but rather arises from an increase in ordering in the material as attested in a reduced spread of the inter-tetrahedral angles.

Vibrational dynamic of ‘strong’ glasses: the case of v-SiO2 and v-GeO2

Journal of Non-Crystalline Solids, 2003

The vibrational dynamic of vitreous germania (v-GeO 2 ) with respect to that of vitreous silica (v-SiO 2 ) has been investigated by means of several inelastic and elastic scattering experiments. These amorphous systems belong to the large family of continuous random network forming glasses. In spite of their topological similarity, some dynamical differences have been singled out. We present experimental data on light Raman scattering at room temperature as well as new elastic and inelastic neutron scattering. Transversal-acoustic character of the vibrations responsible for the density of states excess in the Boson peak energy range is found.

Angular Dependence of the Second Harmonic Generation Induced by Femtosecond Laser Irradiation in Silica-Based Glasses: Variation with Writing Speed and Pulse Energy

World Journal of Nano Science and Engineering, 2015

To control second harmonic generation (SHG) in silica-based glasses is crucial for fabricating photonic devices, such as frequency doubling waveguides. Here, we investigated SHG of laser induced nonlinear optical crystals in silica-based glasses, according to writing speed and pulse energy. We observed two regions with different probing laser polarization angular dependence: a) a well-defined cosine-like curve with period of 180˚ at low pulse energy (0.8 µJ) whatever the writing speed or at high pulse energy (1.4 µJ) with high writing speed (25 µm/s). This is accounted for by a well-defined texture for the nano crystals with their polar axis oriented perpendicular to the writing laser polarization; and b) a double cosine-like curve revealing a second texture of the crystals at high pulse energy (1.4 µJ) with low writing speed (5 µm/s) and with the polar axis oriented closer parallel to the writing laser polarization. Therefore, a SHG dependence on probing laser polarization angle may show high contrast by a correct choice of the writing speed and pulse energy. These results pave the way for elaboration of nonlinear optical devices.

The vibrational modes of glasses

Solid State Communications, 2001

Our recent experimental observations on the harmonic vibrational modes of glasses are presented. Emphasis is placed on normal and densi®ed silica. These results are discussed within the broader current knowledge, including thermal properties and other spectroscopic data that are critically assessed. We ®nd that propagating acoustic modes enter a regime of strong scattering as their wavelength is reduced, and that this leads to an Ioffe±Regel crossover at frequencies of the order of the terahertz, corresponding to wavelengths of several nanometers. At similar frequencies, an excess in the density of states of optical modes, generally called the Boson peak, is observed. Hyper-Raman spectroscopy on these modes clearly shows that in silica they are due to the rocking of small groups of tetrahedra. These ®ndings provide unique and unexpected information on the structure of glasses at the extended length scale, about which so little is known otherwise. The strong elastic inhomogeneity found at this scale might be decisive in determining glass properties, and even stability, and this will justify further studies. q

Influence of different poling methods on the second-order nonlinearity in fused silica glasses

Optics Communications, 2000

Fused silica glass samples poled by different methods showed large differences in their second-order optical nonlinearities. Large second-harmonic signals were obtained only when a depletion layer was formed near the anode surface. By comparing the influences of plate poling and corona poling, the necessary conditions to form a depletion layer in fused silica glass are discussed.

Time-domain separation of nuclear and electronic contributions to the third-order nonlinearity in glasses

Journal of The Optical Society of America B-optical Physics, 1998

The electronic and nuclear contributions to the third-order nonlinearity of glasses are separated by use of 100-fs pulses in a time-resolved heterodyne optical Kerr effect technique. A direct estimate of the relative strengths of electronic and nuclear contributions was made by the comparison between the nuclear contribution deduced from the Raman spectra with the Kerr signal. The ratio between the electronic and nuclear response functions was ϳ5/1 in a tellurium oxide glass sample. The time evolution of the nuclear contribution is in good agreement with results deduced from the Raman spectra.

First principles vibrational spectra of tetrahedrally-bonded glasses

Les materiaux vitreux, comme par example la silice amorphe (v-SiO 2 ), l'oxyde de germanium amorphe (v-GeO 2 ), et les verres de la famille des chalcogenides, dont un représentant est le diséléniure de germanium (v-GeSe 2 ), sont actuellement des matériaux clés dans plusieurs applications technologiques. Ils sont notamment employés dans la production des fibres optiques, des dispositifs microélectroniques et pour le stockage d'informations.

Vibrational spectra in glasses

Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties, 2002

The findings of X-ray and neutron scattering experiments on amorphous systems are interpreted within the framework of the theory of Euclidean random matrices. This allows to take into account the topological nature of the disorder, a key ingredient which strongly affects the vibrational spectra of those systems. We present a resummation scheme for a perturbative expansion in the inverse particle density, allowing an accurate analytical computation of the dynamical structure factor within the range of densities encountered in real systems.

Is there a correlation between the first sharp diffraction peak and the low frequency vibrational behavior of glasses?

Physical Review Letters, 1993

Neutron diffraction and light scattering studies have been performed on a network glass subject to structural modifications. Large changes of the first sharp diA'raction peak (FSDP) and the low frequency dynamics (the boson peak) are demonstrated by gradually changing the intermediate range structural ordering, the short range order being preserved. A recently suggested "universal" correlation for glasses between the positions of the FSDP and the boson peak is sho~n to fail; in fact opposite trends are observed.