Raman spectroscopy of femtosecond multipulse irradiation of vitreous silica: Experiment and simulation

Abstract

We report an experimental and numerical study of femtosecond multi-pulse laser-induced densification in vitreous silica (v-SiO2) and its signature in Raman spectra. We compare the experimental findings to recently developed molecular dynamics (MD) approach accounting for bond-breaking due to laser irradiation, together with a dynamical matrix approach and bond polarizability model based on first-principle calculations for the estimation of Raman spectra. We observe two stages of the laser-induced densification and Raman spectrum evolution: growth during several hundreds of pulses followed by further saturation. At the medium-range, the network connectivity change in v-SiO2 is expressed in reduction of the major ring fractions leading to more compacted structure. With the help of Sen & Thorpe model, we also study the short-range order transformation and derive the interbonding Si-O-Si angle change from the Raman measurements. Experimental findings are in excellent agreement with our MD simulations, and, hence, support bond-breaking mechanism of laser-induced densification. Thus, our modeling explains well the laser-induced changes both in the short-range order caused by the appearance of Si-coordination defects and medium-range order connected to evolution of the ring distribution. Finally, our findings disclose similarities between sheared-, permanently-densified-and laser-induced-glass and suggest interesting future experiment in order to clarify the impact of the thermo-mechanical history on glasses under shear, cold-and hot-compression, and laser-induced densification.

Highlighting the impact of shear strain on the SiO2 glass structure: From experiments to atomistic simulations

“…Both studies point out that the creation of 3 fold rings is favored by shear stresses at the expense to larger rings. Indeed, the relative proportion of 3 fold rings increases both for hydrostatic cold compression and uniaxial compression, as was shown already in the case of laser induced densification [48][49]. This increase is linear as a function of the resulting density.…”

“…In particular, we show a significant increase of the 3 fold ring proportion at the expense of larger rings, under hydrostatic compression and more markedly under shear at constant pressure. A similar increase has been also put in evidence from simulations of the densification process under laser irradiation [48].…”

Vibrational and structural properties of P2O5 glass: Advances from a combined modeling approach

“…One can note that the Raman bands ∼870-1250 cm −1 behave silently, which complicates accurate measurements and analysis, whereas the IR spectrum shows strong resonances, especially at ∼950 cm −1 . Since the modes above ∼870 cm −1 are quite spatially localized (PR ∼0.2), we are able to infer information about the intermediate range order (interbonding angle) [51], and hence, in the case v-P 2 O 5 , the IR spectroscopy seems to be preferred to Raman spectroscopy in this frequency range. The most prominent peak around 1400 cm −1 (experiment: 1380 cm −1 ) is mainly due to asymmetric stretching vibrations of terminal oxygens, and its signatures are comparably strong in all vibrational spectra (see Fig.…”

Laser-Induced Structural Modification in Calcium Aluminosilicate Glasses Using Molecular Dynamic Simulations

“…Its enhanced thermal-mechanical properties and wide optical transmissivity, extending from the infrared (IR) to ultraviolet (UV), make it an important material used in industry. The densification of fused silica has been documented under extensive experimental conditions such as: hydrostatic compression 29 , neutron irradiation 30,31 , femtosecond pulse laser irradiation [32][33][34] , and shock-wave propagation 35,36 . Experimental studies in which fused silica was exposed to femtosecond laser pulses, formation of filamentation, ablation, and waveguides have been reported.…”