Cooling rate calibration and mapping of ultra-short pulsed laser modifications in fused silica by Raman and Brillouin spectroscopy

This paper focuses on the preparation of a new extended set of calibrations of cooling rate (fictive temperature) in fused silica determined by inelastic light scattering and its subsequent use to characterize the local cooling rate distribution in ultra-short pulsed laser modification. In order to determine the thermal history (cooling rate, fictive temperature) of fused silica, high resolution inelastic light scattering experiments (Raman and Brillouin spectroscopy) are investigated. Calibrations are performed and compared to literature to quantify structural changes due to a change of fictive temperature. Compared to already existing calibrations, this paper provides an extension to lower and higher cooling rates. Our new set of calibrations is subsequently used to characterize an ultra-short pulsed laser modification in fused silica and to calculate the local fictive temperature distribution. An equation relating the fictive temperature to cooling rates is given. A maximum cooling rate of 3000 K/min in the glass transition region around 1200 °C is deduced from the Raman analysis. The Brillouin observations are sensitive to both the thermal history and the residual stress. By comparing the Raman and Brillouin observations we extract the local residual stress distribution with high spatial resolution. For the first time, combined Raman and Brillouin inelastic light scattering experiments show the local distribution of cooling rate and residual stresses (detailed behavior of the glass structure) for the inside as well as the surrounding of an ultra-short pulsed laser modified zone.