Early Stages of Crystallization of Lanthanum-Borogermanate Glass by a Femtosecond Laser Beam

Abstract

Regions in the bulk of lanthanum borogermanate glass modified by a femtosecond laser beam were studied by means of optical microscopy and confocal Raman scattering (RS) spectroscopy. The obtained data show that, at the stages preceding the formation of an LaBGeO₅ microcrystal, upon irradiation by a femtosecond beam in a certain interval of laser pulse energy germanium nanocrystals precipitate in the zone of local heating. The correlation between the conditions of laser irradiation leading to the appearance of germanium nanocrystals and the conditions ensuring with high probability the crystallization of phases of the low-temperature modification of lanthanum borate and stillwellite-like lanthanum borogermanate suggest that germanium nanocrystals can serve as nuclei for heterogeneous crystallization of LaBO₃ and LaBGeO₃.