Three-dimensional crystallization inside photosensitive glasses by focused femtosecond laser

Using scanning electron microscopy, we analyze the laser fluence dependence of three-dimensional crystallized areas induced in bulk photosensitive glass (Foturan) by focused femtosecond laser pulses exposition and subsequent heat treatment. For low fluences (F 2J∕cm2), the crystallization length is higher than predicted from the energy distribution due to the filamentation which occurs above a critical fluence Fcrit=1.4±0.3J∕cm2. The filamentation length is found to follow the square root dependence F−Fcrit.