Three-dimensional arrays of crystallites within glass by using non-resonant femtosecond pulses

We have demonstrated three-dimensional arrays of crystallites within Ag+-doped glasses. Due to focused irradiation of visible femtosecond pulses, which are non-resonant with the glass absorption, photoreaction, Ag+ + e(-) --> Ag-0, is induced only at the focal points within the Ag+-doped glasses. After heat-treatment, NaF crystallites are precipitated using Ag colloids as nuclei. Glasses doped with Ag+ ions used in this study have no absorption in visible wavelength region and are transparent at irradiated wavelengths of femtosecond laser (400, 630 and 800 nm). Using a laser beam with peak power possible with femtosecond pulses, it is possible to cause photoreaction, Ag+ + e(-) --> Ag-0, even at wavelengths for which linear absorption coefficient is <10(-2) cm(-1). We investigate crystallization by varying laser power and measure a threshold power for crystallization and its wavelength dependence. The photoreaction is explicable assuming filamentation generated by focused irradiation of laser beam with peak power (similar to 10(12) W cm(-2)). Due to the use of transparent light and the presence of a threshold for the photoreaction, it is possible to cause crystallization within the transparent glasses wherever the light is focused. (C) 1999 Elsevier Science B.V. All rights reserved.