Laser modification of glass-ceramics structure and properties: A new view to traditional materials

Glass-ceramics (GCs) usually have glass structure doped with microcrystalls that are responsible for main properties: mechanical, chemical, optical etc. As for optical properties, GCs are non-optical materials due to a strong scattering in the visible range. By now different laser technologies for modification of structure of GCs structure have been developed. Heating of GCs with the use of a laser radiation transforms crystalline phase in to glassy. It results in a change of following physical and chemical properties of the irradiated area as density, volume, viscosity, hardness, transparency, refraction, etc. The most important thing is that optical transparency of GCs drastically increases in the visible and near IR range due to the appearance of a new glassy structure. Variation of laser treatment conditions (power, exposure, wavelength from IR to UV) as well as selection of composition of GCs allows to control mentioned characteristics. We have investigated two compositions of GCs with crystalline phases of TiO₂-SiO₂ (Sitall ST-50) and Li₂O-SiO₂ ("Fotoform"). The change of refractive index and surface relief has been used as the first step for fabrication of optical elements. The second stage was a chemical processing including an ion exchange technique (Li ↔ Na, K, Rb, for "Fotoform") and etching of irradiated and non-irradiated areas. Crystalline and glassy phases have different diffusion coefficient and rates of etching. It allows to modify the refractive index and the surface relief of optical elements.. The other important feature is a difference in the macroscopic volumes of ordered-disordered phases which can be used to produce some surface reliefs etc. As a result of above mentioned research mini- and micro-optical components based on two GCs have been fabricated and demonstrated: lenses and lens arrays, waveguides and other waveguiding components, difractive gratings, integrated diaphragms etc.