Second-order nonlinear optical properties are fundamental for applications such as frequency conversions. Glass ceramics are of great interest for the development of optical elements with meter-scale dimensions for high power laser facilities.

A typical crystallized spherulite.

Now, a research group has reported a reproducible and fast-technique to prepare transparent glass-ceramics, through a phase separation process leading to approximately 30µm crystallized spherical area called spherulites. The group performed Raman and second-order nonlinear investigations using an original multi-scale approach from the nanometer up to the millimeter scale. Both the far field response of the material and the individual response from the crystallites were addressed. For the first time, spherulite crystallization has been linked with a 3-D isotropic second-order nonlinear optical signal. Furthermore, the researchers suggest a mechanism at the origin of this signal, and demonstrate a new approach for isotropic frequency conversion in transparent inorganic materials.

This research is part of the NANONLO European Project MTKD-CT-2006-042301, where French and Greek scientists are investigating new glass-ceramics with a reduced refractive index contrast between the glass matrix and spherulites, for elaborating fully transparent materials. The group say that this will constitute the focus of their future efforts.