Evolution Of Absorption Spectra In The Process Of Nucleation In Photothermo-Refractive Glass.

Photo-thermo-refractive (PTR) glass belongs to a class of photosensitive multi-component silicate glasses which demonstrate photo-thermo-induced precipitation of a crystalline phase. Photo-induced crystallisation of sodium fluoride results in refractive index variations in exposed areas of PTR glass which was successfully applied for phase hologram recording. However, even if this glass is widely used for advanced optical applications such as the stabilisation of laser diodes or spectral beam combining, the detailed mechanism of its photosensitivity is not well known. We present in this paper an analysis of the evolution of absorption spectra of UV-exposed PTR glass at then early stages of the thermal treatment (nucleation). Absorption spectra were measured on samples nucleated at constant temperature for different periods.