Effect of structure and composition of the thermal lensing and permanent laser-induced refractive-index changes in glasses

Abstract

We have previously reported the ability to produce permanent refractive-index gratings in rare earth-doped glasses through the creation of laser-induced local structural changes and have shown how thermal lensing affects the grating properties. We present here the extension of this research to the investigation of the effects of glass structure and composition on thermal lensing and on the ability to produce permanent gratings. New types of lithium borate, lead and magnesium silicates and germanates, and a lead phosphate glass were investigated. The results of four-wave mixing experiments show that the grating scattering efficiency is strongly dependent on the strength of the chemical bonds and the charge to radius ratio of the glass components. The thermal lensing properties of these materials under 7-ns pulsed excitation at 457nm can be attributed to the molecular polarizibility of their components. They are also dependent on lead concentration and are stronger in the silicates and germanates, having continuous random network structures, compared to the phosphates and borates with more constrained chain- and ring-type structures, respectively. A model is presented to interpret the results of thermal lensing experiments.