Glass heating through submicron spots produced with silica microspheres

The emission spectra of phosphate glasses doped with different concentrations of Nd³⁺ ions have been measured and the dependence of the emission intensity on the concentration of doping ions has been explained using energy transfer models. Thus, the optimum concentration in order to obtain the maximum heating of the glass has been theoretically estimated. The glass sample doped with a Nd³⁺ concentration closest to the optimum was covered with silica transparent microspheres with different diameters (2, 7, and 25 μm). The incident laser light at 532 nm was focused through the microspheres producing submicron spots (known as photonic nanojets) that excite the doping ions in the glass and heat the matrix due to non-radiative processes. From this, the heating as a function of the microsphere diameter has been analysed.