The permanent refractive index change induced by ultrashort laser pulses in zinc phosphate glasses has been investigated both at the surface and in bulk. At the sample surface, irradiations have been performed by using loosely focused single fs-laser pulses at different energies. Optical microscopy images of the irradiations illustrate an interferometric pattern in form of concentric Newton rings due to the laser induced multilayer system (unmodified glass, thin laser-modified layer, air). This experimental reflectivity modulation along with simulations based on Abeles theory for multilayer optical systems allows retrieving laser-induced refractive index changes on the order of Δns= -10<sup>-3</sup>. In bulk, fs-laser written waveguides have been generated by translating the sample with respect to a tightly focused laser beam. The so-produced waveguides have been characterized by studying the optical near field of the TEM<sub>00</sub> guided mode at 660 nm and using white light microscopy. The optical changes linked to the inscribed waveguides have been characterized by measuring the far field output profiles yielding values of approximately Δn<sub>b</sub>= +3·10<sup>-4</sup>. The laser-modified optical properties in bulk and at the surface will be linked to the glass structural changes as well as discussed in terms of the role of the incubation effects for multi-pulse processing.
Focused femtosecond laser pulses from a 1 MHz fiber laser were used to create modifications in Er-
Yb doped zinc phosphate glass. Two glasses with similar phosphate glass networks but different
network modifiers were investigated. To understand the resulting changes caused by the
femtosecond laser pulses various characterization techniques were employed: glass structural
changes were investigated with confocal Raman spectroscopy, defect generation as well as local Er
and Yb environment were investigated with confocal fluorescence spectroscopy, and elemental
segregation resulting from heat accumulation effects was ascertained by scanning electron