Z-scan applied to phosphate glasses doped with Er$^{3+}$-Yb$^{3+}$ and silver nanoparticles

We report on the use of Z-scan technique with a beam composed with two modes, to probe the nonlinear optical properties of phosphate glasses doped with Er$^{3+}$-Yr$^{3+}$ and silver nanoparticles. Understanding the linear and nonlinear properties of these materials is crucial to evaluate if they are candidates to be used as gain media in lasers or optical amplifiers. Experiments are carried out by implementing the open-aperture Z-scan technique with bimodal laser pumping ($LG_{00}$ and $LG_{20}$) at 908.6 nm. The analysis is performed using a simplifiedmodel that incorporates nonlinear absorption and saturation intensity of the samples. The advantage of using a beam with a bimodal structure is that it allows us to evaluate the energy transfer between the modes, which is relevant since the optical active media act as an intermediary. This process is incorporated through an effective phenomenological parameter in the model that we use in our analysis.