Spectroscopic characterization of waveguides

Abstract

Since the first experiments on femtosecond laser waveguide writing the question on which mechanisms are responsible for the refractive index change immediately arose. Several efforts have been made in that direction but no conclusive answer has been achieved yet. In fact, it has been observed that several factors determine the actual mechanism dominating the refractive index change, such as the irradiation conditions and the material composition. Understanding the materials change at the microscopic level is however important in terms of optimization of both the fs-laser processing conditions and the material composition. It also can provide more detailed insight into the physical mechanisms involved in the fs-laser modification process to enhance its capabilities. Confocal fluorescence and Raman spectroscopy are powerful tools to investigate the material structure. This chapter will review the results obtained by using these techniques to characterize fs-laser induced structural changes in glass. The focus will be on structures related to waveguides and refractive index changes, since this has been the most active research area of fs-laser processing in glass to date.