Transparent Ho,Yb:YAG crystal waveguide inscribed by direct femtosecond laser writing

Abstract

We report on the dual-line waveguides in Ho,Yb:YAG crystal inscribed by femtosecond laser writing. The efficient single-mode guidance is demonstrated in the type II waveguide structures at 632.8 nm. The confocal micro-Raman spectroscopy is utilized to characterize both the lattice-damaged tracks and strain-affected regions. Contributions of the refractive index changes from the two main lattice changes are further discussed in combination with beam propagation calculations. The micro-luminescence has been studied, demonstrating that the fluorescence of Ho3+ and Yb3+ ions is well preserved in Ho,Yb:YAG waveguide.