Characterization of channel waveguides in Pr:YLiF4 crystals fabricated by direct femtosecond laser writing

摘要

Single tracks and pairs of tracks are written in the volume of Pr-doped LiYF4-crystals using tightly focused femtosecond laser radiation (λ-1045 nm, τ_p = 400-500 fs,f = 0.1-1 MHz). Waveguiding between the tracks is demonstrated and optimized by varying the distance between the tracks and the laser writing conditions. The stress-induced guiding mechanism is explained based on TEM, interference microscopy, near-field and far-field measurements. It is shown that the single-crystalline material is getting poly-crystalline under femtosecond laser irradiation. By measuring the lifetime of the ~3P_1→~3H_5 transition and the emission spectrum at excitation with λ = 444 nm, no influence on these properties of the guided light is observed. This possibly enables the realization of a channel waveguide laser in the visible spectral range.