Broadband Optical Active Waveguides Written by Femtosecond Laser Pulses in Lithium Fluoride

Broadband waveguiding through light-emitting strips directly written in a blank lithium fluoride crystal with a femtosecond laser is reported. Light guiding was observed at several optical wavelengths, from blue, 458 nm, to near-infrared, at 1550 nm. Visible photoluminescence spectra of the optically active F₂ and F₃⁺ color centers produced by the fs laser writing process were measured. The wavelength-dependent refractive index increase was estimated to be in the order of 10^?3–10^?4 in the visible and near-infrared spectral intervals, which is consistent with the stable formation of point defects in LiF.