First Demonstration of Type-A Femtosecond-Written Volume Bragg Gratings using a Gaussian-Bessel Laser Beam

In the past decades, Volume Bragg gratings (VBGs) have been extensively used in many applications. So far, they have been commonly inscribed in photo-thermo-refractive glasses using UV light [1]. Moreover, femtosecond (fs) direct laser writing (DLW) has been employed to obtain VBGs in other materials supported mainly by type-1 refractive-index modifications (An) [2]. Thanks to this approach, there is therefore an evergrowing interest for writing VBGs in new types of glasses capable of generating stronger refractive-index modifications like silver-containing phosphate glasses. These glasses have a distinct modification type referred to as Type A (A for Argentum), related to the spatial distribution of the generated silver clusters around the interaction voxel showing two positive Δn peaks for every laser pass [3], allowing to reach Δn values of up to 2*10-
²
[4].