Femtosecond Inscription of Type-A Volume Bragg Gratings in Silver-Containing Phosphate Glasses

Volume Bragg gratings (VBGs) have gained growing interest over the last decades for diverse applications. Typically, they are produced in photo-thermo-refractive glasses using UV light [1]. Later, femtosecond (fs) laser pulses were used to produce refractive-index modifications $(\Delta \mathrm{n})$ , mainly type-l, in various other materials [2]. To obtain more freedom in designing optical systems, it is desirable to inscribe VBGs in glasses exhibiting a much higher $\Delta \mathrm{n}$ , such as silver-containing phosphate glasses. Indeed, a novel type of $\Delta \mathrm{n}$ has been demonstrated in such glasses, denominated Type-A (A from Argentum), which is related to the spatial distribution of the photo-induced silver clusters around the interaction voxel and exhibits two positive $\Delta \mathrm{n}$ peaks at each laser pass [3], reaching a value of up to $2\times 10^{-2}$ [4]. Recently, we demonstrated the first Type-A VBGs inscribed in silver-containing phosphate glasses with a Gaussian-Bessel beam. The most efficient grating was recorded in $\sim 1$ hour at a velocity of 20 $\mu \mathrm{m}/s$ for a transverse area of $400\times 400\ \mu \mathrm{m}^{2}$ . Indeed, there is a growing interest in writing high throughput VBGs suitable for industrial manufacturing.