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.