  Advanced three-dimensional manufacturing techniques are triggering new
paradigms in the way we design and produce sophisticated parts on demand. Yet,
to fully unravel its potential, a few limitations have to be overcome, one of
them being the realization of high-aspect-ratio structures of arbitrary shapes
at sufficiently high resolution and scalability. Among the most promising
advanced manufacturing methods that emerged recently is the use of optical
non-linear absorption effects, and in particular, its implementation in 3D
printing of glass based on femtosecond laser exposure combined with chemical
etching. Here, we optimize both laser and chemical processes to achieve
unprecedented aspect ratio levels. We further show how the formation of
pre-cursor laser-induced defects in the glass matrix plays a key role in
etching selectivity. In particular, we demonstrate that there is an optimal
energy dose, an order of magnitude smaller than the currently used ones,
yielding to higher process efficiency and lower processing time. This research,
in addition to a conspicuous technological advancement, unravels key mechanisms
in laser-matter interactions essential in chemically-based glass manufacturing
and offers an environmentally-friendly pathway through the use of
less-dangerous etchants, replacing the commonly used hydrofluoric acid.
