Pulses Interacting collectively with glass for Optical Nonlinear Effects in Additive manufactuRing – PIONEAR

Glass offers several desirable properties, including chemical inertness, low thermal conductivity, high electrical resistivity, and optical transparency. These characteristics make it indispensable in medical, pharmaceutical, and chemical setups, as well as in everyday applications. However, glass is brittle, heat-sensitive, and difficult to handle. Femtosecond laser precision micromachining has emerged as a powerful tool for processing glass using commercially available sources at wavelengths near 800–1000 nm. Leveraging nonlinear absorption, these lasers enable highly localized surface and in-volume modifications such as marking, drilling, cutting, and transparent welding. Despite these advances, additive manufacturing of transparent glass remains an unsolved challenge, unlike metals and polymers, where 3D printing is well established.
Lasers, often continuous-wave (CW) sources, are well-suited for localized melting and solidification in metals due to their precise energy deposition. However, this approach is less effective for transparent materials like glass. In such media, CW lasers face significant challenges: minimal absorption leads to poor energy confinement, with most incident energy transmitted or scattered and only a small fraction heating the focal spot. Even slight variations in the absorption coefficient can severely disrupt the energy deposition, reducing control and repeatability. Attempts to address these issues using binding materials or long-wavelength lasers (i. e. CO2-lasers) often introduce defects such as yellowish discoloration, shrinkage, distortion, bubble inclusions, and cracks.
The PIONEAR project proposes a novel approach to glass additive manufacturing based on nonlinear absorption using ultrafast lasers operating in GHz-burst mode. Unlike standard femtosecond pulses, this method distributes the required energy across multiple lower-energy pulses within each burst. In this way, the individual pulses are safely below the ablation threshold, but with sufficient peak power to drive multi-photon absorption. Consequently, our method resembles ultrafast microscopy more than conventional ultrafast material processing. Crucially, the pulses within a burst interact collectively with the glass, as the gaps in the picosecond range between them ensure that transient material effects accumulate throughout the burst. By keeping the burst duration short, heat diffusion beyond the focal volume is minimized.
The PIONEAR project aims to demonstrate a proof-of-concept for additive glass manufacturing, advancing the technology from TRL 1 to 3. Our goal is to establish new fundamental insights into how bursts of closely spaced ultrafast pulses can heat – but not ablate – transparent dielectrics such as glass through nonlinear energy transfer. We will apply these insights to printing mesoscale objects, such as bioengineering scaffolds or optical components like bi- or multi-focal lenses, using glass beads.