New opportunities for industry in redefining the surface properties of materials with ultrashort laser pulses

Ultrashort lasers producing pulses with length from tens of femtoseconds to picoseconds are progressively becoming common tools in the R&D labs to tailor properties of engineered materials. In the recent past years, the nanotexturing and micromachining of surfaces operated with femtosecond laser treatments demonstrated unprecedented capacity of modifying the optical, mechanical, electronic properties of materials, including dielectrics and wide bandgap semiconductors, which are transparent to the laser wavelength in the infrared or visible. The significant advantage with respect to longer pulse lasers can be mainly resumed in the reduced heat-induced effects outside the interaction volume, in the incredibly high-power density which favors nonlinear multiphotonic effects, and in the capability to intrinsically nanotexture the surfaces of materials with a periodicity generally depending on the laser wavelength.

In simple terms, it means direct writing any material with higher spatial resolution, both in the surface and, if transparent, in the bulk, and capability to produce a regular grating on their surface. And surface morphology, especially when nanostructured, influences several physical properties. The main direct implications are the complete change of optical absorptance and reflectance of materials Clear examples are black silicon and even more black diamond, which have been demonstrated to be capable of absorbing almost 100% of the solar spectrum. It is particularly surprising that a natively transparent material such as diamond can absorb such a portion of visible radiation when treated with fs-laser systems.

The radical change of the laser-nanotextured material properties does not stop to the optical interaction, since also the photoelectronic properties can be consequently tailored. It opens up to the feasibility of developing enhanced-sensitivity optical detectors and efficient solar energy converters. But there is more. The use of ultrashort laser pulses can be a key enabling technology for the development of 3D-integrated quantum optoelectronic platforms for future quantum communications and sensing, especially in materials such as diamond, silicon carbide, and boron nitride which can host natively quantum defect centers.

Besides, the mechanical properties can be significantly improved: nanotextured surfaces can be super-hydrophobic, thus suitable for naval and aerospace applications, with the advantage of a higher solidity, since the texturing is obtained on a unique material and not by the integration of a specific layer on the substrate, which may imply a shorter lifetime due to the adhesion interface.

Until today, such applications have been pioneered in R&D labs, including the most strategic ones such as the nuclear fusion sparkle. However, fs-laser systems are now exiting from labs, such as in the case of multiphoton fluorescence microscopes for biological and medical applications thanks to higher contrast and ability to distinguish the different tissues. Not only, since our attention goes especially to materials processing. The present release of fiber-optics fs-laser systems represent reliable, stable, and cheap solutions for the use in industry. Our message directly addresses to industries focusing innovation and sustainability for the future hi-tech markets: manufacturing with the use of ultrashort pulse laser can give an ultimate strategic competitive advantage in the process and product innovation in terms of operational flexibility, resolution, reproducibility, and cost-effectiveness.