Surface improvement of implants is essential for achieving a fast osseo-integration. Technically, the creation of a precise pattern on a titanium alloy surface is challenging. Here, the femtosecond laser was chosen as an innovative technology for texturing with accuracy a nano-micro topography. By adjusting the laser parameters, three biomimetic textures were fabricated on the titanium surface: micropits with nano-ripples in the pits, micropits with nano-ripples around the pits, and a texture with only nano-ripples. Mesenchymal stem cells (MSCs, C3H10T1/2) grown on these surfaces displayed altered morphometric parameters, and modified their focal adhesions in term of number, size, and distribution depending on surface type. These results indicate that the MSCs perceived subtle differences in topography. Dynamic analyses of early cellular events showed a higher speed of spreading on all the textured surfaces as opposed to the polished titanium. Concerning commitment, all the laser-treated surfaces strongly inhibited the expression of adipogenic-related genes (PPARϒ2, C/EBPα) and up-regulated the expression of osteoblastic-related genes (RUNX2, osteocalcin). Interestingly, the combination of micropits to nano-ripples enhanced their osteogenic potential as seen by a twofold increase in osteocalcin mRNA. Alkaline phosphatase activity was increased on all the textured surfaces, and lipid production was down-regulated. The functionalization of metallic surfaces by this high-resolution process will help us understand the MSCs' interactions with substrates for the development of textured implants with predictable tissue integrative properties.

Ultrashort laser pulses can modify the inner structure of fused silica, generating refractive index changes varying from soft positive (type I) light guiding forms to negative (type II) values with void presence and anisotropic sub-wavelength modulation. We investigate electronic and structural material changes in the type I to type II transition via coherent and incoherent secondary light emission reflecting free carrier behavior and post-irradiation material relaxation in the index change patterns. Using phase contrast microscopy, photoluminescence, and Raman spectroscopy, we determine in a space-resolved manner defect formation, redistribution and spatial segregation, and glass network reorganization paths in conditions marking the changeover between type I and type II photoinscription regimes. We first show characteristic patterns of second harmonic generation in type I and type II traces, indicating the collective involvement of free carriers and polarization memory. Second, incoherent photoemission from resonantly and non-resonantly excited defect states reveals accumulation of non-bridging oxygen hole centers (NBOHCs) in positive index domains and oxygen deficiency centers (ODCs) with O2− ions segregation in void-like regions and in the nanostructured domains, reflecting the interaction strength. Complementary Raman investigations put into evidence signatures of the different environments where photo-chemical densification (bond rearrangements) and mechanical effects can be indicated. NBOHCs setting in before visible index changes serve as precursors for subsequent compaction build-up, indicating a scenario of cold, defect-assisted densification for the soft type I irradiation regime. Additionally, we observe hydrodynamic effects and severe bond-breaking in type II zones with indications of phase transition. These observations illuminate densification paths in fused silica in low power irradiation regimes, and equally in energetic ranges, characterized by the onset of thermo-mechanical effects.

Laser writing of longitudinal waveguides in bulk transparent materials degrades with the focusing depth due to wavefront distortions generated at the air-dielectric interface. Using adaptive spatial tailoring of ultrashort laser pulses, we show that spherical aberrations can be dynamically compensated in optical glasses, in synchronization with the writing procedure. Aberration-free structures can thus be induced at different depths, showing higher flexibility for 3D processing. This enables optimal writing of homogeneous longitudinal waveguides over more significant lengths. The corrective process becomes increasingly important when laser energy has to be transported without losses at arbitrary depths, with the purpose of triggering mechanisms of positive refractive index change.

The formation of periodic structures in ultrafast laser-irradiated surfaces implies dynamic coupling between the incoming light and the light-driven material. To capture the mutual influence and feedback between light and evolving surface topographies, we investigate numerically the evolution of metal surfaces irradiated by multiple femtosecond laser pulses of sub-, near-, and slightly above-threshold ablation fluence. The multiphysical model combines Maxwell equations and thermohydrodynamic approach based on electron-ion heat transfer and compressible Navier-Stokes equations and allows us to account for interpulse feedback on the resulting surface topographies. First pulses of the subthreshold energy lead to material swelling, nanocavitation few tens of nanometers below the surface, and, as a result, nanoroughness formation on the initially flat surface. Further pulses contribute to the development of periodic surface structures, enhanced absorption, and increased removal rate. Cavitation in the tips of ripples is found to play a crucial role in modification and regulation of surface topography for sub- and near-threshold ablation fluences. At higher laser pulse energy, thermal ablation is mostly involved in surface modification, and the ablation rate per power reaches its maximum at three to five times the ablation threshold fluence, resulting from the optimal heat penetration depth for laser ablation. The numerical results offer a better understanding of the surface topography modifications upon multipulse femtosecond laser irradiation.

Using coupled electromagnetic and hydrodynamic calculations, we elucidate theoretically the topographic transition from a random metallic surface to a periodic sub‐wavelength grating by ultrashort laser ablation. The origin of this transition lies in the successive selection of hybrid surface waves scattered by random nanoholes. Contrary to the common belief that surface plasmon polaritons play the dominant role in the process and define the grating periodicity, we show that both quasi‐cylindrical and surface plasmon waves are involved, whereas the diversity in the resulting spacings λ /2– λ ( λ is the laser wavelength) is the manifestation of a broad frequency overlap of these waves, controlled by their relative phase shifts with respect to the plasmonic counterparts. The topography evolution imposes the dominant contribution to the surface sub‐wavelength pattern by selecting the appropriate wave character from plasmonic modes to evanescent cylindrical waves. With the radiation dose, the grating periodicity exhibits a pronounced blue shift due to reinforced dipole–dipole coupling between the nanoholes and surface curvatures in the laser‐processed area. This allows the creation of regular patterns with tunable periodicity.