Laser-Induced Periodic Surface Structures (LIPSS) manufacturing is a convenient laser direct-writing technique for the fabrication of nanostructures with adaptable characteristics on the surface of virtually any material. In this paper, we study the influence of 1D laser wavefront curvature on nanoripples spatial regularity, by irradiating stainless steel with a line-focused ultrafast laser beam emitting 120 fs pulses at a wavelength of 800 nm and with 1 kHz repetition rate. We find high correlation between the spatial regularity of the fabricated nanostructures and the wavefront characteristics of the laser beam, with higher regularity being found with quasiplane-wave illumination. Our results provide insight regarding the control of LIPSS regularity, which is essential for industrial applications involving the LIPSS generation technique.

The control of the interaction between materials and biological tissues is a key factor to optimize the overall performance of implants and prostheses integrated into the body. With this objective in mind, biomimetic hierarchical one- and two-dimensional surface patterns textured at the micro and nano scales were fabricated on titanium alloys using femtosecond laser processing. The experimental results show that laser irradiation promotes surface oxidation together with a polarization-dependent nano-ripple formation. Human mesenchymal stem cells were subsequently cultured on different surface patterns aiming at determining their response to the underlying micro and nano structures. The ripple topography was demonstrated to induce a nonfouling behavior, which could be exploited in the fabrication of biomimetic hierarchical surface patterns to develop cell-trapping modules.

In this paper two kind of sensors based on WO3 sputtered by magnetron sputtering and annealed at 600 degrees C have been studied. The first kind was processed by two-dimensional direct laser interfering patterning (DLIP) and the second one without any additional treatment. Morphological and structural characterization have shown a hole structure in a periodic line-pattern for the DLIP-processed sensors and a flat surface for the only-annealed sensors, both with a tetragonal WO3 phase. TOF-SIMS analysis has revealed that the first WO3 layers are reduced for both samples, which could improve sensing performance. Promising response enhancement of DLIP-processed sensors has been observed for low concentrations of NO2 (from 0.5 ppm to 5 ppm) at 200 degrees C, lowering the limit of detection (LOD) to 10 ppb, half of the LOD of the only-annealed sensors (20 ppb). Cross sensitivity to CO and HCHO have been investigated and the sensing mechanisms discussed.

Highly migratory cancer cells often lead to metastasis and recurrence and are responsible for the high mortality rates in many cancers despite aggressive treatment. Recently, the migratory behavior of patient-derived glioblastoma multiforme cells on microtracks has shown potential in predicting the likelihood of recurrence, while at the same time, antimetastasis drugs have been developed which require simple yet relevant high-throughput screening systems. However, robust in vitro platforms which can reliably seed single cells and measure their migration while mimicking the physiological tumor microenvironment have not been demonstrated. In this study, we demonstrate a microfluidic device which hydrodynamically seeds single cancer cells onto stamped or femtosecond laser ablated polystyrene microtracks, promoting 1D migratory behavior due to the cells' tendency to follow topographical cues. Using time-lapse microscopy, we found that single U87 glioblastoma multiforme cells migrated more slowly on laser ablated microtracks compared to stamped microtracks of equal width and spacing (p < 0.05) and exhibited greater directional persistence on both 1D patterns compared to flat polystyrene (p < 0.05). Single-cell morphologies also differed significantly between flat and 1D patterns, with cells on 1D substrates exhibiting higher aspect ratios and less circularity (p < 0.05). This microfluidic platform could lead to automated quantification of single-cell migratory behavior due to the high predictability of hydrodynamic seeding and guided 1D migration, an important step to realizing the potential of microfluidic migration assays for drug screening and individualized medicine. Published under license by AIP Publishing.

Volume-phase gratings (VPGs) were fabricated in CdSxSe1-x quantum-dot-doped borosilicate glass at a low repetition rate (800 nm, 140 fs, 1 kHz). The VPGs were designed based on rigorous coupled wave analysis simulations. Results indicate that the inscribed thickness (L) is the key parameter to maximize the diffraction efficiency at order 1. Microscope images of the cross sections and diffraction efficiency measurements were taken in order to characterize the modification of the material at different laser-inscription parameters. A maximum VPG diffraction efficiency of 67% (at order 1) was achieved. Also, a refractive index change of Delta n = 2.25.10(-3) is estimated from these VPG diffraction efficiency measurements. The measurements regarding polarization-insensitive diffraction efficiency showed that the birefringence produced in the substrate is negligible. (C) 2019 Optical Society of America

Femtosecond laser-induced periodic structures (LIPSS) have been processed on ZnO thin film gas sensor devices for nitrogen dioxide (NO2) detection. From the morphology point of view, the nanostructures have been identified as high spatial frequency LIPSS (HSFL) with an average period of 145 nm. Through Raman analysis, a decrease of the typical wurtzite ZnO structure is shown, with a possible increase of defects such as Zn interstitials. The response under NO2 is enhanced if compared with the only-annealed ZnO thin film for concentrations as low as 1 ppm, reaching 1 ppb of detection limit (LOD) for the sensors with LIPSS. The Zn interstitials defects could be the source of the adsorbed NO2 species increasing the sensitivity. Reproducible results have been measured during 11 weeks in a row.

ZnO thin film sputtered on alumina substrate is processed by Direct Laser Interference Patterning (DLIP). The heat transfer equation has been simulated for interference patterns with a period of 730 nm and two different fluences (85 mJ/cm2 and 165 mJ/cm2). A thermal threshold of 900 K, where crystal modification occurs has been calculated, indicating a lateral and depth processing around 173 nm and 140 nm, respectively. The experimentally reproduced samples have been analyzed from the structural and composition point of view and compared to conventional thermal treatments at three different temperatures (600 ºC, 700 ºC and 800 ºC). Promising properties have been observed for the laser treated samples, such as low influence on the thin film/substrate interface, an improvement of the crystallographic structure, as well as a decrease of the oxygen content from O/Zn = 2.10 to 1.38 for the highest fluence, getting closer to the stoichiometry. The DLIP characteristics could be suitable for the replacement of annealing process in the case of substrates that cannot achieve high temperatures as most of flexible substrates.

We demonstrate a rapid, accurate, and convenient method for tailoring the optical properties of diamond surfaces by employing laser induced periodic surface structuring (LIPSSs). The characteristics of the fabricated photonic surfaces were adjusted by tuning the laser wavelength, number of impinging pulses, angle of incidence and polarization state. Using Finite Difference Time Domain (FDTD) modeling, the optical transmissivity and bandwidth was calculated for each fabricated LIPSSs morphology. The highest transmission of similar to 99.5% was obtained in the near-IR for LIPSSs structures with aspect ratios of the order of similar to 0.65. The present technique enabled us to identify the main laser parameters involved in the machining process, and to control it with a high degree of accuracy in terms of structure periodicity, morphology and aspect ratio. We also demonstrate and study the conditions for fabricating spatially coherent nanostructures over large areas maintaining a high degree of nanostructure repeatability and optical performance. While our experimental demonstrations have been mainly focused on diamond anti-reflection coatings and gratings, the technique can be easily extended to other materials and applications, such as integrated photonic devices, high power diamond optics, or the construction of photonic surfaces with tailored characteristics in general.

We demonstrate the formation of laser-induced periodic surface structures (LIPSS) in boron-doped diamond (BDD) by irradiation with femtosecond near-IR laser pulses. The results show that the obtained LIPSS are perpendicular to the laser polarization, and the ripple periodicity is on the order of half of the irradiation wavelength. The surface structures and their electrochemical properties were characterized using Raman micro-spectroscopy, in combination with scanning electron and atomic force microscopies. The textured BDD surface showed a dense and large surface area with no change in its structural characteristics. The effective surface area of the textured BDD electrode was approximately 50% larger than that of a planar substrate, while wetting tests showed that the irradiated area becomes highly hydrophilic. Our results indicate that LIPSS texturing of BDD is a straightforward and simple technique for enhancing the surface area and wettability properties of the BDD electrodes, which could enable higher current efficiency and lower energy consumption in the electrochemical oxidation of toxic organics. (C) 2017 Optical Society of America