Regulating Morphology and Composition of Laser-Induced Periodic Structures on Titanium Films with Femtosecond Laser Wavelength and Ambient Environment

Highly Regular Laser-Induced Periodic Surface Structures on Titanium Thin Films for Photonics and Fiber Optics

Modern photonic devices demand low-cost, scalable methods for creating periodic patterns over diverse surfaces including nonplanar and tipped ones, the examples of which can be readily found in fiber optics. Laser-induced periodic surface structures (LIPSS) offer an attractive route for fabricating such patterns in a single-step straightforward procedure, where the temporal and spatial locality of the self-interference effects ensure robustness against variations of the laser processing parameters. In this work, we show the LIPSS-assisted oxidation of thin titanium films by near-IR femtosecond laser pulses as a promising technology for the production of regular gratings consisting of rutile ridges. The self-terminating nature of the oxidation process allows the predefinition of the grating relief by the initial thickness of the titanium film, rendering the fabrication process with reproducibility and stability to variations of the laser parameters. LIPSS were found to act as gratings providing a diffraction efficiency above 7%. Such gratings were recorded over sidewalls of the optical fibers as well as their endfaces, allowing free space light coupling into the guided mode at the incidence angles up to 65° exceeding fiber acceptance angles. Additionally, gratings recorded over the polished side of the D-shaped fiber were found to act as a Bragg grating manifesting itself through a narrow resonance (<1 nm) in the reflection spectrum of fiber-guided light and suggesting possible applications in sensing and light management. Finally, by exploiting the high regularity of the formed gratings, we also demonstrated resonant coupling of the incident to the surface plasmon waves on the silver-coated LIPSS. With the large resonance amplitude and the Q-factor as large as 150, LIPSS were justified as an easy-to-fabricate template for plasmonic grating production with high potential for plasmonic biosensing and nonlinear optics.

Effect of Femtosecond Laser-Irradiated Titanium Plates on Enhanced Antibacterial Activity and Preservation of Bacteriophage Stability

Titanium (Ti) is widely recognized for its exceptional properties and compatibility with medical applications. In our study, we successfully formed laser-induced periodic surface structures (LIPSS) on Ti plates with a periodicity of 520-740 nm and a height range of 150-250 nm. To investigate the morphology and chemical composition of these surfaces, we employed various techniques, including field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Additionally, we utilized a drop-shape analyzer to determine the wetting properties of the surfaces. To evaluate the antibacterial activity, we followed the ISO 22196:2011 standard, utilizing reference bacterial cultures of Gram-positive Staphylococcus aureus (ATCC 25923) and Gram-negative Escherichia coli (ATCC 25922). The results revealed enhanced antibacterial properties against Staphylococcus aureus by more than 99% and Escherichia coli by more than 80% in comparison with non-irradiated Ti. Furthermore, we conducted experiments using the Escherichia coli bacteriophage T4 (ATCC 11303-B4) and the bacterial host Escherichia coli (ATCC 11303) to investigate the impact of Ti plates on the stability of the bacteriophage. Overall, our findings highlight the potential of LIPSS on Ti plates for achieving enhanced antibacterial activity against common bacterial strains while maintaining the stability of bacteriophages.

Special Issue "Dynamics and Processes at Laser-Irradiated Surfaces-A Themed Issue in Honor of the 70th Birthday of Professor Jürgen Reif"

The Special Issue "Dynamics and Processes at Laser-irradiated Surfaces" is dedicated to the 70th birthday of Jürgen Reif, retired full professor, former Chair of Experimental Physics II of the Faculty of Physics of the Brandenburg University of Technology Cottbus-Senftenberg in Germany [...].