Femtosecond laser treatment of a glass surface was used to fabricate a multimodal roughness having regular surface ripples with a period of a few micrometers decorated by aggregates of nearly spherical nanoparticles. UV-ozone treatment followed by chemisorption of the appropriate functional fluorosilanes onto the textured surface makes it possible to fabricate a superhydrophobic coating with a specific surface resistance on the order of petaohms on a glass surface. The main advantage of the fabricated coating under severe operating conditions with abrasion loads is the significant durability of its electro-insulating properties. The longevity of the high surface resistivity, even on long-term contact with a water vapor-saturated atmosphere, is directly related to the peculiarities of the surface texture and ripple structure.
Ultrafast intense photoexcitation of a silicon surface is complementarily studied experimentally and theoretically, with its prompt optical dielectric function obtained by means of time resolved optical reflection microscopy and the underlying electron-hole plasma dynamics modeled numerically, using a quantum kinetic approach. The corresponding transient surface plasmon-polariton (SPP) dispersion curves of the photo excited material were simulated as a function of the electron-hole plasma density, using the derived optical dielectric function model, and directly mapped at several laser photon energies, measuring spatial periods of the corresponding SPP mediated surface relief nanogratings. The unusual spectral dynam ics of the surface plasmon resonance, initially increasing with the increase in the electron-hole plasma den sity but damped at high interband absorption losses induced by the high density electron-hole plasma through instantaneous bandgap renormalization, was envisioned through the multi color mapping.
Emission of erosive plasma has been observed during electric probe and optical emission spectral measure ments of plumes produced by single shot femtosecond laser ablation of optical quality surfaces of various materials-copper, titanium, and silicon-at laser fluences well below the corresponding thermal ablation thresholds, replacing presumably electron emission at lower fluences. The onset of erosive plasma correlates on the fluence scale with saturation of dependences of self reflectivity of the pumping femtosecond laser pulses, reflecting the "freezing" of electron dynamics (variation of electron density or temperature) during the pumping pulses, despite the monotonically increasing laser fluences.
Femtosecond laser modification of titanium surfaces was performed to produce microstructured hydrophilic and biocompatible surface layers. Biocompatible nano/microcoatings were prepared for the first time by dry femtosecond laser imprinting of hydroxylapatite nano/micropowder onto VT6 titanium surfaces. In these experiments HAP was first deposited onto the titanium surfaces and then softly imprinted by multiple femtosecond laser pulses into the laser-melted surface metal layer. The surface relief was modified at the nano-and microscales depending on the incident laser fluence and sample scanning speed. Wetting tests demonstrated that the wetting properties of the pristine Ti surface can be tuned through its laser modification in both the hydrophobic and hydrophilic directions.
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