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A semi-analytical model for deterministic surface smoothing of fused silica below the evaporation temperature threshold is presented. Using this model, a method for calculating deterministic track depths for laser polishing fused silica is derived and validated with experiments. Model predictions were in good agreement with experiment across varying laser preheating temperature and power. With the semi-analytical method presented here, deterministic laser smoothing can be achieved in the densification regime to close the process loop of laser polishing. [ABSTRACT FROM AUTHOR]

This study investigates the physical processes involved in picosecond pulse (20-28 ps FWHM) laser ablation of Al 6061, 316L stainless steel, and undoped crystalline Si (〈100〉) over a range of laser wavelength (355 nm and 1064 nm) and fluence (0.1-40 J/cm2). Experimental measurements of material ablation rate show enhanced removal at the 355 nm wavelength, primarily due to laser-plasma interaction (LPI) within the ablative plume that approaches an order of magnitude increase over the measured removal at 1064 nm. A transition in the ablation rate at 355 nm is identified around ∼10 J/cm2 above which the removal efficiency increases by a factor of two to three. Multi-physics radiation hydrodynamic simulations, considering LPI effects and utilizing a novel mixed-phase equation of state model, show that the transition in ablation efficiency is due to the onset of melt ejection through cavitation, where laser-driven shock heating sets the depth of melt penetration and the ensuing release wave from the ablation surface drives cavitation through the imposition of tensile strain within the melt. High-speed pump-probe imaging of the ejecta and ejecta collection studies, as well as scanning electron microscopy of the ablation craters, support the proposed cavitation mechanism in the higher fluence range. The ablation process is critically influenced by LPI effects and the thermophysical properties of the material. [ABSTRACT FROM AUTHOR]

For pulse lengths between 1 and 60 ps, laser-induced modifications of optical materials undergo a transition from mechanisms intrinsic to the materials to defect-dominated mechanisms. Elucidating the location, size, and identity of these defects will greatly help efforts to reduce, mitigate, or eliminate these defects. We recently detailed the role of defects in the ps laser-modifications of silica coatings. We now discuss the similar role of defects in HfO2 1/2-wave coatings and also include the environmental effects on the damage process. By switching between S and P polarizations, we distinguish the effects of defects at the surface from those throughout the material. We find that defects very near the surface are dependent on the environment, leading to worse damage in vacuum than in air. Air suppresses or lessens the effects of these defects, suggesting a photo-chemical component in the mechanism of laser damage in HfO2 coatings. [ABSTRACT FROM AUTHOR]

Single-crystalline vanadium dioxide nanowires (VO2 NWs) have attracted significant interest due to their unique characteristics, which originate from the single-domain metal–insulator phase transition (MIT) property. However, the lack of facile technologies to produce vertical nanowire arrays (NAs) in a large area has limited the mass fabrication of VO2-based devices. Here, an antimony-assisted hydrothermal method is developed for the low-temperature production of wafer-scale vertical VO2 NAs on arbitrary substrates of glass, quartz, and silicon. Sb2O3 plays a key role in the controlled growth of pure VO2 (M1) by modulating the size, density, alignment, and MIT properties of VO2 NAs. Furthermore, the growth mechanism of vertical VO2 NAs is explained. In contrast to conventional fabrication technologies, the weak interaction between NA films and substrates enables a much easier transfer of VO2 NAs for various potential applications. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2), with the first-order metal-insulator phase transition at near room temperature, has attracted increasing attention in the past few decades. With rapid electrical switching, the phase transition in VO2 also triggers the colossal property changes in various aspects, such as optical properties, magnetic properties, and strain, and, thus, enables a wide range of modern applications. In this review, we present a complete picture of the latest advances of VO2, including the fabrication strategies, property modulation, and advanced applications. This review summarizes several typical fabrication methods of VO2 crystals as well as some common problems and their possible solutions. The strategies for the fabrication of single-crystalline VO2 arrays are also discussed to meet the requirements of the high-performance devices at the macro-scale. This review concerns the typical approaches for the modulation of (metal-insulator transition) MIT and emphasizes on the domain study of VO2 single crystals at the nanoscale. We aim at a clear explanation of the effect of various inhomogeneities on the MIT behavior of VO2 and the importance of the accurate control of MIT at the domain level. After summarizing the preparation and modification of VO2, we focus on the applications of this amazing smart material in various aspects, including strain engineering, optical modulation, electrical switching, and multi-responsive sensing. [ABSTRACT FROM AUTHOR]

Using high-sensitivity confocal time-resolved photoluminescence (PL) techniques, we report an ultrafast PL (40 ps–5 ns) from impurity-free surface flaws on fused silica, including polished, indented, or fractured surfaces of fused silica, and from laser-heated evaporation pits. This PL is excited by the single-photon absorption of sub-band gap light, and is especially bright in fractures. Regions which exhibit this PL are strongly absorptive well below the band gap, as evidenced by a propensity to damage with 3.5 eV nanosecond-scale laser pulses. [ABSTRACT FROM AUTHOR]