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Dynamic process of femtosecond laser-induced damage formation in dielectric thin films is reconstructed from a series of time-resolved images. ${\mathrm{Ta}}_2{\mathrm{O}}_5$ single-layer coatings of four different thicknesses have been investigated in transmission mode by means of time-resolved off-axis digital holography. Different processes overlapped in time were found to occur; namely, the Kerr effect, free-electron generation, ultrafast lattice heating, and shockwave generation. The trends in contribution of these effects are qualitatively reproduced by numerical models based on electron-rate equations and Drude theory, which take into account transient changes in the films and interference effects of the pump and probe pulses.

This study aimed to test the effectiveness of ethyl gallate (EG) against S. mutans biofilm formation on solid surfaces (polystyrene, glass) and acidogenicity, and to examine the effect on expression of related genes. The biofilm that is formed by S. mutans bacteria was evaluated using colorimetric assay and optical profilometry, while the pH of the biofilm growth medium was measured with microelectrode. The expression of genes encoding glucan binding protein B (gbpB), glucosyltranferases B, -C, -D (gtfB, -C, -D) and F-ATPase (atpD, atpF) was assessed using a quantitative reverse transcription-polymerase chain reaction (RT-qPCR). It was revealed that all of the EG concentrations significantly suppressed S. mutans biofilm build-up on polystyrene and glass surfaces, and inhibited acidogenicity, in a dose-dependent manner, compared to the activity of untreated bacteria (p < 0.05). The highest concentration of EG (3.53 mM) reduced biofilm formation on polystyrene and glass surfaces by 68% and more than 91%, respectively, and prevented a decrease in pH levels by 95%. The RT-qPCR data demonstrate that the biofilm-producing bacteria treated with EG underwent significant gene expression changes involving the gtfC (a 98.6 increase in fold change), gtfB gene (a 47.5 increase in fold change) and the gbpB gene (a 13.8 increase in fold change). However, for the other genes tested (gtfD, atpD and atpF), the EG treatments did not produce significant expression change compared to the control. EG produced significant gene expression change in three genes—gtfC, gtfB, and gbpB; it has the capacity to inhibit S. mutans biofilm formation on solid surfaces (polystyrene, glass), as well as acidogenicity. Therefore, EG might be used as an antibiofilm and/or anticaries agent for oral formulations in order to reduce the prevalence of dental caries.

Interaction dynamics of two copropagating femtosecond light filaments in sapphire crystal is studied by means of time-resolved off-axis digital holographic and shadowgraphic microscopy with 22 fs temporal and 1 μm spatial resolution. In particular, we demonstrate that filament interaction originates from instantaneous modification of the refractive index resulting from the Kerr effect. Fusion, splitting, and even suppression of the resulting plasma channels induced by interacting filaments was observed by varying time delay between the input pulses. Free electron channels were reconstructed in the form of the time-lapse movie with unprecedented spatial and temporal resolution.