Laser Printing of Chiral Silicon Nanoprotrusions by Asymmetric Donut-Shaped Femtosecond Pulses

Here, we showed formation of chiral nanoprotrusions upon direct laser ablation of bulk crystalline silicon (c-Si) wafer with single femtosecond (fs) pulses having asymmetric donut-shaped intensity profile. Breaking circular symmetry of the irradiating donut-shaped fs-pulse beam was demonstrated to switch the geometry of formed surface nanoprotrusions from regular to chiral, while the chirality of the obtained Si nanostructures was found to promote with a degree of asymmetry of the laser beam. The obtained experimental results explain, for the first time, the formation of previously reported chiral c-Si nanostructures produced via donut-shaped beam ablation in terms of uneven helical flow of laser-melted Si material caused by asymmetry of initial intensity and temperature pattern on laser-irradiated Si surface. Our findings open a pathway towards easy-to-implement inexpensive fabrication of chiral all-dielectric nanostructures for advanced nanophotonic applications.

First indications for reduced mortality of non-target invertebrate benthic megafauna after pulse beam trawling

Two alternative stimulation techniques to reduce mortality in benthic megafauna were tested relative to standard tickler chain beam trawling: longitudinal electrodes (pulse trawl) and longitudinal chains. Longitudinal chains caused higher mortality than pulse trawling in 3 species. Standard trawling gave higher mortality in Echinocardium cordatum than pulse trawling. Between longitudinal chain and standard trawling were no significant differences. This trend in decreasing mortality from longitudinal, to standard and then pulse trawling was confirmed by a similar decline in: i) numbers of significant species mortalities per trawl type, ii) average mortalities, i.e. longitudinal chain caused 41% more mortality than standard trawling and pulse trawling 43% less, iii) pre- and post-trawling community dissimilarities. A significant majority of species showed higher mortalities after longitudinal than after standard trawling and, conversely, lower mortalities after pulse trawling. Trawls with longitudinal chains instead of cross tickler chains increase megafaunal impact. On the contrary, pulse trawling can reduce the impact, although average mortality remains substantial (25%) even in impoverished benthic test assemblages in the southern North Sea. Power, generally was low and reference areas, free of (pulse) trawling, and inhabited by more vulnerable taxa will facilitate higher powered studies on the impact of standard and alternative trawling techniques.