Simple Defocus Laser Irradiation to Suppress Self-Absorption in Laser-Induced Breakdown Spectroscopy (LIBS)

This study introduces a novel and extremely simple way for suppressing the self-absorption effect in laser-induced breakdown spectroscopy (LIBS) by utilizing a defocusing laser irradiation technique. It is claimed that defocusing laser irradiation produces more uniform laser plasma due to lower fluence than tight focus laser irradiation, hence greatly lowering the effect of self-absorption in the laser plasma. KCl and NaCl pellet samples were used to demonstrate this achievement. When the defocus position is adjusted to – 6 mm for KCl and NaCl samples, the self-reversal emission lines K I 766.4 nm, K I 769.9 nm, Na I 588.9 nm, and Na I 589.5 nm vanish. Meanwhile, the FWHM values of K I 766.4 and K I 769.9 nm are 0.29 nm and 0.23 nm, respectively, during -6 mm defocus laser irradiation, as opposed to 1.24 nm and 0.86 nm, under tight focus laser irradiation. Additionally, this work demonstrates that when the laser energy is changed in between 10 to 50 mJ, no self-reversal emission occurs when -6 mm defocus laser irradiation is applied. Finally, a linear calibration curve is generated using KCl at a high concentration ranging between K concentration from 16.6–29%. This simple change of defocus laser irradiation will undoubtedly contribute to the suppression of the self-absorption phenomenon, which disrupts LIBS analytical results.

A minimal subwavelength focal spot for the energy flux

It is shown theoretically and numerically that circularly and linearly polarized incident beams produce at the tight focus identical circularly symmetric distributions of an on-axis energy flux. It is also shown that the on-axis energy fluxes from radially and azimuthally polarized optical vortices with unit topological charge are equal to each other. An optical vortex with azimuthal polarization is found to generate the minimum focal spot measured for the intensity (all other parameters being equal). Slightly larger (by a fraction of a percent) is the spot size calculated for the energy flux for the circularly and linearly polarized light. The spot size in terms of intensity is of importance in light-matter interaction, whereas the spot size in terms of energy flux affects the resolution in optical microscopy.

Transverse intensity at the tight focus of a second-order cylindrical vector beam

In this paper, an effect of a reverse energy flow at the focus of a second-order cylindrical vector beam which passed through amplitude zone plate was investigated with a scanning near-field optical microscope. A comparison of the intensity distribution detected with a pyramidal metallized cantilever with a hole and the characteristics of the light field calculated using a FDTD method and the Richards-Wolf formulas suggests that the cantilever is sensitive to the transverse intensity component rather than the total intensity or the components of the Poynting vector in the backflow region.

The Trilobite’s Eye

The eye of the trilobite has a lens not made of modified chitin or any of the usual optical materials, but of birefringent calcite. Although the trilobite was one of the most common of sea arthropods in the Cambrian period, it became completely extinct at the end of the Permian period, before the advent of the dinosurs. Very few creatures today have calcite lenses. Certainly one of the features that makes a calcite lens undesirable is that it is a birefringent crystal, and the refractive index varies considerably with direction and polarization. This make it difficult to bring light to a tight focus. Yet the trilobites persisted for twice as long as the dinosaurs did. How can an eye using a calcite lens possibly work?

What happens next?

While the new ELGs for reading have a tight focus on specific skills, it is absolutely vital to create a reading-rich environment which spurs children's curiosity, motivation and enjoyment.

Western Assumptions in Non-Western Public Diplomacies: Individualism and Estrangement

Summary Recently, there has been a drive to rebalance public diplomacy scholarship from its predominantly Western origins. However, even as we diversify to non-Western studies, buried assumptions laid in public diplomacy’s foundation may still continue to restrict our view of public diplomacy as a global practice. This Forum essay critically examines two of those assumptions. First, ‘individualism’ — as an ideal of separate, bounded entities — fosters a tight focus on individual actors and action, while often overlooking relational and contextual dynamics. Second, ‘estrangement’ normalises the idea of separation and alienation, a proposition not shared by other traditions that recognise diversity but presupposes inter-connectedness and commonality. From relational and holistic perspectives, mediating diversity is not the same as ‘mediating estrangement’. The goal of exposing assumptions is to recognise their limitations and create space for more relational and holistic perspectives to expand our vision from West/non-West to a range of global public diplomacies.