Ablation efficiency of gold at fs/ps laser treatment in water and air

A comparison of single-pulse laser ablation of gold target by pulses with a 0.3–10 ps duration and a wavelength of 515 nm in air and in water was performed. The radiation was focused on the sample surface through the objectives with numerical apertures NA = 0.65 and 0.25. The influence of the medium, pulse duration, and spot size on the crater morphology was studied. A significant difference in crater morphology was found for different lenses. The ablation efficiency was studied by measuring the profiles of single-shot pulse craters using scanning force microscopy. The contribution of filamentation to the ablation process is shown quantitatively.

GNS561 Exhibits Potent Antiviral Activity against SARS-CoV-2 through Autophagy Inhibition

Since December 2019, SARS-CoV-2 has spread quickly worldwide, leading to more than 280 million confirmed cases, including over 5,000,000 deaths. Interestingly, coronaviruses were found to subvert and hijack autophagic process to allow their viral replication. Autophagy-modulating compounds thus rapidly emerged as an attractive strategy to fight SARS-CoV-2 infection, including the well-known chloroquine (CQ). Here, we investigated the antiviral activity and associated mechanism of GNS561/Ezurpimtrostat, a small lysosomotropic molecule inhibitor of late-stage autophagy. Interestingly, GNS561 exhibited antiviral activity of 6–40 nM depending on the viral strain considered, currently positioning it as the most powerful molecule investigated in SARS-CoV-2 infection. We then showed that GNS561 was located in lysosome-associated-membrane-protein-2-positive (LAMP2-positive) lysosomes, together with SARS-CoV-2. Moreover, GNS561 increased LC3-II spot size and caused the accumulation of autophagic vacuoles and the presence of multilamellar bodies, suggesting that GNS561 disrupted the autophagy mechanism. To confirm our findings, we used the K18-hACE2 mouse model and highlighted that GNS561 treatment led to a decline in SARS-CoV-2 virions in the lungs associated with a disruption of the autophagy pathway. Overall, our study highlights GNS561 as a powerful drug in the treatment of SARS-CoV-2 infection and supports the hypothesis that autophagy blockers could be an alternative strategy for COVID-19.

Identification of the main mixing process in the synthesis of alloy nanoparticles by laser ablation of compacted micropowder mixtures

Alloy nanoparticles offer the possibility to tune functional properties of nanoscale structures. Prominent examples of tuned properties are the local surface plasmon resonance for sensing applications and adsorption energies for applications in catalysis. Laser synthesis of colloidal nanoparticles is well suited for generating alloy nanoparticles of desired compositions. Not only bulk alloys but also compacted mixtures of single-metal micropowders can serve as ablation targets. However, it is still unknown how mixing of the individual metals transfers from the micro- to the nanoscale. This work experimentally contributes to the elucidation of the mixing processes during the laser-based synthesis of alloy nanoparticles. Key parameters, such as the initial state of mixing in the ablation target, the laser pulse duration, the laser spot size, and the ablation time, are varied. Experiments are performed on a cobalt-iron alloy, relevant for application in oxidation catalysis, in ethanol. The extent of mixing in the targets after ablation and in individual nanoparticles are studied by energy-dispersive X-ray spectroscopy and by cyclic voltammetry at relevant conditions for the oxygen evolution reaction, as model reaction. The results point at the benefits of well pre-mixed ablation targets and longer laser pulse durations for the laser-based synthesis of alloy nanoparticles. Graphical abstract

A Geant4 tool for edge-illumination X-ray phase-contrast imaging

The PEPI project is developing a new experimental facility integrating a chromatic photon-counting detector within an edge-illumination (EI) phase-contrast setup. In this context, a novel Geant4-based simulation tool has been introduced with the aim of defining the optimal design of the experimental setup. The code includes a custom X-ray refraction process and allows simulating the whole EI system, comprising a polychromatic and extended source, absorbing masks, substrates, their movement during acquisition, and X-ray detection. In this paper, a realistic spectral detector model is introduced and its energy response validated against experimental data acquired with synchrotron radiation at energies between 26 and 50 keV. Moreover, refraction and transmission images of a plastic phantom are reconstructed from simulation data and successfully compared with theoretical predictions. Finally, an optimization study aiming at finding the effect of the X-ray focal spot size (i.e. spatial coherence) on image quality is presented; the results suggest that, in the considered configuration, the system can tolerate source sizes up to 30 μm, while, for a fixed exposure time, the best signal-to-noise ratio in refraction images is found for source sizes in the order of 10 to 15 μm.

Low-Frequency Content of THz Emission from Two-Color Femtosecond Filament

We experimentally investigate the low-frequency (below 1 THz) spectral content of broadband terahertz (THz) emission from two-color femtosecond filament formed by the 2.7-mJ, 40-fs, 800+400-nm pulse focused into air. For incoherent detection, we screened the Golay cell by the bandpass filters and measured the THz angular distributions at the selected frequencies ν=0.5, 1, 2 and 3 THz. The measured distributions of THz fluence were integrated over the forward hemisphere taking into account the transmittance of the filters, thus providing the estimation of spectral power at the frequencies studied. The spectral power decreases monotonically with the frequency increasing from 0.5 to 3 THz, thus showing that the maximum of THz spectrum is attained at ν≤0.5 THz. The THz waveform measured by electro-optical sampling (EOS) based on ZnTe crystal and transformed into the spectral domain shows that there exists the local maximum of the THz spectral power at ν≈1 THz. This disagrees with monotonic decrease of THz spectral power obtained from the filter-based measurements. We have introduced the correction to the spectral power reconstructed from EOS measurements. This correction takes into account different focal spot size for different THz frequencies contained in the broadband electromagnetic pulse. The corrected EOS spectral power is in semi-quantitative agreement with the one measured by a set of filters.

Hollow core negative curvature fiber based refractive index sensor design and investigation for tuberculosis monitoring

A myriad of pensile but pertinent issues found in the optical fiber sensors can be seeked resolution based on the antiresonant reflecting optical waveguide (ARROW) working principle. Due to its compact structure, the anti-resonance based sensor has several advantages such as high sensitivity response, low confinement loss, and high stability that make the sensor more effective for health monitoring. In this manuscript, an anti-resonance fiber sensor has been proposed for the detection of tuberculosis cells. An analytical structure has been explored to simulate the characteristics of the ARROW. For the suggested structure, the Finite Element Method (FEM) is used to conduct its numerical investigations. The proposed optical sensor working on the ARROW principle was implemented on the Comsol Multiphysics software. From the numerical analysis, it is noted that the designed sensor has reached around 99% sensitivity with negligible confinement loss and single modality due to the excellent light-guiding properties of the anti-resonance fiber. Besides, lots of optical parameters such as effective area, V-Parameter, spot-size along beam divergence have been calculated over the wide wavelength region. The achieved result indicates the various applications suitability of Antiresonant Hollow-Core Fiber (ARHCF) as a tuberculosis sensor.