Topological Fano-resonance with type-II and type-III corner states.

Topological corner states have been used to develop topologically robust Fano-resonant systems immune to structural perturbations while preserving the ultra-sensitive profiles under external factors. In this work, we have extended the possibility of obtaining Fano-resonant systems by introducing type-II and type-III corner states with a large modal surface to this class of resonance. Through photonic lattices with low symmetry, such as C2, it is easy to obtain type-II and type-III corner states due to the tailoring of long-range interactions. Subsequently, one can combine topological cavities of type-II and type-III corner modes with topological waveguides obtained from a first-order topological insulating phase. Our results may pave the way to generate devices suitable for creating non-classical light applicable in quantum computing and ultra-sensitive sensors employing large-area topological states.

Airflow detailed analysis through a face mask using the schlieren technique.

This work presents an exhaustive visualization of the airflow expulsed by a person while breathing, talking, exhaling, and blowing inside a closed room wearing a disposable face mask like those used in hospitals for patient protection and those who care for them. An optical schlieren experimental arrangement was used to obtain some of the relevant physical characteristics of the airflow, such as its refractive index gradient, the distribution of temperature, and the associated velocity field for all the tests developed. We tested three face masks, one of the surgical types and the others of the N95 series with denominations KN95 and 3MN95 (Aura TC-84A-8590). The results show appreciable differences between the masks evaluated; the surgical mask was the one that allowed the most abrupt output airflow through it in the field of view of the experimental setup. However, were also found some differences in the performance of the KN95 and 3MN95 masks. The KN95 face mask had the best performance since it expulsed to its surroundings the lowest airflow with different physical properties to the input airflow. The results obtained are relevant since it was possible to estimate the expulsed airflow velocity as a function of the distance for every face mask tested, which allows for understanding its filtering capacity by restricting the flow of potential pathogens from the mouth or nose of one person to another. Undoubtedly, the airflow behavior determination around a face mask can help to reduce the risk of spreading infectious airborne particles.

Double resonance between corner states in distinct higher-order topological phases.

Recent studies have shown that higher-order topologies in photonic systems lead to a robust enhancement of light-matter interactions. Moreover, higher-order topological phases have been extended to systems even without a band gap, as in Dirac semimetals. In this work, we propose a procedure to simultaneously generate two distinctive higher-order topological phases with corner states that allow a double resonant effect. This double resonance effect between the higher-order topological phases, was obtained from the design of a photonic structure with the ability to generate a higher-order topological (HOTI) insulator phase in the first bands and a higher-order Dirac half-metal phase (HODSM). Subsequently, using the corner states in both topological phases, we tuned the frequencies of both corner states such that they were separated in frequency by a second harmonic. This idea allowed us to obtain a double resonance effect with ultra-high overlap factors, and a considerable improvement in the nonlinear conversion efficiency. These results show the possibility of producing a second-harmonic generation with unprecedented conversion efficiencies in topological systems with simultaneous HOTI and HODSM phases. Furthermore, since the corner state in the HODSM phase presents an algebraic 1/rdecay, our topological system can be helpful in experiments about the generation of nonlinear Dirac-ligh-matter interactions.

Synthesis of gold decorated silica nanoparticles and their photothermal properties.

Silica-Gold Nanostructures (SGNs), composed of a silica core decorated by gold nanoparticles, have the photothermal capacity to transform near-infrared (NIR) wavelengths into heat. This work presents a simple, efficient, and replicable method of synthesis of SGNs and their characterization by: (1) transmission electron microscopy to obtain micrographs of the particles and their corresponding diameter distribution; (2) diffraction patterns showing the amorphous atomic arraignment of the silica and the crystalline atomic arrangement of the gold nanoparticles; (3) zeta potential confirming the stability of the SGNs in a colloidal solution; and (4) thermal images displaying the capacity of SGNs to convert NIR irradiation into heat and their respective increment in temperature. SGNs were synthesized over silica cores with diameters of 63, 83, and 132 nm and decorated with a partial gold shell. They were heated with a coherent light intensity of 340 mW/cm2 with a wavelength of 852 nm. This wavelength is within the range of the optical window of the human body; therefore, SGNs may be used for the photothermal ablation of tumors with no damage to the tissue. The heating of different dimensions of SGNs took 6-8 min of NIR radiation, and their cooling, once the laser was turned off, was in the order of 2-3 min. It was found that SGNs, with a core diameter of 132 nm, have a notable photothermal capacity. That enables them to increase the temperature of their surroundings by 4.4 ºC. This increment in temperature is sufficient to induce cellular necrosis, which makes SGNs a good option for photothermal treatments.