Controlled light scattering of a single nanoparticle by wavefront shaping

Controlling light scattering by nanoparticles is fundamentally important for the understanding and the control of light inside photonic nanostructures, as well as for nanoparticle scattering itself, including Mie scattering. Here, we theoretically and numerically investigate the possibility to manipulate nanoparticle scattering through wavefront shaping that was initially developed to control scattering of light through opaque random media that consist of large numbers of scattering nanoparticles. We find that even a single nanoparticle supports multiple strongly scattering eigenchannels, which opens the opportunity to manipulate scattering with wavefront shaping previously developed for multiple scattered light through opaque random media. We find that these scattering eigenchannels are related to different resonant leaky modes of the scatterer. Moreover, we investigate the spectral correlation of these highly scattering eigenchannels, and demonstrate the coexistence of short range and long range correlations. Our work proposes a new tool to control light-matter interactions with resonant modes via wavefront shaping and constitutes a step towards exploring novel spectral correlations in the scattering of light by nano scatterers, including Mie spheres.Comment: 8 pages, 2tables, 3 figure

3D spatially-resolved optical energy density enhanced by wavefront shaping

We study the three-dimensional (3D) spatially-resolved distribution of the energy density of light in a 3D scattering medium upon the excitation of open transmission channels. The open transmission channels are excited by spatially shaping the incident optical wavefronts. To probe the local energy density, we excite isolated fluorescent nanospheres distributed inside the medium. From the spatial fluorescent intensity pattern we obtain the position of each nanosphere, while the total fluorescent intensity gauges the energy density. Our 3D spatially-resolved measurements reveal that the local energy density versus depth (z) is enhanced up to 26X at the back surface of the medium, while it strongly depends on the transverse (x; y) position. We successfully interpret our results with a newly developed 3D model that considers the time-reversed diffusion starting from a point source at the back surface. Our results are relevant for white LEDs, random lasers, solar cells, and biomedical optics

Robust moir\'e flatbands within a broad band-offset

Photonic analogs of the moir\'e superlattices mediated by interlayer electromagnetic coupling are expected to give rise to rich phenomena such as nontrivial flatband topology. Here we propose and demonstrate a scheme to tune the flatbands in a bilayer moir\'e superlattice by employing the band-offset. The band-offset is changed by fixing the bands of one slab but shifting that of the other slab, which is realized by changing the thickness of latter slab. Our results show that the band-offset tuning not only makes a few flatbands emerge and disappear, but also leads to two sets of robustly formed flatbands. These robust flatbands form either at the AA-stack site or at the AB-stack site, enabling the construction of a tunable, high-quality, and doubly-resonant single-cell superlattice. Moreover, we develop a diagrammatic model to give an intuitive insight into the formation of the robust flatbands. Our work demonstrates a simple yet efficient way to design and control complex moir\'e flatbands, providing new opportunities to utilize photonic moir\'e superlattices for advanced light-matter interaction including lasing and nonlinear harmonic generation.Comment: 5 pages, 5 figure

Controllable nonlinear propagation of partially incoherent Airy beams

The self-accelerating beams such as the Airy beam show great potentials in many applications including optical manipulation, imaging and communication. However, their superior features during linear propagation could be easily corrupted by optical nonlinearity or spatial incoherence individually. Here we investigate how the interaction of spatial incoherence and nonlinear propagation affect the beam quality of Airy beam, and find that the two destroying factors can in fact balance each other. Our results show that the influence of coherence and nonlinearity on the propagation of PIABs can be formulated as two exponential functions that have factors of opposite signs. With appropriate spatial coherence length, the PIABs not only resist the corruption of beam profile caused by self-focusing nonlinearity, but also exhibits less anomalous diffraction caused by the self-defocusing nonlinearity. Our work provides deep insight into how to maintain the beam quality of self-accelerating Airy beams by exploiting the interaction between partially incoherence and optical nonlinearity. Our results may bring about new possibilities for optimizing partially incoherent structured field and developing related applications such as optical communication, incoherent imaging and optical manipulations.Comment: 11pages,6 figure

Caustic analysis of partially coherent self-accelerating beams: Investigating self-healing property

We employed caustic theory to analyze the propagation dynamics of partially coherent self-accelerating beams such as self-healing of partially coherent Airy beams. Our findings revealed that as the spatial coherence decreases, the self-healing ability of beams increases. This result have been demonstrated both in simulation and experiment. This is an innovative application of the caustic theory to the field of partially coherent structured beams, and provides a comprehensive understanding of self-healing property. Our results have significant implications for practical applications of partially coherent beams in fields such as optical communication, encryption, and imaging.Comment: 9 pages, 4 figure

Characterization of explosion propagation of coal dust deposited by gas explosion convolutions in closed pipelines

To explore the propagation characteristics of gas explosion-induced coal dust detonations in enclosed pipelines, a custom-developed experimental system was employed for gas explosions involving accumulated coal dust. Various aspects were focused such as explosion pressure, flame dynamics, and the interplay between pressure and flame in the context of different gas and coal dust concentrations. Additionally, Fluent Numerical simulation software was utilized for analyzing the dispersion behavior of coal dust. The results reveal that the peak explosion pressure inside the closed pipeline is the highest at a 10% gas concentration, surpassing the maximum pressures observed at 12% and 8% concentrations. At a gas concentration of 10% and coal dust mass concentration of 250 g/m3, the explosion pressure exhibits a unique pattern: initially increasing, then decreasing, and subsequently rising again in the gas phase, followed by a continuous ascent in the coal dust phase. As the coal dust concentration increases, this pattern remains evident, with a persistent upward trend in the coal dust section. Conversely, at 8% and 12% gas concentrations, the maximum explosion pressure consistently rises with increasing coal dust concentrations, but shows a declining trend at 10% gas concentration. Furthermore, the time taken for the flame front to traverse the pipeline is positively correlated with the distance traveled. The flame front reaches various checkpoints more rapidly at a 10% gas concentration than at 12% and 8%. The flame’s propagation speed first increases and then decreases over distance, reaching its fastest at 10% gas concentration. The explosion pressure-time curve during a gas explosion in a closed pipeline showcases two peak values. The initial peak is caused by the shock wave preceding the gas explosion. As the flame advances into the coal dust section, the pressure concurrently begins to rise, reaching its second peak as it synchronizes with the flame’s peak. Following the flame signal’s disappearance, the pressure gradually diminishes until the reaction ceases. In the enclosed pipeline, the precursor shock waves and reflected waves contribute to the dispersion of coal dust, forming a “vortex-like” dust cloud. This formation enhances the interaction between the coal dust and the deflagration wave. When the coal dust concentration is fixed, the degree of dispersion at 10% gas concentration is more effective than at 12% or 8%. Furthermore, at a constant gas concentration, the dispersion degree of coal dust decreases as its mass concentration increases