Search

In this paper, an improved multicomponent lattice Boltzmann model is employed to investigate the impact of the gas properties, specifically the gas adiabatic index, on the thermodynamic effects of cavitation bubble collapse. The study focuses on analyzing the temperature evolution in the flow field and the resulting thermal effects on the surrounding wall. The accuracy of the developed model is verified through comparisons with analytical solutions of the Rayleigh-Plesset equation and the validation of the adiabatic law. Then, a thermodynamic model of cavitation bubble composed of two-mixed gases collapsing near a wall is established to explore the influence of the gas adiabatic index γ on the temperature behavior. Key findings include the observation that the γ affects the temperature of the first collapse significantly, while its influence on the second collapse is minimal. Additionally, the presence of low-temperature regions near the bubble surface during collapse impacts both bubble and wall temperatures. The study also demonstrates that the γ affects maximum and minimum wall temperatures. The results have implications for selecting specific non-condensable gas properties within cavitation bubbles for targeted cooling or heating purposes, including potential applications in electronic component cooling and environmental refrigeration.

A multi-wavelength pulse is generated using chemical vapor deposition method (CVD) to fabricate the topological crystalline insulator (TCI) Pb1-XSnXTe as a saturated absorber (SA). Compared with other SA materials, Pb1-XSnXTe have advantages of narrow bandgap and high optical absorption in the near-infrared region. The laser produced a stable four-wavelength lasing configuration characterized by a wavelength spacing of approximately 2 nm, with pulse duration, repetition rate, and signal-to-noise ratio (SNR) of 0.899 to 0.854 µs, 1.08 to 1.15 MHz, and 31.5 dB, respectively. The results indicate that the Pb1-XSnXTe-SA is suitable for pulsed generation in the near-infrared region and its potential in various fields, including super-resolution imaging, high-density optical storage, and three-dimensional laser lithography.

The magnetic nanomaterial Mn3Si2Te6 is a promising option for spin-dependent electronic and magneto-optoelectronic devices. However, its application in nonlinear optics remains fanciful. Here, we demonstrate a pulsed Er-doped fiber laser (EDFL) based on a novel quasi-2D Mn3Si2Te6 saturable absorber (SA) with low pump power at 1.5 μm. The high-quality Mn3Si2Te6 crystals were synthesized by the self-flux method, and the ultrathin Mn3Si2Te6 nanoflakes were prepared by a simple mechanical exfoliation procedure. To the best of our knowledge, this is the first time laser pulses have been generated using quasi-2D Mn3Si2Te6. A stable pulsed laser at 1562 nm with a low threshold pump power of 60 mW was produced by integrating the Mn3Si2Te6 SA into an EDFL cavity. The maximum power of the output pulse is 783 μW. The repetition rate can vary from 24.16 to 44.44 kHz, with corresponding pulse durations of 5.64 to 3.41 µs. Our results indicate that the quasi-2D Mn3Si2Te6 is a promising material for application in ultrafast photonics.

The internal temperature distribution and evolution in cavitation bubble can be investigated numerically by a thermal lattice Boltzmann method. The simulation results are consistent with the calculational results of the Rayleigh-Plesset equation and the temperature equation when the cavitation bubble collapses in an infinite liquid medium and satisfy Laplace’s law. In this work, a cavitation bubble collapsing near a solid wall is explored to investigate the characteristics and effects of the bubble temperature. The progress of the bubble temperature can be clearly captured from a two-dimensional temperature field. The results show that the bubble temperature can reach extremely high values during both its first and its second collapse. The change of the bubble temperature is highly related to the jet velocity and the liquid pressure. Furthermore, the effects on the bubble temperature of the offset parameters, the initial driving pressure and the initial bubble radius are also studied. The present findings are meaningful for the research of thermodynamics of cavitation.

Planar fractal microstructure is observed on the silver film treated by positive corona discharge for the first time. Due to the abundant positive ions driven by the electrical field of positive polarity, surface modification is mainly induced by the plasma oxidation effect, resulting in a large scale of dendritic pattern with self-similarity and hierarchy. In contrast, negative ions dominate the plasma-film interaction under negative corona discharge condition, leading to a different surface morphology without fractal characteristics. A growth model based on the modified diffusion-limited aggregation (DLA) theory is proposed to describe the formation of the dendritic fractal structure, whilst the physics behind is attributed to the electric field directed diffusion of the positive ions around the surface roughness. Numerical simulation verifies the high density of the hot spot in the dendritic pattern, which may enable potential applications in fractal photonic metamaterials.

It is well-established that waves are inhomogeneous in a lossy isotropic medium, and the validation of the classical Snell's law is still questionable for light refraction at the dissipative and dispersive interface. With high absorption, direct experimental investigation is rather difficult due to the extremely short penetration depth; i.e., the skin depth. In this paper, a simple and unified description of this issue is proposed, which can be applied to both materials with anomalous dispersion and in the Drude region. The gradient is found to be incident angle θi-dependent, and the direction of the group velocity may deviate significantly from the phase velocity due to the loss induced permittivity structure. The physics behind the negative refraction effect is explained, and a novel loss induced super-prism effect is also predicted. [ABSTRACT FROM AUTHOR]

It is widely accepted that an off-axis noncanonical vortex moves across the free-space diffracting Gaussian beam without rotation. But our analysis shows that the vortex swirls a while before it approaches infinite. By neglecting the divergence of the host beam, we focus on this rotation characteristics of the vortices in linear homogeneous media. For the symmetrical host beam, it is found that the vortex moves along an elliptical trajectory, while the topological charge and the angular momentum of the vortex core relative to the beam axis are conserved. For the asymmetrical host beam, the vortex trajectory is rather complicated, since the noncanonical parameter varies as the light propagates, resulting in topological charge inversion. But we find that the vortices are always confined in a rectangular area, and the rotation direction is determined by the topological charge. [ABSTRACT FROM AUTHOR]