Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>High-power pulsed lasers provide an ingenious method for launching metal foils to generate high-speed flyers for high-pressure loading in material science or aerospace engineering. At high-temperature and high-pressure laser-induced conditions, the dynamic response of the metals and the mechanism of flyer formation remain unclear. In this study, the overall process of the laser-driven aluminum flyer, including laser ablation, rupture of metal foil, and the generation of the flyer was investigated by molecular dynamics combined with the two-temperature model. It was found that under high laser fluence (over 1.3 J/cm<jats:sup>2</jats:sup> with 200-fs laser pulse duration), the laser induced a shock wave with a peak pressure higher than 25 GPa, which led to shear bands expanding from the edge of the laser ablation zone in the foil. Compared with the cases of low laser fluence less than 0.5 J/cm<jats:sup>2</jats:sup>, the shear band induced by high laser fluence promotes the rupture of the foil and results in a high-speed flyer (&gt; 1 km/s) with better flatness and integrity. In addition, the shock wavefront was found to be accompanied by aluminum crystal phase transformation from face-centered cubic (FCC) to body-centered cubic structure. The crystal structure reverts with the decrease of pressure, therefore the internal structure of the generated flyer is pure of FCC. The results of this study provide a better understanding of the laser-induced shock effect on the foil rupture and flyer quality and forward the development of the laser-driven flyer.</jats:p>

<jats:p>We present an analytical model for cross-Kerr nonlinear coefficient in a four-level N-type atomic medium under Doppler broadening. The model is applied to <jats:sup>87</jats:sup>Rb atoms to analyze the dependence of the cross-Kerr nonlinear coefficient on the external light field and the temperature of atomic vapor. The analysis shows that in the absence of electromagnetically induced transparency (EIT) the cross-Kerr nonlinear coefficient is zero, but it is significantly enhanced when the EIT is established. It means that the cross-Kerr effect can be turned on/off when the external light field is on or off. Simultaneously, the amplitude and the sign of the cross-Kerr nonlinear coefficient are easily changed according to the intensity and frequency of the external light field. The amplitude of the cross-Kerr nonlinear coefficient remarkably decreases when the temperature of atomic medium increases. The analytical model can be convenient to fit experimental observations and applied to photonic devices.</jats:p>

<jats:p>An <jats:italic>N</jats:italic>-stage three-waveguide system is proposed to improve the robustness and the fidelity of the resonant tunneling passage. The analytic solutions to the tunneling dynamics at the output are derived. When the number of subsystems increases, tunneling efficiency approaches to 100% in a large range and resonant tunneling is robust against variations in the phase mismatch and peak tunneling rate.</jats:p>

<jats:p>A high sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber is proposed in this work. In order to achieve high sensitivity and high stability, the gold layer is coated on the side-polished photonic crystal fiber to support surface plasmon resonance. The mixture of ethanol and chloroform is used as the thermosensitive liquid. The performances of the proposed temperature sensor were investigated by the finite element method (FEM). Simulation results indicate that the sensitivity of the temperature sensor is as high as 7.82 nm/°C. It has good linearity (<jats:italic>R</jats:italic> <jats:sup>2</jats:sup> = 0.99803), the resolution of 1.1 × 10<jats:sup>−3</jats:sup> °C, and the amplitude sensitivity of 0.1008 °C<jats:sup>−1</jats:sup>. In addition, the sizes of the small air hole and polishing depth have little influence on the sensitivity. Therefore, the proposed sensor shows a high structure tolerance. The excellent performance and high structure tolerance of the sensor make it an appropriate choice for temperature measurement.</jats:p>

<jats:p>Superbunching pseudothermal light has important applications in studying the second- and higher-order interference of light in quantum optics. Unlike the photon statistics of thermal or pseudothermal light is well understood, the photon statistics of superbunching pseudothermal light has not been studied yet. In this paper, we will employ single-photon detectors to measure the photon statistics of superbunching pseudothermal light and calculate the degree of second-order coherence. It is found that the larger the value of the degree of second-order coherence of superbunching pseudothermal light is, the more the measured photon distribution deviates from the one of thermal or pseudothermal light in the tail part. The results are helpful to understand the physics of two-photon superbunching with classical light. It is suggested that superbunching pseudothermal light can be employed to generate non-Rayleigh temporal speckles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A dual-passband single-polarized converter based on the band-stop frequency selective surface (FSS) with a low radar cross-section (RCS) is designed in this article. The unit cell of the proposed converter is formed by a polarization layer attached to the band-stop frequency selective surface. The simulation results reveal that the co-polarization reflection coefficients below −10 dB are achieved in 3.82–13.64 GHz with a 112.4% fractional bandwidth (the ratio of the signal bandwidth to the central frequency). Meanwhile, a polarization conversion band is realized from 8.14 GHz to 9.27 GHz with a polarization conversion ratio which is over 80%. Moreover, the 1 dB transmission window is obtained in two non-adjacent bands of 3.42–7.02 GHz and 10.04–13.91 GHz corresponding to the relative bandwidths of 68.9% and 32.3%, respectively. Furthermore, the radar cross-section of the designed structure can be reduced in the wideband from 2.28 GHz to 14 GHz, and the 10 dB RCS reduction in the range of 4.10–13.35 GHz is achieved. In addition, the equivalent circuit model of this converter is established, and the simulation results of the Advanced Design System (ADS) match well with those of CST Microwave Studio (CST). The archetype of the designed converter is manufactured and measured. The experiment results match the simulation results well, which proves the reliability of the simulation results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Laser-induced plasmas of dual-pulse fiber-optic laser-induced breakdown spectroscopy with different pulse energy ratios are studied by using the optical emission spectroscopy (OES) and fast imaging. The energy of the two laser pulses is independently adjusted within 0–30 mJ with the total energy fixed at 30 mJ. The inter-pulse delay remains 450 ns constantly. As the energy share of the first pulse increases, a similar bimodal variation trend of line intensities is observed. The two peaks are obtained at the point where the first pulse is half or twice of the second one, and the maximum spectral enhancement is at the first peak. The bimodal variation trend is induced by the change in the dominated mechanism of dual-pulse excitation with the trough between the two peaks caused by the weak coupling between the two mechanisms. By increasing the first pulse energy, there is a transition from the ablation enhancement dominance near the first peak to the plasma reheating dominance near the second peak. The calculations of plasma temperature and electron number density are consistent with the bimodal trend, which have the values of 17024.47 K, 2.75×10<jats:sup>17</jats:sup> cm<jats:sup>−3</jats:sup> and 12215.93 K, 1.17 × 10<jats:sup>17</jats:sup> cm<jats:sup>−3</jats:sup> at a time delay of 550 ns. In addition, the difference between the two peaks decreases with time delay. With the increase in the first pulse energy share, the plasma morphology undergoes a transformation from hemispherical to shiny-dot and to oblate-cylinder structure during the second laser irradiation from the recorded images by using an intensified charge-coupled device (ICCD) camera. Correspondingly, the peak expansion distance of the plasma front first decreases significantly from 1.99 mm in the single-pulse case to 1.34 mm at 12/18 (dominated by ablation enhancement) and then increases slightly with increasing the plasma reheating effect. The variations in plasma dynamics verify that the change of pulse energy ratios leads to a transformation in the dual-pulse excitation mechanism.</jats:p>

<jats:p>A solvable model of lateral line of a fish based on a wave equation with additional boundary conditions on a set of isolated points is proposed. Within the framework of this model it is shown that the ratio of pressures on lateral lines on different fish flanks, as well as the cross section of sound scattering on both the lines, strongly depends on angles of incidence of incoming sound waves. The strong angular dependence of the pressure ratio seems to be sufficient for the fish to determine the directions from which the sound is coming.</jats:p>

<jats:p>This work investigates the active control of a fully developed turbulent boundary layer by a submerged synthetic jet actuator. The impacts of the control are explored by measuring the streamwise velocities using particle image velocimetry, and reduction of the skin-friction drag is observed in a certain range downstream of the orifice. The coherent structure is defined and extracted using a spatial two-point correlation function, and it is found that the synthetic jet can efficiently reduce the streamwise scale of the coherent structure. Proper orthogonal decomposition analysis reveals that large-scale turbulent kinetic energy is significantly attenuated with the introduction of a synthetic jet. The conditional averaging results show that the induction effect of the prograde vortex on the low-speed fluid in a large-scale fluctuation velocity field is deadened, thereby suppressing the bursting process near the wall.</jats:p>

<jats:p>We design a nanostructure composing of two nanoscale graphene sheets parallelly immersed in water. Using molecular dynamics simulations, we demonstrate that the wet/dry state between the graphene sheets can be self-latched; moreover, the wet→dry/dry→wet transition takes place when applying an external electric field perpendicular/parallel to the graphene sheets (<jats:italic>E</jats:italic> <jats:sub>⊥</jats:sub>/<jats:italic>E</jats:italic> <jats:sub>∥</jats:sub>). This structure works like a flash memory device (a non-volatile memory): the stored information (wet and dry states) of the system can be kept spontaneously, and can also be rewritten by external electric fields. On the one hand, when the distance between the two nanosheets is close to a certain distance, the free energy barriers for the transitions dry→wet and wet→dry can be quite large. As a result, the wet and dry states are self-latched. On the other hand, an <jats:italic>E</jats:italic> <jats:sub>⊥</jats:sub> and an <jats:italic>E</jats:italic> <jats:sub>∥</jats:sub> will respectively increase and decrease the free energy of the water located in-between the two nanosheets. Consequently, the wet→dry and dry→wet transitions are observed. Our results may be useful for designing novel information memory devices.</jats:p>