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<jats:p>The characteristics of light propagation through turbulent plasma sheath surrounding the hypersonic aircraft have been studied. The turbulent flow fields around a hypersonic aircraft are given by using the Navier–Stokes (NS) equations and <jats:italic>k</jats:italic>–<jats:italic>ε</jats:italic> turbulence model. Based on the distribution of flow field, refractive index and density of the plasma sheath for a blunt cone are discussed with different flight velocities and altitudes. The refractive index is mainly influenced by the electrons in the turbulent plasma sheath. The influence of different velocities and altitudes on the features of light propagation in the turbulent plasma sheath is analyzed. The results show that as the flight speed increases or the flight altitude decreases, the refractive index fluctuation becomes larger. It is also found that the refractive index fluctuation varies with the incident wavelength. This study shows how the characteristics of an optical beam propagating through plasma sheath are affected by the incident wavelength, flight velocities, and altitudes.</jats:p>

<jats:p>We propose a scheme that can generate tunable double optomechanically induced transparency in a hybrid optomechanical cavity system. In this system, the mechanical resonator of the optomechanical cavity is coupled with an additional mechanical resonator and the additional mechanical resonator can be driven by a weak external coherently mechanical driving field. We show that both the intensity and the phase of the external mechanical driving field can control the propagation of the probe field, including changing the transmission spectrum from double windows to a single-window. Our study also provides an effective way to generate intensity-controllable, narrow-bandwidth transmission spectra, with the probe field modulated from excessive opacity to remarkable amplification.</jats:p>

<jats:p>A flexible broadband linear polarization converter is proposed based on the metasurface operating at microwave band. To achieve bandwidth extension property, long and short metallic arc wires, as well as the metallic disks placed over a ground plane, are combined into the polarizer, which can generate three neighboring resonances. Due to the combination of the first two resonances and the optimized size and thickness of the unit cell, the polarization converter can have a weak incident angle dependence. Both simulated and measured results confirm that the average polarization conversion ratio is over 85% from 11.3 GHz to 20.2 GHz within a broad range of incident angle from 0° to 45°. Moreover, the proposed polarization converter based on flexible substrates can be applied for conformal design. The simulation and experiment results demonstrate that our designed polarizer still keeps high polarization conversion efficiency, even when it adheres to convex cylindrical surfaces. The periodic metallic structure of the designed polarizer has great potential application values in the microwave, terahertz, and optic regimes.</jats:p>

<jats:p>We investigate the incoherent beams with two orthogonal polarizations in nonlocal nonlinear media, one of which is a fundamental Gaussian beam and the other is spiraling elliptic Hermite–Gaussian beam carrying the orbital angular momentum (OAM). Using the variational approach, we obtain the critical power and the critical OAM required for the vector spiraling elliptic Hermite–Gaussian solitons. In the strong nonlocality region, two components of the vector beam contribute to the nonlinear refractive index in a linear manner by the sum of their respective power. The nonlinear refractive index exhibits a circularly symmetrical profile in despite of the elliptic shapes for spiraling Hermite–Gaussian beams. We find that in the strong nonlocality region, the critical power and the rotational velocity are the same regardless of the relative ratio of the constituent powers. The nonlinear refractive index loses its circular symmetry in weak nonlocality region, and the nonlinear coupling effect is observed. Due to the radiation of the OAM, the damping of the rotation is predicted, and can be suppressed by decreasing the proportion of the spiraling elliptic component of the vector beam.</jats:p>

<jats:p>The memory effect is a type of auto correlation observed in linear systems, which is widely used to control scattered light through thin scattering layers. We show that there exists a strong correlation among the optimized phase distributions of adjacent focal points in focusing through scattering media. The numeric simulation and experiment indicate that within the memory effect, the phase difference between the two adjacent focal points shows an optical phase fringe pattern, and the closer the adjacent focal points are, the wider the fringe pattern will be, corresponding to the tilting of a plane wave phase added onto the acquired optical phase distribution at the focal point. This effect can be utilized for achieving optimal phase distributions of focal point scanning without optical phase evaluation via the experiment, which has great potential application in imaging through the scattering medium.</jats:p>

<jats:p>Plasmonic Bragg reflectors are essential components in plasmonic circuits. Here we propose a novel type of plasmonic Bragg reflector, which has very high reflectance for the right-side incidence and meanwhile has extremely large absorption for the left-side incidence. This device is composed of longitudinally asymmetric nanostructures in a metal–insulator–metal waveguide. In order to efficiently analyze, design, and optimize the reflection and transmission characteristics of the proposed device, we develop a semi-analytic coupled-mode model. Results show that the reflectance extinction ratio between plasmonic modes incident from the right-side and the left-side reaches 11 dB. We expect this device with such striking unidirectional reflection performance can be used as insulators in nanoplasmonic circuits.</jats:p>

<jats:p>We propose a method to directly measure phase-related noise characteristics of single-frequency lasers in the 728–980 nm band based on a 120° phase difference interferometer. Differential phase information of the laser under test is demodulated via the interferometer. Other parameters related to the phase noise characteristics such as linewidth at different observation time, phase/frequency noise, power spectrum density of phase/frequency fluctuation, and Allan deviation are further obtained. Frequency noise as low as 1 Hz<jats:sup>2</jats:sup>/Hz can be measured using our system. Then the phase-related noise characteristics of two commercial lasers frequently used in cold atomic clocks are studied systematically by the method. Furthermore, several influencing factors and their relative evolution laws are also revealed, such as the pump current and frequency-locking control parameters. This would help to optimize the laser performance, select laser sources, and evaluate the system performance for cold atomic physics applications.</jats:p>

<jats:p>To combine the technical functions and advantages of solid-core fiber Bragg gratings (FBGs) and hollow-core optical fibers (HCFs), the hollow and filled FBGs in nano-bore optical fibers (NBFs) with nano-bore in the GeO<jats:sub>2</jats:sub>-doped core are proposed. The fundamental mode field, effective mode index, and confinement loss of NBF with 50 nm–<jats:inline-formula> <jats:tex-math><?CDATA $7\,{\rm{\mu }}{\rm{m}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>7</mml:mn> <mml:mspace width="0.25em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_7_074210_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>-diameter hollow and filled nano-bore are numerically investigated by the finite element method. The reflected spectra of FBGs in NBFs are obtained by the transmission matrix method. The hollow FBGs in NBFs can be acheived with (∼5% power fraction in the bore and the (∼0.9 reflectivity when bore diameter is less than <jats:inline-formula> <jats:tex-math><?CDATA $3\,{\rm{\mu }}{\rm{m}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>3</mml:mn> <mml:mspace width="0.50em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_7_074210_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. The filled FBGs can be realized with (∼1% power fraction and 0.98 reflectivity with different fillings including o-xylene, trichloroethylene, and chloroform for 800-nm bore diameter. The feasibility of the index sensing by our proposed NBF FBG is also analyzed and discussed. The experimental fabrication of hollow and filled FBGs are discussed and can be achieved by current techniques. The aim of this work is to establish a principle prototype for investigating the HCFs and solid-core FBGs-based fiber-optic platforms, which are useful for applications such as the simultaneous chemical and physical sensing at the same position.</jats:p>

<jats:p>A method of combining Green’s function retrieval theory and ultrasonic array imaging using Lamb waves is presented to solve near filed defects in thin aluminum plates. The defects are close to the ultrasonic phased array and satisfy the near field calculation formula. Near field acoustic information of defects is obscured by the nonlinear effects of initial wave signal in a directly acquired response using the full matrix capture mode. A reconstructed full matrix of inter-element responses is produced from cross-correlation of directly received ultrasonic signals between sensor pairs. This new matrix eliminates the nonlinear interference and restores the near-field defect information. The topological imaging method that was developed in recent ultrasonic inspection is used for displaying the scatterers. The experiments are conducted on both thin aluminum plates containing two and four defects, respectively. The results show that these defects are clearly identified when using a reconstructed full matrix. The spatial resolution is equal to about one wavelength of the selectively excited mode and the identifiable defect is about one fifth of the wavelength. However, in a conventional directly captured image, the images of defects overlap together and cannot be distinguished. The proposed method reduces the background noise and allows for effective topological imaging of near field defects.</jats:p>

<jats:p>The self-diffusion problem of Brownian particles under the constraint of quasi-one-dimensional (q1D) channel has raised wide concern. The hydrodynamic interaction (HI) plays an important role in many practical problems and two-body interactions remain dominant under q1D constraint. We measure the diffusion coefficient of individual ellipsoid when two ellipsoidal particles are close to each other by video-microscopy measurement. Meanwhile, we obtain the numerical simulation results of diffusion coefficient using finite element software. We find that the self-diffusion coefficient of the ellipsoid decreases exponentially with the decrease of their mutual distance <jats:italic>X</jats:italic> when <jats:inline-formula> <jats:tex-math><?CDATA $X\lt {X}_{0}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>X</mml:mi> <mml:mo>&lt;</mml:mo> <mml:msub> <mml:mrow> <mml:mi>X</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_7_074701_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:italic>X</jats:italic> <jats:sub>0</jats:sub> is the maximum distance of the ellipsoids to maintain their mutual influence, <jats:italic>X</jats:italic> <jats:sub>0</jats:sub> and the variation rate are related to the aspect ratio <jats:italic>p</jats:italic>=<jats:italic>a</jats:italic>/<jats:italic>b</jats:italic>. The mean squared displacement (MSD) of the ellipsoids indicates that the self-diffusion appears as a crossover region, in which the diffusion coefficient increases as the time increases in the intermediate time regime, which is proven to be caused by the spatial variations affected by the hydrodynamic interactions. These findings indicate that hydrodynamic interaction can significantly affect the self-diffusion behavior of adjacent particles and has important implications to the research of microfluidic problems in blood vessels and bones, drug delivery, and lab-on-chip.</jats:p>