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<jats:p>A novel Er:YAG laser system operating at 1645 nm with high pulse-repetition-frequency (PRF) of kHz level is demonstrated. A ring cavity with double gain medium end-pumped by two fiber lasers is utilized to obtain high pulse energy. A novel ‘triple-reflection’ configuration on a piezoelectric actuator (PZT) is adopted to achieve high-repetition-rate at 3-kHz operation with the ramp-fire locking method. Single frequency pulses with maximum average power of 18.3 W at 3 kHz are obtained, and the pulse duration time is 318 ns. The full line width at half maximum (FWHM) of the pulses measured by the heterodyne technique is 1.71 MHz at 3 kHz. To the best of our knowledge, this is the highest PRF single-frequency laser pulses achieved based Er:YAG gain medium.</jats:p>

<jats:p>Ray tracing method is used to study the propagation of collimated beams in a liquid–core cylindrical lens (LCL), which has dual functions of diffusion cell and image formation. The diffusion images on the focal plane of the used LCL are simulated by establishing and solving both linear and nonlinear ray equations, the calculated results indicate that the complex imaging results of LCL in inhomogeneous media can be treated by the law of ray propagation in homogeneous media under the condition of small refractive index gradient of diffusion solution. Guided by the calculation conditions, the diffusion process of triethylene glycol aqueous solution is experimentally studied at room temperature by using the LCL in this paper. The spatial and temporal concentration profile <jats:italic>C</jats:italic> <jats:sup>e</jats:sup>(<jats:italic>z</jats:italic>, <jats:italic>t</jats:italic>) of diffusion solution is obtained by analyzing diffusion image appearing on the focal plane of the LCL; Then, the concentration-dependent diffusion coefficient is assumed to be a polynomial <jats:italic>D</jats:italic>(<jats:italic>C</jats:italic>) = <jats:italic>D</jats:italic> <jats:sub>0</jats:sub> × (1 + <jats:italic>α</jats:italic> <jats:sub>1</jats:sub> <jats:italic>C</jats:italic> + <jats:italic>α</jats:italic> <jats:sub>2</jats:sub> <jats:italic>C</jats:italic> <jats:sup>2</jats:sup> + <jats:italic>α</jats:italic> <jats:sub>3</jats:sub> <jats:italic>C</jats:italic> <jats:sup>3</jats:sup> + ⋅). The finite difference method is used to solve the Fick diffusion equation for calculating numerically the concentration profiles <jats:italic>C<jats:sup>n</jats:sup> </jats:italic>(<jats:italic>z</jats:italic>, <jats:italic>t</jats:italic>). The <jats:italic>D</jats:italic>(<jats:italic>C</jats:italic>)of triethylene glycol aqueous solution is obtained by comparing the <jats:italic>C<jats:sup>n</jats:sup> </jats:italic>(<jats:italic>z</jats:italic>, <jats:italic>t</jats:italic>) with <jats:italic>C</jats:italic> <jats:sup>e</jats:sup>(<jats:italic>z</jats:italic>,<jats:italic>t</jats:italic>). Finally, the obtained polynomial <jats:italic>D</jats:italic>(<jats:italic>C</jats:italic>) is used to calculate the refractive index profiles <jats:italic>n<jats:sup>n</jats:sup> </jats:italic>(<jats:italic>z</jats:italic>,<jats:italic>t</jats:italic>)s of diffusion solution in the used LCL. Based on the ray propagation law in inhomogeneous media and the calculated <jats:italic>n</jats:italic>(<jats:italic>z</jats:italic>,<jats:italic>t</jats:italic>), the ray tracing method is used again to simulate the dynamic images of the whole experimental diffusion process to varify the correctness of the calculated <jats:italic>D</jats:italic>(<jats:italic>C</jats:italic>). The method presented in this work opens up a new way for both measuring and verifying the concentration-dependent liquid diffusion coefficients.</jats:p>

<jats:p>Electro–optic modulator is a key component for on-chip optical signal processing. An electro–optic phase modulator based on multilayer graphene embedded in silicon nitride waveguide is demonstrated to fulfill low-power operation. Finite element method is adopted to investigate the interaction enhancement between the graphene flake and the optical mode. The impact of multilayer graphene on the performance of phase modulator is studied comprehensively. Simulation results show that the modulation efficiency improves with the increment of graphene layer number, as well as the modulation length. The 3-dB bandwidth of around 48 GHz is independent of graphene layer number and length. Compared to modulator with two- or four-layer graphene, the six-layer graphene/silicon nitride waveguide modulator can realize <jats:italic>π</jats:italic> phase shift at a low-power consumption of 14 fJ/bit when the modulation length is 240 μm.</jats:p>

<jats:p>An ultrafast and low-power slow light tuning mechanism based on plasmon-induced transparency (PIT) for two disk cavities aperture-coupled to a metal-dielectric-metal plasmonic waveguide system is investigated numerically and analytically. The optical Kerr effect is enhanced by the local electromagnetic field of surface plasmon polaritons, slow light, and graphene–Ag composite material structures with a large effective Kerr nonlinear coefficient. Through the dynamic adjustment of the frequency of the disk nanocavity, the group velocity is controlled between <jats:italic>c</jats:italic>/53.2 and <jats:italic>c</jats:italic>/15.1 with the pump light intensity increased from 0.41 MW/cm<jats:sup>2</jats:sup> to 2.05 MW/cm<jats:sup>2</jats:sup>. Alternatively, through the dynamic adjustment of the propagation phase of the plasmonic waveguide, the group velocity is controlled between <jats:italic>c</jats:italic>/2.8 and <jats:italic>c</jats:italic>/14.8 with the pump light intensity increased from 5.88 MW/cm<jats:sup>2</jats:sup> to 11.76 MW/cm<jats:sup>2</jats:sup>. The phase shift multiplication of the PIT effect is observed. Calculation results indicate that the entire structure is ultracompact and has a footprint of less than 0.8 μm<jats:sup>2</jats:sup>. An ultrafast responsive time in the order of 1 ps is reached due to the ultrafast carrier relaxation dynamics of graphene. All findings are comprehensively analyzed through finite-difference time-domain simulations and with a coupling-mode equation system. The results can serve as a reference for the design and fabrication of nanoscale integration photonic devices with low power consumption and ultrafast nonlinear responses.</jats:p>

<jats:p>Traffic interruption phenomena frequently occur with the number of vehicles increasing. To investigate the effect of the traffic interruption probability on traffic flow, a new optimal velocity model is constructed by considering the driver anticipation term in the interruption case for car-following theory. Furthermore, the effect of driver anticipation in the interruption case is investigated via linear stability analysis. Also, the MKdV equation is obtained concerning the effect of driver anticipation in the interruption case. Moreover, numerical simulation states that the driver anticipation term in the interruption case contributes to the stability of traffic flow.</jats:p>

<jats:p>Understanding the physical mechanism of structural stability and transition in various polytypes of layered transition metal dichalcogenides under the external stimulus is of crucial importance for their new applications. Here, we investigate the thickness-dependent structural properties of MoS<jats:sub>2</jats:sub> under the condition of hydrostatic pressure in terms of bond relaxation and thermodynamics considerations. For both types of MoS<jats:sub>2</jats:sub> structures, we find that the transition and metallization are significantly modulated by hydrostatic pressure and the number of layers. We establish a pressure-size phase diagram to address the transition mechanism. Our study not only provides insights into the thickness-dependent structural properties of MoS<jats:sub>2</jats:sub>, but also shows a theoretical guidance for the design and fabrication of MoS<jats:sub>2</jats:sub>-based devices.</jats:p>

<jats:p>The fascinating Dirac cone in honeycomb graphene, which underlies many unique electronic properties, has inspired the vast endeavors on pursuing new two-dimensional (2D) Dirac materials. Based on the density functional theory method, a 2D material Zn<jats:sub>3</jats:sub>Si<jats:sub>2</jats:sub> of honeycomb transition-metal silicide with intrinsic Dirac cones has been predicted. The Zn<jats:sub>3</jats:sub>Si<jats:sub>2</jats:sub> monolayer is dynamically and thermodynamically stable under ambient conditions. Importantly, the Zn<jats:sub>3</jats:sub>Si<jats:sub>2</jats:sub> monolayer is a room-temperature 2D Dirac material with a spin–orbit coupling energy gap of 1.2 meV, which has an intrinsic Dirac cone arising from the special hexagonal lattice structure. Hole doping leads to the spin polarization of the electron, which results in a Dirac half-metal feature with single-spin Dirac fermion. This novel stable 2D transition-metal-silicon-framework material holds promises for electronic device applications in spintronics.</jats:p>

<jats:p>A high crystalline quality of SiGe fin with an Si-rich composition area using the replacement fin processing is systematically demonstrated in this paper. The fin replacement process based on a standard FinFET process is developed. A width of less than 20-nm SiGe fin without obvious defect impact both in the direction across the fin and in the direction along the fin is verified by using the high angle annular dark field scanning transmission electron microscopy and the scanning moiré fringe imaging technique. Moreover, the SiGe composition is inhomogenous in the width of the fin. This is induced by the formation of {111} facets. Due to the atomic density of the {111} facets being higher, the epitaxial growth in the direction perpendicular to these facets is slower than in the direction perpendicular to {001}. The Ge incorporation is then higher on the {111} facets than on the {001} facets. So, an Si-rich area is observed in the central area and on the bottom of SiGe fin.</jats:p>