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<jats:p> <jats:italic>We report 10 Gb/s data transmissions using a packaged two-section InGaAsP/InP distributed Bragg reflector (DBR) laser. The tunable DBR laser has a wavelength tuning range of 12.12 nm. The DBR laser has greater than 10.84 GHz 3-dB direct modulation bandwidth within the wavelength tuning range. The 10 Gb/s data transmissions are performed at up to a distance of 30-km</jats:italic>.</jats:p>

<jats:p> <jats:italic>We demonstrate a multi-branch all polarization-maintaining Er:fiber frequency comb with five application ports for precise measurement of atomic/molecular transition frequencies in the near-infrared region. A fully stabilized Er:fiber frequency comb with a nonlinear amplifying loop mirror is achieved. The in-loop relative instability of stabilized carrier-envelope-offset frequency is 5.6 × 10<jats:sup>−18</jats:sup> at 1 s integration time, while that of the repetition rate is well below 1.8 × 10<jats:sup>−12</jats:sup> limited by the measurement noise floor of the commercial frequency counter. Five application ports are individually optimized for applications with different wavelengths (1064 nm, 1083 nm, 1380 nm, 1637 nm and 1750 nm). The beat note between the optical frequency comb and continuous laser exhibits the signal-to-noise ratio of at least 30 dB at a resolution bandwidth of 100 kHz. The in-loop frequency instability of the comb is evaluated to be good enough for measurement of rotation-resolved transitions of molecules below 1 kHz resolution</jats:italic>.</jats:p>

<jats:p> <jats:italic>We report a continuous-wave end-pumped Nd:YVO<jats:sub>4</jats:sub> zigzag slab laser with multilayer amplified spontaneous emission (ASE) absorbing coatings. The coatings are deposited on the slab faces. A five-layer structure consists of SiO<jats:sub>2</jats:sub>-Ti-SiO<jats:sub>2</jats:sub>-Ti-Au, and the thicknesses are 2520 nm, 10 nm, 160 nm, 24 nm and 200 nm, respectively. The designed coatings show good performance for the ASE control in the experimental tests. A stable-unstable hybrid laser oscillator along orthogonal directions in the slab aperture is further configured, achieving the 117W output at a pump of 328 W. The beam quality factors M<jats:sup>2</jats:sup> in the unstable direction and stable direction are 1.57 and 1.66, respectively</jats:italic>.</jats:p>

<jats:p> <jats:italic>We propose a switchable THz metamaterial that can be switched between two functions of half-wave plate and quarter-wave plate. The two switchable functions can be simply achieved by inserting a VO<jats:sub>2</jats:sub> film in the metamaterial design. Finite-difference time-domain (FDTD) simulation results show that the proposed metamaterial can convert <jats:italic>x</jats:italic>-polarized incident wave to <jats:italic>y</jats:italic>-polarized reflected wave when VO<jats:sub>2</jats:sub> is at metal phase, and convert <jats:italic>x</jats:italic>-polarized wave to circularly polarized wave when VO<jats:sub>2</jats:sub> is at insulator phase. The metamaterial performs well in the two functions, i.e., the same broad working frequency band and near perfect polarization conversion. The switching effect originates from the switchable Fabry–Pérot cavity length induced by the phase change of VO<jats:sub>2</jats:sub>. We believe that our findings provide a reference in designing switchable metamaterials.</jats:italic> </jats:p>

<jats:p> <jats:italic>Without prior knowledge of medium parameters, a method is proposed to detect and locate a target in layered media. Experiments were carried out for liquid/liquid and solid/liquid layered media, and the location of a target in them was obtained using three methods combined, i.e., the least-square method, the method of finding minimum dispersal degree of target distribution, and the snapshot time reversal and reverse time migration mixed method. The medium parameters, i.e., the acoustic velocities of upper and lower media as well as the thickness of the upper medium, were inversed simultaneously. The results show that the position of target is consistent with its actual position. Thus, the detection and location of a target in layered media are achieved without prior knowledge of medium parameters, and it overcomes the difficulty that the common time reversal method only detects the target, but cannot locate it.</jats:italic> </jats:p>

<jats:p> <jats:italic>The terahertz (THz) temporal waveform and spectrum from a longitudinal electrically biased femtosecond filament is studied experimentally. The initial direction of the electron motion inside the unbiased filament plasma is deduced from the transformation of the THz temporal waveform with applied fields of opposite polarities. Furthermore, a spectrum shift to lower frequency of the THz spectrum is observed in the presence of a biased field. It agrees well with theoretical predictions.</jats:italic> </jats:p>

<jats:p> <jats:italic>Silane (SiH<jats:sub>4</jats:sub>) is a promising hydrogen-rich compound for pursing high temperature superconducting. Previous high pressure measurements of Raman, x-ray diffraction and theoretical studies on SiH<jats:sub>4</jats:sub> mainly focused on its polymorphic structures above 50 GPa, while the structure and the stability under lower pressure range are still unclear. Here we report an investigation of condensed SiH<jats:sub>4</jats:sub> by Brillouin scattering measurements at high temperature up to 407 K and high pressure up to 18 GPa. Brillouin scattering frequencies of fluid SiH<jats:sub>4</jats:sub> under compression are obtained under isothermal conditions of 300 K, 359 K and 407 K. The SiH<jats:sub>4</jats:sub> becomes unstable with increasing temperature and subsequently decomposes into silicon and H<jats:sub>2</jats:sub>. We find that compression at room temperature induces two velocity anomalies corresponding to a fluid-solid state transition and a phase IV to phase V transition, respectively. Brillouin scattering spectra has been a powerful tool to investigate the fruitful phases and structure transitions in the hydrogen-rich compound under extreme conditions.</jats:italic> </jats:p>

<jats:p> <jats:italic>Polycrystalline BAs<jats:sub>x</jats:sub> (x</jats:italic> = 0.80–<jats:italic>1.10) compounds with different boron-to-arsenic elemental molar ratios were synthesized by a high-pressure and high-temperature sintering method. Compared with other ambient-pressure synthesis methods, high pressure can significantly promote the reaction speed as well as the reaction yield. As the content of arsenic increases from x</jats:italic> = 0.91 <jats:italic>to 1.10, the thermal conductivity of BAs<jats:sub>x</jats:sub> gradually increases from 53 to 65 W⋅m</jats:italic> <jats:sup>−1</jats:sup>⋅<jats:italic>K</jats:italic> <jats:sup>−1</jats:sup>. <jats:italic>Furthermore, the temperature dependence of thermal conductivities of these samples reveals an Umklapp scattering due to the increasing phonon population. This work provides a highly efficient method for polycrystalline BAs synthesis.</jats:italic> </jats:p>

<jats:p> <jats:italic>Recently, natural van der Waals heterostructures of (MnBi<jats:sub>2</jats:sub>Te<jats:sub>4</jats:sub>)<jats:sub> <jats:italic>m</jats:italic> </jats:sub>(Bi<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub>)<jats:sub> <jats:italic>n</jats:italic> </jats:sub> have been theoretically predicted and experimentally shown to host tunable magnetic properties and topologically nontrivial surface states. We systematically investigate both the structural and electronic responses of MnBi<jats:sub>2</jats:sub>Te<jats:sub>4</jats:sub> and MnBi<jats:sub>4</jats:sub>Te<jats:sub>7</jats:sub> to external pressure. In addition to the suppression of antiferromagnetic order, MnBi<jats:sub>2</jats:sub>Te<jats:sub>4</jats:sub> is found to undergo a metal–semiconductor–metal transition upon compression. The resistivity of MnBi<jats:sub>4</jats:sub>Te<jats:sub>7</jats:sub> changes dramatically under high pressure and a non-monotonic evolution of <jats:italic>ρ</jats:italic> (<jats:italic>T</jats:italic>) is observed. The nontrivial topology is proved to persist before the structural phase transition observed in the high-pressure regime. We find that the bulk and surface states respond differently to pressure, which is consistent with the non-monotonic change of the resistivity. Interestingly, a pressure-induced amorphous state is observed in MnBi<jats:sub>2</jats:sub>Te<jats:sub>4</jats:sub>, while two high-pressure phase transitions are revealed in MnBi<jats:sub>4</jats:sub>Te<jats:sub>7</jats:sub>. Our combined theoretical and experimental research establishes MnBi<jats:sub>2</jats:sub>Te<jats:sub>4</jats:sub> and MnBi<jats:sub>4</jats:sub>Te<jats:sub>7</jats:sub> as highly tunable magnetic topological insulators, in which phase transitions and new ground states emerge upon compression.</jats:italic> </jats:p>

<jats:p> <jats:italic>Surface terminations of diamond play an important role in determining the electric properties of diamond-based electronic devices. We report an ultraviolet/ozone (UV/ozone) treatment process on hydrogen-terminated single crystal diamond (H-diamond) to modulate the carrier behavior related to varying oxygen adsorption on surfaces. By UV/ozone treatments, the induced oxygen radicals are chemically adsorbed on the H-terminated diamond and replace the original adsorbed H, which is analyzed by x-ray photoelectron spectroscopy. The concentration of oxygen adsorbed on surface increases from ∼3% to ∼8% with increasing the ozone treatment time from 20 s to 600 s. It is further confirmed by examining the wettability properties of the varying diamond surfaces, where the hydrophobic for H-termination transfers to hydrophilic for partly O-termination. Hall effect measurements show that the resistance (hole mobility) of the UV/ozone-treated H-diamond continuously increases (decrease) by two orders of magnitude with increasing UV/ozone treatment time from 20 s to 600 s. The results reveal that UV/ozone treatment becomes an efficient method to modulate the surface electrical properties of H-diamonds for further investigating the oxygenation effect on two-dimensional hole gas based diamond devices applied in some extreme environments.</jats:italic> </jats:p>