Catálogo de publicaciones - revistas

<jats:p> <jats:italic>High performance optical diode-like devices are highly desired in future practical nano-photonic devices with strong directional selectivity. We demonstrate a kind of giant broadband reciprocity optical diode-like devices by simultaneously using the directional Mie scattering effect and the asymmetric grating diffraction effect. The maximum asymmetric subtraction and the asymmetric transmission ratio can reach nearly 100% and 40 dB at specified wavelength, respectively. In a wide waveband from 500 nm to 800 nm, the asymmetric subtraction and the ratio keep larger than 80% and 3.5 dB, respectively, even under oblique incidence. To the best of our knowledge, this is the best one-way-transmission effect observed in the reciprocity optical diode-like devices. In addition, we further demonstrate that this one-way-transmission effect can bring an effective absorption enhancement on gold films. The giant, broadband and angle-insensitive one-way-transmission effect demonstrated here is far beyond the well-known anti-reflection effect in the light-trapping devices and will bring new design philosophy for nano-photonic devices.</jats:italic> </jats:p>

<jats:p> <jats:italic>We propose a theoretical model (cavityless pulsed solid-state-laser theory) to analyze the pulse characteristics of cavity-less solid-state lasers. A high gain Nd:YVO</jats:italic> <jats:sub>4</jats:sub> <jats:italic>end-pumped cavityless laser system is adopted to verify the theoretical model. It shows that the performance of output energy and pulse width achieved in cavityless configuration is better than that in resonator configuration when the small-signal gain reaches the saturated level. The simulation results calculated by our theoretical model agree very well with the experimental results. This agreement proves the validity of our theoretical model, which has great importance for theoretical analyses of high gain pulsed laser.</jats:italic> </jats:p>

<jats:p> <jats:italic>In traditional semiconductor lasers, it is usual to obtain single lateral mode operation by narrowing the ridge of waveguide, which is sensitive to fabrication inaccuracies. To overcome this shortcoming, a quasi-PT (parity-time) symmetric double ridge semiconductor laser is proposed to reach single lateral mode operation for an intrinsic multi-mode stripe laser. The coupled mode theory is used to analyze the non-Hermitian modulation of the gain (or loss) of the PT symmetric double ridge laser to obtain the coupling coefficient between the two ridge waveguides. Finally, the mode field distributions of the quasi-PT symmetric double ridge laser are simulated before and after the spontaneous PT symmetry breaking, which keep the laser operating in single lateral mode.</jats:italic> </jats:p>

<jats:p> <jats:italic>X-ray ghost imaging (XGI) has opened up a new avenue for damage-free medical imaging. Here energy-selective spectroscopic XGI under poor illumination is demonstrated with a single-pixel detector for the first time. The key device was a specially fabricated Au mask incorporating a new modulation pattern design, by which means images of a real object were obtained with a spatial resolution of 10 μm and a spectral energy resolution of about 1.5 keV. Compressed sensing was also introduced to improve the image quality. Our proof-of-principle experiment extends the methodology of XGI to make possible the retrieval of spectral images with only a single-pixel detector, and paves the way for potential applications in many fields such as biology, material science and environmental sensing.</jats:italic> </jats:p>

<jats:p> <jats:italic>Carbon nanotube@polypyrrole (CNT@PPy) hybrids have been successfully fabricated via a simple in situ chemical oxidation polymerization. The thickness of the PPy shell can be finely controlled in the range of 3.0–6.4 nm. The dielectric loss of core-shell hybrids can be tuned by the shell thickness, resulting in a well-matched characteristic impedance that can enhance electromagnetic wave (EMW) absorption performance. Minimum reflection loss of the hybrid with moderate PPy shell thickness can reach −51.4 dB at 11.8 GHz with a matching thickness of merely 2 mm. Furthermore, the minimum reflection loss values of the hybrid are below −30 dB even at thickness in the range of 1.4–1.9 mm, endowing the possibility of practical application of the hybrids in electromagnetic wave absorption field.</jats:italic> </jats:p>

<jats:p> <jats:italic>High β</jats:italic> <jats:sub>p</jats:sub> <jats:italic>scenario is foreseen to be a promising candidate operational mode for steady-state tokamak fusion reactors. Dedicated experiments on EAST and data analysis find that density gradient</jats:italic> ∇<jats:italic>n is a control knob to improve energy confinement in high β</jats:italic> <jats:sub>p</jats:sub> <jats:italic>plasmas at low toroidal rotation as projected for a fusion reactor. Different from previously known turbulent stabilization mechanisms such as <jats:bold>E</jats:bold> × <jats:bold>B</jats:bold> shear and Shafranov shift, high density gradient can enhance the Shafranov shift stabilizing effect significantly in high β</jats:italic> <jats:sub>p</jats:sub> <jats:italic>regime, giving that a higher density gradient is readily accessible in future fusion reactors with lower collisionality. This new finding is of great importance for the next-step fusion development because it may open a new path towards even higher energy confinement in the high β</jats:italic> <jats:sub>p</jats:sub> <jats:italic>scenario. It has been demonstrated in the recent EAST experiments, i.e., a fully non-inductive high β</jats:italic> <jats:sub>p</jats:sub> <jats:italic>(∼2) H-mode plasma (H</jats:italic> <jats:sub>98<jats:italic>y</jats:italic>2</jats:sub> ≥ 1.3<jats:italic>) has been obtained for a duration over 100 current diffusion times, which sets another new world record of long-pulse high-performance tokamak plasma operation with the normalized performance approaching the ITER and CFETR regimes.</jats:italic> </jats:p>

<jats:p> <jats:italic>We investigate the synergism effect of total ionizing dose (TID) on single-event burnout (SEB) for commercial enhancement-mode AlGaN/GaN high-electron mobility transistors. Our experimental results show that the slight degradation of devices caused by gamma rays can affect the stability of the devices during the impact of high energy particles. During heavy ion irradiation, the safe working values of drain voltage are significantly reduced for devices which have already been irradiated by</jats:italic> <jats:sup>60</jats:sup> <jats:italic>Co gamma rays before. This could be attributed to more charges trapped caused by</jats:italic> <jats:sup>60</jats:sup> <jats:italic>Co gamma rays, which make GaN devices more vulnerable to SEB. Moreover, the electrical parameters of GaN devices after</jats:italic> <jats:sup>60</jats:sup> <jats:italic>Co gamma and heavy-ion irradiations are presented, such as the output characteristic curve, effective threshold voltages, and leakage current of drain. These results demonstrate that the synergistic effect of TID on SEB for GaN power devices does in fact exist.</jats:italic> </jats:p>

<jats:p> <jats:italic>The effects of stretching and compressing on the thermal conductivity (TC) of silicon oxygen chain are studied by means of non-equilibrium molecular dynamics simulation. It is found that stretching can improve TC, and compressing may reduce the TC and can also increase the TC. This mechanism is explained based on the variation of phonon group velocity and the specific heat per volume with stretching and compressing. The distributions of bond angle and bond length under different normalized chain lengths are given. It is found that the bond length and bond angle in the skeleton chain would deviate from their original position. In addition, the phonon density of states (PDOSs) of silicon and oxygen atoms in the chains under different normalized chain lengths are analyzed. The overall trend is that the TC increases and the peaks of PDOSs move towards higher frequency with increasing stretch strain</jats:italic>.</jats:p>

<jats:p> <jats:italic>The contact angle and surface energy values of diamond are systemically investigated in terms of surface treatments (hydrogen- and oxygen-terminations), structure feature (single crystal diamonds and polycrystalline diamond films), crystal orientation ((100), (111) and mixed (100)/(111) orientations), different fluids (probes of polar deionized water and nonpolar di-iodomethane). It is found that the hydrophobic/hydrophilic characteristic and surface energy values of diamond are mainly determined by the surface hydrogen/oxygen termination, and less related to the structural features and crystal orientation. Based on the contact angle values with polar water and nonpolar di-iodomethane, the surface energies of diamond are estimated to be about 43 mJ/m<jats:sup>2</jats:sup> for hydrogen-termination and about 60 mJ/m<jats:sup>2</jats:sup> for oxygen-termination. Furthermore, the varying surface roughness of diamond and fluids with different polarities examined determine the variation of contact angles as well as the surface energy values. These results would be helpful for a more detailed understanding of the surface properties of diamond films for further applications in a broad number of fields, such as optical and microwave windows, biosensors, and optoelectronic devices, etc</jats:italic>.</jats:p>

<jats:p> <jats:italic>We propose a new CaN<jats:sub>4</jats:sub> high pressure structure with the <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic> space group. The <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic>-CaN<jats:sub>4</jats:sub> structure is constituted by the infinite armchair N-chain. The dynamical stability and mechanical stability are verified by the calculations of phonon dispersion curves and elastic constants. The enthalpy difference calculation shows that the <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic> phase is more stable than the reported P4<jats:sub>1</jats:sub>2<jats:sub>1</jats:sub>2 phase. The advantaged properties of <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic>-CaN<jats:sub>4</jats:sub>, such as high nitrogen content (58.3%) and low polymerization pressure (18.3 GPa), allow it to be a potential high energy material. Band structure calculation shows that the <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>m</jats:italic>-CaN<jats:sub>4</jats:sub> structure is a metallic phase. The nonpolar covalent single N–N bond is a sigma bond. The charge transfer between the Ca and N atoms results in an ionic bond interaction</jats:italic>.</jats:p>