Carrier-envelope phase dependence of the duration of generated solitons for few-cycle rectangular laser pulses propagation

We investigate the nonlinear propagation of few-cycle rectangular laser pulses on resonant intersubband transitions in semiconductor quantum wells using an iterative predictor–corrector finite-difference time-domain method. An initial 2π rectangular pulse will split into Sommerfeld–Brillouin precursors and a self-induced transparency soliton during the course of propagation. The duration of generated soliton depends on the carrier-envelope phase of the incident pulse. In our case, not only the near-resonant frequency components but also the low frequency components could contribute to the generation of the soliton pulse when the condition of multi-photon resonance is satisfied. The phase-sensitive property of the solitons results from the phase-dependent distribution of high and low frequency sidebands of few-cycle rectangular pulses.     

Quantum spin Hall effect in silicene and two-dimensional germanium

We investigate the spin-orbit opened energy gap and the band topology in recently synthesized silicene as well as two-dimensional low-buckled honeycomb structures of germanium using first-principles calculations. We demonstrate that silicene with topologically nontrivial electronic structures can realize the quantum spin Hall effect (QSHE) by exploiting adiabatic continuity and the direct calculation of the Z(2) topological invariant. We predict that the QSHE can be observed in an experimentally accessible low temperature regime in silicene with the spin-orbit band gap of 1.55 meV, much higher than that of graphene. Furthermore, we find that the gap will increase to 2.9 meV under certain pressure strain. Finally, we also study germanium with a similar low-buckled stable structure, and predict that spin-orbit coupling opens a band gap of 23.9 meV, much higher than the liquid nitrogen temperature.     

100 W全光纤声光调Q光纤激光器实验研究

 报道了一台全光纤结构主振荡功率放大(MOPA)型掺镱脉冲光纤激光器,以光纤光栅为腔镜,光纤型声光调Q的光纤激光器为种子源,通过两级掺镱双包层光纤放大器实现功率放大。对声光调Q的光纤激光器输出特性进行了研究,比较了不同泵浦波长、不同重复频率对激光输出功率和脉冲宽度的影响,并实现了最短脉冲宽度25 ns、单脉冲能量45 μJ的脉冲激光输出。在重复频率50 kHz时,对脉冲宽度130 ns、平均功率0.6 W的种子光进行放大,得到了平均功率102.5 W、脉冲宽度约240 ns的激光输出。     

强流二极管绝缘体滑闪监测及其影响

 以闪光二号加速器为研究平台, 建立了微分环阵列和Rogowski线圈同时监测二极管电流的方法,监测了二极管绝缘体表面的滑闪现象。根据电流探头测量结果的差异,分析了绝缘体滑闪对电子束流参数的影响。二极管绝缘体出现滑闪,位置附近的微分环波形严重畸变,其它位置的微分环和Rogowski线圈测量结果基本一致。采用距离滑闪位置较远的微分环结果处理二极管束流参数,相对于不出现滑闪时的结果,束流强度和总能量没有明显的变化。绝缘体滑闪沿面局部放电,能量损失较小,尚未对电子束流造成较大影响。     

聚酰亚胺薄膜表面粗糙度的影响因素

 采用热蒸发气相沉积聚合方法（VDP）制备了聚酰亚胺(PI)薄膜,研究了设备、衬底温度、升温过程和单体配比因素对PI薄膜表面形貌的影响。利用干涉显微镜和扫描电镜对薄膜表面形貌进行了分析;利用原子力显微镜测定了薄膜表面粗糙度。结果表明：设定蒸发源-衬底距离为74 cm时可成连续膜;蒸发源采用一段升温和多段升温时,膜表面均方根粗糙度分别为291.23 nm和61.99 nm;采用细筛网可防止原料的喷溅;均苯四甲酸二酐和4,4′-二氨基二苯醚（PMDA和ODA）单体沉积速率比值为0.9∶1时,膜表面均方根粗糙度值可减小至3.30 nm;沉积衬底温度保持30 ℃左右时,膜表面均方根粗糙度为4.01 nm, 随温度的上升,膜表面质量会逐渐变差。     

基尔霍夫近似下激光海面漫反射组网通信特性

 针对激光点对点通信方式的不足,根据舰艇编队通信的实际需要,提出了利用海面作为激光漫反射媒介的一对多的组网通信方法,并且采用基尔霍夫近似的方法对激光海面漫反射通信的特性进行了研究。通过对激光光束入射海面后产生的散射场的分析计算,采用遮蔽函数对计算过程中的阴影效应加以修正,得出了较为准确的2维激光海面双站散射系数和后向散射系数,并进行了实验验证,说明了激光海面漫反射组网通信方法的可行性。     

Exchange enhanced sensitivity gain for solvent-exchangeable protons in 2D 1H-15N heteronuclear correlation spectra acquired with band-selective pulses

Conformational or chemical exchange can cause significant sensitivity loss in NMR spectroscopy through resonance broadening for nuclear spins involved in these processes. While this effect may sometimes be alleviated by manipulating experimental conditions such as temperature, pH, and buffers, conditions optimal for all resonances are not always achievable. As a consequence, any means of recovering or minimizing this exchange-induced sensitivity loss is potentially of significant value in regaining information otherwise lost. We report the experimental observation of significant sensitivity gain for nuclear spins undergoing chemical exchange with solvent (water) at exchange rates ca 1-10 s(-1) in (1)H-(15)N correlation spectra of proteins acquired with band-selective pulses (the SOFAST-HMQC sequence).     

Investigation on F–B–S tri-doped nano-TiO<Subscript>2</Subscript> films for the photocatalytic degradation of organic dyes

F–B–S tri-doped titanium dioxide thin films on common glass were prepared by a modified sol–gel method, in which tetrabutyl titanate (Ti(OC₄H₉)₄) was chosen as the precursor and boric acid (H₃BO₃), sodium fluoride (NaF), and thiourea (N₂H₄CS) were employed as boron, fluorine, and sulfur sources, respectively. The microstructure and optical property were characterized by X-ray diffraction, high-resolution field emission scanning electron microscopy, N₂ adsorption–desorption isotherms, photoluminescence spectrum, and UV–Vis diffraction reflectance spectroscopy. The photocatalytic performances were evaluated by decomposition of organic dyes in solution. The experimental results revealed that the F–B–S tri-doped TiO₂ thin film was composed of uniform round-like nano-particles with the size range of 5–8 nm. F–B–S tri-doping not only significantly promoted the UV-induced photodecomposition activities of TiO₂ films but also extended the optical response of TiO₂ red shift to visible light region, herein improving the visible light-induced degradation of organic dyes. The improvement mechanism by F–B–S tri-doping was also discussed.     

Study of the excitation properties of the Si3O2 cluster under an external electric field

The structure of the Si₃O_x (x=2, 3) cluster is investigated; we find that the geometry of Si₃O₂ is similar to that of Si₃O₃ except for the oxygen-deficient defect structure (Si-Si band) which exists only in the Si₃O₂ cluster. It is known that oxygen-deficient defects are used to explain visible luminescence (especially blue, purple and ultraviolet light) from silicon-based materials, which are directly bound up with the excited states of the molecules. Therefore the excitation properties of the two clusters are also studied. Our results show that the absorption spectrum of Si₃O₂ is concentrated in the visible light region. In contrast, the absorption spectrum of Si₃O₃ is mainly located in the ultraviolet light region. The calculations are perfectly consistent with experimental data and also support the theory of oxygen-deficient defects.     

Measurements on diproton emission from the break-up channels of ~(23)Al and ~(22)Mg

Two-proton relative momentum distributions from the break-up channels 23Al→p+p+21Na and 22Mg→p+p+20Ne at an energy of 60-70 A MeV have been measured together with two-proton opening angles at the projectile fragment separator beamline (RIPS) in the RIKEN Ring Cyclotron Facility. The results demonstrate the existence of diproton emission component from single-step 2He for highly excited 23Al and 22Mg.