Continuous wave stimulated Raman scattering of benzene by fluorescence enhancement in hollow fused silica fiber

We present continuous wave stimulated Raman scattering (SRS) of benzene (C₆H₆) influenced by the fluorescent dye m‐cresol purple in a hollow fused silica fiber (HFSF). Because of the transmission loss of the HFSF filled with C₆H₆, the SRS occurs when the Stokes gain equals the transmission loss, with the loss taken at the Stokes wavelength. The 992 cm⁻¹ stimulated Stokes line has been obtained at the pump wavelength 658 nm, which cannot be obtained at 532 nm because the Stokes wavelength (562 nm) does not locate in the transmission loss. Also, the pump power is 35 mW with m‐cresol purple which is much lower than 800 mW without the dye. The profile of the 992 cm⁻¹ stimulated Stokes is changed, and the weak shoulders of the profile are amplified by fluorescence. These results are expected to be of relevance in applications on the tunable Raman laser at new wavelengths. Copyright © 2011 John Wiley & Sons, Ltd.     

探地雷达超宽带高斯脉冲信号源的设计

脉冲源作为探地雷达的核心部件,其高功率和超宽频带可保证探测距离和探测分辨率,波形的光滑性与稳定性同时也影响着目标成像质量。选用雪崩三极管组成Marx电路输出单极性脉冲,采取措施优化波形中的不光滑部分,精确计算传输线延迟时间,信号反向叠加形成双极性脉冲,设计梳状PCB形式有利于脉冲源的小型化。测量结果表明:脉冲波形平滑对称,正负峰间脉宽为1.64 ns,幅度为812 V(50 负载),拖尾振荡低于总体幅值的10%,和仿真结果吻合较好,符合探地雷达的需求。     

钻孔雷达全向天线的设计与分析

根据钻孔雷达全向天线的设计要求,为减少天线的结构尺寸增加带宽,设计了一种新型电阻加载全向天线。通过理论分析和数值优化,选择了较优的结构尺寸,得到了较佳方向图和带宽。天线外径为65 mm,使用10 mm厚天线罩封装后外径为85 mm;天线的S11小于-10 dB频带为70~260 MHz,带宽约190 MHz。该天线的带宽超过100 MHz,中心频率处增益大于-3 dB,辐射电场脉冲波形拖尾小于主峰幅度1/5,方向图在H面为全向。基于矢量网络分析仪的天线特性测量结果与数值计算结果基本一致,结果表明设计的天线能够满足钻孔测井雷达系统小尺寸宽带的要求。     

Peroxide-mediated transition-metal-free direct amidation of alcohols with nitroarenes

An unusual direct amidation of alcohols with nitroarenes mediated by peroxides has been discovered. The reaction tolerated a wide range of functionalities, and various aromatic amides were obtained in moderate to good yields in the absence of transition-metal catalyst. The peroxides and solvents had a significant impact on the reaction yield.     

Enhancement CH-SRS of benzene mixing with toluene in liquid-core optical fiber at a low excitation power

Stimulated Raman scattering (SRS) of benzene mixing with toluene is studied in liquid-core optical fiber (LCOF) at a low excitation power 3 mJ/pulse. We obtained the intensive SRS of CH stretching vibration at 3060 cm^?1 [CH-SRS]. Neat benzene or toluene does not show the CH-SRS line under the same experimental condition. The CH-SRS threshold at 3060 cm^?1 for the binary solution was 2.5 mJ/pulse. The results suggest that interaction in molecular vibrations can generate strong CH-SRS in LCOF, we assume that the main mechanism of these phenomena to be the laser-induced plasma (LIP) enhancement to CH-SRS, which may provide a simple way to investigate the intermolecular interaction.     

Asynchronous midinfrared ultrafast optical parametric oscillator for dual-comb spectroscopy

Two asynchronous, broadband 3.3 μm pulse trains with a stabilized repetition-rate difference of up to 5 kHz were generated using an ultrafast optical parametric oscillator. The two oscillation channels, each producing ～100 mW average power, ran essentially independently, and weak non-phase-matched sum-frequency mixing between them provided a timing signal that indicated when the asynchronous pulses coincided. The system has immediate applications in incoherent asynchronous optical sampling and, with additional carrier-envelope-offset stabilization, could be applied to coherent dual-frequency-comb spectroscopy.     

Synchrotron radiation phase-contrast X-ray CT imaging of acupuncture points

Three-dimensional (3D) topographic structures of acupuncture points were investigated by using synchrotron radiation in-line X-ray phase contrast computerized tomography. Two acupuncture points, named Zhongji (RN3) and Zusanli (ST36), were studied. We found an accumulation of microvessels at each acupuncture point region. Images of the tissues surrounding the acupuncture points do not show such kinds of structure. This is the first time that 3D images have revealed the specific structures of acupuncture points.     

Heterogeneous bimetallic Pt-Sn/γ-Al2O3 catalyzed direct synthesis of diamines from N-alkylation of amines with diols through a borrowing hydrogen strategy

Direct synthesis of diamines has been efficiently realized from the N-alkylation of amines with diols by means of heterogeneous bimetallic Pt-Sn/γ-Al₂O₃ catalyst (0.5 wt % Pt, molar ratio Pt:Sn = 1:3) through a ‘Borrowing Hydrogen’ strategy under ligand-free conditions. The present methodology provides an environmentally benign route to diamines.