Absorption and luminescence spectroscopy of fused silica by multiple pulses irradiation at 355 nm

In this work, the effects of laser irradiation on fused silica at 355 nm are investigated by using transient absorption spectroscopy and luminescence spectroscopy. Our result shows that no transient absorption or luminescence in the spectra range from 400 nm to 600 nm is observed when laser energy density is below the damage threshold. When the laser energy density reaches the threshold, an initial damage site will be created. After subsequent laser pulses irradiation, the damage size grows. At the same time, the intensity of the transient absorption and luminescence spectra at the damage site also raises remarkably with the laser pulse number increasing. The absorption band from 420 nm to 520 nm is probably related to the absorption of impurity such as metal ion of iron, cerium and copper. Laser modified fused silica exhibits intense broad luminescence bands due to oxygen-deficiency centers at 444 nm and 580 nm.  

Fabrication of silver nanosheets on quartz glass substrates through electroless plating approach

Silver nanosheets (NSs) have been synthesized by an electroless plating approach using a complexation mechanism of triethanolamine (TEA) and Ag⁺ to reduce the oxidation–reduction potential difference and slow down the deposition speed of Ag on quartz glass substrates. The synthesized Ag NSs with 500 nm in edge length and 30 nm in thickness stand on the substrates and are dispersed uniformly. The formation mechanism of Ag NSs is proposed. The formation of Ag NSs is attributed to the molar ratio of AgNO₃ to TEA, the concentration of AgNO₃ and the influence of reaction temperature. This study is important in vertical immobilization Ag NSs on solid substrates, which could provide substrates for catalysis or surface-enhanced Raman scattering.  

低密度Cu掺杂SiO_2复合气凝胶的制备及表征

分别以正硅酸甲酯、醋酸铜为硅源和铜源,通过溶胶凝胶法及CO2超临界干燥技术制备了一系列Cu掺杂SiO2复合气凝胶。采用红外谱仪(FTIR)、扫描电镜(SEM)、X射线能谱仪(EDS)、比表面积和孔隙度分析仪(BET)、动态热机械分析仪(DMA)对样品进行了表征。结果表明随着铜含量的增加,复合气凝胶密度增加,比表面积降低,平均孔径增加,实际掺杂比与理论掺杂比对应增加。该复合气凝胶具有三维网状结构,密度低(40mg/cm3),比表面积高(390m2/g),成型性较好,有望应用于惯性约束聚变(ICF)实验。  

γ-射线辐射还原法制备金属铜掺杂MF气凝胶

采用γ射线辐射还原法,在不同总吸收剂量条件下制备了金属Cu掺杂三聚氰胺-甲醛(MF)有机气凝胶复合材料。利用X-射线衍射仪(XRD)、电感耦合等离子体吸收光谱(ICP-AES)仪和扫描电子显微镜,测试证实了辐射还原法能成功地在MF气凝胶中还原出金属Cu。扫描电子显微镜(SEM)图谱表明在100kGy和200kGy的总吸收剂量下,在MF气凝胶中还原的金属Cu粒子的粒径较小,不会形成金属团聚区,而在较高的总吸收剂量下(大于200kGy),在MF气凝胶中还原的Cu会形成金属团聚区。N2吸附测试表明,还原的金属Cu会堵塞MF气凝胶的一部分微孔和一部分介孔,从而使样品的比表面积和吸附量降低。随着总吸收剂量不断增加,经辐照后样品中金属Cu的含量也不断增加,同时还会影响还原出金属Cu的分布和形貌。  

CO_2活化温度对N-C复合碳气凝胶结构及电化学性能的影响

采用CO2活化工艺对氮掺杂碳气凝胶(N-CA)的结构进行重整,并系统研究了活化温度对活化氮掺杂碳气凝胶(N-ACA)孔结构及电化学性能的影响。利用N2吸附数据、X-光电子能谱(XPS)和元素分析对样品的结构及元素组成进行表征。结果表明,随活化温度的升高,N-ACA的比表面积逐渐增大,其含有的氮原子分数逐渐减少,吡咯氮含量明显增加。利用循环伏安(CV)、电化学阻抗谱(EIS)等测试技术评价了碳气凝胶样品在6mol·L-1 KOH电解液中的电化学性能,结果发现,合理的孔结构与较高的吡咯氮含量是影响电容器比容量的关键因素。在5mV·s-1扫描速率下测试950-N-ACA电极的比电容值高达267.4F·g-1,经1000次充放电后比电容损失值在1.5%以内。  

Simulation study of indirect positron generation by an ultra-short laser

Positron generation by an ultra-short ultra-intense laser in an indirect manner has been studied with two-dimensional particle-in-cell (PIC) and Monte Carlo (MC) simulations. In this generation scheme, positrons are produced with energetic electrons accelerated by an ultra-shot laser pulse propagating through an underdense plasma. The dependence of the positron beam properties on the plasma length and secondary target (converter) thickness was investigated in detail. The simulation results reveal that the positron yield is strongly correlated with the total energy of laser-accelerated electrons; both the temperature and divergence of the positron beam are sensitive to the plasma length; and the positron beam has a pulse duration comparable to the incident electron beam. In addition, it is indicated that even with the optimal converter thickness, only a small fraction (11.4%) of positrons can escape out and most of the detected positrons originate from the back edge of the converter.  

Suppression of the amplified spontaneous emission in ultraintense and ultrashort lasers by a highly efficient saturable absorber

For ultraintense and ultrashort laser facilities, there are few efficient and reliable methods for suppressing the amplified spontaneous emission (ASE) generated in the last several amplifiers. In the paper, we applied a highly efficient saturable absorber to suppress the ASE. Experiments were carried out to study the absorption property of the saturable absorber and the enhancement of temporal contrast with it in the front-end system of the SILEX-I laser facility with a central wavelength of 800 nm. We also analyzed the effects of the saturable absorber on other laser parameters, such as the spectrum, the spatial beam profile, and energy stability. The results show that the saturable absorber is highly efficient and the transmissivity is as high as 90%. The temporal contrast is improved by more than one order of magnitude. Meanwhile, the saturable absorber has little impact on other parameters. With these advantages, the saturable absorber is an efficient, appropriate and convenient solution to suppressing the ASE generated in the front-end system and also in the last several amplification stages for ultraintense and ultrashort lasers.  

Photothermal decomposition of HNS at 532 nm

The photodecomposition of solid 2,2′,4,4′,6,6′-hexanitrostillbene (HNS) at 532 nm, induced by a 10-nanosecond (ns) laser, is investigated by an elaborately designed in situ X-ray photoelectron spectroscopy (I-XPS) experiment and steady-state Fourier transform IR (FTIR) spectroscopies. Numerical integration of the two-dimensional heat conduction equation indicates that the irradiated sample volume is effectively heated and photothermal decomposition takes place. Agreement of results between the I-XPS and FTIR suggests that the nitro-nitrite (NO₂-ONO) isomerization is a main decomposition pathway for HNS.  

Silver nanoplates: controlled preparation, self-assembly, and applications in surface-enhanced Raman scattering

Silver nanoplates were prepared in a dual reduction system with NaBH₄ and sodium citrate both as reducing agents. And then the as-prepared nanoplates could be growing up through multistage growth methodology. The average edge length of Ag nanoplates can be tailored from 40 nm to 260 nm without changing their shape, crystallinity, and the average thickness. Furthermore, the effectiveness of these silver nanoplates as substrates prepared by the silanization self-assembly method toward surface-enhanced Raman scattering (SERS) detection was evaluated by using 4-aminothiophenol (4-ATP) and rhodamine 6G (R6G) as probe molecules. It was found that the enhancement ability of the silver nanoplates film is remarkable lower than that of the spherical silver nanoparticle film. The reason is attributed to the electromagnetic mechanism and chemical mechanism. This work will be of great significance in understanding the SERS enhancement mechanism and in the fabrication of nanoparticle films for biosensing.