Synthesis and photoluminescence properties of a novel red phosphor SrLaGaO4:Mn4+

A novel Mn⁴⁺-doped strontium lanthanum gallate red phosphor SrLaGaO₄:Mn⁴⁺ has been successfully prepared via the conventional solid-state reaction method. Phase purity, photoluminescence excitation/emission spectra, concentration quenching, decay curves, and temperature-dependent photoluminescence have been investigated systematically. SrLaGaO₄:Mn⁴⁺ phosphor exhibits broad excitation band from 250 to 600 nm and emits intense red light centered at 716 nm arising from spin-forbidden transition, ²E → ⁴A₂ of Mn⁴⁺. The optimal dopant concentration of Mn⁴⁺ is determined to be 0.2 mol%. Dipole-dipole interaction is supposed to be the mechanism of concentration quenching. The crystal-field strength Dq, the Racah parameters B and C, and the nephelauxetic ratio β₁ of SrLaGaO₄:Mn⁴⁺ have been calculated according to its luminescent spectra. Our systematic investigation on this new phosphor can provide a reference for the development of red-emitting phosphor.     

Curved drilling via inner hole laser reflection

In this paper, we describe curved hole drilling via the reflection of a laser beam off the sidewall of the drilled hole. A slightly offset laser beam forms a tilted surface at the bottom of the hole, controlling the angle of curvature. An ultraviolet laser beam operating at a wavelength of 266 nm was used. To visualize the hole formation process, borosilicate glass was used as the laser workpiece. This method was able to drill a curved hole with an average angle of ∼3° with curvature beginning at a depth of 400–600 μm. A curved hole with a diameter of <50 μm was achieved. A branched hole was also demonstrated by using the reflection of the tilted sidewall. The curved hole formation process was recorded with a high speed camera. Once the ablated sidewall reached a certain depth, drilling ceased as the laser energy fell below the ablation threshold. Ultimately, judicious selection of an appropriate laser fluence and sidewall angle allow the formation of curved holes.     

Vibrational nonequilibrium and reaction heat effect in diluted hydrogen-oxygen mixtures behind reflected shock waves at 1000 < T < 1300 K

Vibrationally nonequilibrium model of kinetics in the reacting mixture H₂ + O₂ + Ar behind the reflected shock wave is formulated as a non-isothermal process occurring adiabatically at a constant volume. The model takes into account the vibrational nonequilibrium for the starting (primary) H₂ and O₂ molecules, as well as the molecular intermediates HO₂, OH, O₂(¹Δ), and the main reaction product H₂O. Calculation results that simulate experimental data on the ignition induction time measurements in the hydrogen oxygen mixtures behind reflected shock waves by the methods of absorption spectroscopy (monitoring the OH(²Π) radical) and emission spectroscopy (monitoring the OH*(²Σ⁺) radical) at temperatures of 1000 < T < 1300 K and pressures p < 3 atm are compared with experimental data and analyzed. It has been shown that the vibrational nonequilibrium determines the mechanism and rate of the process as a whole. The self-heating effect in diluted reacting mixtures at concentrations of the reacting additive ≤5% is demonstrated and discussed.     

Ni60/WC涂层表面圆凹坑皮秒激光加工关键参数研究

目的 优化激光路径填充方式以减少皮秒加工圆凹坑底部的堆积现象,并探究基于该激光路径填充方式的皮秒激光关键参数对Ni60/WC涂层表面圆形凹坑形貌参数的影响规律。方法 采用搭建的紫外皮秒激光微加工平台在Ni60/WC涂层表面加工预先规划的直径为230μm的圆凹坑,通过白光干涉仪测试加工所得圆凹坑的整体三维形貌对圆凹坑底部形貌进行表征。采用同心圆网格复合激光路径填充方式对圆凹坑底部堆积现象进行优化,并通过单因素法分析该路径下皮秒激光关键参数,即加工功率、扫描次数、扫描速度对圆形凹坑深度、直径和圆度系数的影响规律。结果 通过优化的同心圆网格复合激光路径填充方式加工所得圆凹坑材料去除体积为7.59×10⁶μm³,轮廓算术平均高度为21.37μm,对比原始的网格激光路径填充方式,加工的圆凹坑底部无明显堆积;基于此激光路径填充方式,在测试工艺参数范围内,圆凹坑深度、直径和圆度系数随激光功率的增大呈二次函数增大;随着扫描速度的增大,圆凹坑深度、直径呈线性减小,圆度系数呈线性增大;圆凹坑深度、直径和圆度系数随扫描次数的增加均呈线性增大。结论 同心圆网...     

Atom localization in a four-level alkaline earth atomic system

We propose an atom localization scheme for a four-level alkaline earth atom via a classical standing-wave field, and give the analytical expressions of the localization peak positions as well as the widths versus the parameters of the optical fields. We show that the probability of finding the atom at a particular position can be increased from 1/4 to 1/3 or 1/2 by adjusting the detuning of the probe field and the Rabi frequencies of the optical fields. Furthermore, the localization precision can be dramatically enhanced by increasing the intensity of the standing-wave field or decreasing the detuning of the probe field. The analytical results are quite accordant to the numerical solutions.     

Ground-State Energy Shifts of H-Like Ti Under Dense and Hot Plasma Conditions

In this study, by adopting the ion sphere model, the self-consistent field method is used with the Poisson-Boltzmann equation and the Dirac equation to calculate the ground-state energies of H-like Ti at a plasma electron density from 10^22 cm^-3 to 10^24 cm^-3 and the electron temperature from 100 eV to 3600 eV. The ground-state energy shifts of H-like Ti show different trends with the electron density and the electron temperature. It is shown that the energy shifts increase with the increase in the electron density and decrease with the increase in the electron temperature. The energy shifts are sensitive to the electron density, but only sensitive to the low electron temperature. In addition, an accurately fitting formula is obtained to fast estimate the ground-state energies of H-like Ti. Such fitted formula can also be used to estimate the critical electron density of pressure ionization for the ground state of H-like Ti.     

X射线荧光层析

X射线荧光层析技术是利用内壳层电子跃迁所发出荧光辐射,来测定样品中的元素含量,获取样品内部的结构信息。Wolter型掠入射镜装置的元素灵敏度可以达到100个原子／cm^3,空间分辨率达到微米量级。结合康普顿散射和吸收层析进行成像可使其图像质量得到进一步的提高。而当获得了物体的投影数据以后,可采用各种重建算法来使物体得以准确重现。介绍了几种常用的重建算法,并就其特点进行了比较。     

Hybrid silica–polymer structure for integrated optical waveguides with new potentialities

We report some features of a new waveguide structure in integrated optic providing new potentialities. We propose to use specific polymers as overlayer of ridge silica waveguides. This method can be used to finely tune the superstrate refractive index in order to adjust performances of components. In this paper, we give as examples, the auto-stabilization of integrated Bragg gratings and also, first experiments to realize thermo-optic directional couplers which can be achieved by combining these two materials in the waveguide structure.     

采用SHG-FROG单次测量红外长波长超快激光脉冲宽度和相位

描述了一套二次谐波型频率分辨光学快门(SHG-FROG)装置,用于单次测量红外长波长超快激光脉冲的脉宽和相位信息。针对在该波段宽带的高损伤阈值介质膜镀膜困难,且价格昂贵的问题,采用两个半圆形全反平面银镜来代替传统的半透半反镜进行分光。同时改进后的光路可以减少测量误差,结构更加紧凑且便于调节。采用该装置对基于钛宝石参量放大的红外超快脉冲进行测试,得到当中心波长为1.8μm时,脉宽为66.9 fs,谱宽54.5 nm,谱相中的二阶群延时色散(GDD)为202.9 fs2。     

飞秒激光成丝过程中的太赫兹波超光速传输现象研究

通过使用太赫兹(Terahertz,THz)时域光谱系统,探测从不同长度飞秒激光光丝辐射出的THz脉冲,观察到THz波在飞秒激光成丝过程中超光速传输的实验现象。进一步的分析表明:THz波在等离子体光丝区域的折射率小于其在空气中的折射率,这是使得THz波能够在成丝过程中超光速传输的主要原因。由此可以推测:THz脉冲极有可能是在等离子体光丝中进行导引传输的。最后,通过数值模拟获得了光丝区域内的THz本征模式,从而验证了上述推测。