基于半导体激光的腔增强吸收光谱技术研究

用近红外可调谐分布反馈(DFB)半导体激光器作光源,用反射率为99.7%左右的平凹镜组成的稳定光学谐振腔作吸收池,建立了一套腔增强吸收光谱(CEAS)系统.根据系统工作时激光器与谐振腔的工作状态,将CEAS技术分为三类:控制波长法,控制腔长法及同时扫描波长和腔长法.以二氧化碳(CO2)和甲烷(CH4)为主要样品气体,用控制腔长法和控制波长法CEAS技术对CO2分子在1.573μm附近的吸收光谱做了测量;用扫描腔长和波长法CEAS技术对CH4气体在1.316μm附近的吸收光谱做了测量;考察了三种方法的探测灵敏度和在定量分析方面的能力.实验结果表明,CEAS技术是一种装置简单,操作方便,灵敏度高,稳定性好的定量吸收光谱技术,探测灵敏度达1.15×10-7cm-1.     

Formula for average energy required to produce a secondary electron in an insulator

Based on a simple classical model specifying that the primary electrons interact with the electrons of a lattice through the Coulomb force and a conclusion that the lattice scattering can be ignored, the formula for the average energy required to produce a secondary electron (ε) is obtained. On the basis of the energy band of an insulator and the formula for ε, the formula for the average energy required to produce a secondary electron in an insulator (εi) is deduced as a function of the width of the forbidden band (Eg) and electron affinity χ. Experimental values and the εi values calculated with the formula are compared, and the results validate the theory that explains the relationships among Eg , χ, and εi and suggest that the formula for εi is universal on the condition that the primary electrons at any energy hit the insulator.     

亚波长金属光栅结构的制备与矢量衍射理论分析

利用纳米压印结合溅射和反应离子刻蚀工艺制备了周期为1μm、占空比为0.2的亚波长金属光栅,利用紫外-可见-近红外光谱仪测量了光栅的0级反射光谱。在严格耦合波分析的基础上,把光栅区域电磁场的空间谐波通过勒让德多项式展开,使用多项式展开的谱分析法求解常微分方程,计算了该亚波长金属光栅的反射光谱及磁场分布。实验测量结果同矢量衍射理论计算结果都显示,该光栅在近红外、中红外波段具有表面等离子体共振现象。数值计算结果还表明,对于此类亚波长金属光栅,当光栅的深宽比增加时,其反射光谱中会出现更多的反射谷。