一种可溯源的光谱椭偏仪标定方法

提出了一种用X射线反射术标定光谱椭偏仪的方法.作为一种间接测量方法,光谱椭偏术测得的薄膜厚度依赖于其光学常数,不具有可溯源性.在掠入射条件下,X射线反射术能测得薄膜的物理厚度,测量结果具有亚纳米量级的精密度且与薄膜光学常数无关.在单晶硅基底上制备了厚度分别为2nm,18nm,34nm,61nm及170nm的SiO2薄膜标样,并用强制过零点的直线拟合了两种方法的标样测量结果,拟合直线的斜率为1.013±0.013,表明该方法可在薄膜厚度测量中标定光谱椭偏仪.     

基于飞秒光频梳的压电陶瓷闭环位移控制系统

利用飞秒光频梳、外腔可调谐半导体激光器和法布里-珀罗干涉仪建立了一套压电陶瓷亚纳米级闭环位移控制系统. 将可调谐半导体激光器锁定至光频梳, 通过精确调谐光频梳的重复频率, 实现了半导体激光器在其工作频率范围内的精密调谐. 利用Pound-Drever-Hall锁定技术将带有压电陶瓷的法布里-珀罗腔锁定至半导体激光器, 进而通过频率发生系统控制压电陶瓷产生亚纳米级分辨率的位移. 实验研究发现锁定至光频梳后可调谐半导体激光器1 s的Allan标准偏差为1.68×10^-12, 将其在30.9496 GHz范围内进行连续闭环调谐, 可获得压电陶瓷的位移行程约为4.8 μm; 以3.75 Hz的步长扫描光频梳的重复频率, 实现了压电陶瓷的450 pm闭环位移分辨率并测定了压电陶瓷的磁滞特性曲线. 该系统不存在非线性测量误差, 且激光频率及压电陶瓷位移均溯源至铷钟频率源. 关键词： 光频梳 压电陶瓷 法布里-珀罗腔 可调谐半导体激光器     

Uncertainty reevaluation in determining the volume of a silicon sphere by spherical harmonics in an Avogadro project

To determine the Avogadro constant with a target relative uncertainty of 2 × 10^-8, the uncertainty component of the silicon sphere's volume introduced by the spherical harmonics method, which is usually used in determining the sphere's volume, is reevaluated. By means of representing the shape of the silicon sphere by an ellipsoid with Gaussian white noise in its diameters, the uncertainty of the current mapping methods based on the spherical harmonics theory can be estimated theoretically. It is evidenced that the uncertainty component attributed to the current mapping method is underestimated. To eliminate this effect as much as possible, the number of mapping points should be increased to more than before. Moreover, a new mapping method is proposed to accomplish the equal-area mapping with large number points on the silicon sphere.