Chen L Y, Feng X W, Su Y, Ma H Z, Qian Y H
Appl Opt. 1994 Mar 1;33(7):1299-305. doi: 10.1364/AO.33.001299.
We have designed and constructed a new type of spectroscopic ellipsometer to study the optical properties of materials in the 3500-8000-Å wavelength range. In the system, the analyzer and polarizer are driven 10(4) steps/revolution by two stepping motors that have hollow shafts and rotate synchronously with a speed ratio of 2:1, i.e., A = 2P. Both the polarizer and analyzer are mounted directly on the shafts to avoid mechanical transmission and vibration problems entirely and make the system simple and reliable. An additional source polarizer was placed in the optical path to reduce the slight polarization effects of the light source. The light intensity finally received by the detector contained five components, one dc and four ac, with frequencies of ω(0), 2ω(0), 3ω(0), and 4ω(0), respectively. One can independently obtain the ellipsometric parameters of ψ and Δ as well as the optical constants by calculating any one of the two sets of ac signals, with a raw data self-consistency of better than 0.5%. The incident angle, aligned precisely by a laser beam, was continuously variable through a mechanical system with a computercontrolled resolution of 0.001° or a visual resolution of 0.005°. The system operations, including data acquisition and reduction, high-voltage control of the photomultiplier, incident angle, as well as wavelength setting and scanning, were fully and automatically controlled by a 386-based microcomputer. We self-calibrated the system by adjusting and setting precisely the initial azimuthal angles of the prisms. The results from the measured spectra of the complex refractive index for a gold-film sample are presented, and we show that the data obtained at three different incident angles of 65°, 70°, and 75° are remarkably consistent with one another. A comparison of the two results from the ellipsometry and reflectance measurements is given. The experimental skills and system error reduction are discussed in detail.
我们设计并构建了一种新型的椭圆偏振光谱仪，用于研究波长范围在3500 - 8000埃的材料的光学特性。在该系统中，检偏器和起偏器由两个空心轴步进电机驱动，每转10(4)步，且同步旋转，转速比为2:1，即A = 2P。起偏器和检偏器都直接安装在轴上，完全避免了机械传动和振动问题，使系统简单可靠。在光路中放置了一个额外的光源偏振器，以减少光源的轻微偏振效应。探测器最终接收到的光强包含五个分量，一个直流分量和四个交流分量，频率分别为ω(0)、2ω(0)、3ω(0)和4ω(0)。通过计算两组交流信号中的任意一组，可独立获得椭偏参数ψ和Δ以及光学常数，原始数据的自洽性优于0.5%。通过机械系统精确对准的入射角由计算机控制，分辨率为0.001°，目视分辨率为0.005°，且入射角可连续变化。系统操作，包括数据采集与处理、光电倍增管的高压控制、入射角以及波长设置与扫描，均由基于386的微型计算机完全自动控制。我们通过精确调整和设置棱镜的初始方位角对系统进行了自校准。给出了金膜样品复折射率测量光谱的结果，结果表明在65°、70°和75°三个不同入射角下获得的数据彼此非常一致。给出了椭偏测量和反射率测量两种结果的比较。详细讨论了实验技巧和系统误差的降低。
