Novel Method to Measure the Gravitational Constant

我成功地建立了一个激光多普勒干涉仪，连接到一个高速采样示波器，用它可以测量皮米范围（<10^-12 m）下1~5kHz的振荡幅度。由于在最大采样率为5MHz的情况下，测量到的地面噪声无法降低到1pm/Hz^（1/2）以下，因此首次尝试在极化稳定性方面明显滞后。最后测量到的地面噪声现在是0.13pm/Hz^（1/2）。该仪器在偏振稳定性方面进行了升级，在重组分束器侧的波片前面安装了格兰-泰勒棱镜，在激光输入端安装了法拉第隔离器。此外，通过使用保偏光纤来确保参考光路和信号光路的光路长度相等。这增加了两束光束的相干性，从而也增加了探测器上观察到的条纹的对比度。所进行研究的一个次要方面是确保压电测试芯片的可用性，即使振荡幅度低于1皮米。这对于保持低动态对比度和高测量分辨率非常重要。结果清楚地证明了测试芯片的能力。

I succeeded to build a laser Doppler-interferometer, connected to a high-speed sampling oscilloscope, with which oscillation-amplitudes at 1~5kHz below picometer-ranges (<10^-12 m) could be measured. The first attempt of building such an instrument lagged clearly in polarization stability as the measured ground noise could not be lowered below 1pm/Hz^(1/2) even with a maximum sampling rate of 5MHz. The last measured ground noise is now at 0.13pm/Hz^(1/2).The instrument has experienced upgrades regarding the polarization stability in the form of Glan-Taylor prisms which are now in front of the waveplates on the recombining beam-splitter side and a Faraday isolator at the laser-input. Furthermore, care has been taken to ensure an equal optical path length for both the reference and the signal beam path by using polarization maintaining fibers. This increased the coherence of both beams and thus also the contrast of the observed fringes at the detectors.One minor aspect of the conducted research was to ensure the usability of the Piezo-test chip even for oszillation amplitudes below a picometer. This is important to keep the dynamic constrast low and thus the resolution of the measurements high. The results clearly proof the capability of the test-chip.