Yuan W H, Liu H L, Wei W Z, Ma Z Y, Hao P, Deng Z, Deng K, Zhang J, Lu Z H
MOE Key Laboratory of Fundamental Physical Quantities Measurement, Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology.
MOE Key Laboratory of Fundamental Physical Quantities Measurement, Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology;
J Vis Exp. 2020 Jun 13(160). doi: 10.3791/61175.
Accurate control of the polarization states of laser light is important in precision measurement experiments. In experiments involving the use of a vacuum environment, the stress-induced birefringence effect of the vacuum windows will affect the polarization states of laser light inside the vacuum system, and it is very difficult to measure and optimize the polarization states of the laser light in situ. The purpose of this protocol is to demonstrate how to optimize the polarization states of the laser light based on the fluorescence of ions in the vacuum system, and how to calculate the birefringence of vacuum windows based on azimuthal angles of external wave plates with Mueller matrix. The fluorescence of Mg ions induced by laser light that is resonant with the transition of |3P3/2,F = 4, mF = 4 → |3S1/2,F = 3, mF = 3 is sensitive to the polarization state of the laser light, and maximum fluorescence will be observed with pure circularly polarized light. A combination of half-wave plate (HWP) and quarter-wave plate (QWP) can achieve arbitrary phase retardation and is used for compensating the birefringence of the vacuum window. In this experiment, the polarization state of the laser light is optimized based on the fluorescence of Mg ion with a pair of HWP and QWP outside the vacuum chamber. By adjusting the azimuthal angles of the HWP and QWP to obtain maximum ion fluorescence, one can obtain a pure circularly polarized light inside the vacuum chamber. With the information on the azimuthal angles of the external HWP and QWP, the birefringence of the vacuum window can be determined.
在精密测量实验中，精确控制激光的偏振态至关重要。在涉及使用真空环境的实验中，真空窗口的应力诱导双折射效应会影响真空系统内激光的偏振态，并且很难在原位测量和优化激光的偏振态。本实验方案的目的是演示如何基于真空系统中离子的荧光来优化激光的偏振态，以及如何基于带有穆勒矩阵的外部波片的方位角来计算真空窗口的双折射。与|3P3/2,F = 4, mF = 4 → |3S1/2,F = 3, mF = 3跃迁共振的激光诱导的镁离子荧光对激光的偏振态敏感，并且用纯圆偏振光会观察到最大荧光。半波片（HWP）和四分之一波片（QWP）的组合可以实现任意相位延迟，并用于补偿真空窗口的双折射。在本实验中，基于真空腔体外一对HWP和QWP的镁离子荧光来优化激光的偏振态。通过调整HWP和QWP的方位角以获得最大离子荧光，可以在真空腔内获得纯圆偏振光。利用外部HWP和QWP方位角的信息，可以确定真空窗口的双折射。
