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, Wuhan 430074, People's Republic of China.
Rev Sci Instrum. 2019 Nov 1;90(11):113001. doi: 10.1063/1.5121568.
We present a simple method to measure the degrees of circular polarization (DoCP) of laser light inside a vacuum chamber and the birefringence of a vacuum window by detecting the fluorescence emitted by Doppler cooled ions in an ion trap. Imperfect laser polarization will cause ions to be pumped to the dark state which will decrease the fluorescence rates of the ions. With a simulation based on the rate equations of the relevant energy levels of Mg ions, we find that the fluorescence rate is sensitive to the DoCP of the laser. Based on the simulation result, we present a new method to optimize the DoCP of the laser inside the vacuum chamber by adjusting fast axis azimuthal angles of a half-wave plate and a quarter-wave plate outside the vacuum chamber. The laser light is optimized to be circularly polarized with an uncertainty of the DoCP of 7.8 × 10. With the obtained polarization information on both sides of the vacuum window and treating the vacuum window as an unknown wave plate, the phase delay and the fast axis azimuthal angle of the vacuum window can be determined in the form of Mueller matrix. The phase delay is determined to be 197.60(39)°, and the fast axis azimuthal angle is determined to be 104.00(5)°.
我们提出了一种简单的方法，通过检测离子阱中多普勒冷却离子发出的荧光，来测量真空腔内激光的圆偏振度（DoCP）以及真空窗口的双折射。激光偏振不完善会导致离子被泵浦到暗态，从而降低离子的荧光速率。通过基于镁离子相关能级速率方程的模拟，我们发现荧光速率对激光的DoCP敏感。基于模拟结果，我们提出了一种新方法，通过调整真空腔外半波片和四分之一波片的快轴方位角来优化真空腔内激光的DoCP。优化后的激光被调整为圆偏振，DoCP的不确定度为7.8×10。利用在真空窗口两侧获得的偏振信息，并将真空窗口视为未知波片，可以以穆勒矩阵的形式确定真空窗口的相位延迟和快轴方位角。确定相位延迟为197.60(39)°，快轴方位角为104.00(5)°。
