Presented here is a method to measure the birefringence of vacuum windows by maximizing the fluorescence counts emitted by Doppler cooled 25Mg+ ions in an ion trap. The birefringence of vacuum windows will change the polarization states of the laser, which can be compensated by changing the azimuthal angles of external wave plates.
Yuan, W. H., Liu, H. L., Wei, W. Z., Ma, Z. Y., Hao, P., Deng, Z., Deng, K., Zhang, J., Lu, Z. H. In Situ Measurement of Vacuum Window Birefringence using 25Mg+ Fluorescence. J. Vis. Exp. (160), e61175, doi:10.3791/61175 (2020).