Relationship measurement between ac-Stark shift of ⁴⁰Ca⁺ clock transition and laser polarization direction

Ac-Stark shift of atom levels is caused by an ac-electromagnetic field. As an electromagnetic wave, laser light does induce ac-Stark shift. It is proved experimentally that if the light is linearly polarized, the dynamic polarizability changes with polarization direction. The polarization direction of the linearly-polarized laser is tuned by 720°, and the ac-Stark shifts of the 4S_{1/2, m= 1/2}→3D_{5/2, m= 1/2} clock transitions in ⁴⁰Ca⁺ are measured in steps of 10°. The frequency shifts change with laser polarization in a periodical manner and have values opposite to each other.