Investigation of ac-Stark shifts in excited states of dysprosium relevant to testing fundamental symmetries

We report on measurements of the differential polarizability between the nearly degenerate, opposite parity states in atomic dysprosium at 19797.96 cm$^{-1}$. The differential scalar and tensor polarizabilities due to additional states were measured for the $|M| = 7,...,10$ sublevels in $^{164}$Dy and $^{162}$Dy and determined to be $\bar{\boldsymbol\alpha}_{\scriptscriptstyle BA}^{(0)} = 180\,(45)_\text{stat}\,(8)_\text{sys}$ $\text{mHz}/(\mathrm{V}/\mathrm{cm})^2$ and $\bar{\boldsymbol\alpha}_{\scriptscriptstyle BA}^{(2)} = -163\,(65)_\text{stat}\,(5)_\text{sys}$ $\text{mHz}/(\mathrm{V}/\mathrm{cm})^2$, respectively. The average blackbody radiation induced Stark shift of the Zeeman spectrum was measured around 300 K and found to be $-34(4)$ mHz/K and $+29(4)$ mHz/K for $^{164}$Dy and $^{162}$Dy, respectively. We conclude that ac-Stark related systematics will not limit a search for variation of the fine-structure constant, using dysprosium, down to the level of $|\dot{\alpha}/\alpha|=2.6\times10^{-17}$ yr$^{-1}$, for two measurements of the transition frequency one year apart.