Doubly Excited Autoionizing Rydberg States of Sr

We report the observation of doubly excited autoionizing Rydberg states of Sr, belonging to the configuration $5p_{\frac{1}{2}}$, $\mathrm{nl}$. Our procedure involves a three-step optical excitation process which incorporates Stark switching to reach higher $l$ states not normally accessible because of dipole selection rules. Quantum defects are reported for several $5p_{\frac{1}{2}}$, $\mathrm{ns}$ and $5p_{\frac{1}{2}}$, $\mathrm{nd}$ states. The lifetimes of the $5p_{\frac{1}{2}}$, $\mathrm{ns}$ states are shown to scale as ${\left(n^{*}\right)}^3$, and the lifetimes of the $5p_{\frac{1}{2}}$, $16l$ states are shown to increase dramatically with increasing $l$.