Measurement of the Polarizability of Ba$^{2+}$

The dipole polarizability of Ba$^{2+}$ was determined by spectroscopy of high-L Rydberg levels of Ba$^{+}$, using the Resonant Excitation Stark Ionization Spectroscopy (RESIS) method. Beams of Ba$^{2+}$, obtained by sputtering solid Ba inside a 14 GHz permanent magnet ECR source at Kansas State University, captured a single electron from a dense Rb 12F Rydberg target, forming highly excited Rydberg levels of Ba$^{+}$. Rydberg levels of Ba$^{+}$ with n=19 or 20 and L=5,6,7,8, and 9 were excited to a much higher level using a Doppler-tuned CO$_{2}$ laser and then detected by Stark ionization. The resolved fine structure of these levels, analyzed with the long-range polarization model, determined the polarizability of the ground state of Ba$^{2+}$.