High-Resolution Spectroscopy of Long-Range Molecular States of $^{85}$Rb$_2$

We present analysis of low-$n$ long-range molecular states in $^{85}$Rb$_2$, and additional high-resolution spectra. Our process excites a photoassociation resonance in the $1 \, (0_g^-)$ state which decays to $v''=35$ and 36 of the $a \, ^3 \Sigma _u^+$ state and to the continuum. These bound molecules are excited via a single photon to target states near the $5s + 7p$ asymptote by a frequency-doubled pulse-ampli?ed CW laser with narrow linewidth, under 200 MHz. The long-range portion of the bonding potential is formed by the scattering interaction of the Rydberg electron of a perturbed $7p$ atom scattering from a nearby ground-state atom, in the same manner as trilobite states. We use time-of-flight to selectively measure molecular ions, which are formed via autoionization. This technique gives a two orders-of-magnitude improvement in linewidth over our previous excitation method, which was done by a broader linewidth conventional pulsed laser as reported in Ref. [1]. This work is supported by the NSF and AFOSR.\\[4pt] [1] M. A. Bellos \textit{et al.}, Phys. Rev. Lett. \textbf{111}, 053001 (2013)