Two-photon vibrational transitions in ${\rm O}_2^+$

Vibrational overtones in the ${\rm O}_2^+$ molecule are electric-dipole forbidden and thus intrinsically narrow and immune from some systematic shifts.[1] They could serve as reference frequencies for optical clocks or as probes of new physics such as time-variation of fundamental constants. We report on our attempts to drive these transitions with two photons from a nanosecond pulsed laser. Our goal is to reduce the measurement uncertainty in the vibrational frequency by several orders of magnitude. In addition to an overview of our experiment, we present recent upgrades that reduce the temperature of our molecular beam and increase our signal.\\ \\ 1. R. Carollo, A. Frenett, D. Hanneke, Atoms v.7, 1 (2018)\\ \\ This work is supported by the NSF (RUI PHY-1806223).