Detection of Ultracold Ground-State Molecules by One- and Two-Color Resonance-Enhanced Two-Photon Ionization

One- and two-color resonance-enhanced two-photon ionization (RETPI) is used to detect ultracold ground-state RbCs molecules which are formed via short-range photoassociation from laser-cooled atoms. The transition from the X1Σ+(v = 0) state to the 21Π(v = 10) state of ultracold RbCs molecules shows the consistence of one- and two-color RETPI. A multi-photon photoionization rate model is introduced to interpret the dependence of molecular ion intensity on photoionized laser energy, and can be used to verify the photoionization scheme. This photoionization rate model can be expanded to multi-color photoionization for all kinds of atoms and molecules, which is a powerful method of determining the photoionization scheme.