Ionization spectroscopy in cold rubidium atoms

We demonstrate photoionization spectroscopy in cold rubidium atoms trapped in a working magneto-optical trap. Three-photon ionization with two-photon resonance proceeds along various channels, with the step-by-step 5S–5P–5D transition and with the two-photon excitation of the 5D or 7S state. The processes are monitored by measuring ion signals which allow sensitive spectroscopy of weak transitions in a cold-atom sample.