Laser-stimulated two-step recombination of highly charged ions and electrons in a storage ring

Two-step resonant laser-stimulated recombination of highly charged ions was performed for the first time. Nd:YAG laser pulses overlapped with an ${\mathrm{Ar}}^{18+}$ beam in the electron cooler of the ESR storage ring at GSI induced transitions from the continuum to the n=81 state of hydrogenlike ${\mathrm{Ar}}^{17+}$. To avoid reionization in the bending magnet before reaching the detector, the n=81 population was transferred to a state well below the reionization threshold by a Ti:sapphire laser. Tuning of this laser yielded the n=81 to 36 and 37 transition-line profiles. The two-step method provides access to detailed Rydberg spectroscopy in an electron beam environment.