Transition from second- to first-order dipole-dipole interaction in the excited EuSr molecule.

Abstract

For the first time a transition from a second- to first-order dipole-dipole interaction (van der Waals to resonance interaction) has been observed in a study of the excited EuSr molecule which dissociates into europium 4${\mathrm{f}}^{7}$5s6p ${\mathrm{}}^{8}$${\mathrm{P}}_{9/2}$ and strontium 5${\mathrm{s}}^{2}$ ${\mathrm{}}^{1}$${\mathrm{P}}_{1}$ atoms. The transition was verified by measurement of the wavelength dependence in the quasistatic wings of the cw-laser--excited 4595.3-A\r{} line in Eu broadened by Sr ground-state atoms.