Figure 1

Schematic diagram of the long-range ${\mathrm{Sr}}_2$ molecular potentials (not to scale). The ground and excited molecular states coincide with two ground state atoms, and with one ground and one excited state atom, respectively, at large internuclear separations. The ground state has gerade symmetry and its energy is given by the potential $V_g$, while the excited state ungerade potentials that support dipole transitions to the ground state are $V_{0u}$ and $V_{1u}$, the latter with a small repulsive barrier. All vibrational states of $0_u$ and $1_u$ (dashed and dotted lines, respectively) are separated by more than the natural line width, permitting high resolution PA spectroscopy very close to the dissociation limit when the atoms are sufficiently cold.Reuse & Permissions

Figure 2

Experimental configuration. The $2\mu \mathrm{K}$ atoms are confined in a 1D optical lattice in the Lamb-Dicke regime that allows Doppler- and recoil-free photoassociation spectroscopy. The lattice laser intensity is large enough to confine most atoms in the ground motional state. The 689 nm weak PA laser copropagates with the lattice. The 914 nm lattice wavelength ensures that ${}^{1}S_0$ and the $m_J=\pm 1$ sublevels of ${}^{3}P_1$ are Stark shifted by equal amounts.Reuse & Permissions

Figure 3

The spectra of the long-range ${\mathrm{Sr}}_2$ molecule near the ${}^{1}S_0\mathrm{\text{−}}{}^{3}P_1$ dissociation limit. The horizontal scale is marked on the rightmost panel and is the same for each of the nine blocks; different PA laser intensities were used for each spectrum due to largely varying line strengths. The top labels indicate the interatomic separations that correspond to the classical outer turning points of each resonance.Reuse & Permissions

Figure 4

(a) A line is schematically shown as a sum of Lorentzians with positions and amplitudes given by a continuous thermal distribution. (b) The measured line shapes of the $-222\mathrm{MHz}$ transition at $1.7\mu \mathrm{K}$ (open circles) and $3.5\mu \mathrm{K}$ (solid circles), clearly showing the effect of temperature on the red side of the line. The bottom trace shows the residuals of the $1.7\mu \mathrm{K}$ curve fit.Reuse & Permissions