Observation of Photoassociation Spectra of Ultracold ¹⁷⁴Yb Atoms at ¹S₀–³P₁ Inter-Combination Line

Photoassociation (PA) of cold atoms is a key tool widely used for accurate determination of long-range molecular potentials, measurement and tuning of interatomic interactions, as well as creation of desired cold molecules. We report the observation of PA spectra of ultracold ytterbium (Yb) atoms at the ¹S₀–³P₁ inter-combination line by detecting the resonant loss of atoms trapped in a crossed far-off-resonance trap (crossed-FORT). Eight vibrational levels in the ¹0⁺_u molecular state are observed for PA laser detunings up to 1 GHz with respect to the atomic resonance. The photoassociation resonances have a Lorentzian shape and sub-MHz linewidths due to the ultra low temperature of the atoms, and the resonance positions agree well with that predicted by the semiclassical formula.