Photoassociative spectroscopy at long range in ultracold strontium

Abstract

We report photoassociative spectroscopy of ${}^{88}$Sr${}_2$ in a magneto-optical trap operating on the ${}^1{S}_0\to {}^3{P}_1$ intercombination line at 689 nm. Photoassociative transitions are driven with a laser red-detuned by 600-2400 MHz from the ${}^1{S}_0\to {}^1{P}_1$ atomic resonance at 461 nm. Photoassociation takes place at extremely large internuclear separation, and the photoassociative spectrum is strongly affected by relativistic retardation. A fit of the transition frequencies determines the ${}^1{P}_1$ atomic lifetime ($\tau =5.22\pm 0.03$ ns) and resolves a discrepancy between experiment and recent theoretical calculations.

4 pages, 4 figures, submitted