Quantum Optics Laboratory

We report photoassociative spectroscopy of Sr-88(2) in a magneto-optical trap operating on the S-1(0)-->P-3(1) intercombination line at 689 nm. Photoassociative transitions are driven with a laser red detuned by 600-2400 MHz from the S-1(0)-->P-1(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 P-1(1) atomic lifetime (tau=5.22+/-0.03 ns) and resolves a discrepancy between experiment and recent theoretical calculations.

We investigate systematically pump-probe spectroscopy of cold Rb-87 atoms produced by a magneto-optical trap. The pump-probe spectra are measured without the presence of the trapping beams or any optical molasses. Various polarization configurations of the probe and pump fields result in very different spectra of probe absorption. The observed spectra exhibit a dispersive profile, a dispersionlike profile, a Lorentzian profile, or a dispersive profile plus a Lorentzian profile. The widths of all the spectral profiles are narrower than the natural linewidth of the excited state. Our work clarifies the mechanisms behind these different spectral profiles and provides essential information for the pump-probe spectroscopy of cold atoms.