Near-recoil-limited temperatures obtained by laser trapping on the narrow 1S0-3P1 intercombination transition of neutral strontium

About 2×10⁷ neutral strontium atoms have been loaded into a magneto-optical trap (MOT) that uses the narrow (Γ=2π 7 kHz) intercombination line at 689 nm as the cycling transition. The atoms are second-stage laser cooled to ~10 μK from an initial 5 mK atomic sample (~5×10⁷ atoms), generated in a vapor cell MOT that employs the strong (Γ=2π 32 MHz) cycling transition at 461 nm. To demonstrate the low temperatures of these atoms, optical Ramsey spectroscopy is performed upon the ¹S ₀-³P₁ transition using only two excitation pulses; the time dependence of the fringe contrast indicates an RMS velocity of 3 cm/s for the 689 nm MOT-cooled sample