Optical-dipole trapping of Sr atoms at a high phase-space density

Employing a far-off resonance optical-dipole trap (FORT), we attained a phase-space density exceeding 0.1, or an order to quantum degeneracy. Strontium atoms were magneto-optically cooled and trapped using the spin-forbidden ${}^1{S}_0{-}^3{P}_1$ transition and then compressed into a FORT that was designed to allow simultaneous Doppler cooling. We discussed that the phase-space density was finally limited by the light-assisted collisions occurring in the optical cooling.