Magneto-optical trapping of ⁸⁸Sr atoms with 689 nm laser

We report the experimental realization of strontium magneto-optical trap (MOT) operating on the intercombination transition ¹S ₀-³P₁ at 689 nm, namely red MOT. A 689 nm laser used for cooling and trapping is injection locked to a master laser, whose linewidth is narrowed to 150 Hz by locking to a high finesse optical reference cavity. ⁸⁸Sr atoms pre-cooled and trapped by the broad ¹S₀-¹P₁ transition at 461 nm are transferred to the red MOT with the help of a time sequence controller. The transfer ratio is about 20% and the red MOT's temperature is estimated to be less than 20 μK by the time-of-flight (TOF) image analysis.