Quenched narrow-line laser cooling of 40Ca to near the photon recoil limit -: art. no. 031403

We present a cooling method that should be generally applicable to atoms with narrow optical transitions. This technique uses velocity-selective pulses to drive atoms towards a zero-velocity dark state and then quenches the excited state to increase the cooling rate. We demonstrate this technique of quenched narrow-line cooling by reducing the 1D temperature of a sample of neutral Ca-40 atoms. We cool selected velocities with the S-1(0)(4s(2)) --> P-3(1) (4s4p) 657-nm intercombination line and quench with the P-3(1)(4s4p) --> S-1(0)(4s5s) intercombination line at 553 nm, which increases the cooling rate eightfold. Limited only by available quenching laser power, we have transferred 18% of the atoms from our initial 2-mK velocity distribution and achieved temperatures as low as 4 muK, corresponding to a v(rms) of 2.8 cm/s or 2 recoils at 657 nm. This cooling technique, which is closely related to Raman cooling, can be extended to three dimensions.