Binnewies T, Wilpers G, Sterr U, Riehle F, Helmcke J, Mehlstäubler T E, Rasel E M, Ertmer W
Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany.
Phys Rev Lett. 2001 Sep 17;87(12):123002. doi: 10.1103/PhysRevLett.87.123002. Epub 2001 Aug 30.
Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of (40)Ca atoms has been cooled and trapped to a temperature as low as 6 microK by operating a magnetooptical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method, more than 10% of precooled atoms from a standard magnetooptical trap have been transferred to the ultracold trap. Monte Carlo simulations of the cooling process are in good agreement with the experiments.
