Efficient production and spectroscopy of ultracold potassium molecules in the electronic ground state

Summary form only given. We report results from an efficient new method for producing translationally cold (T<1 mK) potassium molecules in the ground X/sup 1//spl Sigma//sub g//sup +/ electronic state. We use the two-photon "R-transfer" scheme conceptually similar to a proposal by Band and Julienne (1995). First, ultracold potassium atoms in a MOT are photoassociated at long range to the 1/sub g/ molecular electronic state, which correlates to the 1/sup 1//spl Pi//sub g/ state at short range. The resulting molecules are then excited with a second laser to the 5/sup 1//spl Pi//sub u/ or 6/sup 1//spl Pi//sub u/ Rydberg states. These Rydberg states have favorable Franck-Condon factors for spontaneous decay into low vibrational levels of the ground state. The molecules are detected by use of two-color resonant ionization with pulsed lasers. By scanning one of the detection lasers, we observe transitions from several vibrational levels of the X state. The largest observed molecule formation rate in a single vibrational level is about 10/sup 5/ molecules/s for /spl nu/=25. Molecules in the lowest vibrational levels, including /spl nu/=0, are also observed with slightly lower rates of production. The translational temperature of the ground-state molecules is measured by analyzing their ballistic decay from the detection region. It is approximately 500 /spl mu/K, roughly the same as the estimated temperature of potassium atoms in the MOT.