DOUBLE-RESONANCE SPECTROSCOPY OF LASER-COOLED RB ATOMS

Double resonance transitions have been observed in laser-cooled and trapped Rb-85 atoms. The atoms are cooled on the 5S1/2- 5P3/2 transition and the absorption of a weak probe beam tuned to the 5P3/2-4D5/2 transition is detected. The suitability of this transition as a potential secondary frequency standard in the near infra-red is assessed by using the Autler-Townes splitting as a sensitive probe for the shifts induced by the pump laser. The dependence of the splitting on the pump detuning and intensity are measured. Systematic shifts of a few hundred kHz seem realistic, subject to an accurate knowledge of the detuning of the cooling laser. New precise values are also obtained for the hyperfine constants for the 4D5/2 level: A = -5.06 +/- 0. 10 MHz and B= 7.42 +/- 0.15 MHz.