Two-Photon Transitions of ^85Rb 5D_5/2 State by Using an Optical Frequency Comb and a Continuous-Wave Laser

A high-resolution two-photon spectrum of 5S_1/2\to5P_3/2\to5D_5/2 transitions in a thermal ^85Rb vapor cell is presented by using an optical frequency comb and a cw laser. The fluorescence of 6P_3/2\to5S_1/2 spontaneous emission is detected when the cw laser frequency is scanned from the 5S_1/2 ground state to 5P_3/2 hyperfine levels and the optical frequency comb repetition rate is fixed. The hyperfine splittings (F_\rm f=2–5) of the 5D_5/2 excited state are well resolved. The dependences of fluorescence intensities on the cw laser intensity and temperature of ^85Rb vapor cell are studied, respectively. The experimental results are in good agreement with the theoretical analyses.