Two-photon spectrum of ⁸⁷Rb using optical frequency comb

The high precision two-photon excitation measurements for 5S_1/2 (F_g = 2) to 5D_5/2 (F_e = 4 to 1) of ⁸⁷Rb are performed by using an optical frequency comb. The two counter-propagating femtosecond pulses (5S_1/2→5P_3/2 at 780 nm, and 5P_3/2→5D_5/2 at 776 nm) act on ⁸⁷Rb vapor, and the Doppler broadened background signal is effectively eliminated. The temperature and power dependences of the two-photon spectrum are studied in this paper.