Continuous-wave Doppler-free two-photon frequencymodulation spectroscopy in Rb vapor

Frequency-modulation spectroscopy was employed successfully to measure the Doppler-free absorption and dispersion signals originating from several two-photon transitions in 85Rb and 87Rb. The two-photon cross section of the hyperfine transition 5S1/2 (F = 2) → 5D 5/2 (F=4) in 87Rb was determined to be σ(2) ≈ 4 × 10-20cm 4/W. The transition isotope shift (TIS) of the transition 5S1/2 → 5D5/2 between 87Rb and 85Rb was found to be ΔvTIS = +166±2 MHz. © 1983 Optical Society of America.