Intensity of a crossover signal relative to Lamb dips observed in Stark spectroscopy of methane

We have observed twelve triplets of two Lamb dips and a crossover signal in Stark spectroscopy of the ν₃ band of methane using a comb-referenced sub-Doppler resolution spectrometer. The crossover signal consists of two crossover resonances in the Λ- and V-type three-level systems, which overlap each other in frequency under the first-order Stark shifts (Tyurikov et al., 1997). The intensity of the crossover signal relative to the Lamb dips agrees well with a simple calculation based on steady-state solutions of rate equations in weak saturation using the observed intensity ratio of the Lamb dips in the Λ-type three-level system.