Contrast saturation resonances in the absorption band of rubidium molecules

We study Doppler-free saturation resonances in the absorption band of rubidium diatomic molecules in the frequency range near the D2 line of lithium atoms (671 nm). We observe contrast saturation resonances and record a variation in the laser light transmission of 4% due to optical saturation. The large optical nonlinearities in the molecular diatomic gas can be used for investigating the four-wave mixing and other nonlinear effects