Observation of Modulation Transfer Spectroscopy in the Deep Modulation Regime

We observe the modulation transfer spectroscopy on the D₂ line of ⁸⁷Rb in a rubidium cell with acoustic-optic modulator in the deep modulation regime. In this regime, the sidebands of the pump beam are involved in the four-wave mixing processes, which increase the signal gradients and the peak-to-peak amplitudes of both the absorption and dispersion components.