Modulation transfer spectroscopy based on acousto-optic modulator with zero frequency shift

We present a modulation transfer spectroscopy (MTS) configuration based on an acousto-optic modulator by using a variant of the typical double pass structure. One beam is modulated by using an acousto-optic modulator in opposite diffraction order to cancel the carrier frequency shift and produce a modulated pump beam. The line shape performance is investigated theoretically and experimentally. Laser frequency stabilization of the proposed configuration is demonstrated for the ¹³³Cs|6²S_1/2, F=4> →|6² P_3/2, F'=5> transition. The Allan deviations, which are measured by using beat note signals and the three-cornered hat method, are 3.6×10^-11 in an integration time of 100 s and approximately 4×10^-11 in a longer integration time.