Use of AOM-RN as a phase modulator in FM sideband heterodyne technique in the atomic frequency standards

AOM-RN, an acousto-optic modulator designed to operate in the pure Raman-Nath diffraction regime, was applied as an optical phase modulator in FM spectroscopy of saturated absorption resonances, coherent population trapping resonances, sub-natural magneto-optical resonances in Cs vapor, i.e. such kind of optical resonances which are currently employed as the frequency references in metrology of the microwave and optical frequency standards and in magnetometry. We show experimentally that the spatial divergence of the AOM-RN frequency modulated output spectrum, the only seeming disadvantage of AOM-RN, is not an obstacle, as well, to obtain the error signals by means of Pound-Drever-Hall heterodyne technique with the use of high-finesse (up to tens of thousands) Fabry-Perot cavities as the frequency discriminators.