Phase-sensitive detection of optical resonances by using an acousto-optic modulator in the Raman–Nath diffraction mode

A new method for frequency control of an external cavity diode laser without direct modulation of the injection current is proposed. The Pound–Drever optical heterodyne technique or the method of frequency control by frequency-modulated sidebands, in which an acousto-optic modulator operating in the Raman–Nath diffraction mode is used as an external phase modulator, can be employed to obtain error signals upon automatic frequency locking of the diode laser to the saturated absorption resonances within the D₂ line of cesium atoms or to the optical cavity resonances.