Laser frequency stabilisation by the Pound–Drever–Hall method using an acousto-optic phase modulator operating in the pure Raman–Nath diffraction regime

Frequency stabilisation of diode laser radiation has been implemented by the Pound–Drever–Hall method using a new acousto-optic phase modulator, operating in the pure Raman–Nath diffraction regime. It is experimentally shown that, as in the case of saturated-absorption spectroscopy in atomic vapour, the spatial divergence of the frequency-modulated output spectrum of this modulator does not interfere with obtaining error signals by means of heterodyne frequency-modulation spectroscopy with a frequency discriminator based on a high-Q Fabry–Perot cavity with finesse of several tens of thousands.