A novel wavelength locking scheme called acousto-optic frequency modulation (AOFM) is put forward and demonstrated experimentally. The laser frequency is modulated by an acousto-optic modulator, rather than direct dithering on the laser resonator. A new optical configuration is proposed to compensate the angular deflection of the acousto-optic modulator, which is driven by a Direct Digital Synthesis generator with a frequency stability and precision on the order of Hz. This locking scheme is relatively simple and economical, and it can avoid extra frequency and intensity noise due to the direct frequency dither on the laser resonator in the conventional saturation absorption locking scheme. Our scheme provides a new way to improve the noise and stability of the tunable laser.
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