Frequency-modulated laser beam with highly efficient intensity stabilisation

Abstract

The limitation of the amplitude modulation rejection due to the spatial modulation of the output beam of an acousto-optic modulator, which is used in an active laser beam stabilisation system when a frequency modulation of a few megahertz is applied to this modulator, is analysed. It is shown how to overcome this problem, using a single-mode optical fibre at the output of the modulator. A residual amplitude modulation of 10−5 is achieved.