Abstract

The use of intracavity acousto-optic (AO) modulators to generate unidirectional oscillation in ring laser cavities has been described in several publications.^1-5 Various explanations for the mechanism behind this effect were proposed without quantitative predictions. These earlier experiments showed that the sense of unidirectionality could be reversed by submillimeter adjustments of the position of the intracavity optics. It was also noted that when the diffracted beams were prevented from making multiple cavity roundtrips, by the size of the cavity or by the insertion of an aperture, the unidirectional operation became more deterministic, ^2,5 The sign of the tilt angle of the AOM about the Bragg angle then determined the direction of lasing. We have examined the behavior of a Nd:YLF ring laser with an intracavity AOM and have confirmed all these observations. We believe that including the Doppler shift of the light beams scattered toward or away from the acoustic wave direction into the calculation of the Bragg angle provides a full explanation for the AOM optical diode. This paper presents the predictions of this theory and describes experimental measurements that support it.

© 1992 Optical Society of America