A laser tuning mechanism which embodies "spectrally dependent spatial filtering" (SDSF) and contemplates two key elements of the tuning mechanism. The first element of the SDSF tuning mechanism is a spectrally dependent beam distortion (i.e. alteration of the amplitude and/or phase profile of the beam) provided by an SDSF tuning element in a laser cavity. The second element of the SDSF tuning mechanism is an intracavity spatial filter which makes the round trip cavity loss a sensitive function of both beam distortion and cavity alignment. Such a laser can be aligned so that a specific beam distortion, which is provided by the SDSF tuning element at a tunable wavelength, is required to obtain minimum round trip cavity loss, thereby providing tunable laser emission. A preferred embodiment of the SDSF tuning mechanism is an external cavity semiconductor laser having a zeroth order acousto-optic tuning element.