We present a modification of the laser-induced transient grating setup enabling continuous
tuning of the transient grating period. The fine control of the period is accomplished by
varying the angle of the diffraction grating used to split excitation and probe beams. The
setup has been tested by measuring dispersion of bulk and surface acoustic waves in both
transmission and reflection geometries. The presented modification is fully compatible with
optical heterodyne detection and can be easily implemented in any transient grating setup.