 In general, acousto-optic effects are based on the change of the refractive index of a medium due to the presence of sound waves in that medium.Sound waves produce a refractive index grating in the material, and it is this grating that is "seen" by the light wave.These variations in the refractive index, due to the pressure fluctuations, may be detected optically by refraction, diffraction, and interference effects, reflection may also be used.