Acoustic Scattering of Light in a Fabry-Perot Resonator

When a collimated light beam traverses a collimated high-frequency acoustic beam, it is possible for the acoustic beam to scatter light into a single, well-defined angle (into a number of well-defined angles when the acoustic frequency is sufficiently low). The amount of light scattered depends critically on the angle of the light beam relative to the acoustic wavefront (the Bragg angle) and is roughly proportional to the square of the acoustic beam width for constant acoustic intensity. 1 While it is possible to scatter all of the incident light, this usually requires impractically large amounts of acoustic power, especially at frequencies greater than a few tens of megacycles/second. Acoustic scattering of light has considerable experimental interest since it allows a convenient method of probing transparent media to measure such things as elastic and photoelastic constants and acoustic loss or phonon lifetimes. These measurements can be made using thermally generated (Brillouin scattering) 2 ' 3 or externally generated sound. 4 In the latter case, the scattering also allows determination of the acoustic beam shape and direction. In addition, the scattering interaction gives 945