Spontaneous Light Scattering and Acoustooptics

This chapter focuses on spontaneous light scattering and acoustooptics. Spontaneous light scattering means light scattering under conditions such that the optical properties of the material system are unmodified by the presence of the incident light beam. Several physical processes can lead to light scattering. One of the processes is Raman scattering that results from the interaction of light with the vibrational modes of the molecules constituting the scattering medium. Raman scattering can equivalently be described as the scattering of light from optical phonons. Brillouin scattering is the scattering of light from sound waves, that is, from propagating pressure (and hence density) waves. Brillouin scattering can also be considered to be from acoustic phonons. In RayLeigh scattering or Rayleigh-center scattering, light is scattered because of nonpropagating density fluctuations. Formally, it can be described as scattering from entropy fluctuations. It is known as quasielastic scattering because it induces no frequency shift. The scattering of light from sound waves can also be applied to the situation, in which the sound wave is applied to the interaction region externally by means of a transducer. Such acoustooptic devices are useful as intensity or frequency modulators for laser beams or as beam deflectors. Acoustooptic devices are commonly classified as falling into one of two regimes; namely, Bragg scattering and Raman-Nath scattering.