 Traditionally, the type of diffraction, Bragg or Raman-Nath, is determined by the conditions "Q" » 1 and "Q" « 1 respectively, where Q is given by,

which is known as the Klein-Cook parameter.Since, in general, only the first order diffraction maximum is used in acousto-optic devices, Bragg diffraction is preferable due to the lower optical losses.However, the acousto-optic requirements for Bragg diffraction limit the frequency range of acousto-optic interaction.