The diffraction of electromagnetic waves by sound in conducting crystals

The diffraction of electromagnetic waves by sound in conducting crystals is investigated. It is shown that in such crystals a significant contribution to the scattering of electromagnetic waves can be made by electron waves which are generated by a sound wave and accompany it. An estimate shows that in the ‘hydrodynamic’ case ql 1 (where q is the wave number of the sound and l is the electron mean free path) the contribution from an electron density wave to the scattering of electromagnetic waves in the infrared and millimeter ranges in substances with a low electron effective mass (of the type of InSb) can be comparable to the contribution from the lattice deformation waves, or may even exceed it. The results of a concrete calculation of the first and second order intensities of Raman-Nath diffraction in a semiconductor are presented.