Ultrasonic control of terahertz radiation via lattice anharmonicity in   LiNbO3
  We propose a novel tunable terahertz (THz) filter using the resonant acousto-optic (RAO) effect. We present a design based on a transverse optical (TO) phonon mediated interaction between a coherent acoustic wave and the THz field in LiNbO3. We predict a continuously tunable range of the filter up to 4 THz via the variation of the acoustic frequency between 0.1 and 1 GHz. The RAO effect in this case is due to cubic and quartic anharmonicities between TO phonons and the acoustic field. The effect of the interference between the anharmonicities is also discussed. 
R. H. Poolman, E. A. Muljarov, and A. L. Ivanov
cond-mat.mtrl-sci cond-mat.mes-hall