  The manipulation of TO-phonon polaritons and the terahertz (THz) light field
associated with them by means of an ultra-sound acoustic wave is proposed and
illustrated by calculating the TO-phonon-mediated THz response of
acoustically-pumped CuCl and TlCl crystals. We show the high-contrast
acoustically-induced change of the THz reflectivity alongside with multiple THz
Bragg replicas, which are associated with the infrared-active TO-phonon
resonance driven by the ultrasonic wave. The effect, which stems from phonon
anharmonicity, refers to an operating acoustic intensity I_ac ~ 1-100 kW/cm^2
and frequency nu_ac ~ 0.1 - 1 GHz, with possible applications in THz
spectroscopy.
